Molecular Characterization of the Traits Associated with High Temperature Stress Tolerance in Wheat.

Genetic variation in high temperature stress tolerance has been associated with a wide range of physiological traits. Thylakoid membrane (chlorophyll fluorescence) and cell membrane (CMS) damage have been reported to be important traits associated with heat tolerance in wheat. Molecular characterization of those traits can help wheat breeders to improve genetic gain for heat tolerance. The objectives of study were to identify genomic locations associated with those traits. A population of recombinant inbred lines (RILs) derived from Karl 92/Ventnor was evaluated for chlorophyll fluorescence, CMS and SPAD-chlorophyll content. The population was evaluated for those three traits in F₉ and F₁₀ generations under long-term post-anthesis heat stress conditions. Plants were exposed to the high temperature stress (36^o/30^oC day/night temperature; relative humidity 80%; and photoperiod 16/8 hours) after flowering. Chlorophyll fluorescence and SPAD-Chlorophyll content data were collected at 0, 4, 7 and 10 days after high temperature stress, while CMS was measured at 7 and 10 days only. The population was genotyped with 450 molecular markers which included 259 AFLPs, 189 SSRs, and a STS. Two quantitative trait loci (QTLs) were consistently associated with those three traits. The QTL in 7AL showed a highly significant association with all three traits and explained greatest percentage, ranged from 17% to 22%, of total phenotypic variability. The other QTL located on 6AL explained 10% to 16% phenotypic variability of those traits. All three traits were very strongly associated with each other with 65% to 80% of phenotypic variability explained by one other. The results demonstrated that the two QTLs have pleiotropic effects for the three traits. Two SSR markers, BARC49 and GWM276, closely associated with the QTL on 7AL, have potential to be used in marker-assisted selection for high temperature stress tolerance in wheat.