Abstract

Drought is the major sorghum production constraint in Ethopia which necessitates the identification of sorghum genotypes that carry genes (quantitative trait locus, QTL) associated with drought tolerance thereby developing drought tolerant sorghum varieties. The objectives of this study were to identify drought tolerant sorghum genotypes, map chromosomal regions (QTLs) associated with agronomically important traits and identify simple sequence repeat (SSR) markers tightly linked with these QTLs. One hundred and sixty (160) sorghum genotypes (152 landraces and 8 released varieties) were genotyped with 39 SSRs markers and evaluated in the field at Kobo in the off-season using an alpha lattice design replicated three times. Phenotypic data including days to 50% flowering, plant height, panicle weight, grain weight, grain weight per panicle, panicle harvest index, one thousand grain weight and number of grains per panicle were collected. Analysis of variance showed highly significant (P<0.0001) differences among the genotypes for all characters. Most of the characters showed moderate to high phenotypic and genotypic coefficient of variation. Linkage disequilibrium (LD) analysis indicated that in all accessions, 107 loci pairs (32.92%) had a significant (p< 0.05) mean LD of 0.19, with R2 > 0.2 for 33 evaluated loci pairs. Population structure analysis showed that there were four distinct clusters in the studied materials. A total of 10 marker-trait associations were identified using seven different SSR markers. The percentage of the total variation explained by the markers ranged from 2.6% (Xtxp114 with THGT) to 17.76% (Xtxp145 with PHT). The seven SSR markers (xcup53, bSbCIR223, Xtxp114, mSbCIR248, Xtxp145, Xtxp278, and gbsp123) were located on chromosomes 1, 2, 3, 5, 6, 7 and 8, respectively, each chromosome harboring one marker. Most of the identified markers were localized in chromosomal positions that have been previously reported as positions for drought tolerance-related traits, supporting the present findings. The results of this study can serve as initial effort for the association mapping studies in sorghum particularly in Ethiopia as the associated SSR markers are potential candidates for marker-assisted selection to improve drought tolerance in sorghum. However, as this study is the first attempt in the identification of QTLs for drought tolerance using association mapping, the identified QTLs need to be validated in independent or related populations and in different environments before their use in marker-assisted selection.

Key words: Association mapping, drought, population structure, quantitative trait locus (QTLs), sorghum, simple sequence repeat (SSR).