Influence of heat stress on grain yield, grain quality, and protein composition of spring wheat

Wheat (Triticum aestivum L.) plants exposed to higher than usual temperatures during ripening show altered agronomic and grain quality characteristics. Given that seasonal variation in quality creates difficulties in the marketing and processing of grain, improving the genetic adaptation of wheat cultivars to heat stress is an important objective in breeding programs. Some genotypes have been reported to have a thermo tolerant response and could be used as genetic sources for heat tolerance. Six spring wheat cultivars and four elite experimental lines were evaluated in Uruguay. Two field experiments were conducted in years 2001 and 2002 to determine response under natural heat stress conditions, and two greenhouse experiments were conducted to vary duration and timing of heat stress. Grain protein concentration increased with moderate (field conditions) and high heat stress (controlled environment). Heat stress imposed early in grain fill had the greater effect. In field conditions, moderate to high heat stress at mid-grain fill increased test weight and thousand kernel weight. Higher heat stress under controlled environment caused a decrease in thousand kernel weight, without any difference in relation to duration or timing of stress. Rheological properties were affected by heat stress in field conditions. While moderate heat stress throughout grain fill caused stronger dough, moderate to high heat stress at mid-grain fill produced weaker dough. These results suggest a curvilinear response to increasing heat stress for both thousand kernel weight and rheological properties. Impact of heat stress under field conditions was inconsistent on protein molecular weight distribution. Moderate to high heat stress at mid-grain fill lowered level of monomeric proteins, and increased the ratio soluble polymeric proteins/monomeric proteins. Moderate heat stress throughout grain fill decreased percentage of soluble polymeric proteins, and increased percentage of low molecular weight albumins and globulins. No effect of heat stress was detected on protein molecular weight distribution in controlled environment. However, with longer duration of stress, significant genotype x treatment interaction was detected. Cultivars with relatively stable agronomic and quality characteristics were identified and could be used as genetic sources for improving resistance to heat stress.