Resistance to Callosobruchus maculatus Developed Via Gamma Radiation in Cowpea

Among the biotic stresses that affect cowpea (Vigna unguiculata L) productivity, infestation by cowpea bruchid beetles (Callosobruchus maculatus) is a major problem, causing yield losses of up to 100 %. To alleviate this problem, use of resistant varieties is a feasible approach for small-scale farmers. In Zambia, there are no reported sources of resistance to C. maculatus. The objectives of this study were: i) to evaluate certain cowpea mutants, generated at the University of Zambia, for resistance to C. maculatus; ii) to cluster the tested genotypes based on height, number of pods per plant, 100-seed weight, yield ha-1, number of eggs laid and adult emergence; and iii) to evaluate the candidate mutants for protein content. Experiments were conducted at three locations in 2014/15. The mutants, LT 11-5-2-2, BB 7-9-7-5 and BB-14-16-22, were found to be resistant to C. maculatus across locations and they out-performed their respective parents (p< 0.05) in the degree of resistance to C. maculatus. Cluster analysis, using selected agronomic parameters, showed that the selected resistant mutants (cluster B) were more similar to each other (95 %) than to Namuseba and Msandile (included as susceptible genotypes), which clustered at a similarity level of 78 % (cluster A). The mutants, LT 11-5-2-2, BB 7-9-7-5 and BB-14-16-22, showed resistance to C. maculatus, but their protein content was similar to their parents, indicating that this crucial trait had been maintained in the mutants.