Effects Of High Temperature,Drought And Their Combined Stress On Yield Formation Of Summer Maize

This study was conducted from 2020 to 2021 in Huanghuaihai Corn Science and Technology Park of Shandong Agricultural University and State Key Laboratory of Crop Biology.Denghai605（DH605）was selected as the experimental material.High temperature treatment（T）,drought treatment（D）and the compound stress（T-D）treatment were set at the third leaf stage（V3）,the twelfth leaf stage（V12）and tasseling stage（VT）,and taking natural temperature and normal moisture treatment as control（CK）.The effects of high temperature,drought and their combined stress treatments in different growth periods on the yield formation of summer maize were studied in order to provide a scientific basis for the stress resistance and stable yield of summer maize.The main results are as follows:1.Effects of high temperature,drought and their combined stress on yield and its components of summer maizeGrain yield of summer maize was significantly decreased after high temperature,drought and their combined stress.Grain yield was decreased by 6.1%,5.1% and 12.2% after high temperature,drought and their combined stress at V3,while decreased by 9.7%,10.9% and14.8% for stress treatment at V12,and 56.5%,14.0% and 62.3% for stress treatment at VT,respectively,compared to that of CK.It can be seen that high temperature,drought and their combined stress treatments at VT have the greatest impact on yield,followed by V12,and V3,and the impact of compound treatment on yield was greater than that of single treatment.2.Effects of high temperature,drought and their combined treatments on the ear developmental characteristics of summer maizeHigh temperature,drought and their combined stress significantly affected ear developmental characteristics of summer maize.After being subjected to drought,high temperature and their combined stresses at different growth stages,the differentiation of tassel and ear spikes was hindered and ear length was significantly shortened.The combined effects of high temperature and drought on the growth and development of tassel and ear spikes were greater than those of high temperature or drought.Compared with CK,the length of ear under the combined stress of high temperature and drought at V3,V12 and VT were reduced by 15.6%,19.8% and 12.1%,respectively.Compared with CK,the length of tassel under the combined stress of high temperature and drought at V3,V12 and VT were reduced by 20.2%,11.9% and6.1%,respectively.In addition,the different degrees of depression and deformity appeared on the pollen surface of summer maize after high temperature,drought and their combined stress at different growth stages,the filaments were dehydrated and shrunken,the number of villi was reduced and lodging,and the morphological structure was deformed,which significantly affected the fertilization and fruiting of summer maize.The number of fertilized florets of summer maize was significantly decreased after high temperature,drought and their combined stress at different stage.The decrease in the number of fertilized florets under the combined stress of high temperature and drought was significantly greater than that under the single stress of high temperature and drought.Compared with CK,the number of fertilized florets was decreased by 6.5%,3.8% and 8.1% respectively after high temperature,drought and their combined stress at V3.Compared with CK,the number of fertilized florets was decreased by 6.8%,8.0% and 8.7% respectively after high temperature,drought and their combined stress at V12.Compared with CK,the number of fertilized florets was decreased by 43.1%,10.6% and 49.5% respectively after high temperature,drought and their combined stress at VT.It can be seen that high temperature,drought and their combined stress treatments at VT had the greatest impact on ear development of summer maize,followed by V12,and V3.As a result,the number of grains per ear was significantly decreased,leading to a significant reduction of maize yield.3.Effects of high temperature,drought and their combined treatments on grain filling characteristics of summer maizeGrain filling of summer maize was affected by high temperature,drought and their combined stresses at different growth stages,resulting in a significant decrease in grain fresh weight,dry weight and volume,which in turn affected yield.The decrease of grain fresh weight,dry weight and volume under the combined treatment of high temperature and drought was greater than that of single stress.Compared with CK,the fresh grain weight after the combined stress of high temperature and drought at V3,V12 and VT was decreased by 6.4%,6.8% and13.0%,respectively,while grain dry weight decreased by 8.5%,10.3% and 13.1%,and grain volume decreased by 5.1%,5.5% and 11.6% compared to those of CK,respectively.4.Effects of high temperature,drought and their combined stress on photosynthetic characteristics of summer maizeLeaf area index（LAI）and SPAD values of summer maize were significantly reduced after high temperature,drought and their combined treatments at different growth stages,which led to a decrease in the photosynthetic performance and net photosynthetic rate（Pn）of summer maize.The decrease of LAI,SPAD and Pn after combined high temperature and drought treatments were greater than those of single stress.Compared with CK,the LAI of t at V3,V12 and VT was decreased by 12.3%,17.7% and 8.3%,respectively.The SPAD of the combined stress of high temperature and drought at V3,V12 and VT was decreased by 8.7%,12.4% and9.3% compared to that of CK,respectively.In addition,Pn was decreased by 12.2%,14.8% and62.3% after the combined stress of high temperature and drought at V3,V12 and VT,compared to that of CK,respectively.5.Effects of high temperature,drought and their combined treatments on dry matter accumulation and distribution of summer maizeDry matter accumulation of summer maize was significantly reduced after high temperature,drought and their combined stresses,and the combined high temperature and drought treatments had a greater impact on the dry matter accumulation than single stress.Compared with CK,the total dry matter accumulation per plant after the combined stress of high temperature and drought at V3,V12 and VT was decreased by 15.6%,16.2% and 32.9%,respectively.In addition,the combined stress of high temperature and drought at VT stage had the greatest effect on the dry matter accumulation per plant of summer maize,followed by V12,and V3 stage.At the same time,the proportion of dry matter distribution to grains was decreased by 1.9% and 21.1% compared with CK under the combined stress of high temperature and drought at V12 and VT stage,of which decline was greater than that under the single stress of high temperature and drought.6.Effects of high temperature,drought and their combined treatments on the stalk development of summer maizeHigh temperature,drought and their combined stress significantly affected the stalk development of summer maize.After high temperature,drought and their combined treatments,the stem length and stem diameter of the third stem node of summer maize were decreased,and the puncture strength was also decreased.Compared with CK,the puncture strength after the combined stress of high temperature and drought at V3,V12 and VT was decreased by 24.7%,20.6% and 12.5%,and the stem length decreased by 32.2%,37.4% and 23.2%,the stem diameter decreased by 12.0%,12.8% and 12.4%,respectively.At the same time,the microstructure of stems was changed after the combined stress of high temperature and drought.Compared with CK,the area of large vascular bundle was decreased by 21.0%,14.5% and15.5%,and the area of small vascular bundle was reduced by 25.3%,26.7% and 23.4% after the combined stress of high temperature and drought at V3,V12 and VT.The number of vascular bundles was decreased by 20.6%,18.0% and 10.1%,the thickness of scleroderma decreased by 8.6%,16.7% and 14.0%,and the thickness of cortex decreased by 23.1%,19.5%and 9.1% after the combined stress of high temperature and drought at V3,V12 and VT.compared to those of CK,respectively.It can be seen that under the combined stress of high temperature and drought,the thickness of the cortex and the scleroderma of the third shoot node became thinner,the area of large and small vascular bundles became smaller,the number of vascular bundles decreased,the development of the culm was inhibited,and the conduction capacity of the culm decreased.