Diallel analysis for seed yield and yield-related traits in tepary bean (Phaseolus acutifolius A. Gray) under non-stress and drought-stress conditions

Abstract

Tepary bean (Phaseolus acutifolius A. Gray) cultivation is not expansive in Southern Africa due to the unavailability of high-yielding and locally adapted varieties. To deliver well-adapted and new-generation tepary beans in Africa, pre-breeding and breeding of drought tolerant and high-yielding varieties is a critical need. Therefore, the objective of this study was to determine the combining ability effects and genetic components for seed yield and yield-related traits in selected tepary bean genotypes under non-stressed (NS) and drought-stressed (DS) conditions. Seven parents and 21 F2 progenies derived from a half-diallel design were evaluated at two sites in Malawi under NS and DS conditions using a 4 × 7 lattice design with three replications. The genotype × location interaction effect was significant (p < 0.05) for days to 50% flowering (DTF), number of pods per plant (NPP), and seed yield (SY) traits under both NS and DS conditions, implying a differential performance of genotypes across the two locations. The specific combining ability (SCA) × Location interaction effect was significant (p < 0.05) for DTF, NPP, and SY under both water regimes, implying the genetic effects of crosses were affected by test locations. General combining ability (GCA) and SCA mean squares were significant for number of seeds per pod (NSP) and SY under DS condition, indicating additive and non-additive gene effects controlled these traits. Baker’s ratio (BR) > 0.50 for NPP and NSP under DS condition, suggested the preponderance of additive gene effects. The narrow-sense heritability estimates of > 0.60 for NSP under DS condition suggested relatively better trait transmissibility from parents to offspring. G40145, G40148, and G40150 were good general combiners for NPP and SY under both NS and DS conditions. F2 families Zimbabwe landrace x G40138, Zimbabwe landrace × G40150, G40059 × G40145, G40059 × G40148, G40138 × G40150, and G40145 × G40150 were best-specific combiners with enhanced SY of 1.67 tons/ha under DS condition. The selected parents are valuable genetic resources for breeding programs to enhance the NPP and SY. High-performing early-generation families are recommended for genetic advancement and selection across representative growing environments for variety release and commercialization.