Identification Of QTL Favorable Allele For Yield And Fiber Quality Traits In Gossypium Darwinii L

Cotton is an important economiced crop in the world.At present,the most cultivated species in China is Gossypium hirsutum,which yield is higher than others.In order to enrich the genetic diversity and improve the agronomic traits such as yield ang fiber quality of G.hirsutum,wild cotton is selected for distant hybridization.Gossypium darwinii is one of the seven tetraploid wild cotton species,which has the characteristics of drought tolerance,stress resistance and fiber fineness.Therefore,the excellent alleles of G.darwinii can be introduced into G.hirsutum to broad the genetic background and improve the fiber quality and yield traits of G.hirsutum.In this study,the genetic linkage map of the BC1 population between the G.hirsutum and G.darwinii was constructed previously in our lab.A total of 184 SSR markers that evenly distributed on D sub-genome of the genetic map was used to detect the genotypes of 553 individuals from the BC3F2 population.The phenotypic data of BC₃F₂,BC₃F_2:3:3 and BC₃F_2:4:4 population were used to identify QTL for yield and fiber quality traits.The main findings are as follows.1.Analysis of introgression segments of individuals on the D sub-genomeThe genetic background recovery rate of 551 individuals were ranged from70.4%-99.7%,and the average recovery rate was 90.5%,the number of introgression segments were ranged from 1 to 38,and the average number was 14.The length of the introgression segments of the G.darwinii was from 5.3cM to 524.6cM,which covered0.3%-29.6%of D sub-genome,the average length was 160.7cM,and the average introgression rate was 9.1%,the length of the introgression segments is mostly between0-300 cM.2.Analysis of introgression fragment of D sub-genome chromosomesThe genetic background recovery rate in the 13 chromosomes of the chromosome segment introgression line was from 86.1%to 93.8%,and the average genetic background recovery rate was 90.7%,the average length of the homozygous G.darwinii introgression segments of each chromosome was 2.7cM,and the average introgression rate was 1.9%.Among them,homozygous G.darwinii introgression segments of the Chr21 had the longest average length of 6.1cM,and homozygous G.darwinii introgression segments of the Chr14 and Chr24 had the shortest average length of 1.0cM,the average length of heterozygous segments was 10.0cM,and the average introgression rate was 7.0%,heterozygous G.darwinii introgression segments of the Chr21 had the longest average length of 17.2cM,heterozygous G.darwinii introgression segments of the Chr22 had the shortest average length of 6.7cM,the average length of the total introgression segments was 12.6cM,and the average introgression rate was 8.9%,total G.darwinii introgression segments of the Chr21 had the longest average length of 23.3cM,total G.darwinii introgression segments of the Chr14 had the shortest average length of 8.3cM.3.Yield and fiber quality QTL mapingIn this study,a total of 150 QTLs for yield and fiber quality traits were detected.75QTLs related to yield traits including 16 QTLs for seed index,25 QTLs for boll weight and 34 QTLs for lint percentage,which explaining the phenotypic variation of 1.7-5.2%,LOD value ranged from 2.04 to 6.24.75 QTLs for fiber quality traits including 17 QTLs for fiber length,11 QTLs for fiber uniformity,13 QTLs for fibers strength,13 QTLs for fiber micronaire and 21 QTLs for fiber elongation,which explaining the phenotypic variation of 1.9-6.7%,LOD value ranged from 2.01 to 5.36.Among them,the favorable alleles of 61 QTLs derived from G.darwinii,and 89 QTLs derived from CCRI35.20QTLs（qSI19.1,qSI21.1,qLP1.1,qLP1.2,qLP2.1,qLP5.1,qLP7.1,qLP9.1,qLP9.2,qLP14.1,qLP15.2,qLP17.1,qLP18.1,qLP21.1,qFL1.1,qFL11.1,qFS12.1,qFM23.1,qFE8.3,qFE20.1）were detected in two environments,and 4 QTLs（qLP1.3,qLP5.2,qLP13.1,qLP20.1）were detected in three environments.