| Cotton is a leading fiber crop,and also an important protein and oilseed crop in the world.The value of cottonseed as the main by-product of cotton is that it is an important source of animal protein feed,edible oil and biofuel.Upland cotton as the main cultivated cotton species has narrow genetic base and low diversity because of a long period of domestication and selection.Gossypium darwinii,one of the seven allotetraploid cotton species,retains the characteristics such as drought tolerance,nematode resistance,strong salt tolerance,barrenness,and fine fiber under long-term natural selection,and it is an important gene resources for improving cotton.Therefore,it is important to explore the excellent genes of G.darwinii and introduce the excellent genes into upland cotton to breed excellent cultivars.In this study,a population containing 553 single chromosome fragment substitution lines was constructed by backcrossing three generations and then selfing one generation using G.darwinii 5-7 accession as the donor parent and G.hirsutum cultivar CCRI 35 as the recipient parent.Cotton kernel protein content,oil content,palmitic acid content,stearic acid content,oleic acid content,linoleic acid content of BC3F2:3,BC3F2:4,BC3F2:5and BC3F2:6 populations were determined using a Fourier NIR light scanner and QTL localization of seed index and cotton kernel nutritional quality traits in combination with BC3F2 genotypes were performed with the following main finding.1.Encryption of simple sequence repeat（SSR）molecular markers in CSSLs of G.darwiniiBased on the previous study,another 179 SSR markers were selected to genotype the population,and chromosome are distributed with one SSR markers approximately each 5 c M interval.Integrating the previous results,a total of 552 SSR markers covered26 chromosomes,ranging from 92.34%to 99.71%with an average coverage of 98.49%.The genetic background recovery rate of individual ranged from 76.5%to 99.8%,with an average background recovery rate of 91.72%;the length of individual substitution fragments ranged from 7.88 c M to 914.47 c M,with a substitution rate of 0.20%to 23.20%,with an average substitution rate of 8.10%.2.Correlation and analysis of variance between seed index and cotton kernel nutritional quality traitsThe seed index showed a highly significant negative correlation with the protein content of cotton kernel,and protein and oil content,as the main nutrients in cotton kernel,showed a highly significant negative correlation.A highly significant positive correlation was found between protein content and stearic and linoleic acid content,and a highly significant negative correlation was found between palmitic and palmitoleic acid content in cotton kernels.The results of ANOVA showed that environment and genotype had significant effects on the nutritional quality traits of cotton kernel,and its phenotypic traits were influenced by both genes and environment.3.QTL localization for seed index and cotton kernel nutritional quality traitsA total of 167 QTL（16 seed index,19 protein content,13 oil content,13 palmitic acid content,19 stearic acid content,21 oleic acid content,20 linoleic acid content）were detected in four environments and explained phenotypic variation from 2.0%to 28.9%,with additive effect ranging from-6.85 to 2.49.A total of 51 QTL distributed on A sub-genome and 70 QTL on D sub-genome.63 QTL favorable alleles were derived from G.darwinii and 58 QTL favorable alleles were derived from CCRI 35.4 QTL（q SI-17-1,q PC-17-1,qOC-17-1,q SA-17-1）were detected in all four environments,and two QTL（qOC-19-1,qOC-21-1）were detected in three environments,and 22 QTL were detected in two environments.65 QTL distributed within 13 QTL clusters on 17 chromosomes. |
