Quantitative trait loci influencing drought tolerance in grain sorghum (Sorghum bicolor L. Moench)

Drought is a major constraint in sorghum production worldwide. Drought-stre ss in sorghum has been characterized at both pre-flowering and post-floweri ng stages resulting in a drastic reduction in grain yield. In the case of p ost-flowering drought stress, lodging further aggravates the problem result ing in total loss of crop yield in mechanized agriculture. The present stud y was conducted to identify quantitative trait loci (QTLs) controlling post -flowering drought tolerance (stay green), pre-flowering drought tolerance and lodging tolerance in sorghum using an F-7 recombinant inbred line (RIL) population derived from the cross SC56xTx7000. The RIL lines, along with p arents, were evaluated for the above traits in multiple environments. With the help of a restriction fragment length polymorphism (RFLP) map, which sp ans 1,355 cM and consists of 144 loci, nine QTLs, located over seven linkag e groups were detected for stay green in several environments using the met hod of composite interval mapping. Comparison of the QTL locations with the published results indicated that three QTLs located on linkage groups A, G and J were consistent. This is considered significant since the stay green line SC56 used in our investigation is from a different source compared to B35 that was used in all the earlier investigations. Comparative mapping h as shown that two stay green QTLs identified in this study corresponded to stay green QTL regions in maize. These genomic regions were also reported t o be congruent with other drought-related agronomic and physiological trait s in maize and rice, suggesting that these syntenic regions might be hostin g a cluster of genes with pleiotropic effects implicated in several drought tolerance mechanisms in these grass species. In addition, three and four m ajor QTLs responsible for lodging tolerance and pre-flowering drought toler ance, respectively, were detected. This investigation clearly revealed the important and consistent stay green QTLs in a different stay green source t hat can logically be targeted for positional cloning. The identification of QTLs and markers for pre-flowering drought tolerance and lodging tolerance will help plant breeders in manipulating and pyramiding those traits along with stay green to improve drought tolerance in sorghum.