Effect Of Heat Stress On Grain Filling And Major Quality Traits Of Common Wheat

Wheat is one of the most important crops in China, and the yield and quality are the most important parameters for both producers and consumers. Tolerance to heat stress during grain filling stages is a major breeding objective under the global climate change scenarios, and this is particularly important for the North China Winter Wheat Region, contributing 70% of the national wheat production. In the present study, thirteen leading cult ivars and advanced lines from the North China Winter Wheat Region, planted in three locations including Shijiazhuang, Hengshui and Anyang in 2013-2015 wheat season, were used to understand comprehensively how heat stress after anthesis affects the grain filling properties and quality traits. The information will be crucial for breeders to develop cultivars with favorable functionality grown under heat stress condition. The main results were presented as follows.1. The kernel weight and grain filling rate were significant ly influenced by genotype and enviroment, and the duration of grain f illing was mainly influenced by enviroment. The grain weight of wheat under heat stress was signif icantly positively correlated with grain filling rate. The correlation between grain weight and grain filling rate under heat stress w as higher than it under normal, suggesting that grain filling rate palyed a most important role in the formation of grain weight under heat stress and it was a main reason of the difference in heat-resistance among cultivars. The decreased 1000-kernel weight under heat stress was mainly due to the decreased grain filling rate, in which the reduced grain-filling rate of grain-filling fast increase period plays a very important role to influence grain weight. The responses of grain filling properties to heat stress were mainly ralated to cultivars. Finally, we screened a lot of cultivars such as Jingdong8、Zhongmai875、Zhongmai895、CA1062、CA0816、Zhongmai175 and Shimai15 that have good resistence to heat stress. And we also found some cultivars such as Heng08guan29、Hengguan35 and ShiU09-4366 that have poor resistence to high temperature stress. In the present study, the heat resistance of large grain size c ult ivars was higher than middle or small grain size cultivars, the reason of good resistance to heat stress of large grain size cultivars might be its high grain filling rate.2. The results about protein related parameters showed that protein content and kernal hardness were higher under heat stress. The Mixograph parameters including m idline peak t ime, peak integral, time x value and t ime x width were signif icantly increased. Analys is of variance(ANOVA) indicated that flour pasting properties were significantly affected by enviroment and cultivar. Flour pasting properties were signif icantly affected by treatment, with cultivar being the predominant for all parameters. The flour pasting properties parameters including peak viscosity, breakdown, final viscosity and setback were significant ly decreased by heat stress treatment and pasting temperature was signif icantly increased under heat stress condition. The size exclusion chromatography(SEC) analysis with starch indicated that there were no significant differences on distribution of the starch granules and ratio of amylopectin and amylose between treatments. The fluorescence assisted capillary electrophoresis(FACE) analys is with starch showed that there was no signif icant difference on chain length distribut ion(CLD) between treatments, but the starch properties mentioned above varied signif icantly among cultivars. The study on the crystalline structure of starch indicated that the relative crystalinity was significant ly increased under heat stress condition. The starch granule size distribution results indicated that the content of B-type starch granule was significantly decreased by heat stress treatment and the content of A-type starch granule was signif icantly increased under heat stress condition. Starch granules were isolated from wheat flour by wet milling and the starch pasting properties parameters including peak viscosity, trough viscosity, final viscosity and breakdown were signif icantly decreased by heat stress treatment. But the effect of heat stress on starch pasting properties was weaker than flour pasting properties, indicating that the protein in flours might be the other major factor to influence flour pasting properties. Therefore, higher protein content and changes of starch properties under heat stress might be the reason of the significant ly lower pasting properties of wheat flours.