Screening And Identification Of Chinese Wheat Mini-core Collections Germplasms For Low Heavy Metal Accumulation In Grain And Exploring Low Accumulation Alleles

The selection of pollution-safe cultivars(PSCs)is a practicable approach to minimize the influx of heavy metal into the human food chain.A Field experiment was carried out to study the differences of lead,cadmium,zinc and copper accumulation among the grains of Chinese mini-core collection germplasms.And 522 SSR markers which distributed on the wheat genome with population structure were used to analyze the relationship between Cu and Zn contents of grains with genotypes.On the basis of this,we seek the alleles with the potentials of Cu and Zn low accumulation in wheat grain,which provide information for molecular breeding in wheat.The main results are as follows:1.261 wheat varieties were planted in a Nanjing typical Pb and Cd pollution farmland in 2014-2015.The contaminated farmland heavy metal contents were 449.2,2.4 and 532.9 mg·kg-1,for Pb,Cd and Zn,respectively,which were higher than the the Grade ? of environmental quality standard for soil(GB 15618-1995).There was significant difference in heavy metal(Pb,Cd and Zn)concentration in grain among 261 wheat varieties,which were ranged with 0.002-0.920,0.010-0.853,45.773-121.081 mg·kg-1 for Pb,Cd and Zn,respectively.According to the standards on Foods and Products(GB 2762-2012)and(NY861-2004),there were 92,251 and 254 wheat grain samples exceeding the standards for Pb,Cd and Zn,respectively,which proportion were 35.2%,96.2%and 97.3%.Baiqimai,Songruimai,Yunmai34,Shijiazhuang54,Chike,Bendihuanghuamai,Tuokexun,Taishanl,Baipu,Heshangmai,Baipu,Zaowutian,Qianjiaomai,Tanori,Taizhong23 were Pb low-accumulation cultivars in the grain;Baitiaoyu,Qingchun 28,Banjiemang,Hongjinbaoyin,Dalibanmang,Jianmai,Hongdongmai,Baiqitou,Tuokexunl and Zhuoludongmai were Cd low-accumulation cultivars;Hongjinbaoyin,Tumangmai,Rikeze 8,Wenmai 6,Tuokexun,Hongxumai were Zn low-accumulation cultivars;Among the tested cultivars,Tuokexunl had the lowest Pb,Cd and Zn accumulating abilities.2.262 wheat varieties were planted in a Nanjing typical Cu pollution farmland in 2014-2016.The contaminated farmland heavy metal contents were 1150.4 and 213.2 mg·kg-1,for Cu and Zn,respectively,which were close to the the Grade ? of environmental quality standard for soil(GB 15618-1995).There were significant differences in the accumulation capacity of Cu and Zn in 262 wheat varieties.The two-years variation of Cu content in wheat grain were 5.92?16.50 mg·kg-1 and 6.93?21.16 mg·kg-1,respectively.The variation of Zn content in grains were 34.47?82.68 mg·kg-1 and 42.88?91.07 mg·kg-1,respectively.According to the standards on Foods and Products(NY861-2004),The exceeding rates of Cu content were 64.9%and 88.5%in two years,and the exceeding rates of Zn content were 89.8%,93.8%in two years.A total of 262 wheat varieties were divided into five groups.In the end,we draw conclusions based on the field results:Cu low accumulation varieties include;Chushanbao,Baihuama,Hongchunmai,Hongheshangtou,Laoqimai,Xinshuguang 6,Fuzhuang 30,Motuoxiaomai and Heshangmai.Zn low cultivars include:Chushanbao,Shuiyuan86,Banjiemang,KaBKa3,Zangdong 4,Lvhan 328,Xianmai and Hongxumai.Among them,Chushanbao are low Cu and Zn accumulation varieties.3.In this study,we collected 227 wheat accessions heavy metal content in grain for research.Marker-trait association analysis was calculated by mixed linear model(MLM)in software TASSEL 3.0.The results show:19 SSR markers were significantly associated with the average Cu content in two years,at least in relation to the Cu content in one year.Especially,Xwmc59-1A?Xgwm666-5A and Xcfd242-7A were detected in two years.The most significant association sites were the Xgwm155-3A(P=0.001;R2=16.41%)Xgwm88-6B(P=0.001;R2=16.56%)detected in 2015-2016 years,and Xgwm666-5A(P=0.001;R2=14.40%)detected in the two-year mean content.Significant or extremely significant differences were detected on Cu content between varieties conveying favored allele and varieties with other alleles.Among the loci associated with Zn content in at least one trial,we found breeder-favored alleles with strong positive effects at 22 loci on different chromosomes.Especially,Xbarc1121 and Xcfd38 which Located on the sixth chromosome were detected in two years.The most significant correlation is Xcfd35-3D(P=0.001 R2=19.12%)detected in 2014-2015.There were 11 favored alleles which convey significant or extremely significant differences between varieties with other alleles.