Allelic Variation And Candidate Gene Identification Of QTN For Boll Weight In Upland Cotton Germplasm(Gossypium Hirsutum L.)

Cotton is an essential agro-industrial crop across the globe.Improving cotton’s fiber quality and yield potential are primary commercial targets for cotton breeders.Boll number,boll size,average boll weight,and lint percentage are the fundamental factors of cotton lint yield.In this study,we did two experiments.Firstly,two intraspecific F₂ segregating populations were constructed by using bigger boll line crossed with the small boll lines in Gossypium hirsutum and Gossypium arboreum respectively,and then characterize the phenotypic variations and correlation analysis in the F₂ segregating populations of each species for boll-related traits.Secondly,we used data of 1260 accessions associated with boll weight development in Gossypium hirsutum via a genome-wide association study（GWAS）using the EMMAX model.In the former experiment,phenotypic correlation analysis,boll weight（BW）,lint percentage（LP）,boll upper width（BUW）,boll medium width（BMW）,boll lower width（BLU）,and boll length（BL）were studied.In the later experiment,GWAS analysis 53 significant associations were identified related to boll weight development under different environments.In segregation populations,extensive phenotypic differences and transgressive segregation were observed.The results show that most of the correlation clusters were negatively associated with boll weight and lint percentage.The positive correlation clusters were observed among boll upper width（BUW）,boll medium width（BMW）,boll lower width（BLW）,and boll length（BL）.Seven of the twenty-four extracted principal components had eigen values>1.It accounted for 62.2%of the difference between the four F₂ populations.Principal component 1 accounted for 15.1%of the overall variability.The variation in principal component 1 was mainly attributed to boll lower width（BLW）,boll medium width（BMW）,boll upper width（BUW）,boll length（BL）,and boll weight（BW）of the ML population in Gossypium arboreum.However,thorough GWAS analysis,six genes（PCMP-E76,ASIL2,SAUR50,AG,PII-2,LBD16）showed higher expression associated with boll weight development which showed significantly higher expression at tissues and organs level.The results of GWAS analysis with identification of key SNPs and candidate genes for boll weight revealed that these might play a pivotal role in boll weight development in upland cotton.