Genetic analysis of grain yield and yield-attributing traits in navy bean ( Phaseolus vulgaris L.) under drought stress

Navy beans ( Phaseolus vulgaris L.) are an important food and cash crop for export from countries such as Myanmar, United States of America (USA), Ethiopia, China, Canada and Argentina to lucrative markets in north America, Middle East, southern Africa and eastern Europe. Knowledge of the genetic basis of navy bean performance under drought stress (DS) is important for planning appropriate breeding and selection strategies in DS environments. Eight parents and their twenty-eight F 2 progenies generated from an 8 × 8 half-diallel mating design were evaluated to determine combining ability effects and mode of gene action of grain yield (GYD) and yield attributing traits in navy bean under DS and non-stressed (NS) conditions. This information will help to identify parents with superior general combining ability (GCA) estimates and promising cross combinations with superior specific combining ability (SCA) estimates under DS and NS conditions. The experiments were conducted in two locations in a 6 × 6 square lattice design with two replications during the 2020 dry season. Drought stress was moderate across the two locations (drought intensity index = 0.48). General and specific combining ability (GCA; SCA) effects were significant ( p < 0.05) under both DS and NS for most traits indicating the importance of both additive and non-additive gene effects in the expression of the traits. Parents with best GCA for most of the studied traits were G1, G7, G6 and G8 under NS, and G3, G4, G7 and G8 under DS. Among these, only G3 and G6 were considered tolerant to DS because of their high values for drought tolerance index (DTI) and geometric mean productivity (GMP) and low values for percentage grain yield reduction (% GYR) and drought susceptibility index (DSI). The most promising progenies with high values for GYD and its component traits under DS, high values for DTI and GMP and low values for % GYR and DSI were G2 × G3, G2 × G8, G4 × G5 and G6 × G8. There were significant ( p < 0.001; p < 0.05) positive correlations for number of pods per plant and 100-seed weight (SW; g) with GYD under both DS and NS. Good general and specific combiners with desirable values of drought tolerance indices and high significant positive effects under DS should be used further in breeding for drought stress tolerance.