Effects Of Heat Stress At Anthesis-Grain Filling Stage On Grain Quality Formation In Wheat

Extreme high temperature events are becoming more frequent due to the increasing average temperature with global climate change,which means that multiple heat stress events will be observed more during crop growth period,especially for reproductive stage.Flowering and grain-filling stages are the critical periods for the formation of.wheat grain quality and are extremely sensitive to temperature.Heat stress during flowering and grain-filling will have a significant adverse effect on the formation of wheat yield and quality.Therefore,analyzing the effects of multiple heat stress events on the formation of wheat grain quality can provide theoretical basis for making adaptive strategies under future climate change and improving wheat quality to ensure the safety of wheat production in China.In this study,two-year environment-controlled phytotron experiments under different high temperature levels and high temperature durations at flowering,grain filling stage and fl[owering-grain filling stage with Yangmai16 and Xumai30 were conducted to investigate the effects of heat stress at different growth stages on appearance quality,nutritional quality and processing quality of wheat.The main results were as follows:Grain protein contents and its components in two wheat varieties increased obviously with the increase of high temperature level and duration under heat stress treatments at different stages(flowering,grain filling stage and flowering-grain filling stage).High-temperature stress has greater effects on storage proteins(gliadins and gluten)than metabolic proteins(albumin and globulin).The effects of high temperature stress at flowering-grain filling stage on grain protein and its components in two wheat varieties were greater than those under high temperature stress at individual stages(flowering and grain filling stage).The effects of high temperature stress on the Glia/Glu during grain filling stage were greater than those under flowering and flowering-grain filling stage.Grain protein and its components of two wheat cultivars had different sensitivities to different treatment stages,high temperature levels and durations.And grain protein of Xumai30 was more sensitive to high temperature stress than Yangmail6.The changes of grain protein content in the two wheat varieties after three-day high temperature treatments at flowering-grain filling stage were smaller than that under high temperature treatments at individual stages,indicating that three-day high temperature treatments with T2,T3,and T4 in the flowering stage enhanced the heat tolerance and alleviated the effects of high temperature stress at grain filling stages on final grain protein content.Six-day high temperature stress at flowering stage enhanced the adverse effects of high temperature stress at the filling stage in two varieties,showing no positive heat priming effects on grain protein.Three-day heat stress treatment with T4(with average temperature of 34OC)was the best treatment regime for most obvious heat priming effects on grain protein content.High temperature treatments at different stages(flowering,grain filling stage and flowering-grain filling stage)reduced the content of total grain starch and amylopectin in both wheat cultivars significantly,but increased the amylose content significantly.High temperature stress also reduced the duration for starch synthesis and speeds up the grain maturity process.The effects of heat stress at flowering-grain filling stage on grain starch were larger than high temperature stress at individual stages.Three-day high temperature treatment enhanced heat tolerance of grain starch at flowering-grain filling stage in Yangnai16 and Xumai30.Under high temperature stress for 6 days,grain starch showed positive priming effects in Xumai30,but not in Yangmail6.The priming effects of six-day heat stress at flowering in Xumai30 was smaller than that from three-day heat stress at flowering,and three-day heat stress treatment with T4(with average temperature of 34°C)was the best treatment regime for most obvious heat priming effects on grain starch,similar with grain protein.The contents of starch,starch components,and Amylose/Amylopectin of different varieties had different responses to high temperature levels and durations.There was no signiflcant interaction effects between temperature level and treatment durations,and the effects of high temperature level on grain starch was much more obvious than that of high temperature durations.High temperature treatment with different high temperature levels and durations at different stages(flowering,grain filling stage and flowering-grain filling stage)increased the ratio between length and width of grain,gluten content,and sedimentation value,but reduced the length and with of mature grain in two varieties.Under high temperature treatment at same stage,parameters of appearance and processing quality under T4 treatment was significantly different from the control(T1),but there was no significant differences between T2,T3 and Tl.Besides,the effects of heat stress treatment for 6 days on grain appearance and processing quality were more obvious than that under three-day heat stress treatments.The effects of heat stress under flowering-grain filling stage on wheat grain length,width,lengthjwidth and gluten content were greater than that at individual stages,and the effects of heat stress treatments at flowering-grain filling stage were significantly different from the control(TI).Under different high temperature durations,the responses of grain length and sedimentation value of two wheat varieties to heat stress at flowering and grain filling stage were different.The grain length and sedimentation value of Yangmai16 were mostly affected by high temperature treatment at grain filling stage under three-day treatment.But,the effects of three-day heat stress at flowering-grain filling stage on grain length and sedimentation value were greater that other treatment stages in Xumai30.While under the 6-day high temperature treatment,the effects of high temperature treatment at flowering-grain filling stage treatment on the grain length of two wheat cultivars were significantly higher than that under individual stages.The effects of heat stress on the grain sedimentation value under flowering-grain filling stage were lower than that at grain filling stage in Yangmai16,but larger than that at grain filling stage in Xumai30.This study,by comparing the impacts of two-stage high temperature stress(flowering and grain filling stage)with inpacts of high temperature stress at individual stages,enriched the understanding of the responses of wheat grain quality to multiple heat stress events at flowering and grain filling stage.And the possibility of alleviating the effects of high temperature stress at grain filling stage on grain quality by high temperature pr:iming at flowering was also investigated.The results are critical for developing simulation models to quantify the effects of multiple high temperature stresses on wheat grain quality and developing adaptive practices to heat stress under future climate change.