Resistance to Callosobruchus maculatus among cowpea (Vigna unguiculata (L.) Walp) genotypes

Callosobruchus maculatus is an important field-to-store pest that causes close to 100% losses in stored produce. This study aimed at assessing the resistance of cowpea genotypes to C. maculatus infestation. Thirteen cowpea advanced breeding lines pre-selected on the basis of their high grain yield, and three released varieties (Padi-tuya, Kirkhouse Benga and Wangkae) were evaluated in a no-choice experiment. The experiment was laid out in a completely randomized design with four replications under laboratory conditions. Data were collected on mean number of eggs per seed (MEPS), days to first emergence (DFE), adult bruchid emergence (ABE), percentage weight loss (PWL), percentage seed damage (PSD) and median development period (MDP). Dobie's susceptibility index (DSI) was computed and used to classify the genotypes as resistant or susceptible. Significant differences were found among the genotypes for the measured traits, except for DFE and MDP. IT13K-1070-2 had the lowest MEPS, ABE, PWL and PSD. C. maculatus, with high ABE, developed best on Kirkhouse Benga and Wangkae. Wangkae had 100% seed damage at the end of the experiment. Based on the DSI score, IT13K-1070-2 was found to be moderately resistant; the rest of the genotypes were susceptible. Among the susceptible genotypes, IT10K-817-3, IT07K-303-1, SARI-2-50-80, SARI-3-11-100, IT10K-837-1, IT13K-1424-12 and SARVX-09-004 had PWL of less than 16%, indicating tolerance to bruchid infestation. DSI was significantly and positively correlated with ABE (r = 0.81), PSD (r = 0.93) and PWL (r = 0.79). DSI had a significant negative correlation with the final seed weight (r = -0.83). IT13K-1070-2 could serve as a useful source of resistance to the cowpea bruchid in cowpea breeding programs or released as a variety for cultivation.