Kiwifruit (Actinidia spp.) Breeding

Abstract

Kiwifruit are the first representatives of the genus Actinidia to be domesticated and the most recent fruit to be globally commercialized. They present challenges to breeders and orchardists due to long juvenility , dioecy , high heterozygosity , multiple ploidies and climbing growth habit. The first cultivars were selections from the wild or open-pollinated varieties but, since breeding began in New Zealand in the 1970s, progress has been made in several countries. Yellow-fleshed and red-fleshed kiwifruit are now found alongside the original green-fleshed varieties. Global production has increased significantly in recent years, as have the number of cultivars available in some countries. However, many commercially important and globally distributed Actinidia cultivars remain vulnerable to the bacterial canker of kiwifruit pandemic caused by Pseudomonas syringae pv. actinidiae. The molecular genetics revolution is poised to accelerate the development of new cultivars now that the Actinidia genome sequences and low-cost genotyping are becoming available. Conventional breeding is already augmented by marker -assisted selection and now genomic selection will be applied in kiwifruit and their smaller berry -like relatives. The results will soon provide consumers worldwide with a range of appealing flavors, colors, health benefits and fruit formats from the Actinidia genus.

Appendix: Genetic Resources of Actinidia

The following is a list of Actinidia cultivars mentioned in the text and/or of significance. A fuller treatment of characteristics, cultivation techniques, and other details can be found in Huang (2016a). There is little information on the under surveyed diversity available in China or the contents of repositories, botanic gardens, and private collections around the world.

Bounty71	A rootstock recently released in New Zealand that, although low vigor , results in better yields of cvs. Hayward, Hort16A and Zesy002 (commonly known as Gold3) when on heavier soils and under high levels of Psa than Bruno seedling rootstocks
Bruno	A cultivar of A. chinensis var. deliciosa selected in New Zealand by Bruno Just, a contemporary of Hayward Wright, using material derived from the same first introduction into New Zealand. Bruno was inferior to Hayward in fruit size and storage although the vine was more productive. Open-pollinated seedlings of Bruno are still widely used on New Zealand commercial orchards as a rootstock for Hayward and Gold3 scions
Chieftain	A pollinizer widely selected in 1989 from an orchard in New Zealand. It is a highly floriferous hexaploid A. chinensis var. deliciosa that flowers in New Zealand coincident with Hayward, hence its extensive use
Dorì	A yellow-fleshed tetraploid cultivar of A. chinensis var. chinensis bred in Italy (Universities of Udine and Bologna) by Raffaele Testolin and selected in 2003. Released to growers in 2014, it stores well and the vine is resistant to winter cold
Green Light®	A budsport of cv. Hayward identified in the 1980s in Brisighella, Italy and managed by Vivai Co. (Spada pers comm). This A. chinensis var. deliciosa matures earlier than its source and is cultivated in central Italy
Hayward	A hexaploid cultivar of A. chinensis var. deliciosa selected by Hayward Wright and first commercialized in New Zealand in the 1930s. In comparison to other contemporary varieties, it was larger, had a popular flavor , and stored for longer. The hirsute, green-brown fruit are large with green flesh and an acidic taste . After 1975, Hayward became the sole exported green-fleshed variety from New Zealand and therefore the world due to this superior storage
Hongyang	The most widely-planted red-fleshed kiwifruit cultivar. It is an A. chinensis var. chinensis selected in 1990 from multiple trials of open-pollinated seedlings of fruit collected from Henan Province, China. The fruit are sweet and yellow-fleshed with strong red coloration to the locules of the inner pericarp. Although highly susceptible to Psa and with flesh colour development affected by temperature and altitude, it is widely grown in China
Hort16A	A vigorous cultivar of A. chinensis var. chinensis that was commercialized as Zespri Gold and created the international market for yellow-fleshed kiwifruit . As described above, it was a large-fruited, yellow-fleshed kiwifruit with superior flavor bred in New Zealand at the end of the last century. The fruit are almost hairless ovoids with characteristic stylar beaks and an aromatic, tropical flavor . It proved vulnerable to the global Psa outbreak in the early twenty-first century and is no longer grown in commercially significant quantities
HortGem Tahi	A tetraploid cultivar of A. arguta resulting from breeding at Plant & Food Research in New Zealand, sometimes known as kiwiberry or K2D4 and producing fruit sold in Europe under the tradename Nergi®. Bred by Mark McNeilage and released to growers in 2003, the fruit are small (12–16 g) with glossy-to-dull smooth green edible skins
Jintao	An increasingly popular cultivar with Chinese growers . This gold-fleshed variety was selected from vigorous wild vines collected in Jiangxi province, China by the Wuhan Institute of Botany in 1981. It is also grown in Europe under an agreement between the Italian consortium Consorzio Kiwigold® and the Wuhan Botanic Gardens
Jinyan	The most commercially successful interspecific hybrid Actinidia, arising from an A. chinensis var. chinensis × A. eriantha cross made in Wuhan, China in 1984. This tetraploid is grown in China, Italy and Chile and its fruit are even higher in Vitamin C than Hayward
Kramer	A clonal selection from Hayward made by John Kramer and has been widely distributed in New Zealand because it is considered to have fewer fruit faults
Moshan No. 4	A long-flowering pollinizer cultivar selected in China in 1984 from the wild in Jiangxi Province, China. This A. chinensis var. chinensis has a flowering period which overlaps with other var. chinensis and some early var. deliciosa cultivars in China, hence its wide use
Qinmei	This cultivar was until recently the most widely planted kiwifruit cultivar in China. It is a cultivar of A. chinensis var. deliciosa selected from the wild in Shaanxi Province, China in 1979. This vigorous vine produces large, green-brown fruit that can shed their hairs on handling. The flesh is green
Soreli	An early-maturing cultivar of A. chinensis var. chinensis recently released by Raffaele Testolin and Guido Cipriani of the University of Udine, Italy. The fruit are strongly colored but storage life is short
Summer 3373, Summer 4605	Summer varieties were bred in Italy by crossing Hayward with inconstant male and are commercialized together as Summerkiwi™. They are green-fleshed A. chinensis var. deliciosa plants that can be harvested earlier than Hayward but do not store as long
Tomua	The first cultivar to emerge from a directed breeding program of kiwifruit . This early-maturing A. chinensis var. deliciosa with many fruit traits similar to its mother Hayward was briefly commercialized in the late 1990s from New Zealand
TopStar®	A budsport of cv. Hayward identified in 1985 and propagated by the Perotto Carla nursery , Italy. This A. chinensis var. deliciosa is a less vigorous, more easily managed vine than cv. Hayward and yields hairless fruit but is no longer cultivated in significant quantities
Wilkins Super	A budsport of cv. Hayward identified in 1979 on a New Zealand orchard. This A. chinensis var. deliciosa yields longer, larger, cylindrical fruit than its source
Zesh004 (Syn. Green14)	A green-fleshed sweet-flavored hybrid of A. chinensis var. chinensis and A. chinensis var. deliciosa bred by Alan Seal in New Zealand that can be harvested earlier than Hayward. Commercialized in the early 2010s as Zespri® Sweet Green, production levels remain low at the time of writing
Zesy002 (Syn. Gold3)	A large-fruited gold-fleshed cv. of A. chinensis var. chinensis that replaced Hort16A when Psa struck New Zealand. It is a tetraploid resulting from the combination by Russell Lowe of unreduced gametes of diploid cv. Hort16A and a tetraploid pollinizer