The Agronomy and Economy of Ginger

Abstract

The chapter eloquently discusses the history of ginger starting from the botanical generic term zingiber (Latin term) which has its origin in Tamil (South Indian language) word Ingiver, meaning ginger rhizome. The place of ginger in Indian history is also discussed. The role of ginger vis-à-vis the spice trade is also discussed. The place of ginger in South Asia, even in Africa, is also discussed. The chapter further discusses the botany; morphology; anatomy, in particular the rhizome anatomy; development of oil cells; root apical organization; ontogeny of buds, roots, and phloem; pre-cambial differentiation of anatomical features of ginger in comparison with related taxa; floral anatomy; biology; self-incompatibility; embryology; cytology; cytogenetics; palynology; pollen morphology; physiology of ginger, including effect of growth regulators; genetic resources; their conservation, in vitro conservation; biochemical variability; crop improvement; and breeding strategies, including mutation breeding, polyploidy breeding, etc.

15.1 Introduction: A Peek into the History of Ginger

Among the spices of the world, ginger assumes considerable importance, along with turmeric, as one of the most important and sought-after medicinal spices. Ginger, botanically known as Zingiber officinale Rosc., belongs to the family Zingiberaceae and in natural order Scitamineae (Zingiberales of Cronquist 1981). Owing to its universal appeal, its spread has been rapid to both tropical and subtropical countries, from the China–India region, where ginger has been cultivated from time immemorial. Ginger was most valued for its medicinal properties, in ancient times, and also played a very important role in primary health care in India and China. As a carminative, it was widely used in European medicines as well.

The Latin term zingiber was derived from the ancient Tamil (one of the regional languages of Southern India–Tamil Nadu) word Ingiver, meaning ginger rhizome. Arab traders, in search of spices, took the term to Greece and Rome and from there to Western Europe. The present-day name of ginger in most Western European countries is derived from this ancient term. Examples of this are ingefaer (Danish), gember (Dutch), ginger (English), zingibro (Esperanto), barlik ingver (Estonian), inkivaari (Finnish), gingembre (French), and ingver (German). A catalog of these names, along those related to Indian languages, is given in Table 15.1.

Table 15.1 Ginger—its varied names

Earlier some authors thought that the term zingiber was derived from the ancient Indian Sanskrit singavera (Purseglove et al. 1981; Rosengarten 1969; Watt 1872), meaning antler-like or horn-shaped, indicating the shape of the rhizome. It is improbable because Sanskrit was not popular those days in the regions in question. Ginger was exported from the Malabar Coast, Kerala, India, and the Arab traders might have used only the prevalent local Tamil name for trading the commodity. Mahindru (1982) opined that the original word for ginger was, in all probability, a pre-Dravidian one and that it is found with minor variations in about 20 languages extending from China and the islands of the Pacific Ocean to England. In some languages, there are separate terms for fresh and dried ginger, which points to the fact that both forms of ginger are put to specific use (Table 15.2).

Table 15.2 Equivalent names for ginger in some languages

As early as the second century ad, ginger was one among the very few items on which duty was levied at the Alexandria port of entry, during the time of the Roman Empire (Flukiger and Hanbury 1879). During subsequent periods and in the Middle Ages, ginger was on the list of privileged goods in the European trade, and a duty was levied. In England, it must have been well known even before the Norman Conquest, for it is frequently named in the Anglo-Saxon beech books of the eleventh century, as well as in the Welsh “Physicians of Myddvai” (Parry 1969). During the thirteenth and fourteenth centuries, next to pepper, ginger was the most common and most precious spices, costing nearly seven scrolling per pound or about the price of a sheep. The merchants of Italy during the thirteenth and fourteenth centuries knew three kinds of ginger, belledi, colombino, and micchino. Belledi is an Arabic word meaning “country” and was probably the common ginger. Colombino referred probably to Columbum, Kollam, or Quilon (in the State of Kerala), an ancient port on the southern Malabar Coast of Kerala State, and micchino is the ginger brought from Mecca (which again only comes from the Malabar Coast; Mahindru 1982; Watt 1872). The literature also indicates that ginger preserved in syrup (called green ginger) was also imported to the Western world during the Middle Ages and was regarded as a delicacy of the choicest kind. In Zanzibar on the east coast of Africa, ginger is regarded as auspicious and is absolutely necessary to the Savara tribe for their religious and marriage functions.

There is mention of ginger in the Koran (ref: 76: pp. 15–17), which says “Round amongst them (the righteous in paradise) is passed vessels of silver and goblets made of glass…a cup, the admixture of which is ginger.” In the Middle Ages, ginger was considered to be so important a spice that the street in Basle where Swiss traders sold spices was named Imbergasse, meaning “ginger alley” (Rosengarten 1969). In Henry VIII’s time, ginger was recommended against plague. It was during that time that “gingerbread” became popular, and it turned out to be the favorite of Queen Elizabeth I and her court. The legend has it that around 2400 bc, a baker on the Isle of Rhodes near Greece prepared the first gingerbread, which shortly thereafter found its way to Egypt, where the Egyptians savored its excellent flavor and served it on ceremonial occasions. The Romans distributed it to the entire Roman Empire (Farrell 1985).

In the Middle Ages and until the end of the nineteenth century, English tavern keepers used to have ground ginger in constant supply for the thirsty customers to sprinkle on top of their beer or ale and then stir into the drink with a red-hot poker (Rosengarten 1969). The Western world herbalists and naturalists knew the great qualities of ginger, as confirmed by the well-known British herbalist John Gerard. He writes in his treatise (Gerad, 1577, cited by Parry 1969) that “ginger is right good with meat in sauces” and adds further this spice is “of an eating and digesting quality, and is profitable for the stomach, and effectively opposeth itself against all darkness of the sight, answering the qualities of pepper” (Parry 1969).

15.2 India and Ginger

Ginger was not significant as a spice in ancient India, unlike black pepper or cardamom, but was mahabbeshaj, mahashoudha, literally meaning the great cure, the great medicine. For the ancient Indian, ginger was the God-given panacea for a number of ailments. That may be the reason why ginger found a place of pride in ancient Ayurvedic texts of Charaka (Charaka Samhita) and Sushruta (Sushruta Samhita). In Ashtanga Hridaya Vagbhata (a very important ancient Ayurvedic text), ginger is recommended along with other herbs for the cure of elephantiasis and gout, for extenuating the juices, and for purifying the skin from all spots arising from scorbutic acidities. Ginger is also recommended when exotic faculties were impaired due to indigestion.

Rabbi Benjamin of Tudela, who traveled between 1159 and 1173 ad and gave an account of spices grown on the West Coast of India, is credited to be the first to have mentioned ginger cultivation. He gives a vivid description of the place and trade in spices as well as cultivation of spices in and around the ancient port of Quilon (now Kollam) in Kerala State, India (Mahindru 1982). Marco Polo (ad 1298) in his famous travelogue writes “good ginger also grows here and is known by the name of Quilon ginger. Pepper also grows in abundance throughout the country” (translation by Menon 1929). Another explorer, Friar Odoric (ad 1322), writes: “Quilon is at the extremity of pepper forests towards the south. Ginger is grown here, better than anywhere else in the world and in huge quantities.” In those days, Calicut (now Kozhikode), Cochin (now Kochi), Alleppey (now Alappuzha), and Quilon (now Kollam) were the ports through which all the spices were traded with the Western world. Nicolo Corai (ad 1430) describes Calicut as the “Spice Emporium of the East.” He described it as a maritime city of eight miles in circumference, a notable emporium for the entire India, abounding in black pepper, aloe, ginger, and a large kind of cinnamon, myrobalans, and zedoary. Linschotten (1596) gives a very interesting account of the spices. He states that ginger grew in many parts of India, but the best and the most exported ones grew on the Malabar Coast. He described the method of cultivation and preparation that appear to be similar to the present-day practices. Linschotten also wrote about the ginger trade and mentioned that ginger was mainly brought to Portugal and Spain from the West Indies, indicating the fact that the Portuguese were successful in cultivating ginger extensively in Jamaica and the adjoining West Indies islands. Flukiger and Hanbury (1879) wrote: “… it (ginger) was shipped for commercial purposes from the Islands of St. Domingo, as early as 1585 and from Barbados in 1654.” Reny (1807) mentions that “in 1541, 22053 cwt of dry ginger was exported from West Indies to Spain” (Watt 1872).

The most significant event in the history of spice trade was the landing of Vasco da Gama on the West Coast of India. da Gama started from Lisbon in Portugal, arrived at Mozambique in March 1498, and from there reached Mlinde by the end of April. The King of Mlinde had advised da Gama to sail to Calicut (now Kozhikode in Kerala State, India) and arranged for an Arab pilot to help him. This Arab brought the Portuguese explorer across the Arabian Sea in 20 days, and on March 17, 1498, da Gama anchored in Kappad, a tiny hamlet near Calicut, on the Malabar Coast. Following this, a wave of expeditions arrived on the West Coast of India, known at the time as the Malabar Coast, and the spice trade with Europe flourished. The arrival of the Portuguese also signaled the end of the Arab monopoly on the sea route and, consequently, on the spice trade. da Gama reentered India commanding an armada of 15 ships. Through the technique of intimidation, coercion, and bribe, he entered into an understanding with the then king of the independent Kochi State to obtain all the rights for a free trade in spices. Subsequently, in 1513 ad, a treaty was signed with the King of Calicut as well (known as the Zamorin then and now), ending the decade-long “spice war” between the Arabs and the Portuguese, securing for the Portuguese not only a big stake in spice trade but also in getting a foothold to enter India as part of the future of the colony. Subsequently, the Dutch and the British came into the fray, but the latter succeeded in remaining in India for the longest period. Hence, if one traces Indian history, colonization of India starts with a “spice war.” Though the British succeeded in usurping Indian territory for the longest period, when the East India Company handed over the power to the British crown, the Portuguese and French also succeeded in having their colonies within India. Goa, an island city on the western coast near Mumbai (formerly Bombay), was the colony of the Portuguese until about the mid-1960s, when the late Prime Minister Jawaharlal Nehru had to use military force to get the Portuguese evacuated. The French managed to keep their stranglehold through clever politics, and Mahe, an island town near Calicut, still enjoys special status as a “union territory,” with its citizens able to opt for French citizenship. Indeed, spice was the focal point in all these historical developments in India. Through the treaty that the Portuguese entered into with the Zamorin Government in Calicut (Kerala State), the former obtained a license to trade spices freely. The inefficient government and tendency to bribery of the Zamorin led to this development. There was then no restriction to procure ginger directly from the growers (Mahindru 1982). All these developments led to historical consequences.

The enhanced demand for pepper and ginger in Europe made the Portuguese exert pressure on the farmers to cultivate more and more of these crops. This helped the growers in a way, as it freed them from the bondage of big marketers. But the Portuguese could not continue singly for long. The Dutch arrived on the scene, and they practically drove out the whole Portuguese from the West Coast. The Dutch controlled the spice trade in India only for a short time, because their main focus was on East Asia, namely, countries like Indonesia and Suriname. In Kerala State, India, where they made a presence, war broke out between them and the King of Travancore State, and the Dutch were defeated. As time passed, the British arrived on the scene, and they could maneuver to corner the entire spice trade in India.

While these developments took place on the West Coast in India, North India was being ruled by Emperor Akbar, and he gave a great impetus to spice cultivation both in North and in West India. This was a policy of the Mogul Empire. Ginger obtained a special impetus as it was an ingredient in most vegetarian and nonvegetarian dishes of the Mogul. For instance, in Ain-i-Akbari, written by Akbar’s Prime Minister Abul Fazl, an account is provided about the various dishes in vogue during the Mogul period. In Ain 27 (f), he records that the market prices of spices and ginger was relatively cheaper than many others. Dried ginger was 4 dinar per seer (a measure in those times, rightly corresponding to a pound), and fresh ginger was 2.5 dinar per seer. He mentioned that pickled green ginger was available at 2.5 dinar per seer. Ginger was, hence, a common man’s spice, unlike black pepper and saffron, the spices of the privileged (Mahindru 1982). Ginger was widely grown in the West Coast of Kerala State from time immemorial. Subsequently, its cultivation spread to other parts of India, mainly to undivided Bengal and northeastern India. Buchanan (1807), who journeyed through the various heartlands of various kingdoms that existed in southern India in those times, made many references on the cultivation of various spices, including ginger, on the Malabar Coast. Ridley (1912) gives a detailed description of agricultural practices prevalent in the nineteenth-century India. About ginger and turmeric, he noted “The planting of ginger and turmeric was preferred under the shade of orchard trees … The output of ginger was 2500 pounds per acre … Green ginger was sold at rupees four for 25 pounds. The cost of cultivation worked out to about rupees 250 per acre” in the book A Hand Book of Agriculture authored by N. Mukherjee. This translates to the farmer earning Rs 166 per acre as profit (66.4%) from ginger. The quantity of rhizomes required for planting was estimated at 100 pounds per “bigha” (1600 sq. yards). Harvested ginger was processed before being sold in the market. Different methods were followed in the processing of ginger in different regions. In Maharashtra (Khandesh region), the processing was done as follows:

The rhizomes were dug up, cleaned of dirt and roots and boiled in a wide-mouthed vessel, and then dried. After drying for a few days, the rhizomes were steeped in diluted lime water, sun dried, and again steeped in stronger lime water and buried for fermentation. Later the rhizomes were dried and marketed. The product was known as “Sonth”. Watt (1872)

The practice adopted in Bengal was: “Ginger was first brushed with a hand brush to remove dirt and steeped overnight in lime water; subsequently rinsed in clear water and dried slowly on a brick oven.” The Bengal province in those days extended to the Himalayan Mountains, and ginger cultivation was prevalent in these parts. Campbell, who wrote the book Agricultural and Rural Economy of the Valley of Nepal, states that ginger was carefully grown in Nepal and the produce “ … is reckoned by the people of the neighbouring plains of Tirhoot and Sarun of very highest flavor and superior to the produce of their own country” (Watt 1872). The author also provides details of ginger cultivation prevalent in these regions.

Sir Baden Powell, the legendary founder of the Boy Scout movement, reported the following practice:

The rhizomes were dried up by placing them in a basket suspended by a rope and shaking for two hours each day for three days. Later, these were sundried for eight days and again shaken in the basket and re-dried for 48 hours in the basket itself. This removed the scales and skins, making the produce suitable for marketing. (Watt 1882)

In the nineteenth century in Bombay province, ginger was processed by peeling the rhizome with a piece of metal or tile and later drying it in the sun.

The Cochin ginger (ginger that came from the Cochin principality and exported from Cochin) was processed similarly as the Bombay ginger. Harvested rhizomes were heaped for a few days and then washed thoroughly to remove dust and soil. The outer skin was peeled off using a bamboo splinter, washed again, and dried in the sun. Often, the dried ginger was heaped in lime water for a few hours and redried to improve the appearance.

A bigha of ginger crop yielded 10 mounds of produce fit for sale, at the rate of Rs 6 per mound. The prevailing rate for ginger during the end of the nineteenth century was Bengal Rs 10.6/cwt; Bombay Rs 9/cwt; and Sind Rs 11.6/cwt. In Madras province (including Cochin in Kerala State), ginger was available at 20 paise per kg (Mukherjee, quoted by Ridleey, 1912).

It is also of historical importance to record the first detailed chemical investigations on ginger by J.O. Thresh (Year Book of Pharmacy, 1879, 1881, and 1882). He analyzed a sample of Cochin ginger that was found to contain the ingredients listed in Table 15.3.

Table 15.3 Chemical constituents of Cochin ginger

15.3 Global Centers of Ginger Cultivation

There is no wild state in which ginger occurs in nature. The most probable place of its origin is Southeast Asia, but it has been cultivated from time immemorial in India and China. No definite information exists on the primary center of domestication. On account of the ease of transporting the ginger rhizome over long distances, it has spread throughout the tropical and subtropical regions of the Southern Hemisphere. In fact, ginger is the most widely cultivated spice (Lawrence 1984).

The principal ginger-growing countries are India, China, Jamaica, Taiwan, Sierra Leone, Nigeria, Fiji, Mauritius, Indonesia, Brazil, Costa Rica, Ghana, Japan, Malaysia, Bangladesh, the Philippines, Sri Lanka, the Solomon Islands, Thailand, Trinidad and Tobago, Uganda, Hawaii, Guatemala, and many other Pacific Ocean islands.

15.3.1 India and Other South Asian Countries

India is the largest producer of ginger, with an annual production of about 263,170 t from an area of 77,610 ha, contributing approximately 30–40% of world production. Productivity is rather low, at about 3428 g/ha. Of the total production, 10–15% is exported to about 50 countries worldwide. The crop occupies the largest area in Kerala State (19%), followed by Odisha State (17%), Meghalaya (12%), West Bengal (12%), and Arunachal Pradesh (6%). Kerala and Meghalaya together account for nearly 40% of India’s production. In terms of productivity, Arunachal Pradesh stands first with an average yield of 7164 kg/ha, followed by Meghalaya with an average yield of 5139 kg/ha. Mizoram and Kerala harvest on average 5000 and 3428 kg/ha, respectively.

15.3.2 Nigeria

It was in 1927 that large-scale cultivation of ginger started in Nigeria, in the southern part of Zaria, especially within Jemma’s federated districts, as well as in the adjoining parts of the plateau. Nigeria has attempted to widen the genetic base of the crop through introduction of ginger cultivation mainly from India. Currently, Nigeria is one of the largest producers and exporters of split-dried ginger. The annual production is around 90,000 metric tons from a total area of 17,400 ha.

15.3.3 Jamaica

Ginger is grown in the hills of South Central Parish of Manchester and in the Christiana Area Land Authority. There is also some production in the border parishes of Clarendon, Trelawny, and St. Elizabeth, as well as in the hills of St. James, Hanover, and Westmoreland in the North-West. The area involved in ginger cultivation was about 65,000–70,000 acres in the past, but now that has dwindled considerably, and the current production is below 1000 t.

15.3.4 Fiji

Early European settlements introduced ginger as an export crop in Fiji in 1890. The Indian migrants started large-scale cultivation subsequently. The major production areas are Suva Peninsula, especially in Tamarua, Colo-i-Suva, and Tacinua districts. Ginger has also spread to Sawani, Waibu Nabukaluka, and Viria districts. The area under cultivation is around 1000 ha.

15.3.5 Ghana

In Ghana, early attempts at growing ginger were not successful, but with the launching of the economic recovery program in 1983, ginger cultivation was promoted by the new government in place. Large-scale production was taken up in the Kadzebi district. The production reached 80,000 t in 1990. However, production declined subsequently. Currently, the country produces over 1000 t.

15.3.6 Australia

It was during the World War II that ginger gained a foothold in Australia as a commercial crop in Queensland. A farmer introduced it in Buderim in 1920, a small town north of Brisbane in Queensland, which has been the center of ginger production ever since. The growers are concentrated in Buderim, Nambour, North Arm, and Eumundi. Production was over 6200 t in 1974. It has increased since then, and the entire produce is processed into preserved ginger and other ginger products. However, ginger production declined since then, and currently the crop occupies only a very little area, and production is processed mainly by the famous Buderim Ginger Company into more than a hundred value-added products.

15.3.7 Sierra Leone

Sierra Leone remained a ginger producer for over 100 years. The crop is grown along the railway lines, laid under British administration, around Freetown, Bola, Kennama, Pendembu, and Njala, as well as in the Moyamba district and parts of East Kano. Sierra Leone ginger was traditionally known as African ginger. It is less aromatic but is more pungent than other varieties grown for commercial purposes (Lawrence 1984).

15.3.8 Mauritius, Trinidad, and Tobago

In Mauritius, ginger is grown in all districts on the island, although most of the production comes from Pamplemousses and Flacqdisbiets. Guajana has a small-scale ginger cultivation in the northwestern region. Current production is around 500 metric tons in Mauritius. In Trinidad and Tobago, ginger is a traditional spice which is grown mixed with other crops.

15.3.9 Southeast Asia

Southeast Asia is a major center of ginger production. It comes mainly from China, Thailand, Taiwan, Korea, and Vietnam. China produces the most, followed by Thailand, Korea, and Vietnam. China has an acreage ranging from 5000 to 80,000 ha. It is cultivated in the provinces of Shandong, Guangdong, Zhejiang, Anhui, Jiangxi, and Hubei. The largest variability in ginger is seen in China, where many distinctly different morphotypes have been identified. Available figures indicate a production of about 2,400,000 t. The country consumes internally the major share of ginger produced, with many ginger products being available in commercial markets.

Taiwan has only 3000–4000 ha under ginger, and the produce is marketed mainly as a vegetable. It is grown either as an intercrop between tea or as a pure crop on hill slopes.

Thailand and Korea produce ginger only for domestic consumption. The former produces about 3000 t from about 12,000 ha. The Republic of Korea produces about 8000 t from about 4200 ha, clearly indicating that Thailand is way behind the Republic of Korea in ginger production.

15.3.10 Indonesia

With more than 10,000 ha under ginger cultivation and a production level of around 77,000 metric tons, which is a high-yield level, Indonesia is another important producer of ginger. The main ginger belt in Indonesia is the Java–Sumatra island region.

15.3.11 Sri Lanka

Sri Lanka grows ginger mixed with turmeric, cocoa, coffee, jackfruit, areca nut, coconut, or green vegetables, mostly in a haphazard manner. It is cultivated mostly in the central eastern provinces of the island in Yatinuwara, Harispatta, Siyambalagoda, and Girijama. Ginger production is mostly consumed locally and goes into the production of ginger beer and ginger ale.

15.3.12 Philippines

In the Philippines, ginger is produced in Los Baños, Laguna; Tanauan, Batangas; and Silang, Cavite. The current area under ginger cultivation extends to about 5000 ha with a total production of about 29,000 metric tons.

Many other countries, such as Nepal, Bangladesh, Bhutan, Cameroon, Costa Rica, Kenya, the Reunion Islands, and the United States, produce ginger in small quantities for domestic consumption.

According to the Food and Agriculture Organization (FAO) in Rome, ginger production is looking up because of increase in production area and higher productivity, which are definitely bound to increase in the coming years. The crop is coming under a growing demand in the State of Kerala, India, with a huge domestic market for both fresh and dried ginger.

15.4 Uses of Ginger

A unique plant, ginger is used universally. Ancient Indians considered ginger as the “mahashoudha” (the great medicine). It is an ingredient in several drinks and sweetmeat products. The plant thus possesses a combination of many attributes and properties. As ginger contains a variety of important constituents (Table 15.3), its use can be wide ranging. The characteristic organoleptic properties are contributed by the volatile oil and nonvolatile solvent-extractable pungent compounds. Among the many components, α-zingiberene is the predominant component of the oil. Gingerol and shogaol are the pungency-contributing constituents. The refreshing aroma and the pungent taste make ginger an essential ingredient of most world cuisines and of the food-processing industry. The solvent-extracted oleoresin is available in convenient consumer packets. Ginger powder is also an ingredient in many masala (Indian curry powder) mixes. In Western countries, ginger finds its most widespread use in the making of gingerbread, biscuits, cakes, puddings, soups, and pickles. Ginger ale, ginger beer, and ginger wine are widely used soft drinks. Ginger is one of the most widely used medicinal plants in the traditional Indian systems of medicine, namely, Ayurveda, and also in Chinese and Japanese systems of medicine. According to Ayurveda, ginger has both carminative and digestive properties. It is believed to be useful in anorexia, dyspepsia, and suppression of inflammation. Dry ginger is useful in dropsy, otalgia, cephalgia, asthma, cough, colic, diarrhea, flatulence, nausea, and vomiting. Pharmacological investigations have indicated its usefulness in preventing nausea and vomiting associated with chemotherapy, pregnancy, travel, and seasickness. Ginger also has antiplatelet and hypolipidemic activity and an anxiolytic effect. In addition to Ayurveda, ginger is in wide use in Indian folklore medicine as a cure for indigestion, fever, colic, and any ailment associated with the digestive system.

One of the most important value-added products to emerge is “ginger tea,” brought out by Tata Group (biggest Indian corporate house).

Ginger is an important constituent of both Chinese and Japanese medicine. In the Chinese Materia Medica, ginger is indicated, for example, in the treatment of vomiting, diarrhea, light-headedness, blurred vision, dyspepsia, tremors, decrease in body temperature, and high blood pressure. In both Chinese and Japanese systems of medicine, fresh and dry ginger is used for different purposes.

15.5 Botany of Ginger

Genus Zingiber belongs to the family Zingiberaceae, which is distributed in tropical and subtropical Asia and Far East Asia, and consists of about 150 species. Zingiberaceae is of considerable importance as a member of the “spice family.” The spice family includes, most importantly of all, black pepper, the “king” of spices; cardamom, the “queen” of spices; turmeric; nutmeg; allspice; cinnamon; and so on. These crops have great economic and medicinal values. Zingiberaceae was earlier divided into subfamilies Costoideae and Zingiberoideae, which were subsequently given independent family status as Costaceae and Zingiberaceae. Three tribes were recognized in the subfamily Zingiberoideae by investigators such as Peterson (1889) and Schumann (1904). And the genus Zingiber was included in the tribe Zingiberaceae along with Alpinia, Amomum, and some others. This tribe is characterized by the absence of lateral straminodes or staminodes that are united to the labellum, in comparison with the tribe Hedychieae, in which the lateral staminodes are well developed. Subsequently Holttum (1950) removed Zingiber from Zingiberaceae and renamed it as Alpimeae. His argument was that Zingiber is closer to the genera under Hedychieae as their lateral staminodes appear as lobes at the base of the labellum, whereas in Alpinia, these staminodes are well developed. Many subsequent investigators accepted the opinion of Holttum. Burtt and Smith (1983), however, felt that the contention of Holttum is nomenclaturally incorrect and, hence, proposed that Zingiber should be in an independent tribe.

The first documentation of ginger was by Van Rheede (1692) in his Hortus Indicus Malabaricus (Vol 11), the first-ever written account of the plant species of India. The author described the cultivated Zingiber species, Zingiber officinale, under the local name inschi (inchi). The Indian species was first botanically described by Roxburg (1810), who reported 11 species and placed them in 2 sections based on the nature of the spike: Section 1 Spikes Radical and Section 2 Spikes Terminal.

Baker (1882) carried out an exhaustive survey of Zingiberaceae of the Indian Peninsula for The Flora of British India (J.D. Hooker). In this he recognized the following four sections:

• 1. Cryptarithm Horan—Spikes are produced directly from the rhizome and are very short and dense; peduncle very short comprising of 11 species.

• 2. Lampuzium Horan—Spikes are produced from the rhizome on more or less elongated peduncles with sheathing scariose bracts comprising of ten species.

• 3. Pleuranthesis Benth—Spike peduncle arising from the side of the leafy stem comprising of just one species.

• 4. Dymczewiczia (Horan) Benth—Spikes terminal on the leafy stem comprising of two species.

15.5.1 Zingiber Boehmer

Boehmer and Ludwig, def Gen. PI 89, 1760, nom. cons. Benth & Hook. f. Gen. PI. The above classification was accepted by subsequent investigators includingSchumann (1904). Holttum (1950) provided the following description of the genus: Rhizomes at or near the surface of the ground, bearing leaf shoots close together. Leaf shoots short to moderately tall, often with many leaves. Leaves thin in texture, never very large (rarely more than 50 cm long), sessile or with quite short petioles, the ligule short to long, deeply bilobed or entire. Inflorescence on a separate shoot without normal leaves (rarely at the apex of the shoot); scape usually erect, short or long, clothed with two-ranked sheaths that are often colored red; spike short or long, slender or thick, cylindrical, ovoid, or tapering to a narrow apex, elongating gradually. Bracts fairly large, usually bright colored, red or yellow, usually thin fleshy, closely imbricating or with apices free, margins plane or inflexed. One flower in the axil of each bract; flowers fragile or short-lived. Bracteoles one to each flower, facing the bract, thin and narrower than bract, usually persisting and enclosing the fruit, split to the base, never tubular.

Calyx thin, tubular spathaceous usually shorter than the bracteole but sometimes longer. Corolla tube slender, usually about as long as the bract; dorsal lobe usually broader than the others, erect, narrowed to the tip, and hardly hooded; edges inflexed, lateral lobes usually below the tip and on either side of it, sometimes joined partly together by their adjacent sides and to the tip; color usually white or cream. Labellum deeply three-lobed (the side lobes representing staminodes) or rarely the side lobes hardly free from the mid-lobe, side lobes erect on either side of the stamen, mid-lobe shorter than or not greatly longer than the lateral corolla lobes, its apex usually retuse or cleft; color cream to white or more or less deeply suffused with crimson or purple. Filament of stamen short and broad, anther rather long, narrow; connective prolonged into a slender curved beak-like appendage as long as the pollen sac, with inflexed edges, containing the upper part of the style. Stigma protruding just below the apex of the appendage, not thickened, with a circular apical aperture surrounded by stiff hairs. Stylodes usually slender and free, not surrounding the base of the style. Ovary glabrous or hairy, trilocular with several ovules in each loculus. Fruit with a fleshy wall when fresh, more or less leathery when dry, smooth, hairy, enclosed by a persistent bract or bracteole, dehiscent loculicidally within the persistent bracts. Seed ellipsoid, black or dark brown, covered by a thin saccate white aril with irregularly lacerate edges.

The main distinguishing features of the genus are (A) long, curved, anther-appendage embracing the style; (B) the three-lobed lip (the side lobes are staminodes, which are relatively broad and fused more or less to the mid-lobe or lip proper); and (C) the relatively large bracts, each with a single flower and nontubular bracteole, more or less imbricating on a lengthening inflorescence (Z. clarkei from Sikkim State, India, is an exception that has 2–4 flowers to each bract). The bracts are often, but not always, colored; in some species, they change color as they grow older. The color of the lip is an important distinguishing character.

The genus contains about 150 species, of which 34 have been traced to China (Shu 2003) and 24 to India (Baker 1882). The main centers of diversity are South China, Malaysia, Northeast India, Myanmar region, and the Java–Sumatra region of Indonesia. Shu (2003) has recently revised the Chinese species. The only species extensively used as a flavoring agent for food is the true ginger, Z. officinale. Some species, such as Z. zerumbet and Z. cassumunar, are well known for their uses in native medicine. Z. mioga is used as a spice, and its flower buds are in great demand in Japan as a vegetable.

15.5.2 Zingiber officinale Rosc.

Roscoe, New arrangements of the plants of the monandrian class usually called “Scitaminea,” Trans. Linn. Soc. 8:348, 1807; Valeton, Bull. Buitenz, 2nd Ser; xxvii, 128, 1818; Flukiger and Hanbury, Pharmacographia, 574, 1874; Engler, Pflanzenw. Ost.- Afrikes and Nachbargebiete, B. Natzpflanzen; 264, 1895; Schumann, Zingiberaceae, in Das Pflanzenrich, 4, 46, 179, 1904. Inschi, Rheede, Hort. Malabaricus, 11, 23–25, 1692.

Rhizome entirely pale yellow within or with a red external layer. Leafy stems to about 50 cm tall, 5 mm in diameter, glabrous except for short hairs near base of each leaf blade; leaf blades commonly about 17 cm × 1.8 cm; rather dark green, narrow evenly to slender tip; ligule broad, thin, glabrous, 5 mm tall, slightly bilobed. Scape slender, 12 cm tall, the upper sheaths with or without short leafy tips; inflorescence approximately 4.5 cm long and 15 mm in diameter; bracts approximately 2.5 cm × 1.8 cm; green with pale submarginal band and narrow translucent margin; margins incurved, lower bracts with slender white tip. Bracteoles as long as bract; calyx with ovary 12 mm long; corolla tube 2.5 cm long, lobes yellowish, dorsal lobe 18 mm × 18 mm (flattened), curving over the anther and narrowed to the tip, laterals narrower. Lip (mid-lobe) nearly circular, approximately 12 mm long, and wide, dull purple with cream blotches and base, side lobes about 6 mm × 4 mm; free almost to the base, colored at mid-lobe; anther cream, 9 mm long, appendage dark purple, curved, 7 mm long (Holttum 1950). The species is sterile and does not set seeds.

15.6 Taxonomical Notes

Roscoe (1807) described Z. officinale from a plant in the botanic garden at Liverpool as “Bracteis ovato-lanceolatis, laciniis corolla revolutis, nectario trilobata” and referred to it as Amomum zingiber Willd. Sp.PI. 1:p6. Willdenow (1797) extended Linnaeus’s description “Amomum scapo nude, spica ovata” with “squamis ovatis, foliis, lanceolatisbad apicem margine ciliates.” Linnaeus’s (1753) Amomum zingiber is the basionym for the species. The genus Amomum of Linnaeus is a nomenclatural synonym of the conserved generic name, Zingiber Boehm (Burtt and Smith 1983). The specific epithet “zingiber” could not be used in the genus Zingiber. Thus, Z. officinale was adopted as the correct name for ginger. The specimens available in most of the herbaria are without flowers, and it is assumed that Linnaeus based his description on the account and figure given by Rheede in Hortus Indicus Malabaricus. The figure given by Rheede is the designated lectotype of the species Z. officinale Rosc. (Jansen, 1781). The species epithet officinale is derived from Latin, meaning “work shop,” which in early Latin was used to mean pharmacy, thereby implying that it had medicinal value.

15.7 The Morphology and Anatomy of Ginger

The ginger plant is a herbaceous perennial grown as an annual crop. The plant is erect, with many fibrous roots, aerial shoots (pseudostem) with leaves, and underground stem (rhizome). The roots of ginger are of two types, fibrous and fleshy. After planting, many roots having indefinite growth grow out of the base of the sprouts. These are the fibrous roots, and the number of such roots keeps on increasing with the growth of tillers. The fibrous roots are thin, with root hairs, and their function is mainly absorption of plant nutrients and water from soil. When the plant grows further, several fleshy roots of indefinite growth are produced from the lower nodes of the mother ginger rhizome and primary fingers. These roots are thicker, milky white in color, with few root hairs, and with no lateral roots. Such roots carry out functions of anchorage as well as conducting vessels for water and nutrient absorption. During the initial growth, the apical bud of the rhizome piece planted grows out and becomes the main tiller or mother tiller. As this tiller grows, its base enlarges into a rhizome. This is the first formed rhizome knob and is frequently referred to as the “mother rhizome.” From either side of the mother rhizome, branches arise and they grow out and become the primary tillers. The bases of these tillers become enlarged and develop into the primary fingers. The buds on these primaries develop in turn into secondary tillers and their bases into secondary fingers. The buds on the secondary fingers in turn can develop into tertiary tillers and tertiary fingers.

The aerial shoots have many narrow leaves born on very short petioles and with sheaths that are long and narrow, and the overlapping sheaths produce the aerial shoot. A pair of ligules is formed at the junction of leaves and sheath. The leaves are arranged in a distichous manner.

Ginger is a subterranean stem (rhizome) modified for the vegetative propagation and storage of food materials. The stem has nodes with scale leaves and internodes. Except for the first few nodes, all others are axillary buds. When the rhizome bit is used to plant (“seed rhizome” or “set”), there may be one or more apical buds on it; however, normally only one bud becomes active. When large pieces are used, more than one bud may develop simultaneously. If more than one branch from the parent rhizome is responsible for the ultimate growth and development of the adult rhizome, the branches of the mature rhizome lie in the same plane (Shah and Raju 1975a).

The pattern of rhizome branching shows that the main axis developing from the apical bud, which is the first developing branch, has 7–15 nodes, which later becomes an aerial shoot. Once this axis becomes aerial, the subsequent growth of the rhizome is due to the development of the axillary buds situated above the first 2–3 nodes of the underground main axis. These axillary branches are plagiotropic and quickly show orthotropic growth at their distal region and subsequently become aerial shoots. A similar pattern of growth continues for successive branches to form a sympodial growth pattern. A few axillary buds at the distal end of the branch remain dormant. The number of primary branches may be two, three, or four. These primary branches arise on either side of the main axis. Subsequent development of the secondary, tertiary, and quaternary branches is on the abaxial side of the respective branches. Irrespective of the number of primary branches, the subsequent branches lie in the same place, although alteration of this scheme is seen sometimes. A mature rhizome may consist of 6–26 axillary branches with foliage leaves or only with sheath leaves, and they show negative geotropic response (Shah and Raju 1975a).

The number of nodes in each rhizome branch varies. The main axis (mother rhizome) and the subsequent branches (primaries) have 6–15 nodes. The internal length of the rhizome branches ranges from 0.1 to 0.15 cm and varies even in a single branch. The internodal length is more in the secondary, tertiary, and quaternary branches, and in the aerial stem, it ranges from 3 to 7 cm. In the underground stem, the nodes have scale leaves which ensheath and protect the axillary buds. These scale leaves fall off, or may be lost, so that in mature rhizomes, only the scars remain. Young scale leaves have pointed tips which help in the penetration into the soil.

The distal few nodes of the rhizome have sheath leaves. At the early stage of development, they lack an apparent slit due to overlapping of their margins. Subsequently, a longitudinal slit is formed through which the shoot tip projects. After the development of 6–12 scale leaves and 3–5 sheath leaves, the foliage leaves are produced. A foliage leaf consists of a leaf sheath, a ligule, and an elliptical-lanceolate blade. The leaf sheath is about 15–18 cm long, and the lamina is about 12–15 cm long. Above its region of insertion, the sheath encircles the internode; and from the side opposite to its origin, up to the ligule, the sheath is open longitudinally. A distinct midrib is present only in the lamina. The phyllotaxy of the scale leaves on the rhizome and foliage leaves on the aerial stem is distichous, with an angle of divergence of about 180°. Within the bud, leaves have imbricate aestivation (Shah and Raju 1975a).

15.8 Rhizome Anatomy

The early investigations on the anatomy of ginger were carried out mainly by pharmacognosists, and they concentrated on the officinal part, the rhizome, either dry or fresh (Futterer, 1896). A comprehensive survey on the anatomy of the plants belonging to Zingiberaceae was that of Solereder and Meyer (1930), in the classical work Systematische Anatomie der Monokotyledonen (Systematic Anatomy of the Monocotyledons). They provided anatomical notes on 18 genera and some 70 species (Tomlinson 1956). Subsequently, Tomlinson (1956) supplemented the information and filled in the gaps. However, no information was available on the developmental anatomy. Some investigations were carried out by Aiyer and Kolammal (1966), Pillai et al. (1961), and Shah and Raju (1975b). Recently, investigations on developmental anatomy of the rhizomes, oil cells, and associated aspects were carried out (Ramashree et al. 1997, 1998, 1999; Ravindran et al. 1998). The following discussion is based on the studies of the abovementioned researchers.

The transection (TS) of a fresh, unpeeled rhizome is almost circular or oval, about 2 cm in diameter, with the outline almost regular. The TS shows a light brown-colored outer border and a central zone 1.2 cm in diameter marked off by a yellowish ring from an intermediate cortical zone. A distinct continuous layer of epidermis is generally present, consisting of a single row of rectangular cells; in some cases, it may be ruptured. Within this is the cork, varying in thickness, from 480 to 640 μm, and differentiated into an outer region of 300–400 μm in thickness, composed of irregularly packed, tangentially elongated, slightly brown-colored cells; then there is an inner zone of 6–12 regular rows of thin-walled, rectangular to slightly tangential elongated cells arranged in radial rows. They measure 30 μm × 30 μm to 114 μm × 48 μm. (Note: cork tissue develops after the harvest and during storing. Hence, when a rhizome is cut soon after harvest, one may not encounter much cork tissue.) A cork cambium is not evident. Inner to the cork is the cortex that is about 4 mm in thickness, composed of thin-walled large hexagonal to polygonal parenchymal cells. The cortical cells are heavily loaded with starch grains. These grains are large, simple, and ovoid, with length varying from 15 to 65 μm. Scattered within the cortex are numerous oil cells which contain large globules of yellowish green color. The outermost thre to five rows of cortical cells are not rich in oil content. Many scattered, collateral, closed vascular bundles are present, of which the greater number is seen in the inner cortical zone. The large bundles are partially or entirely enclosed in a sheath of separate fibers, whereas the smaller bundles are devoid of any fiber. Each vascular bundle consists of phloem, composed of small thin-walled polygonal cells with well-marked sieve tubes and xylem composed of one to nine vessels with annular, spiral, or reticulate thickenings. These vessels have a diameter varying from 21 to 66 μm. In the enclosing sheath of fibers, the number of cells varies a lot. There are 4–48 fibers or occasionally more. These fibers are very long, but less than 1 mm, have a diameter from 10 to 40 μ, and are not straight but undulative in character. The inner limit of the cortex is marked by a single-layered endodermis composed of thin-walled, rectangular cells, much smaller than the cortical cells, with their radial walls slightly thickened and free from starch grains. The endodermis is lined by a pericycle composed of a single row of thin-walled, slightly tangentially elongated cells devoid of any starch grains.

The stele that forms the bulk of the rhizome consists of parenchymal cells similar to those of the cortex, with starch grains and oil globules and a large number of irregularly scattered vascular bundles. Just within the pericycle, a number of very small vascular bundles are arranged in a ring. These bundles have only one to three vessels and a small phloem. No fibers are present enclosing these small bundles. Generally, the vascular bundles present within the stele are slightly larger than those present in the cortex. The stele contains more oil cells and starch grains than the cortex (Aiyer and Kolammal 1966).

15.8.1 Rhizome Enlargement

Rhizome enlargement in ginger is due to the activity of three meristematic zones. Very early in the development of the rhizome, a zone of meristematic cells is formed at the base of a young scale leaf primordium of the developing rhizome. These meristematic cells develop into the primary thickening meristem (PTM) and procambial stands. The meristematic activity of the PTM is responsible for the initial increase in the width of the cortex. The second type is the actively dividing ground parenchyma. The third type is the secondary thickening meristem (STM), in which fusiform and ray initials are clearly visible. The STM develops just below the endodermoidal layer.

At a lower level, in the rhizome from the shoot bud apex, the PTM can still be identified. The scattered vascular bundles develop from the PTM or procambial cells. Such groups of cells can be identified by the plane of cell division. The differentiation of procambial cells into vascular tissue takes place at different stages of rhizome growth. Unlike in many monocots, in the ginger rhizome, there is a special meristematic layer along with the endodermoidal layer, and this layer consists of cambium-like cells. The cells are thin-walled and arranged in a biseriate manner. In certain loci, where the vascular bundles develop, these cells are elongated with tapered ends and appear similar to the fusiform initials with an average of 62.34 μm length and 8.12 μm width in mature stages. Between these fusiform initials, some cells show transverse divisions to form ray initials. The presence of the cambium-like layer is an important feature in rhizome development. From this layer, inverted and irregularly distributed groups of xylem and phloem are formed along the intermediate layer. The cells outer and inner to the cambial layer become filled with starch gains.

15.8.2 Development of Oil Cells and Oil Ducts

Oil cells are present in the epidermis or just below the epidermis of the leaf, petiole, rhizome, and root. In the rhizome, oil cell initials are present in the meristematic region. They are spherical and densely stainable. The initiation of oil cells and formation of ducts occur in the apical parts of shoots and roots and start much before the initiation of vascular elements. Secretory ducts are formed both schizogenously and lysigenously (Ravindran et al. 1998; Ramashree et al. 1999).

15.8.3 The Schizogenous Type

The schizogenous type of secretory duct originates in the intercalary meristem of the developing regions. The ducts are initiated by the separation of a group of densely stained meristematic cells through dissolution of the middle lamella. Concurrent separation of the cells leads to the formation of an intercellular space bordered by parenchymal cells. These ducts are anastomosed and appear branched in longitudinal section. Further separation of the bordering cells along the radial wall leads to widening of the duct lumen.

15.8.4 The Lysigenous Type

The lysigenous type of duct formation is more frequent in the meristematic region but occurs in mature parts as well. There are four stages involved in its development, which are initiation, differentiation, secretion, and quiescence. These steps are a gradual process that occurs acropetally.

15.9 Initiation and Differentiation

In shoot apex, the meristematic cells are arranged in tiers. In between these cells, certain cells in the cortical zone are distinguishable from the rest by their large size, dense cytoplasm, and prominent nucleus. Such cells act as the oil cell mother cell. Anticlinal and periclinal divisions of these cells result in a group of oil cell initials. Cytoplasmic vacuolation initiates in the oil cells at a distance of about 420 μm from the shoot apex. Subsequently, the surrounding cells also enlarge in size, showing cytoplasmic and nuclear disconfigurations. Further development leads to the disintegration of nuclear content of the central cell, which stretches toward the intercellular space. Later, the central cell disintegrates, and the contents of the cell spill into the cavity thus formed. This process that takes place in adjacent cells leads to the formation of a duct. The duct can be either articulated or nonarticulated and becomes gradually filled up with the cell contents of the lysed cells. Once the lysogeny of the central cell is completed, the adjacent cells also lyse gradually in a basipetal manner, resulting in the widening of the duct lumen. These stages occur between 1500 and 3000 μm from the apex.

15.10 Secretion

The differential oil cells start a holocrine type of secretion and expel their contents into the duct. Then the next cell (in acropetal order) becomes differentiated into an oil cell and starts elimination of its contents, followed by lysis. Simultaneously, the primary tissues continue to become differentiated into new oil cells and reach the secretory stage. The secretion fills the duct in young stages, but the quantity becomes reduced gradually, and finally the ducts appear empty. This could happen because of the diffusion of oil basipetally and radially; such oil particles are deposited in the cells and can be seen as black masses inside the cells as well as in the intercellular space. Such stages are noticed about 3250 μm from the root tip (Ravindran et al. 1998; Ramashree et al. 1999).

15.11 Quiescence

In the mature rhizome, the ground parenchyma does not undergo further division and differentiation into the duct. In this stage, the cells adjacent to the duct become storage cells, containing numerous starch grains and large vacuoles. An empty cell or cells with distorted cytoplasm appear along the duct lumen. Quiescence and secretory stages are visible from the third month onward after planting. In primary tissues, the oil duct development is schizogenous, whereas further development proceeds both schizogenously and lysigenously.

15.12 Root Apical Organization

The root apical organization in ginger together with many other zingiberaceous taxa was first reported by Pillai et al. (1961). They found that the structural organization of ginger root apex differs from that of other taxa (such as Curcuma, Elettaria, and Hedychium). In ginger, all zones in the root apex originate from a common group of initials. From the rim of this common group, calyptrogen, dermatogen, periblem, and plerome become differentiated. Raju and Shah (1977) also reported a similar observation in ginger and turmeric. The following discussion is adapted from Pillai et al. (1961).

The root cap is not differentiated into columella and a peripheral zone, and hence, there are no separate initials for these regions. The cells in this region are arranged in vertical superimposed files. The cells arise by the activity of a meristem, which can be easily differentiated from the rest of the region. Pillai et al. (1961) named this meristematic region columellogen. In TS, the cells of the columella form a compact mass of polygonal cells in the center with the cells of the peripheral region arranged in radiating rows around it.

In the root body, two histogens could be distinguished: (i) the plerome concerned with the formation of stele and (ii) the protoderm–periblem complex concerned with the formation of the outer shell to the stele including periblem and dermatogen. The protoderm–periblem complex is located outside the plerome and is composed of a single tier of cells. The cells of this zone located on the flanks exhibit T-divisions, which help the tissue to widen out. Periblem consists of the initials of the cortex extending from the hypodermis to the endodermis. The hypodermis arises from the inner layer of the protoderm–periblem initials. The cells composing this tissue vacuolate earlier than the outer cells of the cortex.

The endodermis differentiates from the innermost periblem cells. Outside the plerome dome, all cells of the periblem exhibit T-divisions initially, but subsequently in development show anticlinal divisions, and the endodermis is differentiated at that time.

Plerome has at its tip a group of more or less isodiametric cells. On the sides of the plerome dome is the uniseriate pericycle. Near the dome, cells take less stain because of their quiescent nature. The metaxylem vessel elements with wider lumens can be seen near the plerome dome. The isodiametric cells at the very center of the plerome divide like a rib meristem to give rise to the pith. In TS, passing near the tip of the plerome dome, the initials can be distinguished as a compact mass of isodiametric cells, surrounded by radiating rows of periblem cells.

15.12.1 Cytophysiological Organization of the Root Tip

The root tip can be distinguished into two zones on cytological ground:

• 1. The quiescent center: This zone is found at the tip of the root body, characterized by its cells having (a) cytoplasm highly strained with pyronin-methyl green and hematoxylin, (b) smaller nuclei and nucleoli, (c) cell divisions less frequent, and (d) vacuolation noticeable in most.

The median longisection of this group of cells is in the shape of a cup with the rim forward. The above characteristics show their state of rest and are called the quiescent center. This zone includes cells belonging to all the structural histogens of the root body (i.e., not structurally delimitable). It gradually merges with the zone outside, the meristematic zone. Raju and Shah (1977) studied the root apices of ginger, mango ginger, and turmeric with azure B staining to localize DNA and RNA contents in order to identify the quiescent center. A quiescent center was present in all three cases as indicated by the light stainability of its cells. In longisection, the quiescent center resembles the inverted cup.

• 2. The meristematic zone: This zone is shaped like an arch surrounding the quiescent center on the sides of the root body. The cells of this zone have the following features: (a) cytoplasm deeply stained with pyronin-methyl green and hematoxylin, (b) divisions more frequent, (c) larger nuclei and nucleoli, and (d) vacuolation absent or not prominent.

The meristematic zone includes the cells of all the structural histogens of the root body. The percentage of cell division is much lower in the quiescent center compared to the meristematic zone. This character combined with the response of these cells to stains such as pyronin-methyl green indicates that these cells are in a state of comparative repose and hence are not synthesizing nucleic acids (Pillai et al. 1961). The distance between the tip of the root body and the nearest mature phloem element, which carries the metabolic products required in the active cells, was reported to be 480–490 μm. This led to the suggestion that the cells at the tip of the root body go into quiescence because of the dearth of sufficient metabolites (Pillai et al. 1961).

15.13 Ontogeny of Buds, Roots, and Phloem

The ontogeny of ginger was investigated by Shah and Raju (1975b), Ramashree et al. (1998), and Ravindran et al. (1998). In a longisection, the shoot apex is dome-shaped with a single tunica layer, below which the central mother cell zone is present. The flank meristem is situated on either side of the central mother zone. The leaf is initiated from the outer tunica layer and from the flank meristem. The shoot apical organization and acropetal differentiation of procambial strands are closely related to the phyllotaxy. At an even lower level basipetally in the rhizome axis, additional inner cortical cells are produced by a lateral PTM or procambium in which the resulting cells are radial rows.

15.13.1 The Nature of the Shoot Apex

Shah and Raju (1975a) studied the nature of the shoot apex in ginger. In all the stages of growth in the shoot apex, a single layer of tunica occurs, showing only anticlinal divisions. Cytohistological zonation based on staining affinity is not observed at any stage. The distal axial order (cr) includes the central group of corpus cells dividing periclinally and anticlinally and the overlying cells of the tunica. The peripheral zone is concerned with the initiation of the next leaf primordium and formation of the leaf sheath on the opposite side. It is delimited by the shell zone on the rhizome apices, which appears as an arc of narrow cells in median longitudinal section. The peripheral zone (pr₂) is associated with the initiation of the next leaf primordium. In the rhizome apices, it is also associated with the initiation of the axillary buds. As the phyllotaxy is distichous, this zone is opposite to pr₁ in median longisections. Pith cells differentiate in the inner axial zone (rr).

Seven developmental stages of the apical bud have been recognized (Shah and Raju 1975b). In the first stage (dormant apex), the shoot apex lies in a shallow depression, the apex measures 116–214 μm × 45–70 μm. A few cells toward the flank showed increased concentrations of DNA as evidenced by dense staining. Some cells of pr₁ and pr₂ showed dense stainability for C-RNA (cytoplasmic RNA). The outer corpus cells show peripheral divisions. In the second stage, the apex is dome-shaped, and its width and height are 94–165 μm and 35–75 μm, respectively. Zones pr₁ and pr₂ show denser histological staining than cr and rr zones. A biochemical zonation is present at pr₂ that shows deep staining for DNA. The apex at stage three measures 74–140 μm in width and 53–86 μm in height and is dome-shaped. The cells of the inner axial zone are vacuolated. The shoot apex dome at stage four is 140–160 μm high and 90–116 μm wide. Outer corpus cells are vertically elongated. At stage five, the apex is a low dome having 214–248 μm height and 53–75 μm width. Cells of the pr₂ zone show dense staining. The apex of stage six is prominently dome-shaped having a width of 169–200 μm and height of 87–96 μm. During stage seven, the underground branch reaches the soil level. The shoot apex is 91–112 μm in width and 134–167 μm in height.

All of the underground branches of ginger show a negative geotropic response. Two kinds of apices are found in ginger: the apices which are low dome and surrounded by either scale leaves or leaf bases; and they are dome-shaped and raised on an elongated axis. In the base of the rhizome apices, cells derived from the inner axial zone elongate tangentially and contribute to the widening of the axis. In certain cases, these cells extend up to the base of the axillary buds. In a dormant apex, they are thick-walled and contain starch grains. These cells are distinct in the dormant or early active rhizome apex and constitute latitudinal growth meristem. During the vascular differentiation, a few cells of this meristem develop into procambium. During subsequent development of the rhizome apex, the cells derived from the inner axial elongate and contribute to the pith.

15.13.2 Procambial Differentiation

The peripheral or flank meristem divides periclinally and produces parenchymal cells. Some of the cells are distinguishable from the rest by deeper stainability, smaller size, less or no vacuolation, and darkly stained nuclei. These are the procambial initials, and each such group contains 15–20 cells. Subsequently, these cells elongate, vacuolation increases, and they develop gradually into sieve tubes. Protophloem differentiation precedes that of protoxylem. The collateral differentiation of phloem and xylem with parenchymal bundle sheaths becomes distinct after an intermediate stage of random differentiation of the bundles. Ultimately, the vascular bundles are found scattered in parenchymal ground tissue. In TS, an endodermoidal layer is also visible during the development (Ravindran et al. 1998; Ramashree et al. 1998).

15.13.3 Axillary Bud

The development of leaves and scale leaves that encircle the shoot apex in ginger rhizomes is in a clockwise direction. The axillary bud meristem is first discernible in the axillary position on the adaxial sides of the third leaf primordium from the apical meristem as a distinct zone by the stainability of the constituent cells and multiplane division of the cells in the concerned peripheral meristem sectors. The axillary buds thus originate as a cellular patch in the adaxial side of a leaf or scale leaf of the node. In a fully developed axillary bud, the cytohistological zones akin to the main shoot apex can be distinctly observed. The development of a new rhizome is by the enhancement of a dormant axillary bud, which acts just like the main shoot apex. The procambial cells and the ground meristem cells divide, and parenchyma as well as vascular tissues add thickness to the newly enhanced axillary bud. Likewise, many buds become active during favorable conditions, each of which produces secondary or tertiary rhizomes. The axillary buds show vascularization by the activity of the procambial strands of the mother rhizome, and procambial cells originated from the differentiation of the parenchymal cells.

15.13.4 Development of the Root

The adventitious root primordial becomes different endogenously from the endodermoidal layer of the rhizome. Roots always develop just below the nodal region. The TS of the rhizome reveals that the endodermoidal layer and the pericycle become meristematic and undergo periclinal and anticlinal divisions resulting in a group of root initials. This is in direct connection with the vascular ring situated beneath the endodermoidal layer. The root primordial is of the open type having common initials for the cortical meristem, root cap, and protoderm. The actively dividing and deeply staining central cylinder shows vascular connections with the rhizome vasculature. As the enlarging root primordial emerges through the cortex, the cortical cells are crushed and torn apart. Normally, these roots originate from the lateral or opposite side of the axillary bud and scale leaf.

15.13.5 Phloem

As a rule, there is no secondary growth in monocots. However, the rhizome structure of ginger provides evidence of both primary and secondary growth having a well-developed endodermoidal layer and cambium. The vascular bundles are collateral, closed, and scattered in the ground parenchyma. The phloem element consists of the sieve tube, companion cells, parenchyma, and fiber.

15.13.6 Sieve Tube

Phloem cells originate from a group of actively dividing procambial cells of PTM. These cells can be distinguished from the surrounding cells by their meristematic activity, stainability, and size of the nucleus. During development, a procambial cell elongates and becomes thick-walled with cytoplasm and a prominent nucleus; this is the sieve tube mother cell. It undergoes a longitudinal unequal division, and the resulting smaller cell gives rise to the companion cell. This cell continues to divide, forming four to eight cells. The large cell is the sieve cell. It has cytoplasm and nucleus in early stages, which degenerate during the development into the sieve tube. During further development, the vacuolation increases, and the cytoplasm shrinks and appears like a thread along the wall. At the same time, the nucleus disintegrates, and the cell assumes the features of the enucleated sieve tube element. The transverse wall of the sieve tube changes to simple sieve plates with many pores and with very little callose deposition. The first sieve tube element can be distinguished at a distance of 720–920 μm from the shoot apex.

In the ginger rhizome, four to eight companion cells per sieve tube element are arranged in the vertical lines with transverse end walls. They may vary from 18 to 32 μm in length and 7–19 μm in width. The sieve tube elements are arranged end to end to form columns of sieve tubes. The length of a sieve tube element varies from 57.5 to 103.8 μm, the average being 76.8 μm. The width varies from 5.29 to 10.35 μm, the average being 8.76 μm (Ramashree et al. 1998). At the early stage of development, the slime body is present in the sieve tube, which appears to be amorphous but homogenous. Subsequently, the slime body disintegrates.

Development of a sieve tube in ginger is pycnotic, similar to the second type of nuclear degeneration reported by Esau (1969). The sieve element passes through a “fragmented multinucleated stage,” a unique feature in the ontogeny of the multinucleated sieve tubes as reported by Esau (1953).

15.13.7 Phloem Parenchyma

The phloem parenchyma cells are comparatively larger than the companion cells and smaller than the normal cortical parenchymal cells. The increase in size of the phloem element is proportional to the growth of the rhizome. Some older phloem parenchymal cells become lignified into thick phloem fibers.

15.14 Anatomical Features of Ginger in Comparison to Related Taxa

Ginger has many species-specific anatomical variations. These variations were shown in a comparative investigation of ginger and three other related species (Ravindran et al. 1998), and the salient features are given in Table 15.4.

Table 15.4 Comparative anatomy of four species of Zingiber

The salient features in Table 15.4 present important anatomical similarities and differences among the four species investigated. Ginger has distinct anatomical features compared to other species, such as the absence of periderm, short-lived functional cambium, the presence of xylem vessels with scalariform thickening, helical and scalariform-type xylem tracheids, scalariform perforation plate, outer bundles with a collenchymatous bundle sheath, and high frequency of oil cells. The oil cell frequency was found to be 17.8/mm² in ginger, whereas the corresponding frequency in the other species was 9.5, 5.3, and 2.8/mm² in Z. zerumbet, Z. marostychum, and Z. roseum, respectively. Species differences were also noticed in fiber length, fiber width, and fiber wall thickness. Histochemical studies indicated Z. zerumbet has greater amount of fibers than the others.

In general, xylem elements in Zingiber consist mainly of tracheids and rarely of vessels. The secondary wall thickening in the tracheids of ginger is of two types, scalariform and helical. The rings, or helices, are arranged in either a loose or a dense manner. The helical bands are found joined in certain areas giving ladderlike thickening. The width of helical tracheids is less than that of scalariform tracheids. Similar tracheids are present in Z. macrostachyum, whereas in Z. zerumbet and Z. roseum, only scalariform thickening occurs (Ravindran et al. 1998). Xylem vessels occur in ginger and not in other species. Snowden and Jackson, while studying the microscopic characters of ginger powder, recorded that the vessels are fairly large, reticulately thickened, less commonly spiral, and annularly thickened.

15.14.1 Leaf Anatomical Features

The leaves of ginger are isobilateral. The upper epidermal cells of leaf are polygonal and predominantly elongated at right angles to the long axis of the leaf. In the lower epidermis, the cells are polygonal and irregular, except that at the vein region, where they are vertically elongated and thick-walled. The epidermal cells in the scale and sheath leaves (the first 2–5 leaves above the ground are without leaf blades) are elongated and parallel to the long axis of the leaf. Oil cells in the upper and lower epidermis are rectangular, thick-walled, and suberized. Unicellular hairs are present in the lower epidermis of the foliage leaves. Occasionally, a hair is present at the polar side of the stomata. Ginger leaves are amphistomatic. A distinct substomatal chamber is present. Stomata are either diperigenous or terraperigenous. Occasionally, anisocytic stomata are also observed. The subsidiary cells are completely aligned longitudinally with the guard cell. The lateral subsidiary cells may divide to form anisocytic stomata. Occasionally, three to five lateral subsidiary cells are formed by further division (Raju and Shah 1975).

The guard cells on the foliage leaves are 40.6 μm long, whereas those on the sheath and scale leaves are only 28.9 μm long. The stomata on the scale leaves are rarely on the sheath leaves, which show pear-shaped guard cells with a large central pore. The nuclei of the guard cells are smaller than those in the subsidiary cells. Raju and Shah (1975) also reported the uncommon wall thickening at the polar ends of the guard cells. This wall thickening may be restricted to the outer wall at the polar regions or may also be extended to the common inner cell wall.

Tomlinson (1956) provided a brief note on the petiolar anatomy of ginger. The shorter petiole shows a swollen pulvinus-like appearance. The TS just above the pulvinus shows typical structure with two bundle arcs, air canals, and collenchymas. The TS through the pulvinus shows a different structure. Here, air canals and assimilating tissues are absent; there is extensive hypertrophy of ground tissue parenchymal cells and abundant deposition of tanniferous substances. The most striking feature according to the author is the collenchymatous thickening of the cells of the bundle sheath. Below the pulvinus structure is again normal as that of the pulvinus region. Table 15.5 gives the comparative leaf anatomical features of the four species of Zingiber.

Table 15.5 Leaf anatomical characteristics in four species of ginger

The stomata are tetracyclic in all the species. The first two subsidiary cells are parallel to the guard cells, and the other two lie at right angles. In Z. officinale, Z. roseum, and Z. macrostachyum, there is a special thickening of the upper and lower sides of the guard cell, but Z. zerumbet showed some extra thickening on the corners of subsidiary cells. The stomatal index was higher in Z. zerumbet. Guard cells were the largest in Z. zerumbet, followed by Z. officinale and Z. macrostachyum. In Z. roseum, the guard cells were shorter and broader. The leaf anatomical characteristics in four species of ginger are given in Table 15.5.

15.14.2 Stomatal Ontogeny

Raju and Shah (1975) described the structure and ontogeny of stomata of ginger. Here, the differentiation of a guard cell, mother cell, or a meristemoid occurs by an asymmetrical division of protodermal cells. The meristemoid is distinguished from the adjacent protodermal cells by its small size, dense sustainability of cytoplasm, and less vacuolation. The anticlinal wall of the meristemoid appears lightly stained with periodic acid-Schiff (PAS) reaction than the lateral walls of the epidermal cell and the meristemoid. The epidermal cell on either side of the meristemoid divides to form a small subsidiary cell. This epidermal cell shows dense sustainability for nuclear DNA. The young lateral subsidiary cells are smaller than the epidermal cells. Subsequently, the meristemoid divides to form a pair of guard cells. The epidermal cells that lie at the polar region of the guard cell may divide occasionally and completely about the stomatal complex and appear as subsidiary cells (Raju and Shah 1975).

15.14.3 Anatomical Features of Dry Ginger

In commercial ginger rhizome (peeled dried rhizome), the outer tissue consisting of the cork, the epidermis, and the hypodermis is scraped off. Hence, the TS of processed rhizome consists of the cortex, endodermis, pericycle, and central cylinder or the vascular zone. The epidermis (of dry unpeeled ginger) is frequently disorganized, consisting of longitudinally oblong-rectangular cells; the cork consists of several layers of oblong-rectangular, thin-walled suberized cells. The cortex is made of (i) thin-walled parenchymal cells containing plenty of starch grains, (ii) brown-colored oleoresin and oil cells scattered throughout the cortex, and (iii) fibrovascular bundles. There is an unbroken endodermis made of tangentially elongated cells with thickened suberized radial walls. Below the endodermis, there is a pericycle that consists of an unbroken ring of tangentially elongated cells.

The central cylinder consists of outer and inner zones. In the outer zone, adjoining the pericycle, there is a vascular bundle zone with fibers. Fibrovascular bundles and oleoresin cells occur in the central zone of the central cylinder. The ground tissue of the central cylinder consists of thin-walled parenchymal cells containing starch.

The fibrovascular bundles are large. In longisections, the fibers are long with moderately thick walls and a wide lumen. The vessels are large and scalariform, except in the vascular bundle zone, adjoining the pericycle, where large reticulate vessels, scalariform vessels, and some special vessels occur.

Starch grains are present in abundance. The granules are ovate, and many are characterized by a protuberance at one end. They vary in size to about 45 μm in length and 24 μm in width. Under polarized light, the granules exhibit a distinct cross through the hilum at the tapering end (Parry 1962).

15.15 Microscopic Features of Ginger Powder

Ginger rhizome powder is pale yellow or cream in color with a pleasant, aromatic odor and a characteristic and pungent taste. The diagnostic characteristics of ginger powder are as follows:

• 1. The abundant starch granules are mostly simple, fairly large, flattened, oblong to subrectangular to oval in outline with a small pointed hilum situated at the narrower end; infrequent granules show very faint transverse striations. Compound granules with two components occur very rarely.

• 2. The fibers usually occur in groups and may be associated with the vessels; they are fairly large, and one wall is frequently dentate; the walls are thin and marked with numerous pits, which vary from circular to slit-shaped in outline; very thin transverse septa occur at intervals. The fibers give only a faint reaction for lignin.

• 3. The vessels are fairly large and usually occur in small groups associated with the fibers; they are reticulately thickened, frequently showing distinct, regularly arranged rectangular pits, and are often accompanied by narrow, thin-walled cells, containing dark brown pigment; a few smaller, spirally thickened vessels also occur. All the vessels give only a faint reaction to lignin.

• 4. The oleoresin cells in uncleared preparations are seen as bright yellow ovoid to spherical cells occurring singly or in small groups in the parenchyma.

• 5. The abundant parenchyma is composed of thin-walled cells, rounded to oval in outline with small intercellular spaces; many of the walls are characteristically wrinkled; the cells are filled with starch granules or oleoresin. Occasionally, groups of parenchyma are associated with thin-walled tissue composed of several rows of collapsed cells.

15.16 Floral Anatomy

Rao and Gupta (1961), Rao and Pai (1959, 1960), and Rao et al. (1954) investigated the floral anatomy of the members of Scitamineae, in which a few species of Zingiber were also included. The floral anatomy of Z. ottensi, Z. macrostachyum, Z. cernuum, and other Zingiber species was reported by these investigators. On account of the basic similarities in floral characters, it is presumed that the floral anatomical features will also be identical. The following discussion is based on the reports of the abovementioned investigators. The floral anatomical features of Z. cernuum (which is different from Z. officinale only by the absence of staminodes) show that the peduncle contains two rings of vascular bundles with a few strands in the central pith. The inner ring gives off three dorsal bundles of the carpels outward, and the latter then divides into three large strands alternating in position with the dorsal bundles of the carpels. The central strands unite first into one bundle for a short length and fuse with the vascular tissue immediately to the outside. The three large bundles divide first into smaller inner placental bundles and a large outer parietal bundle. The parietal bundle travels into the septa and sends a few outward branches into the ovary wall. The placental bundles in the axile area bear the ovular traces. The posterior parietal bundle is larger and divides even at a lower level than the other two into two or three. A transverse section through the basal part of the ovary at this level shows the following: (i) a comparatively thick ovary wall in which there are numerous vascular bundles almost irregularly scattered; (ii) in each of the three septa, there is a prominent bundle that may divide into two; and (iii) in the placental zone, there are 6–10 strands that bear traces for the ovules. Most of the potential bundles are exhausted in supplying the ovules, while one or two may fuse with the nearest parietal bundle. The loculi extend for a considerable distance above the ovuliferous zone, and in this terminal part of the ovary, the number of bundles in the ovary wall is reduced by fusions among themselves, and all of them form almost a single ring near the level where the loculi end. Just on top of the ovary, the three parietal strands, which have already divided into two or three bundles, extend laterally and form a broad network-like cylinder of vascular tissue. This network establishes vascular connections (anastomoses) with the peripheral bundles. The three loculi continue upward into a X-shaped stylar canal. After the anastomosis, the vascular tissue directly forms (i) an outermost ring of about 15 small bundles for the calyx and (ii) a next inner ring of about 25 larger strands for the corolla and androecial members, and (iii) toward the center a number of small scattered strands arrange somewhat in the form of an arc. The stylar traces are given off from the two margins of this arc-like group, and they stand close to the two arms of the Y-shaped stylar canal. The numerous small bundles, arranged at first as an arc, break up into two groups, which supply the two epigynous glands present in anterolateral positions. The tubular basal parts of the calyx containing the sepal traces referred to earlier are at first separated, and, at the same level, the two epigynous glands also separate. A very short distance above the style also separates.

The basal part of the floral tube contains a ring of vascular bundles, an additional bundle in the median posterior position, and a pair of closely placed bundles on either side. The median posterior strand and the double strands on either side constitute the supply to the functional stamen. One of the component bundles of each double strand divides into two in such a way as to result in a third bundle that lies toward the inner side with its xylem pointing to the outside. On the anterior side of the floral tube, the vascular bundles divide and form two rings, whereas on the posterior face, external to the stamen traces, there is only one ring of bundles. The latter are for the labellum, whose margins are fused to a short distance with those of the filament. The outer ring of bundles is for the corolla.

The flat filament receives (i) a small median bundle; (ii) a triple strand on either side of it, the constituent bundles of which more or less fuse together; and (iii) two or four minute strands toward either margin. The lateral triple strands are opposite the line of attachment of the anther lobes to the filament. The minute marginal traces disappear quickly, leaving only a small median bundle and the two lateral large composite ones. These run in parallel manner upward, and the composite strands of each lateral group fuse together more or less completely, so that the anther connective contains a small median and two large lateral bundles. Above the level of the anther, the connective is continued upward as a narrow flat plate with margins incurved and enclosing the style. Each of the two composite lateral strands becomes smaller and divides into two. Thus, in the terminal part of the filament, five bundles are present, of which one is the median one. The median bundles fade out first, leaving a pair of bundles on either side. The bundles of each pair then fuse together giving only two bundles, which run right up to the tip and disappear.

The style receives only two traces, and these run throughout its length without any branching. The styled canal is narrow, Y-shaped, the arms of the Y pointing to the posterior side. Toward the tip, the arms of the stylar canal spread out so that the canal appears as a curved slit in transverse sections. It then widens out into a large canal, which opens freely to the outside. The two vascular bundles of the style become more prominent in this terminal part and then disappear (Rao and Pai 1959).

15.17 Floral Biology

Ginger flowers are produced in the peduncled spikes arising directly from the rhizomes. The oval or conical spike consists of overlapping bracts, from the axils of which flowers arise, each bract producing a single flower. The flowers are fragile, short-lived, and surrounded by a scariose, glabrous bracteole. Each flower has a thin tubular corolla that widens up at the top into three lobes. The colorful part of the flower is the labellum, the petaloid stamen. The labellum is tubular at the base, three-lobed above, pale yellow outside, dark purple inside the top and margins, and mixed with yellow spots. The single fertile anther is ellipsoid, two-celled, and cream-colored and dehisces by longitudinal slits. The inferior ovary is globose, the style is long and filiform, and the stigma is hairy. Flowering is not common and is probably influenced by climatic factors and photoperiod. On the West Coast of India (Kerala State), most of the cultivars of ginger flower if sufficiently large rhizome pieces are used for planting. When rhizomes are left unharvested in pots, profuse flowering occurs in the following growing season. Flowering is also reported from the East Coast of India (Bhubaneshwar in Odisha State). However, ginger does not usually flower or flowers very rarely in the growing areas of such locations as Himachal Pradesh, Uttar Pradesh, West Bengal, and Northeast India. Holttum (1950) reported that ginger seldom, if at all, flowers in Malaysia. Flowering is reported from South China, but not from North China, and also from Nigeria. In general, ginger does not flower under subtropical or subtemperate climatic conditions. Japanese investigators reported that flowering leads to yield reduction. Ginger is shown to be a quantitative short-day plant (Adaniya et al. 1989).

Jayachandran et al. (1979) reported that the flower bud development took 20–25 days from the bud initiation to full bloom and 23–28 days to complete flower opening in an inflorescence. Flower opening takes place in an acropetal succession. Anthesis is between 1:30 PM and 3:30 PM under the climatic conditions prevailing in the West Coast (Malabar region) of Kerala State, India. Anther dehiscence almost coincides with flower opening. The flowers fade and fall the following day in the morning. There is no fruit setting.

Das et al. (1999) reported floral biology in four cultivars of ginger (Bhaisey, Ernad Chernad, Gorubathan, and Turia local). They observed that anthesis under greenhouse and field conditions took place at around 1 PM−2 PM under coastal conditions of Odisha State, India. Flowers were hermaphroditic with pin-and-thrum-type incompatibility, and dehisced pollen grains did not reach the stigma. Selfing and cross-pollination did not produce any seed set.

15.18 Self-Incompatibility

Dhamayanthi et al. (2003) investigated the self-incompatibility system in ginger. They reported that heterostyly with a gametophytically controlled self-incompatibility system exists in ginger. Flowers are distylous, there are long (“pin”) and short (“thrum”) styles. The “pin” type has a slender style that protrudes out of the floral parts, which are short, covering not even half the length of the style. The stigma is receptive before the anthesis, whereas the anthers dehisce after 15–20 h. The anthers are situated far below, and hence the pollen grains cannot reach the stigma. In case of the “thrum” style, the stigma is very short, and the staminodes are long and face inward. However, the occurrence of thrum styles is very rare among cultivated ginger. According to the abovementioned investigators, this heterostyly situation may be a contributing factor to the sterility in ginger. However, this may not be very important as almost all cultivars are the “pin” type and pollination is entomophilous, mostly by honeybees. Dhamayanthi et al. (2003) have also reported inhibition of pollen tube growth in the style, and this was interpreted to be due to incompatibility. Adaniya (2001) reported the pollen germination in a tetraploid clone of ginger, 4×Sanshu. Pollen germination was the highest at around 20 °C, and pollen tube growth in the style was greatly enhanced at 17 °C. At this temperature, the pollen tubes penetrated into the entire length of the style in 66.7% of the styles analyzed. Pollen stored for 3 h at 40–80% RH completely lost its viability, whereas pollen incubated at 100% RH retained relatively high germinability. When the RH was low, the pollen tube in the style stopped growing. Hence, for pollen to germinate and grow in the stylar tissue, relatively low temperature (approximately 20 °C) and 100% RH are essential.

15.19 Embryology

The embryology of ginger has not been investigated critically until now, and it is rather amazing that such an economically important species has been ignored by embryologists from their investigations. Possibly, absence of flowering and seed set in most growing regions could have been an important contributory factor for this lack of interest and investigation in this specific field. However, some scanty information is available in a related species, namely, Z. macrostachyum. The embryological features of the genera in Zingiberaceae are similar, and hence, the information on Z. macrostachyum may as well be applicable to ginger.

The embryo sac development follows the Polygonum type (Panchakshrappa 1966). The ovules are anatropous, bitegmic, and crassinucellate and are born on an axil placentation. The inner integument forms the micropyle. In the ovular primordium, the hypodermal archesporial cell cuts off a primary parietal cell and a primary sporogenous cell. The former undergoes anticlinal division. The sporogenous cell enlarges into a megaspore mother cell, which undergoes meiosis forming megaspores. The chalazal spore enlarges and produces the embryo sac. Its nucleus undergoes three successive divisions resulting in an eight-nucleate embryo sac. Prior to fertilization in Z. macrostachyum, the synergids and antipodals degenerate. The fate of the nuclei in the embryo sac of ginger (which is a sterile species) is not known. However, some studies have indicated that a postmeiotic degeneration of the embryo sac can happen (Pillai, personal communication).

15.20 Cytology, Cytogenetics, and Palynology

15.20.1 Mitotic Studies

The chromosome number of ginger was reported as 2n = 22 by Moringa et al. (1929) and Sugiura (1936). Darlington and Janaki Ammal (1945) cited a report from Takahashi (1930) who claimed 2n = 24 for Z. officinale. A more detailed study was carried out by Raghavan and Venkatasubban (1943) on the cytology of three species, namely, Z. officinale, Z. cassumunar, and Z. zerumbet, and all the three had the somatic chromosome number 2n = 22. Based on the differences in ideogram morphology, the abovementioned researchers concluded that the chromosome morphology of Z. officinale was different from that of the other two species. Darlington and Janaki Ammal (1945) reported two “B” chromosomes in certain types of ginger in addition to the normal complement of 2n = 22. Chakravorti (1948) also found 2n = 22 in ginger. He concluded that in view of the normal pairing of 11 bivalents in species, such as Z. cassumunar and Z. zerumbet, Z. mioga having a somatic chromosome number 2n = 55 is to be considered as a pentaploid. Table 15.6 gives a summary on the question of chromosome number.

Table 15.6 The Chromosome Reports on Zingiber

Ratnambal (1979) investigated the karyotype of 32 ginger cultivars (Z. officinale) and found that all of them possess a somatic chromosome number of 2n = 22. The karyotype was categorized based on Stebbin’s classification (Stebbins 1958), which recognizes three degrees of differences between the longest and the shortest chromosome of the complement and four degrees of differences with respect to the proportion of the chromosome that are acro-, meta-, and telocentric. An asymmetrical karyotype of “1B” was found in all the cultivars except cultivars of Bangkok and Jorhat, which have a karyotype asymmetry of 1A (Ratnambal 1979). Table 15.7 details karyotypes of various cultivars, which only exhibited minor differences.

Table 15.7 Karyotype variation in ginger cultivars

15.20.2 Meiosis

Ratnambal (1979) and Ratnambal and Nair (1981) investigated the process of meiosis in 25 cultivars of ginger. These cultivars exhibited much intercultivar variability in meiotic behavior. The presence of multivalent and chromatin bridges was found to be a common feature in most cultivars investigated by Ratnambal (1979). The presence of multivalent in a diploid species indicates structural hybridity involving segmental interchanges, and 4–6 chromosomes are involved in the translocations as evidenced by quadrivalents and hexavalents. This structural hybridity might be contributing to the sterility in ginger.

Structural chromosomal aberrations have occurred at all stages of microsporogenesis in ginger. The predominant aberrations were laggards, bridges, and fragments at anaphase as follows: (i) laggards, bridges, and fragments, irregular chromosome separation, and irregular cytokinesis at anaphase and (ii) micronuclei and supernumerary spores at the quartet stage. Ratnambal (1979) had shown a positive linear regression between pollen sterility and chromosomal aberrations at anaphase II and aberrant quarters. Structural chromosomal aberrations have been attributed to as the cause of sterility in ginger. But how such a diploid species such as ginger came to acquire a complicated meiotic system which led to chromosomal sterility is not well understood. A hybrid origin followed by continuous vegetative propagation can be one reason for the abnormal chromosomal behavior (Ratnambal 1979). Beltram and Kam (1984) studied meiotic features of 33 species in Zingiberaceae, including the 9 species of Zingiber. They observed various abnormalities such as aneuploidy, polyploidy, and B chromosomes. They also confirmed the diploid nature of the Malaysian ginger (x = 11) and the pentaploid nature of the Japanese ginger Z. mioga.

Das et al. (1998) studied meiosis and sterility in four ginger cultivars (Bhaisey, Ernad Chernad, Gorubathan, and Thuria local) and reported a 30.35–40.5% meiotic index in them. Pollen mother cells showed incomplete homologous pairing at metaphase I and spindle abnormalities (e.g., late separation, laggards, sticky bridges) at anaphase, leading to high pollen sterility. Das et al. (1999) opined that the sterility might be due to nonhomology of bivalents, with irregular separation of genomic complements leading to sterile gamete formation. The absence of germination pores on the pollen grains has also been indicated as an impediment to seed set.

15.20.3 Pollen Morphology

The earlier investigators (Dahlgen et al. 1985; Stone et al. 1979; Zavada 1983) were of the opinion that the pollen grains of the family are extineless, possessing a structurally complex intine (Hesse and Waha 1982). However, subsequent studies indicated that in the majority of the Zingiberaceae, an extinous layer does exist, although it is poorly developed in many taxa (Chen 1989; Kress and Stone 1982; Skavaria and Rowley 1988). Recent palynological investigations have demonstrated differences in pollen structure between sections of Zingiber: The Sect. Zingiber has spherical pollen grains with cerebroid sculpturing, whereas Sect. Cryptanthium has ellipsoid pollen grains with spirostriate sculpturing (Chen 1989; Liang 1988). The pollen of Zingiberaceae is usually classified as inaperturate, but Zingiber is an exception. Some investigators have described the pollen of ginger plant as monosulcate (Dahlgen et al. 1985; Zavada 1983), while others have described it as inaperturate (Chen 1989). The pollen is spherical or ellipsoidal. The spherical pollen grains have a cerebroid or reticulate sculpturing. The grains have a length of 110–135 μm and width of 60–75 μm. The pollen grains have a 2–3-μm-thick coherent extine. The intine consists of two layers, a 5-μm-thick outer layer and 2–3-μm-thick inner layer adjacent to the protoplast. The outer layer is radially striated. The inner layer has a distinct, minute fine structure. No apertures are present. It has been indicated that the entire wall functions as a potential germination site (Hesse and Waha 1982). Nayar (1995) studied the germinating pollen grains of 22 taxa in Zingiberales including Z. roseum and Z. zerumbet and reported that the pollen grains possess an extine containing sporopollenin. Inside this layer there is a well-defined lamellated cellulosic layer (described as the outer layer of intine by earlier researchers), which is the medine. The intine is membranous and consists of cellulose and protein and is, in fact, the protoplasmic membrane. At germination, a solitary pollen tube develops that has the protoplasmic membrane (intine) as its wall and pierces the outer layers smoothly even in the absence of a germ pore or aperture. The stainability percentage ranges from 14.7 in cultivar Thingpuri to 28.5 in cultivar Pottangi and cv. China. Usha (1984) observed 12.5% and 16.4% stainability in cultivars Rio de Janeiro and Moran, respectively. Pollen germination ranged from 8% in cultivar Sabarimala to 24% in cultivar Moran (Dhamayanthi et al. 2003). Pillai et al. (1978) reported 17% pollen germination in cultivar Rio de Janeiro. The pollen tube growth in vitro was maximum in cultivar China (488 μm) and minimum in cultivar Nadia (328 μm). The number of pollen tubes ranged from 6.5 (in cultivar Nadia) to 16.7 (in cultivar Varada) (Dhamayanthi et al. 2003).

15.21 Physiology of Ginger

15.21.1 Effect of Day Length on Flowering and Rhizome Enlargement

Ginger is grown under varying climatic conditions and in many countries in both the northern and the southern hemispheres. It is generally regarded as being insensitive to day length. Adaniya et al. (1989) carried out a study to determine the influence of day length on three Japanese ginger cultivars (Kinoki, Sanshu, and Oshoga) by subjecting the plants to varying light periods in comparison with natural daylight. In three cultivars, as the light periods decreased from 16 to 10 h, there was inhibition of vegetative growth of shoots and the underground stem. The rhizome knobs became more rounded and smaller. As the day length increased to 16 h, the plants grew vigorously, and the rhizome knobs became slender and larger and active as new sprouts continued to appear. When the light period was extended to 19 h, there was reduction in all of the growth parameters, and they were on par when the light period was just 13 h. It appears that the vegetative growth was promoted by exposure of the plant to a longer light period, up to a certain limit, whereas rhizome enlargement was accelerated under a relatively lower light period. The results also suggested that a relatively short-day length accelerated the progression of the reproductive growth, whereas relatively long day length decelerated it. Ginger plant is therefore described as a quantitative short-day plant for flowering and rhizome enlargement (Adaniya et al. 1989). These researchers have also observed intraspecific variations in photoperiodic response; cultivar Sanshu responded more sensitively, while Kinoki was more sensitive than Oshoga. They concluded that such an intraspecific response to the photoperiod could be related to their traditional geographical distribution. Kinoki and Sanshu are early-duration cultivars adapted to the northern part of Japan in Kanto District, and Oshoga is a late-duration cultivar adapted to the southern Japan (Okinawa to Shikoku districts).

Sterling et al. (2002) investigated the effects of photoperiod on flower bud initiation and development in Zingiber mioga (myoga or Japanese ginger). Plants grown under long day conditions (16 h) and short-day conditions (8 h) with a night break produced flower buds, whereas those under short-day conditions (8 h) did not. This failure of flower bud production under short-day conditions was due to abortion of developing floral bud primordia rather than a failure to initiate inflorescence production. It was concluded that although for flower development in myoga a quantitative long day requirement must be met, flower initiation was day neutral. Short-day conditions also resulted in premature senescence of foliage and reduced foliage dry weight.

15.21.2 Chlorophyll Content and Photosynthetic Rate in Relation to Leaf Maturity

Xizhen et al. (1998b) investigated the chlorophyll content, photosynthetic rate (Pn), malondialdehyde (MDA) content, and the activities of the protective enzymes during leaf development. Both chlorophyll content and Pn increased with leaf expansion and reached a peak on day 15 and then declined gradually. In the first 40 days of leaf growth, the MDA content of leaves remained constant, and superoxide dismutase (SOD) activity showed a little decrease. After 40 days, the MDA content increased markedly, and SOD activity dropped substantially. Peroxidase (POD) and catalase activities exhibited a steady increase during 60 days. Xizhen et al. (1998b) concluded that senescence in ginger leaf sets in when leaf age reaches about 40 days.

Xizhen et al. (1998a) also investigated the photosynthetic characteristic of different leaf positions and reported that the Pn of mid-position leaves was the highest followed by the lower leaves and Pn was lowest in upper leaves. The light compensation point of different leaf positions was from 18.46 to 30.82 μmol/1 m². It was highest in mid-position leaves and lowest in lower leaves. The light saturation point ranged from 624.8 to 827.6 μmol/1 m². The values were 624.8, 827.6, and 799.5 μmol/1 m², respectively, in the upper, middle, and lower leaves. CO₂ compensation points in upper, middle, and lower leaves were 1543.3, 1499.0, and 1582.0 μl/l. The diurnal variation of Pn in different leaf positions gave a double-peak curve, the first peak was at about 9 AM, and the second appeared from 1 PM to 2 PM.

15.21.3 Stomatal Behavior and Chlorophyll Fluorescence

Dongyun et al. (1998) studied the chlorophyll fluorescence and stomatal behavior of ginger leaves. Ginger leaves were enclosed individually in cuvettes and studied to find out the relationship between photosynthesis and changes in microclimate. Stomatal conductance (gsc) increased and was saturated at relatively low values of high intensity (400 μmol/l). At different leaf temperatures, gsc peaked at 29 °C, but transpiration (tr) increased with increased irradiance and temperature. Increasing external concentrations of CO₂ caused gsc to increase but were relatively insensitive to increasing soil moisture availability until a threshold was attained (0.5–2.0 g/g). At a soil moisture content of 2–3.5 g/g, gsc increased approximately linearly with increased transpiration. Fluorescence (Fv/Fm, electron transfer in PS II) decreased with increasing photon flux density (PFD). In leaves exposed to high PFD, and varying temperatures, Fv/Fm was the lowest at 15 °C and the highest at more than 25 °C. In leaves exposed to low PFD, Fv/Fm remained at a similar value over all temperatures tested.

15.21.4 Photosynthesis and Photorespiration

Zhenxian et al. (2000) measured using a portable photosynthetic system and a plant efficiency analyzer the photosystem inhibition of photosynthesis and the diurnal variation of photosynthetic efficiency under shade and field conditions. There were marked photoinhibition phenomena under high light stress at midday. The apparent quantum yield (AQY) and photochemical efficient of PS II (Fv/Fm) decreased at midday, and there was a marked diurnal variation. The extent of photoinhibition due to higher light intensity was severe in the seedling stage. After shading, AQY and Fv/Fm increased, and the degree of photoinhibition declined markedly. However, under heavier shade, the photosynthetic rate declined because of the decline in carboxylation efficiency after shading. Shi-jie et al. (1999) investigated the seasonal and diurnal changes in photorespiration (Pr) and the xanthophyll cycle (L) in ginger leaves under field conditions in order to understand the role of L and Pr in protecting leaves against photoinhibitory damage. The seasonal and diurnal changes of Pr and L of ginger leaves were marked, and Pr showed diurnal changes in response to PFD, and its peak was around 10 AM–12 PM. Pr declined with increasing shade intensity. The L cycle showed a diurnal variation in response to PFD and xanthophyll cycle pool. Both increased during the midday period and peaked around noon. The results, in general, indicated that Pr and the xanthophyll cycle had positive roles in dissipating excessive light energy and in protecting the photosynthetic apparatus of ginger leaves from midday high light stress.

Xizhen et al. (2000) have also investigated the role of SOD in protecting ginger leaves from photoinhibition damage under high light intensity. They observed that on a sunny day, the photochemical efficiency of PS II (Fv/Fm) and AQY of ginger leaves declined gradually in the morning but rose progressively after noon. The MDA content in ginger leaves increased, but the Pn declined under midday high light stress. SOD activity in ginger leaves increased gradually before 2 PM and then decreased. At 60% shading in the seedling stage, Fv/Fm and AQY of ginger leaves increased, but the MDA content, SOD activity, and Pn decreased. Pn, AQY, and Fv/Fm of ginger leaves treated with diethyldithiocarbamic acid (DDTC) decreased whether shaded or not, but the effect of DDTC on shaded plants was less than that on unshaded plants. These researchers concluded that midday high light intensity imposed a stress on ginger plants and caused photoinhibition and lipid peroxidation. SOD and shading played important roles in protecting the photosynthetic apparatus of ginger leaves against high light stress.

Xizhen et al. (1998a) have investigated the effect of temperature on photosynthesis of the ginger leaf. They showed that the highest photosynthetic rate and apparent quantum efficiency was under 25 °C. The light compensation point of photosynthesis was in the range of 25–69 μmol/m²; it increased with increasing temperature. The light saturation point was also temperature-dependent. The low light saturation point was noted at temperatures below 25 °C. The CO₂ compensation point and the saturation point were 25–72 and 1343–1566 μl/l, respectively, and both increased with the increase in leaf temperature.

Xianchang et al. (1996) investigated the relationship between canopy, canopy photosynthesis, and yield formation in ginger. They found that canopy photosynthesis was closely related to yield. In a field experiment using a plant population of 5000–10,000 plants/666.7 m² area, they obtained a yield increase from 1.733 to 2.626 kg, which is almost a twofold increase. The Pn increased from 8.16 μmol CO₂/m² l (ground) s⁻¹ to 14.66 and the LAI from 3.21 m²/m² to 7.02 m²/m². The unit area of branches (tillers) and LAI were over 150/m² and 6 m²/m², respectively, in the canopy of the higher yield class. The canopies over 7000 plants per 666.7 m² satisfied these two criteria, and among them there were no significant differences in height, number of tillers, LAI, canopy photosynthesis, and yield. Diurnal changes in the canopy Pn showed a typical single-peak curve, which was different from the double-peak curve obtained from the single leaf Pn.

15.21.5 Effect of Growth Regulators

Investigations have been carried out to find out the various growth regulators on ginger growth, flowering, and rhizome development. The principal objective of such investigations is to break the rhizome dormancy, to induce flowering and seed set, and to enlarge the rhizome, followed by enhanced yield. Islam et al. studied the influence of 2-chloroethylphosphonic aid (Ethrel or Ethephon) and elevated temperature treatments. Exposure of ginger rhizome pieces to 35 °C for 24 h or to 250 ppm Ethrel for 15 min caused a substantial increase in shoot growth during the first 23 days of growth. Ethrel was more effective in increasing the number of roots per rhizome piece by a factor 4.0 and the number of shoots having roots by a factor of 3.7 (both at day 16). Relatively low concentrations of Ethrel (less than 250 ppm) were sufficient to produce maximum responses in terms of shoot length parameters, although significant increases in the number of shoots per seed piece, the number of rooted shoots, and the total number and length of roots per seed piece occurred even up to the highest concentrations of 1000 ppm studied by Islam et al. Treatment of Ethrel was found to be effective in reducing the variability in root growth, but shoot growth variability had increased particularly at concentrations below 500 ppm.

Furutani and Nagao (1986) investigated the effect of daminozide, GA, and Ethephon on flowering, shoot growth, and yield of ginger. Field-grown ginger plants were treated with three weekly foliar sprays of GA (0, 1.44, and 2.88 mM), Ethephon (0, 3.46, and 6.92 mM), or daminozide (0.3, 1.3, and 6.26 mM). GA inhibited flowering and shoot emergence, whereas Ethephon and daminozide had no effect on flowering but promoted shoot emergence. Rhizome yields were increased with daminozide and decreased with GA and Ethephon.

Ravindran et al. (1998) tested three growth regulators—triacontanol, paclobutrazol, and GA—on ginger to find out their effect on rhizome growth and developmental anatomy. Paclobutrazol- and triacontanol-treated rhizomes resulted in thicker-walled cortical cells compared to GA and control plants. The procambial activity was higher in plants treated with triacontanol and paclobutrazol. In the cambium layers, the fusiform cells were much larger in paclobutrazol-treated plants. Growth regulator treatments did not affect the general anatomy, although dimensional variations existed. The numbers of vascular bundles were more in plants treated with paclobutrazol and triacontanol. Paclobutrazol-treated plants exhibited greater deposition of starch grains than other treatments. The fiber content in the rhizome was less in GA-treated rhizome. A higher oil cell index and higher frequency oil cells were observed in paclobutrazol-treated rhizomes. GA treatment also led to considerable increase in the number of fibrous roots.

15.21.6 Growth-Related Compositional Changes

Baranowski (1986) studied the cultivar Hawaii for 34 weeks and recorded the growth-related changes of the rhizome. The solid content of the rhizome increased throughout the crop season, but there was a decline in the acetone extractable oleoresin content of dried ginger. However, the oleoresin content on a fresh weight basis was roughly constant.

The (6)-gingerol content of ginger generally increased with the age of the rhizome on a fresh weight basis. These results indicate the basis for the gradual increase in pungency with maturity. On a dry weight basis, gingerol generally exhibited a linear increase with maturity up to 24 weeks, followed by a steady decline through the rest of the period. The results in general indicate that it may be advantageous to harvest ginger early (i.e., by 24 weeks) for converting to various products.

15.22 Genetic Resources

The history of domestication of ginger is not definitely known. However, the crop is known to have been under cultivation and use in India and China for the last 2000 years or even more. China is probably the region where domestication started, but little is known about the center of origin of the plant, although the largest variability in the crop exists in China. Southwestern India, known as the “Malabar Coast” (in Kerala State) in ancient times traded ginger with the Western world, which definitely indicates its cultivation in this region. This long period of domestication might have played a major role in the evolution of this crop which is sterile and propagated only vegetatively. Ginger has rich cultivar diversity, and most major growing tracts have cultivars which are specific to the area. These cultivars are mostly known by the region’s name. Cultivar diversity is richest in China. In India, the diversity is more in the Kerala State and in northeastern India. Being clonally propagated, the population structure of this species is determined mainly by the presence of isolation mechanisms and the divergence that might have resulted through the accumulation of random mutants. Presently, there are more than 50 ginger cultivars possessing varying quality attributes and yield potential being cultivated in India, although the spread of a few improved and high-yielding ones cause the disappearance of the traditional land races. The cultivars popularly grown (cultivar diversity) in the various ginger-growing states in India are given in Table 15.8. Some of these cultivars were introduced in India, and the cultivar Rio de Janeiro, an introduction from Brazil, has become very popular in Kerala State. Introductions such as China, Jamaica, Sierra Leone, and Taffin Giwa are also grown occasionally.

Table 15.8 Major ginger-growing states of India and their popular cultivars indicating diversity in the ginger plant

Among the ginger-growing countries, China has the richest cultivar diversity. Among the cultivars, Zaoyang of Hubei province is a very important one. Zunji big white ginger of Guizhou rovince is another important cultivar. Also, Chenggu Yellow of Shaanxi province, Yulin round fleshy ginger of Guangxi province, and bamboo root ginger and Mianyang ginger of Sichuan are other important ones. Xuancheng ginger of Anhui, Yuxi yellow ginger of Yunan, and Taiwan fleshy ginger may also be counted as important cultivars of China. Many of these cultivars have unique morphological markers for facilitating identification.

In general, the cultivar variability is much less in other ginger-growing countries. Tindall (1968) reported that there were two main types of ginger grown in West Africa. These differ in color of the rhizome, one with a purplish red or blue tissue below the outer scaly skin, whereas the other has a yellowish white flesh. Graham (1936) reported that there were five kinds of ginger recognized in Jamaica known as St. Mary, Red eye, Blue turmeric, Bull blue, and China blue. But Lawrence (1984) reported that only one cultivar is grown widely in Jamaica. According to Ridley, three forms of ginger were known in Malaysia in earlier times. These were Halia betel (true ginger); Halia bara or padi, a smaller-leaved ginger with a yellowish rhizome used only in medicine; and Halyia udanf, red ginger having red color at the base of the aerial shoot. A red variety of ginger Z. officinale var. rubra (also called pink ginger) has been found and decsribed in Malaysia. In this cultivar, the rhizome skin has a reddish color. A variety called Withered Skin also has been reported. In the Philippines, two cultivars are known, the native and the Hawaiian (Rosales 1938). In Nigeria, the cultivar Taffin Giwa (bold yellow-colored ginger) is the most common one encountered, the other being Yasun Bari, the black ginger.

In many cases, the major production centers are far from the areas of origin of the crop concerned (Simmonds 1979). This is true of ginger as well. The Indo-Malayan region is very rich in zingiberaceous flora (Holttum 1950). Considering the present distribution of genetic variability, it is only logical to assume that the Indo-Malayan region is probably the major center of genetic diversity for ginger. It may be inferred that geographical spread accompanied by genetic differentiation into locally adapted populations caused by mutations could be the main factor responsible for variations encountered in cultivated ginger (Ravindran et al. 1994). In India, the early movement of settlers across the length and breadth of the Kerala State and adjoining regions, where the maximum ginger cultivation is found, and the story of shifting cultivation in northeastern India (the second major ginger-growing sector in India) are well-documented sociological events. The farmers invariably carried along with them small samples of the common crops that they grew in their original place and domesticated the same in their new habitat, in most cases virgin forestlands. Conscious selection for different needs such as high fresh ginger yield, good dry recovery, and less fiber content over the years has augmented the spread of differentiation in this crop. This would have ultimately resulted in the land races of ginger today (Ravindran et al. 1994).

15.22.1 Conservation of Ginger Germplasm

In India, major collections of ginger germplasms are maintained at the Indian Institute of Spices Research (IISR) in Calicut, Kerala State, India, under the administrative control of the Indian Council of Agricultural Research in New Delhi, India. The other global collection and conservation center is the Research Institute for Spices and Medicinal Plants in Bogor, Indonesia. Concerted efforts in collection and conservation of ginger germplasms are underway in India. At present, the ginger germplasm conservatory at IISR has 645 accessions which include exotic cultivars, indigenous collections, improved cultivars, mutants, tetraploids, and related species (IISR 2002). In addition, 443 accessions are maintained at different centers of the All India Coordinated Research Project on Spices (AICRPS) and the National Bureau of Plant Genetic Resources (NBPGR), Regional Station, Thrissur AICRPS (in Kerala State, India); details of many collections centers are given in Table 15.9. The principal constraint involved in the conservation of germplasms of ginger is the widespread prevalence of soilborne diseases, of which rhizome rot caused by Pythium spp. (such as P. aphanidermatum, P. myriotylum, and P. vexans) and the bacterial wilt caused by Ralstonia solanacearum (Pseudomonas solanacearum) are the most devastating. Additionally, infection by the leaf fleck virus is also causing major worry for conservation. In field conditions, these diseases are extremely difficult to control, once the onslaught occurs, and subsequently they spread. Hence, in the National Conservatory for Ginger at IISR, ginger germplasm is conserved in specially made cement tubs under 50% shade, as excessive shade assists the spread of the disease. This is a nucleus gene bank to safeguard the material from the deadly diseases and to maintain the purity of germplasm from adulteration, which is very common during field planting. Every year, part of the germplasm is planted in the field for their evaluation of performance and the recording of important growth traits (Ravindran et al. 1994). The collections are harvested every year and replanted in the following crop season in fresh potting mixture. On harvest of the rhizomes, each accession is cleansed and dipped in fungicidal and insecticidal solutions to control disease spread and stored in individual brick-walled cubicles lined with sawdust or sand in a well-protected building to preclude any damage by rodents or other intruding animals.

Table 15.9 Germplasm collections of ginger in India

15.22.2 In Vitro Conservation

In vitro conservation of ginger germplasm is a safe and complementary strategy to protect the genetic resources from epidemic diseases and other natural disasters. This is also an excellent method to supplement the conventional conservation strategies. Conservation of ginger germplasm under in vitro conditions by slow growth was standardized at IISR, Calicut, Kerala State, India (Geetha 2002; Geetha et al. 1995; Nirmal Babu et al. 1996). By this method, ginger could be stored up to 1 year without subculture in half-strength MS medium 10 gel/l each of sucrose and mannitol in sealed culture tubes. The survival percentage of such stored material is 85%. At IISR, over 100 unique accessions of ginger are being conserved under in vitro gene bank as medium-term storage of germplasm (Geetha 2002; Ravindran et al. 1994). The possibility of storage at relatively high ambient temperatures (24–29 °C) by subjecting the ginger and related taxa to stress factors was explored by Dekkers et al. (1991). The increase in the subculture period was better with an overlay of liquid paraffin. After 1 year, 70–100% survival was observed.

Ravindran and associates (Anon 2004) standardized the use of synthetic seeds in the conservation process. Synthetic seeds, developed with somatic embryos encapsulated in 5% sodium alginate gel, could be stored in MS medium supplemented with 1mg/l benzyladenine (BA) at 22 ± 2 °C for 9 months with 75% survival. The encapsulated beads on transfer to MS medium supplemented with 1.0 mg/l benzylaminopurine (BAP) and 0.5 mg/l naphthalene acetic acid (NAA) germinated and developed into normal plantlets. The conservation of germplasm through microrhizome production was also investigated, and it was found that microrhizomes can be induced in vitro when cultured in MS medium supplemented with higher levels of sucrose (9–12%). Such microrhizomes can be easily stored for more than 1 year in culture. Without any acclimatization, 6-month-old microrhizomes can be directly planted in the field. The microrhizomes can thus be used as a disease-free seed material and for propagation, conservation, and exchange germplasm (Geetha 2002). This microrhizome technology is amenable for automation and scaling up.

Cryopreservation is a strategy for long-term conservation of germplasm (Ravindran et al. 1994). Efforts are continuing at IISR and NBPGR for developing such strategies. Cryopreservation of ginger shoot buds through an encapsulation–dehydration method was attempted by Geetha (2002). The shoot buds were encapsulated in 3% sodium alginate beads and pretreated with 0.75 M sucrose solution for 4 days and dehydrated in an air current from laminar airflow and then immersed in liquid nitrogen. Beads conserved like this on thawing and recovery exhibited 40–50% viability. The cryopreserved shoot beads were regenerated into plantlets. The studies carried out at IISR showed that vitrification and encapsulation–vitrification methods are more suitable for the cryopreservation of ginger shoot buds (Nirmal Babu, personal communication/unpublished data).

15.22.3 Characterization and Evaluation of Germplasm

A clear knowledge of the extent of genetic variability is essential for formulating a meaningful breeding strategy. Under a low variability situation, selection programs will not yield worthwhile benefits. In any vegetatively propagated species, the extent of genetic variability will be limited unless samples are drawn from distinctly different agroecological situations. Studies on genetic variability for yield and associated characters in ginger indicated the existence of only moderate variability in the germplasm. Little variability exists among the genotypes that are grown in the same area; however, good variability has been reported among cultivars that came from widely divergent areas.

One hundred accessions of ginger germplasm were characterized based on morphological, yield, and quality parameters (Ravindran et al. 1994). Moderate variability was observed in many yield and quality traits (Table 15.10). The number of tillers per plant had the highest variability, followed by rhizome yield/plant. Among the quality traits, the shogaol content recorded the highest variability, followed by crude fiber and oleoresin. None of the accessions possessed resistance to the causal organism of leaf spot disease, caused by Phyllosticta zingiberi. Quality parameters such as dry recovery and oleoresin and fiber contents are known to vary with soil type, cultural conditions, and climatic pattern (Ravindran et al. 1994).

Table 15.10 Mean, range, and coefficient of variation (CV%) for yield attributes and quality traits in ginger germplasm

Mohanty and Sarma (1979) reported that expected genetic advance and heritability estimates were high for the number of secondary rhizome and total root weight. Genetic coefficient of variation was high for weight of root tubers. Rhizome yield was positively and significantly correlated with the number of pseudostems (tillers), leaves, secondary rhizome fingers, tertiary rhizome fingers, total rhizome, plant height, leaf breadth, girth of secondary rhizome fingers, and number and weight of adventitious roots. Studies indicated that straight selection was useful to improve almost all the characters except the number of tertiary fingers and straw yield. Rattan et al. (1998) reported that plant height was positively and significantly correlated with the number of leaves, leaf length, rhizome length and breadth, and yield per plot. The number of leaves per plant was positively and significantly correlated with rhizome length, breadth, and yield. The rhizome length was also related to rhizome breadth and yield. Positive correlation of rhizome weight with plant height, tiller number, and leaf number was reported by Sreekumar et al. (1982). Mohanty et al. (1981) observed significant varietal differences for all the characters except for the number of tiller per plant and number of leaves per plant. Pandey and Dobhal (1993) observed a wide range of variability for most of the characters investigated by them. Rhizome yield per plant was positively associated with plant height, number of fingers per plant, weight of fingers, and primary rhizome weight/yield.

At IISR, Sasikumar et al. (1992) studied the 100 accessions of ginger germplasm for variability, correlation, and path analysis. They found that rhizome yield was positively correlated with plant height, tiller and leaf number, and leaf length and width (Table 15.11). Plant height also had a significant and positive association with leaf and tiller number as well as length and width of leaf. The association of leaf number with tiller number, leaf length, and width was also positive and statistically significant. Tiller number had a significant negative association with dry recovery. Leaf width had a positive significant association with dry recovery.

Table 15.11 Path analysis in ginger

Yadav (1999) reported a high genotypic coefficient of variation for length and weight of secondary rhizomes, weight of primary rhizomes, number of secondary and primary rhizomes, and rhizome yield per plant. High heritability, coupled with high genetic advance as a percentage of mean, was observed for plant height, leaf length, suckers per plant, number of mother and secondary rhizomes, weight of primary rhizome, and rhizome yield per plant, indicating that desirable improvement in these traits can be brought about through straight selection. Plant height followed by the number of tillers per plant and leaf length had a maximum direct effect on rhizome yield (Singh 2001).

Nybe and Nair (1979) suggested that morphological characters are not reliable to classify the types, although some of the types can be distinguished to a certain extent from rhizome characters. All the morphological characters were found to vary among types except for leaf breadth, LAI, and number of primary fingers. Mohandas et al. (2000) found that all the cultivars differed significantly in tiller number and leaf number. Yield stability analysis revealed that cultivars Ernad and Kuruppampady were superior, indeed, as they showed high rhizome yield, nonsignificant genotype–environment interaction, and stability in yield.

15.22.4 Biochemical Variability

Oleoresin of ginger is the total extract of ginger containing all the flavoring principles as well as the pungent constituents. The oleoresin contains two important compounds—gingerol and shogaol—the two constituents which contribute to the pungency of ginger. On long-term storage, gingerol gets converted to shogaol. The quality of ginger thus depends on the relative content of gingerol and shogaol. Zachariah et al. (1993) classified 86 ginger accessions into high-, medium-, and low-quality types based on the relative contents of the quality components. There are many ginger cultivars with high oleoresin content. A few of them, such as Rio de Janeiro, Ernad Chernad, Wayanad, Kunnamangalam, and Meppayyur, have high gingerol content as well. The intercharacter association showed a positive correlation with oleoresin, gingerol, and shogaol.

Shamina et al. (1997) investigated the variability in total free amino acids, proteins, total phenols, and isozymes using 25 cultivars. Moderate variations were recorded in the case of total free amino acids, proteins, and total phenols. Isozyme variability in the case of polyphenol oxidase, peroxidase, and SOD was reported to be low, indicating only a low level of polymorphism. The quality parameters of ginger cultivars are detailed in Table 15.12.

Table 15.12 Range, mean, and coefficient of variation in quality components in ginger cultivars

Table 15.13 contains information on germplasm evaluation. The screening details of ginger varieties/cultivars/accessions are given in Table 15.14.

Table 15.13 Evaluation of ginger germplasm for rhizome yield and yield attributes

Table 15.14 Screening of ginger germplasm against pests and diseases incidence

15.22.5 Path Analysis

The partitioning of phenotype correlation between yield and morphological characteristics into direct and indirect effects by the method of path coefficient analysis revealed that plant height exhibited a high direct effect as well as high indirect effect in the establishment of correlation between yield and other morphological characters (Nair et al. 1982; Ratnambal 1979). Rattan et al. (1998) indicated that the number of leaves per plant had maximum direct contribution to yield per plant, followed by rhizome breadth.

Das et al. (1999) reported very high positive direct effects of stomatal number, leaf area, leaf number, and plant height on rhizome yield. Leaf temperature, RH of leaves, stomatal resistance, and rate of transpiration showed negligible effects. The direct effect of leaf number on rhizome yield was very high (0.631), and this trait is recommended for use as a selection criterion for improving rhizome yield. The study of Pandey and Dobhal (1993) revealed that the strongest forces influencing yield are weight of fingers, width of fingers, and leaf width. Singh et al. (1999) grouped 18 cultivars into 3 clusters under Nagaland conditions based on D² analysis. The major forces influencing divergence of cultivars were rhizome yield per plant, oleoresin, and fiber contents.

Sasikumar et al. (1992) carried out path analysis using 100 accessions of ginger. They reported that plant height followed by leaf length exhibited the highest direct effect on the rhizome yield. Dry recovery had a negative direct effect on yield. All other direct effects were negligible. The highest indirect effect was for leaf number through plant height, followed by leaf length, again through plant height. In turn, plant height exerted a moderately good indirect effect on rhizome yield. Moderate indirect effects were also noticed in the case of leaf width (through plant height), leaf length, and leaf number (through leaf length). However, the researchers noticed a residual effect of 0.8217, thereby indicating that the variability accounted for in the study was only 18%. They concluded that plant height should be given prime importance in a selection program, as this character had positive and significant correlation as well as a good direct effect on rhizome yield.

Multiple regression analysis using morphological characters indicated that the final yield could be predicted fairly accurately taking into consideration the plant height, leaf number, and breadth of last fully opened leaf on the 90th and 120th days after planting (Ratnambal et al. 1982). Rattan et al. (1998) found that to improve the yield per plant, emphasis should be laid on the number of leaves per plant and rhizome length by employing partial regression analysis. Rai et al. (1999) reported that higher rhizome yields were strongly associated with chlorophyll-a, carbohydrate, and lower polyphenol levels in the leaf. Leaf protein contents showed significant correlation with carbohydrates and the chlorophyll a/b ratio. The chlorophyll a/b ratio also showed a highly positive correlation with the leaf carbohydrate content. However, polyphenols showed a significant positive correlation with chlorophyll-b and carotenoids with chlorophyll-a and chlorophyll-b.

15.23 Crop Improvement

Crop improvement research efforts on ginger are constrained due to the absence of seed set. As a result, clonal selection, mutation breeding, and induction of polyploidy were the crop improvement methods employed. More recently, somaclonal variations arising through the callus regeneration are also being made use of in crop improvement work. Most of the research in this area was carried out in India. The major breeding objectives are high yield, wide adaptability, resistance to pests and diseases (such as rhizome rot and bacterial wilt and Fusarium yellows), improvement in quality parameters (oil, oleoresin), and low fiber. Work in this area is carried out mainly at the IISR, Calicut; the AICRPS Center at High Altitude Research Station, Pottangi, under the administrative control of the Orissa University of Agriculture and Technology, Bhubaneshwar, Odisha State; and AICRPS (All India Coordinated Research Project on Spices) Center at the Y.S. Parmar University of Horticulture and Forestry at Solan, Himachal Pradesh, India.

Crop improvement research carried out until now is confined mainly to germplasm collection, evaluation, and selection. A large number of collections have been assembled at IISR, and these collections have been evaluated for yield and quality characters. In addition, a few introductions from other countries have also been made use of for breeding research. Some of the indigenous cultivars have been known to be high yielders and of good quality. In general, variability was found to be limited in cultivars grown in the same region, but wider variability is met within cultivars growing in geographically distant locations.

Khan (1959) reported the high-yielding capacity of Rio de Janeiro. In a trial with 18 cultivars, the yield of Rio de Janeiro was found to be double of China and Kerala (Thomas 1966). Kannan and Nair (1965), Muralidharan and Kamalam (1973), and Thomas and Kannan (1969) also found that cultivar Rio de Janeiro was found to be superior compared to other cultivars. However, the percentage of ginger recovery was lesser than that from cultivar Maran. Randhawa and Nandpuri (1970) evaluated 15 cultivars during 4 years and reported that none could outyield the local cultivar Himachal local under colder conditions of Himachal Pradesh. Jogi et al. (1978) also reported that the local cultivar Himachal produced the highest yield, followed by cultivar Rio de Janeiro.

Trials carried out at Kasaragod in Kerala State under the All India Coordinated Research Project on Spices indicated that the yield potential of cultivars Rio de Janeiro, Burdwan, and Jamaica (AICSCIP 1978) was quite high. In Assam, cultivar Nadia outyielded other cultivars (Aiyadurai 1966).

Nybe et al. (1982) evaluated 28 cultivars for their yield potential and noted that the fresh and dry ginger yields among them varied significantly. Fresh rhizome yield was highest in the cultivar Nadia, followed by cultivars Maran, Bajpai, and Narasapattam. Cultivar Nadia also gave the highest yield of dry ginger. Sreekumar et al. (1982) found that cultivars Rio de Janeiro and Kuruppampady were the very best yielders.

Muralidharan (1972) investigated the varietal performance of ginger in Wayanad, Kerala State, and concluded that the cultivar Rio de Janeiro gave the highest yield, whereas the yield of dry ginger was lower compared to that from other cultivars. Dry ginger yield was highest in the cultivar Tura. Cultivars Maran, Nadia, and Thingpuri are the other high yielders and were, more or less, on par with cultivar Rio de Janeiro in their performance. This author recommended cultivar Rio de Janeiro for fresh ginger production and cultivars Maran, Nadia, and Thingpuri if the aim is to obtain high quantities of dry ginger.

15.24 Evaluation and Selection for Quality

Jogi et al. (1978) evaluated 14 cultivars and reported that the fiber content ranged from 4.62% (Poona) to 6.98% (Narasapattam). Cultivar Karakkal was lowest in dry ginger recovery followed by cultivars Wayanad local and Rio de Janeiro. Cultivar Rio de Janeiro had the highest oleoresin content, whereas cultivar Karakkal had the highest oil content. Crude fiber was least in cultivars Nadia and China.

Nybe et al. (1982) evaluated 28 cultivars and reported that cultivars Rio de Janeiro and Maran had higher oleoresin content, 10.53% and 10.05%, respectively. Essential oil was highest in cultivar Karakkal (2.4%), and crude fiber was highest in Kuruppampady (6.47%). Sreekumar et al. (1982) found that the dry ginger recovery ranged from 17.7% in cultivar China to 28.0% in cultivar Tura. Cultivars having more than 22% dry recovery (Maran, Jugijan, Ernad Manjeri, Nadia, Poona, Himachal Pradesh, Tura, and Arippa) are suitable for dry ginger production.

15.25 Breeding Strategies

15.25.1 Conventional Method: The Clonal Selection Pathway

The clonal selection pathway has been the most successful breeding method in the absence of seed set. The steps involved are the collection of cultivars from diverse sources and their assemblage in one or more locations; evaluation of cultivars for superiority in yield, quality, or stress resistance; selection of promising lines; replicated yield trials in multilocations; selection of the best performers; their multiplication and testing in large evaluation plots; and finally their release for commercial cultivation. For a cultivar to be released, it should give a yield increase of 20% or more over the ruling standard cultivar. This strategy has been used successfully to evolve the present-day cultivars, which have been developed mainly for higher yield adaptability and quality, as depicted in Table 15.15.

Table 15.15 Elite cultivars developed and released for commercial cultivation

The general breeding objectives in most breeding programs have been high yield, high quality, resistance to fungal and bacterial pathogens, bold rhizomes, high dry recovery, and low fiber content. Resistance to Pythium (the causal organism of rhizome rot) and Ralstonia solanacearum (fungus causing bacterial wilt) has so far not been encountered. In one such selection program carried out at IISR, 15 cultivars short-listed from the germplasm evaluation program were tested in replicated trials for 4 years in 5 locations. Results are shown in Table 15.16. This effort led to the selection of Varada, one of the most important cultivated cultivars now in south and central India. The data presented in Table 15.16 also demonstrate the influence of genotype–environment interaction. The quality characters of these accessions are detailed in Table 15.17.

Table 15.16 Yield and dry recovery of ginger at different ginger-growing locations in India

Table 15.17 Yield, dry recovery, and quality of promising ginger accessions at IISR

In another trial for increasing the rhizome size, 15 bold rhizome accessions short-listed from the germplasm were tested in multilocation plots. Results are given in Table 15.17. Based on the overall superior performance, accessions 35 and 107 were selected, multiplied, and released for cultivation under the names IISR Rejatha and IISR Mahima, respectively (Sasikumar et al. 2003). Clonal selection programs for crop improvement were carried out at the High Altitude Research Station in Pottangi, Odisha State, and the Department of Vegetable Crops at the Y.S. Parmar University of Horticulture and Forestry, Solan, Himachal Pradesh. The former came out with the selections Suprabha and Suravi and the latter with the selection Himgiri. Details on yield and recovery of bold rhizome selections are given in Table 15.18.

Table 15.18 Yield and recovery of bold rhizome selections

15.25.2 Mutation Breeding

Ginger is not amenable to any conventional recombination breeding programs due to its inherent sterility. Induction of variability through mutations, chemical mutagens, ionizing radiation, and tissue culture (somaclonal variations) has been attempted by a few researchers (Gonzalez et al. 1969; Raju et al. 1980). In a general scheme for a mutation, rhizome bits were treated with chemical mutagens or irradiated with gamma rays. Ginger buds are sensitive to irradiation, and the LD₅₀ was reported to be below 2 Krd. The LD₅₀ (50% of the lethal dose) for germination was reported to be between 1.5 and 2.0 Krd (Giridharan 1984). Jayachandran (1989) treated the ginger cultivar Rio de Janeiro with gamma rays ranging from 0.5 to 1.5 Krd and ethylmethane sulfonate (EMS) at 2.0–10.0 mM and studied VM1 and VM2 generations to isolate useful mutants. This investigation revealed that the percentage of sprouting, survival, and height of plants decreased as the mutagen dose was increased. The LD₅₀ in the study for sprouting and survival was found to be between 0.5 and 1.0 Krd of gamma rays and below 8 mM of EMS.

Mutagen treatment affected tiller production; in the 1.5 Krd treatment, there was 45% reduction, whereas in 10 mM EMS, there was 61% reduction in tiller production. The mutagen treatment did not affect pollen fertility or improve seed set. Rhizome yield was affected in a dose-dependent manner.

Jayachandran (1989) analyzed the VM2 generation and found a significant reduction in plant height as the dose increased. The mean tiller number indicated transgression to either side of the control treatment. Similarly, the mean rhizome yield in the VM2 generation indicated shifts in both the directions, with the lower doses of the mutagens giving positive shifts and the higher doses giving negative shifts. The variation in rhizome yield ranged from 1 to 1320 g/plant. This same author found that lower doses of gamma rays (0.5–0.75 Krd) and EMS (2–4 mM) are more effective in inducing wider variations. Screening against the soft rot pathogen, Pythium aphanidermatum, and bacterial wilt caused by Ralstonia solanacearum did not reveal any change in pathogenic susceptibility. Jayachandran (1989) observed that the effects of mutagen treatment in the subsequent generations vanished, indicating the operation of strong diplontic selection.

Nwachukwu et al. (1994) irradiated rhizomes of two Nigerian cultivars (Yasun Bari and the yellow ginger Taffin Giwa) at a dose of 2.5–10.0 Gy gamma rays (Gy (Gray) is the unit of absorbed dose; 1 Gy = 100 Krd). In these cultivars, the GR 50 (50% growth reduction) was found to be at 5 and 6 Gy in Taffin Giwa and Yasun Bari, respectively. The LD₅₀ was found to be 8.75 Gy for both cultivars.

Mohanty and Panda (1991) reported the isolation of a high-yielding mutant from the VM3 generation. They employed EMS, sodium azide, colchicine, and gamma rays as mutagenic agents, and five cultivars, namely, UP, Rio de Janeiro, Thingpuri, PGS-10, and PGS-19, were treated and investigated in V1, V2, and V3 generations. Twenty promising individual clumps (“mutants”) were selected for evaluation. One of them V1K1-3 gave the highest rhizome yield of 22.08 t/ha, which was found to be significantly higher than the top yielder Suprabha. Six top yielders were further tested in comparative yield trials and multilocational field trials. The results indicated that V1K1-3 was superior and has been subsequently released for commercial cultivation in India under the name “Suravi.”

The genotype differences were consistent over the locations tested, and V1K1-3 was found to outyield all the others tested at all the locations. This line has a dry recovery of 23%. The rhizomes are plump with cylindrical fingers having dark glazed skin and dark yellow flesh with bulging oval tips and finger nodes, which are covered with deep-brown scales. This genotype has an oil content, oleoresin content, and crude fiber content of 2.1%, 10.2%, and 4.0%, respectively.

Tashiro et al. (1995) investigated induced isozyme mutations to find out the possible use of isozyme analysis as markers for detecting mutants at an early stage or under an in vitro culture system. They employed cultivars Otafuku, Kintoki, and Shirome Wase, and excised shoot tips were treated with 5 mM methyl nitrosourea (N-methyl-N-nitrosourea—MNU) for 5–20 min and cultured on MS medium supplemented with 0.05 mg NAA and 0.5 mg BA/l. Regenerated plants were analyzed to locate mutations in the following isozymes: glutamate dehydrogenase (GDH), glutamate-oxaloacetate transaminase (GOT), malate dehydrogenase (MDH), 6-phosphogluconate dehydrogenase (6-PGDH), phosphoglucomutase (PGM), and shikimate dehydrogenase (SKDH). Analysis of the untreated control gave uniform isozyme profiles, in the case of all the three cultivars. Five of the twenty-one MNU-treated plants had isozyme profiles which differed from the basic pattern of GOT, 6-PGDH, PGM, and SKDH. All of these isozyme mutants expressed morphological variations, such as multiple shoot formation, dwarfing, and abnormal leaves. The results indicated that treating shoot tips with MNU and then culturing them in appropriate media can recover mutants and that isozyme analysis is a good technique in detecting the rate of mutation and, hence, is useful in mutation breeding programs.

15.25.3 Polyploidy Breeding

Induced polyploidy has been tried in ginger to introduce variability and improve pollen and ovule fertility, growth, and yield. Ratnambal (1979) reported induction of polyploidy in the cultivar Rio de Janeiro through colchicine treatment. The tetraploids showed stunted growth and had reduced length and breadth of leaves. However, in this case a stable polyploidy line could not be established, and all the plants reverted to diploidy in the succeeding generations.

Ramachandran and Nair (1982) reported successful production of stable tetraploid lines in cultivars Maran and Mananthody. The polyploids were more vigorous than the diploids and flowered during the second year of induction. The stable tetraploid lines (2n = 44) had larger, plump rhizomes and gave high yield (198.7 g/plant). However, the essential oil content was lower (23%) than in the original diploid cultivar. There was considerable increase in pollen fertility in the tetraploids. These tetraploids are maintained in the germplasm collection, at IISR, Calicut, India.

Adaniya and Shirai (2001) induced tetraploids under in vitro conditions by culturing shoot tips in MS solid medium containing BA, NAA, and 0.2% w/v colchicines for 4, 8, 12, and 14 days and transferred the shoot tips to medium without colchicines for further growth. More tetraploids were recovered from buds cultured for 8 days. Induced tetraploid lines of the cultivars (4×Kintoki, 4×Sanshu, and 4×Philippinecebu 1) were later transferred to the field where they flowered. These tetraploids produced pollen with much higher fertility and germinability than the diploid plants (0.0–1.0% in the diploid plants as against 27.4–74.2% in the tetraploids).

Buderim Ginger Co., the commercial ginger company in Queensland, Australia, has developed and released for commercial cultivation a tetraploid line from the local cultivar. This line, named Buderim Gold, is much higher yielding and has plump rhizomes that are ideally suitable for processing (Buderim Ginger Co. 2002). Nirmal Babu et al. (1996) developed a promising line of cultivar Maran from somaclonal variants. This line is high yielding with bolder rhizomes and taller plants. In addition to somaclonal variation, other biotechnological approaches have been initiated to evolve disease-resistant genotypes.

The breeding strategies currently in use will not be useful to solve many of the serious problems besetting the ginger crop. Despite extensive search, no genes resistant to the most devastating disease of ginger, the rhizome rot, caused by Pythium, or Fusarium wilt or bacterial wilt, could be located in the germplasm collection. The absence of sexual reproduction and seed set imposes a severe restriction in the efforts of plant breeders to develop disease-resistant cultivars. Recourse to biotechnological approaches might provide solutions. However, efforts in this line are scanty. Resorting to recombinant DNA technology, using resistant genes to the target pathogen from other related plants, might be a viable path in evolving resistant ginger plants. This is, indeed, a long drawn-out effort, and it is hazardous to guess when a reliable solution would evolve. Until such times, cultural methods, such as good phytosanitation, crop rotation, and recourse to biocontrol agents, would be the only alternative. Even ginger nutrition is based on classical textbook knowledge. Recent advances in soil fertility and plant nutrition have shown that there are alternatives to classical methods of fertilizing crop plants. A well-nurtured ginger plant will be less susceptible to pest infestation. The case in point is with reference to the devastating “quick wilt” in Piper nigrum (black pepper), caused by the Phytophthora fungus, where Zn was found to be intimately involved (Nair 2002). A revolutionary soil testing program, now globally known as “The Nutrient Buffer Power Concept,” developed by Nair (1996), as opposed to classical textbook knowledge, has shown important alternatives (Nair 1969). It is for the ginger plant breeders, physiologists, agronomists, soil scientists, and especially biotechnologists to evolve a strategy, by pooling and sharing knowledge, as opposed to the watertight approaches currently being employed in India, and also perhaps elsewhere in the world, which will open up a new chapter in stable ginger production, currently ravaged by diseases and pests, and lead to production stability. This will open up a new chapter in ginger production across the world, where the crop is an important economic mainstay for millions of poor, marginal, and often rich farmers.