QTL Mapping For Yield And Fiber Quality Traits From The Chromosome Segment Substitution Lines Of G.mustelinum

Cotton occupies an important position in the national economy.It is not only a natural fiber crop,but also an oil crop,as well as a high-protein crop.Gossypium hirsutum is the most widely cultivated,accounting for more than 95%of the world’s raw cotton production,but its fiber quality is poor,which unable to meet the further requirements of textile technology.Moreover,the genetic basis of G.hirsutum is narrow,and intraspecific hybridization can not achieve the genetic improvement of important agronomic traits.Gossypium mustelinum is one of the five wild tetraploid cotton species,with abundant fiber quality variation and significant resistance to insect pests and Verticillium wilt.Therefore,the superior allele of G.mustelinum can be introgressed into G.hirsutum,and the genetic basis of G.hirsutum can be broadened,thereby achieving the simultaneous improvement of yield and fiber quality traits in G.hirsutum.This study obtained 564 individuals of BC3F2 population by three backcrossing and one self-crossing with G.hirsutum（CCRI35）of high quality and abundant variety as the recurrent parent,G.mustelinum as the donor parent.Based on the BC1 high-density genetic linkage map of CCRI35×G.mustelinum by our lab,SSR molecular markers distributed on 13 chromosomes of the D sub-genome were evenly selected to genotype individuals of BC₃F₂ population,and combined the A sub-genome genotype data to construct G.mustelinum chromosome segment substitution lines.Further combining phenotypic data of BC₃F₂,BC₃F_2:3:3 and BC₃F_2:4:4 populations,QTL mapping for cotton yield and fiber quality related traits were identified.The main findings are as follows:1.Construction and substitution segments analysis of CSSLs in G.mustelinumA total of 372 SSR molecular markers,which included 181 markers from 13chromosomes of the D-subgroup in this study and 191 markers from the A-subgroup detected in the previous period,were selected to genotype 564 individuals in BC3F2population by GGT2.0 software.Analysis showed that 1 individual did not contain G.mustelinum segments,so a set of chromosome segment substitution lines（563individuals）was successfully constructed.The genetic background recovery rate of each individual in BC₃F₂ population was between 81.2%to 98.7%,and the average recovery rate was 90.6%.The number of G.mustelinum substitution segment was from 6 to 47,with an average substitution segment number was 23.9;The length of total G.mustelinum substitution segment was ranged from 39.1cM to 708.4cM,and the average total substitution segment length was340.5cM,which covered 8.7%of genome.In addition,the average genetic background recovery rate in 26 chromosomes of the chromosome segment substitution line was 88.5%,and Chr25 was as high as 95.6%,Chr17 was low to 62.0%.The average length of total G.mustelinum substitution segments contained of each chromosome in chromosome segment sub-stitution lines was 13.6cM and average segment rate was 9.0%,of which the longest length of total G.mustelinum substitution segments in Chr01 was up to 25.1cM and the shortest length in Chr25 was 5.5cM.The average length of homozygous G.mustelinum substitution segments length contained in each chromosome was 3.0cM and average segment rate was 2.0%,of which the longest length of homozygous G.mustelinum substitution segments in Chr01 was up to 6.0cM and the shortest length in Chr25 was 1.1cM.The average length of heterozygous G.mustelinum substitution segments length contained in each chromosome was 10.4cM and average segment rate was 6.8%,of which the longest length of heterozygous G.mustelinum substitution segments in Chr01 and Chr10was up to 18.4cM and the shortest length in Chr25 was 4.4cM.2.QTL mapping of yield and fiber quality related traitsBased on genotype results and genotypic data of yield and fiber quality traits in BC₃F₂,BC₃F_2:3:3 and BC₃F_2:4:4 populations,a total of 121 QTL using MapQTL6.0 of interval mapping were identified,which were unevenly distributed on 26 chromosomes,of which 55 QTLs were detected in the A sub-genome and 66 QTLs were detected in the D sub-genome.These are 18 QTL for boll weight,26 QTL for seed index,19 QTL for lint percentage,16 QTL for fiber length,13 QTL for fiber uniformity,11 QTL for fiber strength,9 QTL for fiber micronaire and 9 QTL for fiber elongation,LOD value was ranged from 2.04 to 8.81,explaining phenotypic variation from 2.0%to 11.5%.Of the total 121 QTL,46 QTLs favorable alleles were derived from G.mustelinum,and 75QTLs favorable alleles were derived from G.hirsutum.In addition,25 QTLs were detected in two environments,6 QTLs（qBW1.1,qSI8.2,qSI21.1,qLP7.1,qLP8.1 and qLP20.1）were proved to be stable in all three environments and 44 QTLs were distributed on 13 QTL clusters.The G.hirsutum background G.mustelinum chromosome segment substitution line constructed in this research has provided the important new materials for cotton breeding research and the QTLs of yield and fiber quality related traits were identified in this study lay the foundation for the subsequent fine mapping and functional identification of candidate genes.