The genetic evaluation of bruchid resistance in seed of cowpea

Abstract

Seed resistance of cowpea (Vigna unguiculata L. Walp.) to bruchids at the F3 plant generation was assessed by various methods. The most discriminating variable for measurement of seed resistance was mean emergence day, followed by percentage of adult emergence up to an optimum time, then in descending order, percentage of undamaged seed, mean number of holes per seed and percentage loss in seed weight. The simplest reliable variable to use for assessment of resistance to bruchids was the percentage of undamaged seed with zero emergence holes. However, greater control and manipulation of egg laying on seeds would be required to obtain uniform infestation. Three (or less) eggs per seed is suggested as acceptable. Care, particularly on the uniformity of eggs laid, is necessary when using percentage seed weight loss as an index of resistance. The other variables are laborious to estimate. In general, seed weight, number of eggs per seed, seed testa texture and number of seeds per sample did not appear to influence estimates of resistance, with the exception of seed weight loss. The natural rate of increase of bruchids, which is a critical variable for measurement of resistance, was very difficult to estimate with consistency.