Characterization and association mapping for drought adaptation in Ethiopian sorghum (Sorghum bicolor (L.) Moench) germplasm

Knowledge of drought related traits and their mechanisms of drought adaptation are the key component in selecting genotypes that withstand the effects of drought in sorghum. The objectives of this study were to assess genetic variability among sorghum germplasm, to map QTL associated with root and shoot traits, and to identify tightly linked SSR markers. The experiment was carried out at Jimma University under greenhouse condition. One hundred thirty-six sorghum genotypes were characterized for twelve traits using a high throughput root phenotyping platform in a randomized complete block design with three replications. Among these genotypes, 108 of them were used for studying population structure and trait-marker association analysis using 39 SSR markers. The analysis of variance indicated that highly significant difference (P < 0.01) were observed among the genotypes for all the studied traits. The coefficients of correlation showed that there was a significant positive and negative association among different drought related traits. The first three principal components (PCs) with eigenvalues greater than one accounted for 56.4% of the total genotype variation, the remaining 43.60% accounted for the last nine principal components. All 136 genotype were grouped into four clusters whereby a different member within a cluster being assumed to be more closely related in terms of the trait under consideration with each other than that member in different clusters is. Moderate genotypic variation was exhibited for leaf area, shoot fresh weight, shoot dry weight, root to shoot ratio and root angle. Highest phenotypic variation was exhibited for leaf area, shoot fresh weight, shoot dry weight, root dry weight and root to shoot ratio. Broad sense heritability ranged from 19.35% for root length to 71.08% for shoot fresh weight and high heritability was recorded for shoot fresh weight (71.08%), leaf area (70.22%) and root angle (66.22%). High heritability combined with high genetic advance was observed for shoot fresh weight, root angle, and leaf area. The 108 genotypes were grouped into three distinct subgroups. The plots of LD (r2) showed a clear trend on linkage disequilibrium decay and based on trend line it is around 15–20 cM. A total of 25 significant marker-trait associations/QTLs (P ≤ 0.05) were detected with 14 SSR markers.