| Heavy metal pollution in farmland is an important environmental problem facing China’s current agricultural production.It has important research significance to reduce heavy metals entering the food chain.In this study,262 Chinese wheat mini-core germplasms were used as experimental materials to conduct field experiments in a heavy metal Cd-contaminated farmland in Kunshan at Jiangsu Province,Jiyuan and Weihui at Henan Province,in order to screen out Cd high and low accumulation wheat varieties.At the same time,correlation analysis of grain Cd content-genotype was carried out using 512 SSR markers distributed on the whole genome of wheat.In order to correlate with the site of wheat grain Cd content,the allelic variation locus associated with heavy metal Cd was screened,which laid a foundation for molecular breeding.On the other hand,foliar barrier agents were sprayed during the critical period of wheat growth and development,in order to screening barrier agents that can significantly reduce the accumulation of Cd in wheat grains,and further study the inhibition mechanism.This experiment combined wheat low Cd accumulation varieties with foliar spray barriers to inhibit the accumulation of wheat grain Cd,in order to achieve safe production of wheat in mild heavy metal cadmium contaminated farmland.1.The Cd content in the soil of each farmland has exceeded the national heavy metal pollution risk screening value of agricultural land,close to the control value(GB15618-2018).The evaluation results show that the farmland soil has serious ecological hazards.262 Chinese wheat mini-core germplasms as experimental materials,the multi-point field experiment was used to explore the difference of Cd accumulation among different wheat varieties.The study found that the Cd content of wheat grains in each experimental point exceeded the national food safety limit of 0.1 mg·kg-1 was compared with the difference of Cd accumulation among the four experimental points.It was found that the Cd content in the wheat grains of the four experimental points was not significantly different among different grain colors and different varieties(P>0.05).K-means clustering of heavy metal Cd content in wheat grain was carried out.The results of Kolmogorov Smirnov Test showed that the frequency distribution of wheat grain Cd content in each experimental point was approximately normal distribution.In addition,according to the Cd content of different varieties at different experimental points and different years,six low-accumulation Cd varieties of wheat grain were selected,namely:Baitiaoyu,Hongdongmai,Hongjinbaoyin,Xiaosanyuehuang,Hanzhongbai and Qingchun28.Five high-accumulation Cd wheat varieties were Shanmai,Zipi,Huadong6,NonglinlO and Shanglinxiaomai.2.In order to obtain the molecular markers associated with the accumulation of heavy metal Cd in wheat grains,based on the population structure and genetic relationship,the correlation model of Cd content in 246 wheat seeds was analyzed by the mixed model(MLM)method in TASSEL 3.0 software.The optimal linear unbiased prediction value(BLUP)of grain Cd content of each wheat variety in different experimental points was calculated by Genstat software,and the BLUP value was correlated with the marker.Correlation results showed that 9 loci were significantly correlated with Cd content in wheat kernels(P≤0.05),and 4 of them showed a significant correlation with wheat grain Cd content(P<0.01),respectively.Xgwml48-2B,Xgwm515-2A,Xgdm98-6D and Xwmc486-6B.Among them,Xgwml48 located on chromosome 2B has the largest interpretation rate of phenotypic variation(R2=5.12%).Furthermore,the effects of dominant alleles on Cd content in wheat grain were analyzed.It was found that the four excellent allelic variations related to Cd accumulation in wheat grain were Xgwm148142,Xgwm297144,Xgwm526138 and Xgwm565140,respectively.The interpretation rate of phenotypic variation ranged from 3.23.%～5.12%,of which the marker site Xgwm148 has the highest interpretation rate for phenotypic variation,which is 5.12%.Xgwm297 had the most allelic variation,and the allelic variation frequency was 17.48%.When the Cd content of alleles and other alleles were observed,the above four mutation sites showed higher Cd accumulation,and the Xgwm565140 allelic variant gene The Cd content is the highest.The five excellent allelic variations associated with low Cd accumulation in wheat grains were Xgwm515125,Xgdm98147,Xbarc12184,Xgwm297146 and Xwmc363122,and their interpretation rates for phenotypic variation ranged from 3.66%to 4.81%,with Xgwm515 pairs on chromosome 2A.The phenotypic variation has the largest interpretation rate of 4.81%.The most allelic variation was found on Xwmc363,and the allelic variation frequency was 68.3%.When the Cd content of alleles and other alleles were observed,the mutations of the above five loci showed lower Cd accumulation,which was located at 2B.Moreover,it was found that the excellent allelic variation gene has an additive effect on wheat grain Cd accumulation.3.The best application period and application method of wheat leaf barrier agents were explored by field experiment and pot experiment.Different leaf barrier agents were sprayed on wheat during the three growth stages of wheat,namely at the booting stage,heading stage and filling stage,and the wheat seeds,hulls,and different leaves and different intemodes were sampled after wheat ripening.The content of nutrients Fe,Zn,Ca,Mn.The results showed that 50 μM sodium nitroprusside(SNP),0.1 mM Na2EDTA,0.5 mM ZnSO4 and 2 mM H2BO3 could significantly reduce the Cd content in wheat grains,and found that the filling period was the most effective period for the application of foliar barrier agents..It was found that foliar application of barrier agents mainly inhibited the transport of Cd to the flag leaf and the internode under the wheat ears,reduced the accumulation of Cd in the flag leaf and the internode under the wheat ears,inhibited the transport of Cd to wheat grain,and reduced the content of Cd in wheat grains.4.Wheat Cd low accumulation varieties(Baitiaoyu,Hanzhongbai and Hongjinbaoyin)and normal wheat varieties(Aikang58)as experimental materials,foliar spraying Zn and SNP was carried out.It was found that compared with normal varieties,after spraying 0.5 mM ZnSO4 and 50 μM SNP,the Cd content of the aboveground part of Cd low accumulation wheat varieties decreased significantly,and the transport coefficient of Cd decreased,which reduced Cd transfer from root to shoot.In this experiment,wheat low Cd accumulation varieties were combined with foliar spray barrier agents to inhibit the accumulation of Cd in wheat grains,in order to gain safe production of wheat in heavy metal Cd contaminated farmland. |
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