QTL Mapping And Genetic Analysis Of Main Components In Upland Cottonseeds

Cotton(Gossypium spp.)is one of the most important crops around the world.The main purpose of cotton production was to obtain high-quality cotton fiber,and cottonseeds were only used as fertilizer or feed for ruminants such as cattle and sheep.In fact,cottonseed has a high nutritional value and is a potential source of protein and edible oil.With the growth of the world population,the demand for protein and oil will become more and more great and cottonseed will become an important food resource for the growing human being sooner or later.Therefore,it is of both theoretical and practical significance for improving the cottonseed quality to conduct comprehensive research on cotton seed quality traits in genetic and QTL mapping.In this study,188 RILs population derived from intraspecific hybrid between ‘HS46’(P1)and ‘MARKCBUCAG8US-1-88’(P2),as well as their two parents were used in the experiments.Seed samples harvested from four environments of three years in Sanya,Hainan,as the sample set.Based on the calibration model of near-infrared reflectance spectrum(NIRS)established in our lab,13 cottonseed quality traits for each sample such as protein contents were analyzed.Using the genetic model of quantitative traits in diploid seeds of dicotyledonous plants including genotype and genotype interaction with environment,the genetic effect,genetic rate,genetic correlation,and genetic effect prediction of 13 upland cottonseed nutritional traits were analyzed.In addition,using high-density intraspecific genetic map constructed in our lab with Cotton 63 K Illumina SNP chip,and the QTL mapping and their genetic effects for four cottonseed nutritional traits included protein contents were conducted with the complete interval mapping method.The main results were as follows.The contents of 13 cottonseed nutritional traits in 188 RILs population derived from intraspecific hybrid from four environments were measured and analyzed.The average contents of protein,oil,phytic acid,gossypol,isoleucine,leucine,lysine,phenylalanine,valine,alanine,arginine,glutamic acid,and glycine among four environments were 40.19%,36.88%,0.82%,0.52%,1.17%,2.16%,1.73%,2.16%,1.59%,1.45%,4.61%,7.64%,and 1.51%,respectively,and the highest component in cottonseeds was protein,while the lowest ones were phytic acid and gossypol.Among all the amino acids in cottonseeds,glutamic acid was the highest one and isoleucine was the lowest one.The values of each trait in the RILs population were normal distributionThe correlation analysis of cottonseeds quality traits showed that there was a significant negative correlation between protein and oil contents.Both correlation between protein contents and phytic acid or gossypol contents were weak.However,there was a very high correlation between the protein contents and 9 amino acids,indicating that the contents of protein and amino acid could be increased synchronously in breeding.There was no significant correlation between oil contents and the contents of phytic acid or gossypol.There was a significant negative correlation between oil contents and all the amino acids.There was no significant correlation between phytic acid and gossypol or amino acid,and gossypol was not significantly correlated with the amino acids measured.In addition,there was a significant positive correlation among the nine amino acid components,indicating that no matter how the environment changed,the contents of one amino acid could be improved while increasing the contents of any other amino acid.At the single-locus level,a total of 408 main-QTLs(m-QTL)and 256 pairs of epistasis-QTLs(e-QTLs)were located by using the complete interval mapping method.Forty-one m-QTL and 92 pairs of e-QTLs that controlled the protein could explain the total variation of 8.04-66.45%.There were 34 m-QTL and 67 pairs of e-QTLs controlling oil contents,respectively,which could explain the total variation of 12.82-84.56%.There were 26 m-QTL and 1 pair of e-QTL controlling gossypol,respectively,which could explain the total variation of 21.92-82.19%.The total variation of 22.82-90.44% could be explained by 8 m-QTL and 2 pairs of e-QTLs for phytic acid contents.The phenotypic variances(PV)rate of e-QTLs were higher than that of m-QTL for most nutritional quality traits,indicating that epistasis was very important for the performance of nutritional quality traits.Moreover,environment was a key factor affecting the expression of m-QTL and e-QTL related to nutritional quality traits.