Identification of quantitative trait loci associated with pre-flowering drought tolerance in sorghum

Drought tolerance is an important agronomic trait but the genetic and physiological mechanisms that condition its expression are poorly understood. Molecular genetics and quantitative trait loci analysis provide a new and powerful approach to understand better the inheritance and expression of this trait. The purpose of this study was to use molecular markers to identify genetic loci associated with the expression of pre-flowering drought tolerance in sorghum [Sorghum bicolor (L.) Moench]. Two genotypes with contrasting drought reactions, TX7078 (pre-flowering tolerant, post-flowering susceptible) and B35 (pre-flowering susceptible, post-flowering tolerant), were selected as parents for a sample of recombinant inbred (RI) lines. Ninety-eight RI lines were evaluated in two different years under conditions of pre-flowering drought and full irrigation. This information was used to quantify the drought tolerance of each line. The population was also genotyped with 150 RAPD and 20 RFLP markers that mapped to 17 linkage groups. By means of these markers, six regions of the genome were found to be specifically associated with pre-flowering drought tolerance. Eight additional regions were more generally associated with yield or yield components under fully irrigated conditions. Several loci were associated with the expression of drought tolerance under both mild and severe drought stress conditions.