Abstract

Drought limits crop production worldwide, reducing yields by up to 70%. Lablab bean, suited for arid and semi-arid regions, shows notable drought tolerance, yet Kenya lacks improved drought-tolerant lablab varieties. This study aimed to (i) identify drought-tolerant lablab genotypes based on morphological and physiological traits and (ii) assess the combining ability of seven parental genotypes and 21 crosses to find promising combinations. In a controlled glasshouse experiment, ten genotypes were tested under well-watered, moderate, and severe water stress conditions using a split-plot design. Combining ability was studied using a 7×7 half-diallel design, creating 21 F2 crosses evaluated in a screen house in Uganda. Data on eight morphological and ten physiological traits showed significant genotypic differences, with severe stress reducing growth parameters and delaying flowering. Drought stress decreased fresh weight, dry weight, relative water content, photosystem II yield, and chlorophyll content, while increasing non-photochemical quenching. Genotypes D1, D3, and D7 performed best under stress. Additive gene action governed physiological traits, while non-additive action influenced morphological traits. Genotypes D3 and D8 were strong general combiners, and crosses D3×D8, D3×D5, and D5×D10 showed high yield potential, making them ideal candidates for breeding drought-tolerant lablab varieties.

Key words: Drought stress, Lablab purpureus, combining ability, morphology, physiology.