Effects Of Exogenous ABA On Pre-harvest Sprouting And Quality Of Wheat

Pre-harvest sprouting（PHS）resulted from higher rainfall during the harvest period is one of the crucial reasons degrade food uses quality of wheat flour in Southwest wheat production region of China.This study was carried out to investigate the inhibition effect of exogenous abscisic acid（ABA）to pre-harvest sprouting,and the changes in grain quality with respecting to PHS sensitivity was also measured.In view of this,two cultivators with pre-harvest sprouting resistance（white-seeded wheat Zhongkemai 138;red-seeded wheat Mianmai 367）were used as experimental materials.The anti-photodegraded ABA(0,50,100 mg.L^-1)were sprayed at 15（initial filling stage）,30（late filling stage）and 35 days（physiological maturity stage）after anthesis（DAA）to investigate the changes in germination traits,α-amylase activity and grain quality.The specific results are as follows:1.The application of 50～100mg.L^-1ABA at 30DAA could inhibit PHS,with the optimum spraying time achieved at 30DAA.In normal years（2018）,the wheat spraying with 50mg.L^-1ABA was better than other treatments as compared to the control,the germination rate of Zhongkemai 138 was reduced by 13.8%and 3.8%at physiological maturity and dough stage,respectively,and the PHS sensitivity cultivator（Mianmai367）was decreased by 23.5%and 9.7%,respectively,as compared with control.In 2019（rainy season）,spraying with 100 mg.L^-1ABA performed better than other treatments with the germination rate of Zhongkemai 138 was reduced by 22.5%and 19.6%during the physiological maturity and dough stage,respectively,as compared with control,and PHS sensitivity cultivator（Mianmai 367）was reduced by 10.0%and 12.0%than that of control,respectively.Meanwhile,the inhibitory effects of ABA were all released at 60 days after harvest,and did not affect subsequent seed germination.2.Exogenous application of ABA could reduceα-amylase activity and inhibitedα-amylase activity,which further delayed the hydrolysis of starch in 35-45DAA.Compared with the control,theα-amylase activity and soluble sugar content were decreased by 30.1%,and 41.9%,respectively,and the starch content was 10.2%higher when the 100 mg.L^-1ABA was spraying at 45 DAA.3.Exogenous spraying of ABA could delay the decrease of 1000-grain weight and bulk density caused by pre-harvest sprouting during rainy years in the harvest period,and the delaying effect was stronger with the increase of ABA concentration.1000-grain weight and bulk density were 2.1%and 1.2%higher at 50mg.L^-1ABA treatment compared to the control,and they were 2.4%and 2.5%higher than CK when treated with 100mg.L^-1ABA.However,there was no significant difference in each index during different spraying periods,but the kernels per spike,1000-grain weight,yield per plant and bulk density were sprayed at 30 days after flowering for two years than in other spraying periods（except the1000-grain weight in 2019 and kernels per spike in 2018）.4.After spraying with ABA,the protein quality could be improved to a certain extent.The sedimentation value in 2018 was 4.3%higher at 100 mg.L^-1compared to the control.In 2019,the sedimentation value and dry gluten content increased by 8.8%and 17.8%respectively compared with CK,and the wet gluten content and gluten index increased by2.3 and 5.4 percentage points from CK,respectively.In addition,the protein quality of wheat sprayed at 30 days after flowering for two years was higher than other spraying periods.5.Exogenous ABA showed a greater impact on the starch content with the amylopectin content and total starch content increased by 8.1 and 7.6 percentage point,and the amylose/amylopectin ratio decreased by 18.2%after spraying 100mg.L^-1ABA.Further,the pasting properties of flour were also improved with the falling value,peak viscosity,trough viscosity,disintegration value,recovery value,final viscosity,and peak time at 100mg.L^-1in 2018 increased by12.4%-26.5%compared to CK,and the increase rate was20.9%-51.4%compared to CK in 2019.In summary,the application of 50-100mg.L^-1ABA at 30DAA could effectively reduce pre-harvest sprouting by inhibitingα-amylase induced starch hydrolysis without decline the protein quality,and thereby improved the pasting properties of wheat flour by enhancing amylopectin and total starch contents,reducing the ratio of amylose and amylopectin.Therefore,the application of 50-100mg.L^-1ABA at 30DAA was highly recommended for farmers to enhance the pre-harvest sprouting resistance and reducing the losses in food uses quality in Southwest wheat production region of China.