Investigating the Genetics of Scab Resistance and Yield Components in Cowpea (Vigna unguiculata)

Abstract

Background: Economically important traits have complex inheritance and are environmentally influenced, thus making selection for such traits more difficult. Breeding efforts to develop varieties with resistance to the disease require an understanding of the genes that confer resistance to the disease in terms of their heritability and gene action in Ugandan germplasm. Purpose: This study was conducted to determine the relative importance of GCA and SCA, and hence additive and non-additive effects in the inheritance of resistance to scab infections, and heritability of yield and yield-related traits in the new breeding populations. Research Method: Eleven cowpea lines (four resistant, five moderately resistant and two susceptible) were selected as parents and crossed using a half diallel mating design to generate information on the genetics of control of scab disease resistance, yield and yield-related traits in cowpea (Vigna unguiculata). 55 F2 progenies and their parents (11) were evaluated at two locations (Kabanyolo and Serere) using an 11 × 6 lattice design. Data were collected for grain yield and yield related traits such as days to 50% flowering, number of branches per plant, number of peduncles per plant, number of pods per peduncle, number of pods per plant, pod length (cm), seeds per pod, and 100 seed weight (g). Data were analysed using Griffing’s method 4 model 1. Phenotypic correlation coefficients (rp) for scab disease incidence, severity, AUDPC, yield and yield-related traits were determined using IBM SPSS Statistics version 22. Findings: Combined analysis of variance for the two locations revealed highly significant differences (P < 0.001 and P < 0.01) among the genotypes for all 12 traits studied but showed no significant genotype by location (G × L) interaction effect on any of the traits. Coefficient of genetic determination in the narrow and broad sense, analogous to narrow and broad sense heritability, respectively, were generally low, ranging from 1.23 % - 27.12% (h2) and 7.4 % -71.91 % (H2). The low values of Baker’s ratio (BR) (< 0.5) for most of the traits suggested that non-additive gene effects were more important except for number of pods per plant which indicated additive gene effects were more important (BR = 0.80) and number of seeds per pod (BR = 0.5) which indicated both additive and non-additive gene effects were important.  Alegi, NE15 and NE48 were identified as parental lines with negative general combining ability (GCA) effects for improvement of scab disease resistance for both locations while SECOW5T was identified as the only parent with high positive GCA for improvement of both 100 seed weight (g) and grain yield (K/ha) of cowpea across the two locations. A cross between WC35B*WC66 had the best SCA effects for scab disease resistance. Conclusion: The study confirmed earlier reports that additive gene effects were important for scab disease resistance. Six crosses, viz. Alegi*NE50, Alegi*WC36, ACC12.2W*SECOW5T, NE15*SECOW5T, NE48*WC36 and WC10*WC36 were identified as the best hybrids (crosses) for the improvement of cowpea yields across the locations. Originality/Value: The study reveals potential parental lines and crosses for enhancing scab resistance and yield in cowpea, contributing to breeding strategies and crop improvement efforts.