Evaluation of near-isogenic sorghum lines contrasting for QTL markers associated with drought tolerance

Drought is the most important constraint on crop production in the world today. Although selection for genotypes with increased productivity in drought environments has been an important aspect of many plant breeding programs, the biological basis for drought tolerance is still poorly understood. We have been conducting a genetic research program directed at developing a better understanding of drought tolerance in sorghum [Sorghum bicolor (L.) Moench]. Several quantitative trait loci (QTL) associated with pre-flowering and post-flowering drought tolerance were previously identified in a recombinant inbred mapping population. In the current study, near-isogenic lines (NILs) were developed and used to test the phenotypic effects of three different genomic regions associated with various measures of agronomic performance in drought and/or non-drought environments. In most cases, NILs contrasting for a specific locus differed in phenotype as predicted by QTL analysis, NILs contrasting at QTL marker tM5/75 indicated large differences in yield across a range of environments. Further analysis indicated that differences in agronomic performance may be associated with a drought tolerance mechanism that also influences heat tolerance. NILs contrasting at QTL marker tH19/50 also differed in yield under drought and non-drought conditions, The analysis of these NILs indicated that these differences may be influenced by a drought tolerance mechanism that conditions plant water status and the expression of staygreen. NILs contrasting at QTL marker t329/132 differed in yield and seed weight. These differences appear to be the result of two QTL that ale closely linked in repulsion.