Analyses Of Heterosis Traits And QTL Mapping In An Elite Hybrid Cotton Cultivar Lumianyan 15

Cotton is the most important renewable natural textile fiber in the world and it is the cornerstone of textile industries worldwide. With the development of social demand and the revolution of textile technology, the cotton industry is confronted with problems in how to control the cost of production and how to increase the yield per unit area and how to meet the expansion demands of higher quantity, so it is important to breed and plant cotton varieties with low cost, high yield production and superior fiber quality. Hybrid cotton could greatly inerease yield,modestly improve fiber quality and enhance tolerance to stresses. However, the heterosis of cotton has not been used extensively as that of rice and corn, because of lack of combinations with strong heterosis and the high cost of producing Fl seeds in cotton so we are in dire need to study the molecular genetic mechanism of heterosis in cotton to promote selection of elite hybrid cotton varieties. This study was carried out to utilize the 613 & R55 (parental lines), Lumianyan15 (F₁), F₂ and F_2:3 populations. Lumianyan15 was the most widely cultivated cotton hybrid in China from 2001 to 2005. Replicated field experiments were conducted at two locations in one year, and field data combined with molecular marker technique for tagging the QTLs of yield and fiber characters, to reveal the preliminary molecular genetic mechanism of heterosis in cotton.The main results were as follows:The results of correlation analysis of seed cotton yield and yield traits of the three subpopulations showed that at different environmental conditions, boll number per plant showed significant positive correlation with seed cotton yield followed by boll weight which was in accordance with multivariate regression and path analyses. Therefore, we can conclude that boll number per plant is the most important selection criterion in the cotton breeding programs. The results of correlation analysis of yield and fiber traits of the three subpopulations illustrated that boll number per plant, boll weight and ginning out turn had significant negative correlation with fiber quality traits.A total of 12117 pairs of SSR primers were used to screen parents to find polymorphism, 151 polymorphic primer pairs were used to evaluate 558 F2 populations and as a result 154 polymorphism loci were found. The software of Joinmap3.0 with LOD of 7.0 was used to analyse data, a total of 116 loci were grouped into 25 linkage groups and covered 892.25cM, approximately 20.05% of the total length of the cotton genome. The average number of markers per linkage group is 4.64 and the average distance of markers is 7.76cM. A total of 19 groups have been anchored to the chromosomes based on the results of previous studies.A total of 77 QTLs for yield traits and 46 QTLs for fiber quality were detected in three subpopulations with software of WinQTLCartographer2.5 by Compose Interval Mapping(CIM)method. A total of 12 QTLs could be detected at more than two locations, which can explain greater phenotypic variations. The analysis of the QTLs effects of yield and fiber quality traits, which exhibited mid-parent heterosis, showed that dominant effects were the main source of heterosis in Lumianyan15.