Abstract
Considerable effort has been made to improve drought-stress tolerance in sorghum by incorporating the stay-green trait into drought-susceptible elite sorghum varieties. Keeping track of the several genes involved in the expression of this complex trait during the breeding program is an enormous task. In this study, the fidelity of recently identified SSR markers were tested for introgression of stay-green QTLs into elite sorghum lines. Of the 102 SSR loci tested, seventy- eight (78) markers were found to be polymorphic between the donor lines (B35 and E36-1) and the recipient lines (Sekedo and Seredo). In total, 25 polymorphisms were detected in SSR loci flanking key stay-green quantitative trait loci (QTLs) from the B35 donor line, and 6 in E36-1. In B35, 5 SSR markers were linked to the QTL StgA, 6 linked to StgB, 3 linked to Stg1, 2 linked to Stg2, 4 linked to Stg3 and 5 linked to Stg4. In contrast, only 6 polymorphic SSR markers were detected in the vicinity of key QTLs found in E36-1. Two were linked to LGA, 1 to LGJ and 3 to LGG. No markers were found linked to QTL LGD and LGH. Similar SSR polymorphisms were observed for markers needed to recover the recurrent parent genomes (RPG) in the subsequent backcross generations. These findings reveal the limitations of using E36-1 as a donor parent in marker-assisted selection (MAS) programmes for improvement of drought tolerance. Low hybridization efficiency (22.5%) was achieved using the anther dehiscence method. Such low hybridization efficiency requires use of molecular markers to easily identify plants harbouring the required genotypes. Key words: Stay-green, drought tolerance, quantitative trait loci (QTL), simple sequence repeat (SSR) markers, polymorphism.
Highlights
Sorghum (Sorghum bicolor (L) Moench) is the fifth most important cereal crop grown worldwide (FAO and ICRISAT, 1996)
More polymorphic markers flanking key stay-green quantitative trait loci (QTL) were observed in crosses involving the donor source B35 (25 in total) than in E36-1 (6 in total)
In B35, 5 simple sequence repeat (SSR) markers were linked to the QTL StgA, 6 linked to StgB, 3 linked to Stg1, 2 linked to Stg2, 4 linked to Stg3 and 5 linked to Stg4
Summary
Sorghum (Sorghum bicolor (L) Moench) is the fifth most important cereal crop grown worldwide (FAO and ICRISAT, 1996). Sorghum plays an important role in food security and income of many rural households. This is mainly attributed to its ability to tolerate drought (Esele, 1988). Sorghum is mostly cultivated in the drier areas of the Eastern, Northern and South-western regions of Uganda, where it occupies more than 80% of the total area under cultivation (Ebiyau and Oryokot, 1996). These are dry and hot low land areas characterized by short rainy seasons with low and erratic rainfall. Tolerance to drought is indicated when plants remain green and fill the grain normally (Rosenow et al, 1996; Sabadin et al, 2012)
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