Quantitative and molecular characterization of heat tolerance in hexaploid wheat

Understanding the genetic basis of tolerance to high temperature is important for improving the productivity of wheat (Triticum aestivum L.) in regions where the stress occurs. The objective of this study was to estimate inheritance of heat tolerance and the minimum number of genes for the trait in bread wheat by combining quantitative genetic estimates and molecular marker analyses. Two cultivars, Ventnor (heat-tolerant) and Karl 92 (heat-susceptible), were crossed to produce F-1, F-2, and F-3 populations, and their grain-filling duration (GFD) at 30/25 degreesC 16/8 h day/night was determined as a measure of heat tolerance. Distribution of GFD in the F-1 and F-2 populations followed the normal model (chi(2), p > 0.10). A minimum of 1.4 genes with both additive and dominance effects, broad-sense heritibility of 80%, and realized heritability of 96% for GFD were determined from F-2 and F-3 populations. Products from 59 primer pairs among 232 simple sequence repeat (SSR) pairs were polymorphic between the parents. Two markers, Xgwm11 and Xgwm293, were linked to GFD by quantitative trait loci (QTL) analysis of the F-2 population. The Xgwm11-linked QTL had only additive gene action and contributed 11% to the total phenotypic variation in GFD in the F-2 population, whereas the Xgwm293-linked QTL had both additive and dominance action and contributed 12% to the total variation in GFD. The results demonstrated that heat tolerance of common wheat is controlled by multiple genes and suggested that marker-assisted selection with microsatellite primers might be useful for developing improved cultivars.