Study On The Mitigation Effect Of 2,4-epibrassinolide On Dry-hot Wind Stress Of Wheat

Dry-hot wind is the main agricultural meteorological disaster in the winter wheat region of northern China,which can reduce the wheat filling rate and affect wheat yield.Brassinolide can increase the photosynthetic rate of plants and enhance their resistance to stress such as high temperature and drought.Therefore,this experiment provides theoretical basis and technical support for enhancing the ability of wheat to resist dry-hot wind by exploring the regulation mechanism of spraying appropriate concentrations of 2,4-epibrassinolide on hormone content,antioxidant enzyme activity,chlorophyll content,chlorophyll fluorescence parameters,photosynthetic gas exchange parameters and other indicators in wheat flag leaf under dry-hot wind stress.This experiment was conducted at the South Campus Experimental Station of Shandong Agricultural University from October 2020 to June 2021 and from October 2021 to June 2022 during two wheat growth seasons.The planting materials were the dry-hot wind sensitive variety Jinan17（JN17）and the dry-hot wind resistant variety Liangxing77（LX77）.The split zone design was used,with the main area being a dry-hot wind shed and a field control,and the sub area being sprayed with 2,4-epibrassinolide(0.1mg L^-1)and water control.The main research results are as follows:1.Research on the damage mechanism of dry-hot wind stress on wheat during the filling periodDry-hot wind stress significantly increased the spike leaf temperature of two varieties of wheat,causing a rapid increase in the content of ABA,JA,and SA in the flag leaf of wheat,affecting the balance of hormones in the wheat body.The continuous dry-hot wind stress has disrupted the antioxidant enzyme system in wheat,leading to the continuous accumulation of reactive oxygen species,resulting in a 15%-32%decrease in chlorophyll content in wheat leaves,a 1%-6.2%decrease in maximum photochemical efficiency（Fv/Fm）of PSII,and a13.4%-40.2%decrease in photosynthetic performance index（PI abs）,significantly affecting wheat yield.2.The regulatory effect of exogenous application of 2,4-epibrassinolide on wheat under dry-hot wind stressSpraying 2,4-epibrassinolide alleviates the stress of dry-hot wind by increasing the ability of wheat to regulate hormones.Compared to spraying water,spraying 2,4-epibrassinolide can significantly reduce the content of ABA and JA in the flag leaf of the two varieties.On the contrary,it increases the SA content.The content of ABA and JA in JN17 flag leaf decreased by 6%-21%and 13.4%-23.4%,respectively,while the SA content increased by 4.9%-31.5%;ABA and JA in LX77 flag leaf decreased by 4%-14%and 7.7%-16.4%,respectively,while SA increased by 5.8%-18.4%.2,4-epibrassinolide reduced the inhibitory effect of ABA on stomata,promoted stomatal opening,accelerated wheat transpiration rate,and reduced the temperature of wheat spike and leaf,alleviating the stress of high temperature on wheat.Among them,the temperature of JN17 spike and leaf decreased by 1.27℃and 2.4℃,respectively,while the temperature of LX77 spike and leaf decreased by 0.87℃and 1.6℃,respectively.Spraying 2,4-epibrassinolide alleviated the stress of dry-hot wind on wheat by regulating the activity of antioxidant enzymes.It increased the activity of antioxidant enzymes such as SOD,POD,and CAT in the flag leaves of two varieties of wheat,reduced the oxidative damage of reactive oxygen species to chloroplast membranes,and maintained a high level of chlorophyll content in the leaves.Among them,the activity of SOD,POD,and CAT in the flag leaf of JN17 increased by 9.9%-28.6%,8.8%-32.2%,and 22.5%-65.7%,respectively;The activities of SOD,POD,and CAT in LX77 flag leaf increased by 8.5%-31.4%,6.3%-50.2%,and 18.9%-27.3%,respectively.Spraying 2,4-epibrassinolide alleviated the stress of dry-hot wind on wheat by regulating the absorption and transmission of PSII light energy.Compared to spraying water,spraying 2,4-epibrassinolide significantly increased the maximum photochemical efficiency and photosynthetic performance index of wheat chloroplasts,enhanced the net photosynthetic rate of wheat,and improved photosynthesis.Spraying 2,4-epibrassinolide can improve wheat yield.Compared to spraying water,spraying 2,4-epibrassinolide promotes the transport of wheat assimilates under dry-hot wind conditions,increases thousand grain weight,and increases yield.JN17’s yield increased by 9.2%and 7.5%in the two years,while LX77’s yield increased by 4.9%and 2.3%in the two years,respectively.For the variety,the improvement effect of 2,4-epibrassinolide on various aspects of dry-hot wind sensitive variety JN17 is more significant than that of dry-hot wind resistant variety LX77.