QTL analysis of the stay-green trait using a recombinant inbred line population in Sorghum

F Wacera and W Sakamoto

Institute of Plant Science and Resources, Okayama University

The stay-green trait is a mechanism by which plants adapt to post-flowering drought stress thus enhancing continued photosynthesis and grain filling, leading to higher yields and biomass. Our study aims at identifying stay-green QTLs at the seedling stage and characterizing the genes responsible for it in sorghum. 252 Recombinant inbred lines (RILs) were derived from a cross between BTx623, the genome reference sequence possessing stay-green characteristics; and a non stay-green Japanese landrace, NOG. The F6 population was used to obtain high-resolution genotyping data with >3,700 markers via RAD sequencing. Comparative analysis of chlorophyll content readings taken from the second and third leaves of 24-day-old seedlings grown in a controlled growth chamber, allowed us to identify seven stay-green QTLs. Two QTLs on chromosomes 2 and 6 were found to be consistent in two replications, and these also explained the highest phenotypic variation among all the QTLs. Additional QTLs obtained from leaf 2 were located on chromosomes 1, 6 and 8, while measurements from leaf 3 yielded additional QTLs on chromosomes 1, 2, 3, and 7. The total phenotypic variation explained by the QTLs obtained from chlorophyll measurements of the second and third leaves were 19% and 23%, respectively. The presence of two consistent QTLs suggests that these might be major QTLs involved in the expression of the stay-green trait in our sorghum lines. Further genotypic analysis on these RILs is underway to attain a population that can be used for linkage analysis and moreover, field trials to complement this data are currently ongoing.