QTL Mapping Of Agronomic Traits In A Subgenome From Chromosome Segment Introgression Lines Of Gossypium Darwinii L Introgressed In G.hirsutum

Cotton is an important natural fiber crop in the world,and is widely grown around the world.Upland cotton has high yield and wide adaptability and produces 95%raw cotton,but its micronaire value is relatively high.G.darwinii is a hetero-tetraploid wild species,which has the characteristics of stress resistance,drought tolerance and fiber fineness.The construction of G.darwinii chromosome segment substitution lines（CSSLs）within the genetic background of Upland cotton can explore the beneficial genes of G.darwinii for yield and fiber quality,broaden the genetic background of Upland cotton,and cultivate high-quality upland cotton.In this study,Upland cotton cultivar CCRI35 with high yield was used as recurrent parent,and G.darwinii accession 5-7 as the donor parent to construct the CSSLs.The genotypes of 553 individuals in the BC₃F₂ population were detected by SSR markers evenly distributed on the genetic linkage map of G.darwinii and Upland cotton constructed in the previous study.The genotype-detected data,yield and fiber quality data BC₃F₂ population and BC₃F_2:3 population were used to map QTL.The main results were as follows:1.Construction of the CSSLs and detecting genotypesIn the study,a total of 190 SSR markers evenly distributed on the genetic linkage map of G.darwinii and Upland cotton constructed in the previous study,were selected for genotyping 553 BC₃F₂ individuals.Among them,3 individuals don’t have introgression fragments,and the chromosome segment substitution lines containing 550individual plants was constructed.2.Introgression segments of Individuals on the A subgenomeThe average genetic background recovery rate of 550 individuals was 91.8%,the maximum background recovery rate was 99.8%,and the minimum value was 72%.The length of introgression segments from G.darwinii ranged from 4.09-568.23cM.Accounting for 0.2-27.8%of the total genetic length,and the average length of the introduced fragment was 163.41cM;The average length of the introduced homozygous fragment was 39.61cM,the average introgression rate was 1.94%,and the maximum length was 212.57cM,the minimum was 0cM,the introgression rate of the introduced fragment was 0-10.4%;the average length of the introduced hybrid fragment was123.80cM,the average introgression rate was 6.01%,and the maximum length of the introduced hybrid fragment was 523.62cM,and the minimum was 0cM.The introgression rate of hybrid fragments is 0-25.6%;The number of introgression segments ranged from 1-35.3.Introgression fragment of A subgenome chromosomesThe average genetic background recovery rate of 13 chromosomes was 92.09%,the genetic background recovery rate of the chromosome 11 was the highest,was95.31%,and the recovery rate of the chromosome 9 was 88.07%.The average length of the total introgression fragments,the introgression homozygous fragments and the introgression hybrid fragments all were the chromosome 5,the chromosome 1,the chromosome 5,longest,and the average length were 19.26cM,4.66cM,and 14.63cM,respectively.The average length of the total introduced fragments,the introduced homozygous fragments and the introduced heterozygous fragments were the chromosome 4 shortest,and the average length were 5.13cM,0.79cM and 4.24cM,respectively.4.Cotton yield and fiber quality QTL mappingA total of 65 QTLs of yield and fiber quality were detected in this study.There were 9 QTLs（qLP1.3,qLP2.1,qLP5.1,qLP5.2,qLP7.1,qLP9.1,qLP9.2,qFS12.1,qLP13.1）detected in both environments.39 QTLs related to yield traits were detected,explaining phenotypic variation of 1.7-4.8%.Among them,there are 7 QTLs related to seed index,explaining phenotypic variation 1.9-3.5%,12 QTLs related to boll weight,explaining phenotypic variation 1.7-4.7%,and 20 QTLs related to lint percentage,explaining phenotypic variation 1.8-4.8%.26 QTLs related fiber quality,explaining phenotypic variation of 1.9-6.7%.there are 4 QTL related to fiber length,explaining2.3-6.4%of phenotypic variation,4 QTLs related to fiber uniformity,explaining 2-4.3%of phenotypic variation;4 QTLs related to fiber strength,explaining phenotypic variation 2.1-5.4%;There are 6 QTLs related to fiber micronaire value,explaining phenotypic variation 2.3-5.8%;8 QTLs related to fiber elongation,explaining phenotypic variation at 2.2-6.7%.The favorable alleles of 25 QTLs were derived from G.darwinii,and the favorable alleles of 40 QTLs were derived from CCRI35.