Sorghum is an important source of food, feed, and biofuel, especially in the semi-arid tropics because this cereal is well adapted to harsh, drought-prone environments.Post-flowering drought adaptation in sorghum is associated with the stay-green phenotype.Alleles that contribute to this complex trait have been mapped to four major QTL, Stg1-Stg4, using a population derived from BT3642 and RT37000.Near-isogenic RT37000 lines containing BT3642 DNA spanning one or more of the four stay-green QTL were constructed.The size and location of BT3642 DNA regions in each RT37000 NIL were analysed using 62 DNA markers spanning the four stay-green QTL.RT37000 NILs were identified that contained BT3642 DNA completely or partially spanning Stg1, Stg2, Stg3, or Stg4.NILs were also identified that contained sub-portions of each QTL and various combinations of the four major stay-green QTL.Physiological analysis of four RT37000 NILs containing only Stg1, Stg2, Stg3, or Stg4 showed that BT3642 alleles in each of these loci could contribute to the stay-green phenotype.RT37000 NILs containing BT3642 DNA corresponding to Stg2 retained more green leaf area at maturity under terminal drought conditions than RT37000 or the other RT37000 NILs.Under postanthesis water deficit, a trend for delayed onset of leaf senescence compared with RT37000 was also exhibited by the Stg2, Stg3, and Stg4 NILs, while significantly lower rates of leaf senescence in relation to RT37000 were displayed by all of the Stg NILs to varying degrees, but particularly by the Stg2 NIL.Greener leaves at anthesis relative to RT37000, indicated by higher SPAD values, were exhibited by the Stg1 and Stg4 NILs.The RT37000 NILs created in this study provide the starting point for in-depth analysis of stay-green physiology, interaction among stay-green QTL and map-based cloning of the genes that underlie this trait.

Sorghum stay-green QTL individually reduce post-flowering drought-induced leaf senescence