Evaluation of Stay-Green QTL Combinations in Improved Sorghum Germplasm to Enhance Terminal Drought Tolerance

Sorghum production in semi-arid tropics across globe is mainly constrained due to the post-flowering drought. The ‘stay-green’ trait is the best-characterized component of post-flowering drought tolerance in sorghum, contributing to grain and stover yield maintenance under terminal drought stress and improving livestock feed value of straw. In recent studies at ICRISAT-HQ, Patancheru six stay-green QTLs identified from the best-studied source, B35 were backcrossed and validated in several genetic backgrounds. But breeding experiments have shown that any single stay-green QTL alone does not adequately protect sorghum yield from post-flowering drought stress in most environments. To better understand the interaction of these QTLs and their effect on the stay-green expression, we developed double QTL introgression lines in half-diallel fashion (Seven and eight introgression lines in R16 and S35 backgrounds, respectively). Each true F₁ plant confirmed by genotyping 20 polymorphic SSRs i.e. 3-4 markers per QTL, was selfed, and F_1:2 population was planted in Randomized Complete Block design with three replications under stress condition in summer 2013 along with P₁, P₂ and F₁s. For each cross 50 F₂s per replication were selected randomly and the data of agronomic traits and weekly Green Leaf Area (GLA) were recorded on selected F₂ plants while P₁, P₂ and F₁ were evaluated on plot basis. This observed data will be utilized to study the relative effectiveness of various gene combinations under stress conditions, which is essential in optimizing selection of stay-green QTL combinations for development of improved germplasm.