Effects Of Exogenous Brassinosteroid On Yield And Quality Of Winter Wheat Under High-temperature Stress After Anthesis

In recent years,with global warming,the frequency and intensity of high-temperature stress in crop production have been increasing,which has gradually become an important abiotic factor restricting agricultural production.The grain filling stage of wheat is a critical period for the formation of yield and quality.High temperature during this period will significantly inhibit the formation of wheat yield and quality,causing serious adverse effects on wheat production.Studies have shown that brassinosteroid（BRs）is involved in regulating crop growth and development.However,the effect of exogenous BRs on wheat yield and quality under high-temperature stress after anthesis is not clear.Based on this,two winter wheat varieties（lines）Shuangda 1（high-temperature sensitive,SD1）and Luomai 18（high-temperature insensitive,LM18）with different temperature sensitivity were selected as experimental materials.The effects of high-temperature stress（HT treatment）and exogenous BRs(10μmol L^-1)on wheat antioxidant system,soluble sugar content,yield and component factors,protein and starch content in grains and their physical and chemical properties were studied.The effect of exogenous spraying BRs on the yield and quality of winter wheat under high-temperature stress was discussed.The main results of this study are as follows:1.Compared with CK,HT increased the activities of SOD,CAT and MDA in leaves,especially in 2020-2021,the heat resistance of SD1 was significantly lower than that of LM18.HT aggravated the degree of cell membrane damage,accelerated leaf senescence,and significantly reduced soluble sugar and starch content.However,foliar application of BRs under high temperature stress significantly increased leaf antioxidant enzyme activity,reduced MDA content,inhibited cell membrane lipid peroxidation,increased leaf chlorophyll content,net photosynthetic rate,soluble sugar and starch content,delayed leaf senescence,and enhanced wheat resistance.2.At the early stage of grain filling,HT significantly reduced the thousand-grain weight of wheat,and the response of different varieties to high temperature was significantly different.Especially in 2020-2021,the 1000-grain weight of LM8 decreased by 11.52%under HT treatment,while that of SD1 decreased by 68.43%.However,exogenous BRs（CK+B）had no significant effect on 1000-grain weight at room temperature,but exogenous brassinosteroid（HT+B）could significantly increase the 1000-grain weight of wheat under HT conditions,with an increase of 2.71%～7.70%compared to HT.The decrease of 1000-grain weight caused by high temperature stress is the main factor causing the decrease of yield,and spraying BRs under high temperature mainly improves yield by increasing 1000-grain weight.3.HT significantly affected wheat grain quality.HT caused a significant decrease in grain formation and stability time of winter wheat,and the percentage of crude protein increased.HT+B treatment increased the formation and stability time and decreased the percentage of crude protein.In addition,our study also found that compared with CK,HT significantly reduced the amylose content,amylopectin content and total starch content of SD1 and LM18.Among them,in 2020-2021,the starch of high temperature sensitive variety SD1 decreased by 39.84%～72.46%,but the starch of high temperature sensitive variety LM18 decreased by 1.86%～9.65%.Compared with HT,the starch content of SD1 and LM18 increased significantly under HT+B treatment,and the amylose,amylopectin and total starch content increased by 7.87%-32.37%,0.98%-32.37%and 2.79%-12.65%,respectively.Under HT,the morphology of starch granules appeared pits,damage,pitting,and even fracture,and the range and degree of damage were greater than CK,and the range and degree of damage of SD1 were much larger than LM18.Under HT+B treatment,the degree and range of starch damage decreased,and the pits on the surface of starch granules decreased.Under HT,the particle size of starch and the crystallinity of starch increased significantly,which led to the further increase of starch gelatinization time and gelatinization temperature,and finally decreased the starch quality of winter wheat.The trend of the two varieties remained at a relatively consistent level.However,under HT+B treatment,the morphology and particle size of starch were significantly improved,the crystallinity decreased,the energy required for cooking time decreased,and the cooking time decreased.Among them,the starch quality of LM18 was slightly higher than that of SD1.Based on the study of this experiment,spraying brassinosteroids can increase wheat yield and improve wheat starch quality under high temperature stress.Therefore,in the event of high-temperature stress,we can use 10μmol L^-1 brassinosteroid to alleviate high-temperature stress.