Identification Of Grain Type And Grain Weight Traits In Maize Germplasms And Genome-wide Association Analysis (GWAS)

Maize(Zea mays L.)is one of the three major cereal crops in the world,and high yield is still the primary goal of maize breeding.Grain traits such as grain length,grain width,grain thickness and 1000-grain weight are the key factors to determine yield.Germplasm resources of maize in China are extremely rich,and some local varieties have played an important role in production.However,the vast majority of local maize germplasms have not been fully exploited,especially in Zhejiang,which has shown outstanding problem.Therefore,phenotypic identification and genome-wide association analysis of grain type and grain weight traits of maize germplasms can provide specific germplasms or key genes for breeding new maize varieties with high yield.In this study,517 maize germplasms with high genetic diversity were planted in three environments in Dongyang,Lin ’an,Zhejiang and Ledong,Hainan.Grain length,grain width,grain thickness and 1000-grain weight were measured to screen specific maize germplasms.Genome-wide association analysis was conducted by combining with existing genotypes in the laboratory to screen SNP loci related to grain traits and explore the candidate genes.The main conclusions are showed as follows:(1)Grain traits identification.The phenotypic identification results showed that the population polymorphism of 517 maize germplasms were high,and the frequency distribution of grain length,grain width,grain thickness and 1000-grain weight of these maize germplasms measured in Dongyang,Lin ’an and Ledong showed a single-peak curve.These data of grain traits were focused on 8.5 ～ 9.0 mm,8.0 ～8.5 mm,4.4 ～ 4.7 mm,and 220 ～ 250 g,respectively,which were consistent with normal distribution or approximately normal distribution.The phenotypic quantitative traits could be analyzed by genome-wide association analysis.Correlation analysis showed that 1000-grain weight had significant positive correlation with grain length,grain width and grain thickness,and grain width had significant positive correlation with grain thickness and grain length.(2)Screening of specific Germplasms.The germplasms with excellent grain length at all three test sites was Jinyun Wuyun Tuyumi.There were ten germplasms with excellent grain traits at the two test sites,such as the grain length of Bentangbaolu and Suyu 10,the grain width of Baiyumi M90,Longshanyumi and 120 Tianyumi;the grain thickness of 8902;1000-grain weight of Wuyun Tuyumi,CML114,SY3073 and 120 Tianyumi.In addition,according to the mean ranking of trait performances of the three test sites,Ye8001,Wuyun Tuyumi and so on were selected as the germplasms with long grain.Meiyumi,Qushanyumi and so on were wide grain germplasms.CIMBL87,CML170 and so on were thick germplasms.SY3073,8902 and so on were high 1000-grain weight germplasms.These specific germplasms can be used as ideal material for breeding new maize varieties with high yield.(3)GWAS analysis and mining of the candidate genes.A mixed linear model was used for genomewide association analysis of grain traits.In addition to chromosome 9,103 SNP loci were detected on other chromosomes that were significantly related to grain traits.There were 5 SNPS related to grain length,26 SNPS related to grain width,30 SNPS related to grain thickness and 42 SNPS related to 1000-grain weight,the phenotypic variation was explained by 1.33% to 23.77%.Dongyang test site had the largest number of significant correlation loci for grain traits.Since the correlation population was dominated by local varieties in Zhejiang province,most of which were spring maize,the phenotypic identification in spring could better reflect the variety characteristics,while the grain traits in other two places were greatly affected by the environment,and fewer significant loci were detected.A total of 41 candidate genes were found by screening the genes near the associated sites,among which 4 were related to grain length,7 to grain width,13 to grain thickness,and 17 to thousand grain weight.In conclusion,this thesis mainly identified the grain type and 1000-grain weight of 517 maize germplasms,which were mainly local varieties in Zhejiang Province,and conducted genome-wide association analysis.A number of specific germplasms and candidate genes were extracted,which laid a solid foundation for the full utilization of Zhejiang local germplasms and the breeding of new maize varieties with high yield.