Zn Biofortification In Winter Wheat Grain As Affected By Foliar Zn Combined With Biostimulants,Insecticides And Fungicides

Zinc(Zn)deficiency is an important form of malnutrition globally,and caused mainly by low dietary intake.In recent years,Agronomic biofortification strategy(soil or foliar application of Zn fertilizer)is considered to be the most direct and effective approach to overcome human zinc(Zn)deficiency,especially in developing countries and their rural areas.Wheat is the one of the most important staple crop for Chinese citizens and also the main source of zinc.While the main wheat-growing area in China overlaps with Zn deficient or potentially Zn deficient soil region,leading to the low grain Zn concentration and bioavailability.In this area,applying Zn fertilizer to soil has no significant effect on grain Zn concentration while foliar Zn application has already been proved as an effective and rapid method to improve grain Zn concentration and its bioavailability.However,it has not been widely accepted and used in a large scale due to energy and time-consuming.Therefore,it is urgent to explore the effect of foliar Zn combined with biostimulants or pesticides(widely used in practice)on grain Zn concentration and its bioavailability.Three different field experiments were conducted in current study to investigate whether Zn combined with different types of biostimulants or pesticides affects grain Zn concentration and its potential mechanism.Main results were summarized as below:(1)A two-year field experiment(2014.10-2016.06)was conducted to determine the effects of soil N application(0,120 and 240 kg N/ha)and foliar Zn together with biostimulants on grain yield parameter,grain Zn concentration and Zn bioavailability.The results indicated that soil N application was an effective measure to increase the yield of wheat.Foliar zinc combined with biostimulants could significantly improve the kernel grain weight and the treatment foliar zinc together with seaweed extract(Zn+AE)obtained the best effect(compared with sprayed distilled water and foliar Zn increased by 14.4% and 6.7%,respectively).The concentration of grain Zn and Fe could be effectively enhanced by the soil N application and foliar Zn combined with biostimulants.The effects of foliar zinc plus fulvic acid(Zn+FA),zinc plus seaweed extract(Zn+AE)showed the best.In addition,the application of appropriate amount of nitrogen fertilizer and Zn combined with biostimulants can significantly reduce the grain phytic acid content.Under the condition of soil applied medium and high amount nitrogen fertilizer,foliar Zn plus different biostimulants can also make grain phytic acid/Zn molar ratio reduced to 20 or less.It can be seen that foliar zinc together with different types of biostimulants can effectively improve the Zn concentration and its bioavailability,which is an effective way to optimize the strategy of foliar zinc fertilizer alone.(2)Another field experiment was conducted to investigate the effects of foliar Zn respectively combined with the corresponding pesticide in anthesis period and filling stage on grain Zn biofortification.The results showed that different treatments during these two spraying time had no significant effect on grain yield and nitrogen content.Foliar Zn combined with the corresponding pesticide in two periods can significantly enhance the grain Zn concentration and reach the target value of wheat grain zinc biofortication.Among them,at the anthesis stage,foliar zinc and commonly used fungicide Methyl thiophanate obtain the best grain zinc concentration(compared to a foliar thiophanate alone and foliar Zn alone increased by 210% and 13%),while at the filling stage,foliar Zn together with differen pesticides showed the equivalent Zn-rich effect.Meanwhile,foliar Zn combined with different pesticides significantly reduced the grain phytic/Zn molar ratio.It can be seen that the combination of zinc and different pesticides in two periods is an effective measure to improve the zinc concentration and its bioavailability.(3)In order to effectively fit the foliar zinc application with the real field prevention management measures of diseases and pests in the northern wheat production area,the third field experiment was conducted to determine the effect of foliar zinc combined with different insecticide and fungicide at the anthesis stage and the filling stage.The results showed that the method could also significantly increase the grain Zn concentration and decrease the phytic/Zn molar ratio,and the highest grain Zn concentration and best Zn bioavailability were obtained in the treatment of foliar Zn combined with Thiophanate methyl-acetamiprid and foliar Zn plus beta-cypermethrin-triadimefon,respectively.(4)Further measurement was conducted to clarify the mechanism of the effectiveness of different insecticide and fungicide on grain zinc concentration in different stages,Tris-HCl extraction method were used to measure the soluble Zn concentration and the insoluble Zn concentration.The results showed that the foliar zinc plus methyl thiophanate-acetamiprid mainly increased the concentration of insoluble Zn of the grains,while sprayed with zinc fertilizer alone and foliar zinc plus beta-cypermethrin-triadimefon enhanced the soluble Zn content of the grain mostly,and the rate of increases were more than 1 times.To sum up,foliar Zn combined with biostimulants or pesticides is an effective and feasible strategy to enhance the wheat grain zinc concentration and bioavailability,and could maintain good N and Fe content in the main wheat-producing areas of China.