| With the global warming,high temperature has become one of the abiotic limiting factors of wheat production.According to the statistics of meteorological data of Jinan in Shandong province in the past 50 years,high temperature is common during wheat filling and the duration is long,especially in the middle of filling.In order to clarify the high temperature sensitive period of wheat filling in this area and its influence on main cultivars,we explore the effect of nitrogen fertilizer to ease high temperature stress.Our study carried out on the effect of high temperature lasting 3-9 days,10-16 days and 17-23 days after flowering on the grain yield and quality of seven wheat cultivars and their physiological mechanisms in Ji’nan and Jiyang,Shandong Province from 2017 to 2019,and conduct the research of the effect of nitrogen application rate(180 kg·hm-2,240 kg·hm-2,300 kg·hm-2)on photosynthetic fluorescence characteristics,filling characteristics,dry matter accumulation,transportation and distribution,sucrose and starch contents and related synthase activities and grain yield formation of different heat-resistant wheat.The main results are as follows:(1)High temperature in different periods after flowering accelerates flag leaf senescence and reduces yield.Compared with lasting 3-9 days and 17-23 days after flowering,high temperature lasting 10-16 days after flowering significantly reduced the SPAD value,photosynthetic rate,Fv/Fm and (?)PSII of flag leaves after 3 days of high temperature stress,and significantly reduced the grain filling rate,dry matter accumulation at maturity and its’ translocation to grain and distribution,significantly reduces the thousand-grain weight,the number of grains per spike,and the yield with a yield reduction rate of 9-20%.10-16 days after flowering is the high temperature sensitive period for the formation of wheat yield.(2)Under the high temperature stress of high temperature sensitive period,that is 10-16 days after flowering,Jimai 44,Jimai 23,Jimai 22 and 164034 significantly increased SPAD value of flag leaves,photosynthetic rate,Fv/Fm and (?)PSII after 3 days of stress,compared to Xinmai 26,Gaocheng 8901 and Linmai 2,and significantly increased the SOD and CAT activities of flag leaves after 7 days of stress,significantly reduced the MDA content of flag leaves after 7 days of stress,and significantly improved the dry matter accumulation and its transportation to grains and distribution,significantly increased the thousand-grain weight,the number of grains per spike and the grain yield.The Jimai 44,Jimai 23,Jimai 22 and 164034 strains were classified as heat-resistant cultivars,and Xinmai 26,Gaocheng 8901 and Linmai2 were classified as heat-sensitive cultivars.(3)The stress during the high temperature sensitive period after flowering reduced the dry matter accumulation,the amount of transportation to the grain and distribution,resulting in reducing the grain yield.Compared with 180 kg·hm-2 and 300 kg·hm-2,nitrogen application rate of 240 kg·hm-2 significantly increased the SOD,CAT activity,protein content,SPAD value,photosynthetic rate,Fv/Fm and (?)PSⅡ of flag leaves after 7 days of stress,significantly reduced MDA content,the enzyme activity of direction of sucrose synthase(SS-Ⅰ)and grain sucrose synthase(SS-Ⅱ)of flag leaf,significantly increased the enzyme activity of SPS,SSS and SBE;significantly improved the dry matter accumulation,the transportation to the grain and its’ rate during the maturity period,contents of starch and insoluble protein in grains,and significantly increased the thousand-grain weight,the number of grains per ear,and the grain yield.Nitrogen application rate of 240 kg·hm-2 is the best nitrogen application rate to reduce yield loss after stress during the high temperature sensitive period after flowering.In conclusion,under the conditions of our study,high temperature stress after flowering at different periods accelerated flag leaf senescence,reduced the dry matter accumulation,translocation and its’ rate to the grain at maturity period,and resulting in the yield loss.High temperature stress at 10-16 days after flowering has the greatest impact on yield formation.It can be seen that 10-16 days after flowering is high temperature sensitive period for wheat yield formation.Heat-resistant cultivars have higher photosynthetic rate,dry matter accumulation,translocation and transport rate to grain and yield,under high temperature in the sensitive period after flowering.Nitrogen application rate of 240 kg·hm-2 significantly improved the dry matter accumulation,transport amount to the grain and its’ rate,the starch content and insoluble protein content of the grain after high temperature stress in the sensitive period after flowering.Therefore,the application of heat-resistant varieties and the nitrogen application rate of 240 kg·hm-2 is a measure to reduce the yield loss rate of wheat after high temperature in the sensitive period after flowering. |
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