Quantitative Trait Loci (QTL) Analysis of Reproductive Stage Heat Tolerance in Wheat.

This study was conducted to identify and map QTLs for yield components and heat tolerance of wheat in response to two kinds of heat treatment (short term-and long term-heat treatment) during seed formation in a set of 62 RILs derived from a cross of ‘7C' (heat resistant variety) and ‘Seri M82' (heat susceptible variety) in environmentally controlled growth rooms and field. Phenotypic variations of yield components (kernel number, kernel weight, spike number and grain filling duration) were evaluated as indicators of heat tolerance / susceptibility. Most of the phenotypic variations of yield components exhibited a normal distribution in response to heat stress treatments. This suggests that the yield component responses to high temperature stress are likely quantitatively inherited. A transgressive segregation pattern compared to the two parents was observed in several yield traits. This suggests that genetic variation from optimal recombination from the two parents have occurred in the progeny population. The Pearson correlation coefficients revealed significant correlations between yield components. This suggests the probability of co-segregation of genes controlling each yield components. The heritability of the individual yield components was low (0.42 to 25%, 0.1~ 2% for heat tolerance). One hundred two polymorphic SSRs markers among 323 SSRs markers tested were used to construct a linkage coverage and average interval distance of 1860.2 cM and 18.2 cM/marker, respectively. Eighty-one QTLs for yield components and 68 QTLs for heat tolerance were detected with high LOD values (2.50~8.35 for yield components, 2.51~ 9.37 for heat tolerance) and that explained significant phenotypic variations (7~40% for individual QTL for yield components, 2~40 % for individual heat tolerance QTLs) from seven individual environments and the four individual heat stress environments, respectively. Specifically the regions between wmc48 and wmc89, and between wmc622 and wmc332 on the chromosome 4A and 6A, respectively possessed QTLs for both yield components and heat tolerance from various environments.