Mapping QTL Controlling Cottonseed Oil And Protein Content In Upland Cotton

Cotton is the most important fiber crop in the world,and cottonseeds contain high levels of protein and fat.Cottonseed is the important sources of oil and animal feed protein.So far,upland cotton(G.hirsutum L.)has been the largest planting area of cotton cultivars worldwide,accounting for over 95% of fiber production.Cottonseed oil is not only rich in essential fatty acids,especially linoleic acid,but also an important source of protein,which contains almost all kinds of amino acids.Oil content and protein content are quantitative traits controlled by multiple genes,which are easily affected by environment.So it is difficult to improve the oil content and protein content of upland cotton by means of traditional genetic improvement methods.The rapid development of molecular marker technology and high-throughput sequencing technology is an important technical support to molecular breeding of cotton.The high-density genetic map is the basis for the further study of identifying quantitative trait loci(QTL)and map-based cloning.However,due to the narrow genetic basis of upland cotton which results in the relatively low polymorphic DNA markers,the detection efficiency of QTL is low and the present intraspecific genetic maps of upland cotton are characterized with less loci and the average distance between markers is large.All of these factors make it difficult to meet the needs of map-based cloning and marker-assisted selection(MAS).Therefore,it is very important to construct high-density genetic linkage maps and identify QTL controlling cottonseed oil and protein contents.Based on the previous work,new SSR markers were designed according to the genome sequence of G.raimondii to update the genetic map using the(Yumian1×M11)recombinant inbred line(RIL)population.At the same time,the QTL controlling oil content and protein content were identified in upland cotton.The main results are as follows: 1.The phenotypic analysis of cottonseed oil content and protein contentIn the two environments of 2015 and 2016,the cottonseed oil content of M11 was 9.82% higher than that of Yumian1,and the protein content of Yumian1 was 1.18% higher than that of M11.The phenotypic data of RIL population showed that there was a wide range of variation,the transgressive segregation for these two traits was observed and distributed continuously.Correlation analysis showed that there was an extremely significant negative correlation between oil content and protein content.2.SSR markers polymorphism and RIL population genotypingA total of 12,560 new SSR primer pairs designed from the reference genome sequence of G.raimondii were used to screen Yumian1 and M11.As a result,497 primers showed polymorphism,accounting for 3.96% of total primers.These polymorphic primers were used to genotype the(Yumian1×M11)RIL population,and 501 loci were obtained.The newly obtained 501 SSR markers and the 577 SSRs obtained in our previous study were examined by c2 test.A total of 220 loci were distorted from the expected Mendelian segregation ratio 1:1(P<0.05),accounting for 20.4 % of the total loci.Among them,97 loci tend to Yumian1(44.1 %),and 123 loci bias M11(55.9 %).3.Updated genetic mapA total of 1078 loci were applied to construct the genetic map which included 1025 loci,covered 3446.5 cM with an average of 3.36 cM between adjacent markers.Agenome contained 366 loci,spanning 1631.1 cM with an average distance of 4.46 cM between adjacent markers;D-genome contained 659 loci,spanning 1815.4 cM with an average distance of 2.75 cM between adjacent markers.4.QTL controlling oil and protein contentBased on the data of oil content and protein content and updated genetic map,8 QTL controlling oil content and 6 QTL controlling protein content were detected.The 8 QTL controlling oil content were located on 8 chromosomes,explaining the phenotypic variation from 10.7% to 48.2%,whereas the 6 QTL controlling protein content were located on 5 chromosomes,explaining from the phenotypic variation from 11.1% to 38.3%.Among them,qOC17.1,qPC08.1 and qPC17.1 which detected in 2 years environment were stable QTL.