IDENTIFICATION OF WHEAT GENOTYPES TOLERANT TO THE EFFECTS OF HEAT-STRESS ON GRAIN QUALITY

High-temperature stress (>35 degrees C) during the grain-filling perio d has the potential to modify grain quality. A consequent weakening of dough properties has been reported for many wheat genotypes. The expe riment described in this article was designed to identify wheat genoty pes that might be tolerant to the effects of heat stress on grain qual ity and to further assess the molecular basis of these changes. A dive rse set of 45 wheat genotypes was exposed to 10 hr of 40 degrees C on each of three consecutive days in a phytotron. Mean values for all gen otypes (with unheated control samples, all in duplicate) showed highly significant changes (P < 0.001) in 1,000 kernel weight (-17% differen ce for heat stressed minus control), protein content (17% increase), d ough mixing time in a 2-g Mixograph (-13%), and resistance breakdown ( 17%). The general weakening of dough due to heat was accompanied by a decrease in glutenin-to-gliadin ratio and in the percentage of very la rge glutenin polymers. Bound lipid content increased, and there was a general reduction (-9%) in the proportion of small (B-type) starch gra nules. For all these attributes, reactions for individual genotypes ra nged from little change (tolerance to heat stress) to considerable cha nge (susceptible to heat stress). A group of genotypes was thus identi fied that should be useful in breeding attempts to stabilize wheats ag ainst heat-related variations in grain quality. Markers identified as potentially useful in breeding for tolerance include the presence of t he Glu-Dld allele (glutenin subunits 5 and 10), and increases in glute nin-to-gliadin ratio and in the percentage of very large glutenin poly mers.