PROGRESS IN MAPPING AND MARKER-ASSISTED SELECTION TO IMPROVE DROUGHT TOLERANCE IN GRAIN SORGHUM

¹ Department of Plant and Soil Science, Texas Tech University, Lubbock, TX 79409,USA

² Texas A & M University Agricultural Research and Extension Center, Lubbock, TX 79401, USA

Drought is a major limiting factor in crop productivity. Moisture stress during both pre and post-flowering stages reduces sorghum yield drastically. Therefore, improvement in both pre and post-flowering drought tolerance is necessary to improve and stabilize productivity of sorghum in stress environments. Quantitative Trait Loci (QTLs) for stay green, a post-flowering drought tolerance trait were identified using three recombinant inbred line (RIL) populations developed from B35 x Tx7000, B35 x Tx430, and SC56 x Tx7000 cross combinations, where B35, SC56 are stay green lines and Tx7000, Tx430 are non stay green lines. We have also mapped the QTLs for pre-flowering drought tolerance after evaluating two of the above RIL populations. The consistency of QTLs across environments, genetic background, and the feasibility of combining both pre-flowering and post-flowering drought tolerances in sorghum will be discussed. Near-isogenic lines (NILs) for stay green QTLs have been developed using marker-assisted selection to dissect the QTL regions and to determine the effect of QTLs in stress environments. Simultaneously, BAC (Bacterial Artificial Chromosomes) subcloning, comparative mapping and DNA pooling are being employed to saturate the QTL regions. BAC contigs have been generated and currently effort is being made to cover the stay green QTL regions through chromosome walking and to identify the corresponding stay green QTL regions in rice. Physical mapping of these QTL regions will not only facilitate the cloning of the determinants responsible for the stay green trait but also will lead to better understanding of the drought tolerance in sorghum and other crop species.