Mapping QTL For Yield And Fiber Quality Traits From A(G.hirsutum Cultivar × G.hirsutum Race Punctatum) Population

Cotton is the world’s leading natural fiber crop,and it is also an important source of oil and protein.It belongs to the genus Gossypuim that consists of more than 50species of cotton,including 45 diploid species and seven tetraploid species.Globally,there are four major cultivated cotton cultivars,namely diploid G.arboreum L.and G.herbaceum L,and tetraploid G.hirsutum（upland cotton）and G.barbadense L.Out of these,upland cotton contributes of more than 95%of the world’s raw cotton production.Since 2011,China’s cotton planting area has been decreasing year by year,while people’s demand for cotton fiber products is increasing simultaneously.In addition,the requirement for high-quality fiber also grew with the continuous improvement of human living standards.In order to satisfy the increased demand of high fiber products,researchers have intercrossed different varieties to obtain superior cultivars with desired traits.In this study,G.hirsutum cultivar CCRI35 and G.hirsutum race punctatum were used as parents of an F₂ population.This is because G.hirsutum races are ideal materials to cross with tetraploid cultivated cotton and obtain fertile posterity since they possess the same number of chromosomes.In addition,G.hirsutum races are highly genetically variable and have high quality agronomic traits,such as disease resistance,drought resistance,low tolerance,salt tolerance,cold resistance,and male sterility making them better than other cultivars.The hybrid from these two parents had superior traits that provide important genetic resources for improving cotton quality and resistance.The main results are as follows:1.Performance of fiber quality traitsThe distribution range of cotton yield and fiber quality traits were large and continuous in all the three environments.Correlation analysis showed that there was a significant negative correlation between lint and seed index in all three environments,and there was a very significant positive correlation among fiber elongation,fiber length,fiber uniformity and fiber strength.2.Detection of Primer Polymorphism and Population GenotypeIn total 13022 pairs of SSR primers were used in this study to screen the polymorphism between CCRI35 and TX-230,and 856 pairs of effective polymorphic primers were obtained with a polymorphism ratio of 6.57%.These 856 pairs of primers were used to detect the genotype of F₂ population and 872 loci were obtained.Among all the 850 loci,215 loci showed partial segregation,with a partial segregation ratio of 25.3%.Among them,126 segregation loci（27.6%）were found on the A subgenome,and 89（22.7%）segregation markers were found on the D subgenome.3.Construction of the genetic mapA genetic linkage map with 30 lineage groups consisting of 850 polymorphic loci was constructed,covering 3623.7 cM,which occupies approximately 81.3%of the G.hirsutum genome.The average distance between markers is 4.3 cM.Among them,A-genome contained 456 markers covering a length of 1854.6 cM with an average genetic distance between markers of 4.1 cM.The D-genome contained 394 markers and covered a length of 1769.26 cM with an average genetic distance between markers of 4.5 cM.4.Detection of yield and fiber quality QTLs.In this study,a total of 162 QTLs were identified,including 86 for yield and 76for fiber quality.For stable QTLs,ten of these QTLs were detected in all the three environments and 30 QTLs were detected in two environments.Lint percentage had the highest number of QTLs detected（49）while fiber uniformity had the least number of QTLs detected（6）.