Morpho-physiological and multivariate assessment of stay-green sorghum (Sorghum bicolor (L.) Moench) genotypes under drought stress in Ethiopia

Drought is a major abiotic constraint that severely limits crop growth, development, and yield worldwide. In Sorghum bicolor (L.) Moench, post-flowering drought stress is particularly detrimental, significantly reducing grain yield and biomass accumulation. Enhancing drought tolerance through the stay-green trait remains a key breeding objective to improve productivity under water-limited conditions. A field experiment was conducted at Efratana Gidim District using an irrigation scheme to impose two water regimes: post-flowering water deficit and well-watered conditions. The trial was arranged in an alpha-lattice design to evaluate performance and determine genetic variation for yield and related traits among stay-green introgression near-isogenic sorghum lines. Analysis of variance revealed highly significant (p ≤ 0.001) and significant (p ≤ 0.05) genotypic differences for most traits under both moisture regimes. Broad-sense heritability ranged from 46.6% for chlorophyll content at flowering (CHlF) to 93.1% for plant height (PHT) under water deficit, and from 67.2% (CHlF) to 94.7% (PHT) under well-watered conditions. Genetic advance as a percentage of the mean varied from 5.49% (CHlF) to 80.68% (photosynthetic rate at the hard-dough stage, AG) under water deficit, and from 4.85% (days to maturity, DTM) to 58.33% (peduncle exertion, PedEx) under well-watered conditions. Cluster analysis grouped the genotypes into four and five clusters under the respective moisture regimes. Principal component analysis (eigenvalues > 1) explained 78.05% and 74.03% of the total phenotypic variation under water-deficit and well-watered conditions, respectively. Substantial morpho-physiological diversity was observed among the evaluated sorghum lines. Under drought stress, chlorophyll maintenance showed direct positive inherent effect (CHlG, 0.431) on grain yield; the stay-green genotype ETSC16140 gave the maximum grain yield (4037.9 kg ha–1). Under well-watered set, the maximum grain yield was also obtained from the stay-green genotype ETSC16227 (5887.2 kg ha–1). Furthermore, thirteen stay-green introgression lines exhibited consistently superior grain yield performance across both water regimes. These genotypes constitute valuable breeding materials for sorghum improvement programs aimed at enhancing drought tolerance in semi-arid environments.