Research On The Response Mechanism Of Rice Stubble Wheat To Weak Light In Jianghan Plain

The wheat region in the middle and lower reaches of the Yangtze River is one of major food production bases in China,but at present,the wheat production in this area is affected by the gradual decrease of solar radiation,frequent and continuous rainy days after anthesis,which seriously affects the yield and quality of wheat.Although previous studies have acquired some achievements in the changing trend of wheat yield and physiological mechanism under low light stress.But in Jianghan Plain,there is no report on the breeding and extension of adaptive main wheat varieties and the control measures of stress resistance in wheat production.Therefore,it is urgent to select a batch of wheat varieties suitable for planting in Jianghan Plain.Meanwhile,the response of different resistant varieties to low light and the mitigative effect of exogenous growth regulators on wheat stress were also studied,for laying a theoretical foundation and technical support for the establishment of wheat stress resistance optimization cultivation system.In 2017-2018,48 wheat varieties from Hubei,Henan,Anhui,Jiangsu and other regions were selected for shading treatment in the filling period.Through the study of biomass,harvest index,yield and yield components,different resistant wheat varieties were screened.Based on the previous year,nine varieties including Xiangmai 55,Zhengmai 9023,Yangmai 158,Yangmai 20,Fumai No.8,Yangmai 13,Emai 170,Shengxuan No.6 and Fumai 1228 were selected in 2018-2019 to carry out the shading test during the filling period,and the effects of shading on carbon,nitrogen and yield of different resistant wheat varieties were studied.In addition,experiments of shading and spraying growth regulators in different periods were conducted in 2017-2019 to study the mitigation effect of 6-BA on low light stress.The main results are as follows:1.There was a positive correlation between yield reduction and biomass reduction(b),harvest index reduction(H),thousand-grain quality reduction(T)and the sum of them(B+H+T),which indicated that the biomass reduction,harvest index reduction,thousandgrain quality reduction and the superposition effect of them could be used as the screening index of low light resistant varieties.According to the cluster analysis of the selection indexes of varieties with low light tolerance,Xiangmai 56,Wanximai 0638,Xiangmai D31,Yangmai 22,Nannong 0686,Wanke 06290,Xiangmai 55,Zhengmai 9023,Luomai 6010,Fumai No.8,Nongda 195,Jingmai 102,Yangmai 158,Zhengmai 7698,Fumai No.9,Xiangmai 55 are weak light insensitive varieties.2.Shading increased the chlorophyll content of wheat flag leaf during the filling stage.The change between treatments was not obvious due to the self-regulation of plant body in the early and middle stages of filling,but the difference between treatments in the late stage of filling increased significantly.Shading also changed the canopy structure.The leaf area index of the control treatment increased first and then decreased slowly.The leaf area index of the shading treatment decreased significantly compared with the control,while the extinction coefficient of the shading treatment was basically consistent with the change trend of the leaf area index.3.Shading after anthesis inhibited the accumulation of dry matter in wheat plants.The decrease of light radiation led to the shortage of supply of photosynthate after anthesis.The accumulation of dry matter in vegetative organs of shading treatment was significantly less than control.The growth curve of grain weight was compressed,and the dry weight of grain decreased significantly in the rapid growth period.Finally,the total accumulation of dry matter in the middle filling period and the mature period was significantly decreased.The transport amount of assimilates before anthesis and their contribution to grain increased than control,while the transport amount of assimilates after anthesis and their contribution to grain decreased with the decrease of harvest index.4.Shading inhibited the redistribution of nitrogen from vegetative organs to grains,and more nitrogen remained in vegetative organs.The amount and rate of nitrogen transfer from storage before anthesis to grain decreased significantly in shading treatment,which increased the dependence of nitrogen accumulation on nitrogen absorption after anthesis.Although the amount of nitrogen accumulation after anthesis increased,it could only partially compensate for the decrease of nitrogen transfer before anthesis,and eventually lead to the decrease of nitrogen accumulation in wheat grain.5.Spraying 6-BA increased the yield of Zhengmai 9023 and Yangmai 23 during shading at the booting stage,but the difference was not significant;while it significantly increased the yield of shading treatment at anthesis,mainly because it can increase the grain filling rate and prolong the filling process,making the grain weight significantly higher than shading treatment.In addition,spraying 6-BA can promote the accumulation and transport of dry matter in shading treatment,the dry matter assimilates of grain dependent on the assimilates after anthesis at a large extent,and ultimately improve the yield of shading.Spraying exogenous 6-BA before shading at anthesis can alleviate the adverse effects of shading and reduce the yield loss caused by shading at flowering stage.