SummaryRemarkable parallels link the development of varietal mixtures across subsistence farming systems. Mixtures are grown and persist because they prolong harvest and income flow and provide diversity of diet. From our review of research on agronomic and disease aspects of mixtures in modern agriculture, it is also clear that improved stability and decreased disease severity are common features of mixtures relative to their components in monoculture. Such advantages are of value to both modern and subsistence agriculture. However, in the majority of cases, the yield advantage of mixtures is small. Overall, we conclude that varietal mixtures are presently a viable strategy for sustainable productivity in subsistence agriculture, have potential for improvement without sacrifice of diversity, are an important resource for future global food production and may have an expanding role in modern agriculture in situations where qualitative uniformity is not the guiding priority.

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The F, progenies of crosses between several cowpea (V. unguicuiata ) lines were investigated for variation of eye pattern and seed coat colour. It was found that three (W, H, O) and five (R, P, B, M, K) maior genes control eye pattern and seed coat colour, respectively. The recessive gene (oo) for restricted eye pattern enables the underlying basic white or cream seed coat colour to be observed. A similar effect is obtained with the recessive gene (n-) for colour expression. The expression of mottling (V), possibly a seed coat pattern, may not be observed when it is combined with the genes for certain eye patterns. The significance of these findings in breeding for consumer preference for specific seed coat colour i.s discussed.