Induced plant mutagenesis is a powerful technique to create genetic variation for agronomic traits and drought tolerance selection programs. The objective of this study was to determine the response of elite sorghum (Sor- ghum bicolor [L.] Moench) lines developed via gamma-radiation for grain yield, component traits, and drought tolerance to select best performing lines for cultivation in water-stressed environments. Ten newly developed mutant lines and four check varieties were evaluated in two growing seasons under drought-stressed (DS) and non-stressed (NS) conditions in Namibia. Mutant lines were evaluated using a factorial experiment laid out in a randomized complete block design with three replications in custom-made rainout-shelter facility. Data on grain yield and yield-related traits were collected and drought tolerance selection indices were computed using mean genotype yield under non-stressed condition and drought-stressed condition. Data were subjected to standard analysis of variance, correlation and principal component analyses. The interaction effect of genotype × drought stress × season was non-significant for most assessed traits suggesting the relatively stable performance of the test lines for selection. Grain yield response of test genotypes varied from 0.55 to 2.27 t/ha under DS and 1.84 to 4.05 t/ha in NS conditions. Grain yield positively and significantly (P < 0.05) correlated with harvest index (r = 0.79), panicle weight (r = 0.75) and panicle length (r = 0.37), and negatively correlated with days to flowering (r = − 0.35) under DS condition. Principal component (PC) analysis identified two PCs accounting for 96.35 % of total genotypic variation based on drought tolerance selection indices. Biplot analysis using a combination assessed traits allowed selection of drought tolerant mutant lines designated as ML4, ML10, ML6, and ML5 with mean grain yield of 2.27, 2.05, 1.89 and 1.67 t/ha under DS conditions, in that order. The selected lines are recommended for further multi-environment evaluations for release and large-scale production in Namibia or other related agro-ecologies.
