Resistance of landrace and commercial cowpea genotypes to Callosobruchus maculatus attack

Abstract

In the northern and north-eastern regions of Brazil, the cultivation of cowpea (Vigna unguiculata L.) is socially and economically important. However, attack by weevils makes storage difficult. Landrace genotypes exhibit high genetic variability, which can confer resistance to pest attacks. In this study, the susceptibility of landrace genotypes of cowpea to the attack of the weevil (Callosobruchus maculatus (Fabr., 1775)) was assessed. A total of 13 genotypes were used (11 landraces and two commercial genotypes). Biological parameters (number of eggs; daily, accumulated, and final emergence; the instantaneous rate of population increase) of C. maculatus, and loss of cowpea seed mass were analysed. The treatments were composed of 30g of each genotype and 20 adult insects in an entirely randomised design with ten replicates. A principal component analysis and grouping analysis were performed due to the similarity between the genotypes, and three groups were described. Group 3 (‘BRS Pujante’, ‘Ligeiro’, and ‘Tardão’ genotypes) had the highest oviposition/number of eggs, daily emergence, number of emerging insects, and instantaneous rate of population increase. Group 2 (‘Azulão’, ‘Costela de Vaca’, and ‘Rabo de Tatu’ genotypes) showed intermediate values, and group 1 (‘Bala’, ‘Canapú’, ‘Corujinha’, ‘Manteiguinha’, ‘Moita’, ‘Seridó’, and ‘Sempre Verde’ genotypes) had the lowest values for all those variables. The commercial genotypes were grouped in groups 1 (‘Sempre Verde’) and 3 (‘BRS Pujante’) and showed similar behaviour to the landrace genotypes of those groups. This study demonstrated that the genotypes in group 3 are susceptible to the attack of C. maculatus, while those in group 1 showed antibiosis resistance. Utilization of insect-resistant genotypes can reduce cowpea infestation and synthetic insecticide application, leading to a positive economic impact.