The role of wild vegetable species in household food security in maize based subsistence cropping systems

WV species integrated as part of the main diet have a role in the management of hunger and specifically micronutrient deficiencies. Their main role is as relish (Oniang’o et al. 2003), that is, they are used as complement for staple diets (such as phutu, pap, sadza or ugali), made mainly from maize meal and sometimes other cereals such as sorghum (Sorghum bicolor L. Moench) and pearl millet (Pennisetum typhoides). They are thus an integral component of the main meal of the day as usually they are the main relish with which the staple maize dish is eaten. They are usually prepared as the preferred relish on their own or as substitute for exotic vegetables in stews and soups in cases where meat and other vegetables cannot be afforded. However, where an alternative relish is available, they can be referred to as a supplement (Kepe 2008). Relish is an indispensable part of the African diet (Smith and Ezyaguirre 2007; Oniang’o et al. 2003) as the main staple cereal is not normally eaten in the absence of relish. Thus the presence of relish directly impacts on the consumption of the bulk of the main staple even though the relish is required and consumed in smaller proportions relative to the staple.

It is evident from the foregoing that WV play a significant role in food system stability at the household level. Food system instability is determined by the temporary or permanent loss of access to the resources needed to consume adequate food (FAO 2008). The temporal variability in the occurrence of WV, due to their seasonal availability in response to the changes in seasons of the year, certainly causes instability in local rural food systems, especially among those vulnerable groups who depend totally on them for relish (see Modi et al. 2006; Vorster et al. 2007; Shackleton 2003; Lewu and Mavengahama 2010, 2011).

One attribute of WV, about which there is general agreement among researchers, is their potential to combat ‘hidden hunger’ (Tisdale et al. 1990; Harvestplus 2011). This is especially important among low income earners and the rural population (Lewu and Mavengahama 2010) as the vegetables are not purchased. The nutritional composition of WV has been, and continues to be, characterised and they generally have been reported to be rich in micronutrients especially beta carotene, zinc, and iron, the principal nutrients whose absence from a diet results in ‘hidden’ hunger. Several studies conducted on indigenous vegetables have suggested that they generally have higher levels of various nutrients than the conventionally cultivated species (Flyman and Afolayan 2006b; Ndlovu and Afolayan 2008; Odhav et al. 2007; Steyn et al. 2001; Nesamvuni et al. 2001). Micronutrient malnutrition affects more than half of the world population, particularly in developing countries (WHO 2000). In 2000, the World Health Report identified iron, vitamin A, zinc and iodine deficiencies as the most serious health constraints worldwide (WHO 2000; Faber and Wenhold 2007). Besides nutritional benefits, it has been suggested that the utilisation of these vegetables represents significant savings of cash in the household (Shackleton 2003).

More research needs to be conducted on the ability of WV to contribute nutrients to the body. This is because research has suggested that nutrients from WV may not be bioavailable. The food security concept of food utilization goes beyond food use and includes how a person is able to absorb essential nutrients from the consumed food (FAO 2008) and includes the concept of bioavailability. The bioavailability of nutrients is influenced by the presence in a meal of substances that either promote or inhibit absorption of nutrients by the gut (Lonnerdal 2003; Gupta et al. 2006). These substances, which include phytate, oxalate and polyphenols are variously called anti-nutrients or anti-nutritional factors. They occur not only in WV but also in cultivated vegetables and fruits (oxalate), cereal and legume seeds (phytate) and beverages such as tea and coffee (polyphenols) (White and Broadly 2009). It is estimated that only about 25 % and 5 % of the zinc in cereals and legumes, respectively, is bioavailable.

The bioavailability of the nutrients in WV has not been widely characterised. WV (and other foods) may be rich in mineral nutrients but these nutrients may not be easily available (bio-availability) due to anti-nutritional substances such as phytate and tannins which bind zinc, calcium and iron. If WV are mixed with other foods in the diet their anti-nutrients could render the micronutrients from the staples unavailable. However, as noted earlier, anti-nutrients also occur in beverages like coffee and tea and have therefore been present in diets for a long time.

The widely observed practice of mixing several WV species in one cooking vessel highlights their contribution to dietary diversity in terms of more vegetable types as well as in terms of choice of relish. Although most researchers have emphasized the superior nutritional composition of these species, this is not their only merit. There are other reasons behind the use of these species. It is not uncommon for the urban wealthy to be found visiting certain places where ethnic (traditional) foods are prepared, looking especially for these vegetables and other traditionally prepared meals (as alluded to by Kepe 2008). They provide variety to otherwise monotonous cereal based diets (see Michaelsen et al. 2009; Maholtra and Passi 2007). Providing different types of these WV can reduce this monotony by adding different tastes and colours to diets.

Although edible indigenous plant species have been utilised as food for centuries (Vorster et al. 2008; Adebooye and Opabode 2004) current research has indicated that the use of WV in South Africa is in decline (Steyn et al. 2001; Modi et al. 2006). Flyman and Afolayan (2006b) have suggested that reliance on introduced exotic vegetables was the primary reason for the decline in Southern Africa. Lack of knowledge about nutritional composition, cooking methods and ways of preservation have also been suggested as reasons for low use of WV (Flyman and Afolayan 2006b). Mnzava (1997) referred to `strongly localized importance’ as also reducing utilisation. This localized importance has also been alluded to by Jansen van Rensburg et al. (2007) who reported that although Corchorus olitorius (Jews mallow/wild okra) occurs in Limpopo, KwaZulu-Natal and Eastern Cape, it is only consumed in Limpopo because people in the other provinces do not like its sliminess. Rubaihayo (2002) and Vorster et al. (2008) have suggested that the indigenous knowledge base of these vegetables has been eroded due to environmental and socio-cultural changes brought about by migration of labour, increased urbanisation and the promotion of cash crop farming instead of subsistence farming. Bharucha and Pretty (2010) have noted that food security is presently dependent on only a narrow variety of cultivated species.

Although they carry a ‘food for the poor’ and ‘famine food’ tag for some groups, the fact remains that WV are indeed an important last resort during famine. For some rural groups mired in the deprivation trap and perpetual poverty WV are substitutes for food crops (Kepe 2008). There are some groups in society who would not ordinarily eat these vegetables under circumstances of adequate food availability but would consume them under difficult conditions of droughts and famines. It is possible that for some people who are in poverty these foods become such a part of their diets that even when circumstances change for the better, the attachment to these foods does not go away. Thus a drought induced famine would have social-cultural effects on wild vegetable use as suggested by Bharucha and Pretty (2010).

WV increase agro-biodiversity at the household level. This agro-biodiversity helps in buffering against the accumulation and multiplication of pests and diseases; it also provides important cover for the soil at the edges of the fields or fault lines in the field which are prone to erosion – their roots together with other weeds hold the soil in place and reduce raindrop impact. This is especially true for the widely occurring species such as black jack (Bidens pilosa) and pigweed (Amaranthus hybridus). The hardiness of WV ensures that they thrive in both drought and flood times and as a result they are available during harsh environmental conditions when most cultivated crops would have failed. They are thus resilient and their increased utilisation and cultivation would introduce resilience into the food systems of most subsistence farmers (see Bradford 2010).