Effects Of Spraying KH₂PO₄ On Grain Weight Formation Under High Temperature Stress During The Filling Period Of Wheat

In the Huang-Huai-Hai Plain,high temperature weather is prone and frequent during the wheat filling period,which threatens the stable and high yield of wheat in this area.In order to explore the effects of spraying KH₂PO₄after anthesis on grain weight formation of wheat under heat stress during grain filling stage,and a winter wheat variety‘Annong 0711’was selected as the test material,which widely cultivated in the local region.The 0.3%KH₂PO₄solution was sprayed on the third and eleventh days after anthesis,respectively.In the field,the heat stress treatments were simulated by using plastic film shed form 20th to24th days after anthesis.In this experiment,four treatments were set up.i.e.,spraying water（CK）,water+combined with heat stress（HT）,0.3%KH₂PO₄（KDP）and 0.3%KH₂PO₄combined with heat stress（PHT）.The effects of different treatments on flag leaves chlorophyll content,photosynthetic performance,protective enzyme activity,malondialdehyde content,non-structural carbohydrates（NSC）content in vegetative organs,grain filling rate and starch content,dry matter accumulation and distribution,grain yield of wheat were investigated to explore the physiological mechanism of spraying 0.3%KH₂PO₄on grain weight formation under heat stress during the wheat filling period.The findings are as follows:（1）Spraying 0.3%KH₂PO₄after anthesis significantly increased chlorophyll content and photosynthetic performance in flag leaves before high stress,increased the protective enzymes activity and decreased MDA content.Heat stress treatment significantly reduced the chlorophyll content of flag leaves,but the decreased of chlorophyll content was relatively small when sprayed with 0.3%KH₂PO₄,and maintained a higher net photosynthetic rate and protective enzyme activity in flag leaves,while the intercellular carbon dioxide concentration and MDA content decreased significantly.（2）Spraying 0.3%KH₂PO₄after anthesis significantly increased the average grain filling rate,prolonged grain filling time,and significantly increased grain weight.Heat stress treatment significantly reduced the average grain filling rate at grain filling period,resulting in a decrease in 1000-grain weight of superior and inferior grains at maturity stage.Compared with CK,the 1000-grain weight of superior and inferior grains under HT treatment decreased by 1.08%and 5.97%,respectively.Compared with KDP,the1000-grain weight of superior and inferior grains under PHT treatment decreased by0.85%and 1.61%,respectively.（3）Spraying 0.3%KH₂PO₄after anthesis significantly increased the soluble sugar and sucrose content of wheat flag leaf and stem+sheath,and the starch accumulation of superior and inferior grains were significantly increased.Heat stress significantly reduced the NSC content in wheat plants,but spraying 0.3%KH₂PO₄treatment still maintained the higher soluble sugar and sucrose content and improved the grain starch accumulation in wheat vegetative organs after heat stress.（4）Spraying 0.3%KH₂PO₄after anthesis significantly increased dry matter accumulation after anthesis and maturity,increased the contribution rate of dry matter accumulation after anthesis to grain,and significantly increased grain yield.Heat stress treatment significantly increased the dry matter translocation before anthesis and its contribution rate to grain,and decreased the dry matter accumulation,grain yield and harvest index at maturity stage.Compared with HT,the yield of CK,PHT and KDP increased by 9.46%,11.06%and 16.79%,respectively,and the increase of yield by spraying 0.3%KH₂PO₄was due to the significant increase of 1000-grain weight.In summary,spraying 0.3%KH₂PO₄after anthesis can enhance the activity of protective enzymes in flag leaves under heat stress during grain filling period,reduce the accumulation of MDA,delay the senescence process of flag leaves,maintain its photosynthetic capacity,increase the dry matter production after anthesis,prolong the grain filling time,increase the NSC content in vegetative organs,and finally effectively alleviate the adverse effects of heat stress on grain weight formation.