Screening of cowpea ( Vigna unguiculata (L) Walp.) types for resistance to cowpea aphid borne mosaic disease

Abstract

The screening of fifty nine cowpea varieties through sap inoculations for CAMV resistance under field conditions has shown two varieties namely V-317 and V-276 as highly resistant, Other sixteen varieties were found highly tolerant, seven tolerant and the remaining thirty four susceptible. Analysis of variance revealed significant differences among varieties for days to first flowering, days to maturity, plant height at maturity, number of primary branches per plant, number of pods per plant, number of seeds per pod, length of pod, hundred seed weight, seed yield per plant, CAMV disease incidence, Cercospora leaf spot infection, rust disease infection, Pea aphid infestation, Epilachna beetle infestation. Analysis of variance for number of hairs per unit area of leaf has no significant difference among varieties. High values of GCV, PCV, heritability and genetic advance were observed for length of pod, number of primary branches per plant and hundred seed weight suggesting the reliability of these characters during selection programme for their improvement.

Observations on the reactions to major pests and diseases other than CAMV, have shown four varieties as highly resistant to Cercospora leaf spot, six varieties to rust disease infection, five varieties to Epilachna beetle infestation and none to pea aphid infestation. Correlation analysis has revealed positive significant correlation of seed yield per plant with number of seeds per pod, length of pod and hundred seed weight. Genetic divergence using Mahalanobis’s D2 technique was studied on 59 cowpea varieties. Based on this they were grouped in eight clusters. Intra cluster distance was less than inter cluster distance. The maximum divergence was observed between cluster V and VII.