Genetic analysis and QTL mapping of oil content and seed index using two recombinant inbred lines and two backcross populations in Upland cotton

Cottonseed is one of the main by-products of cotton. To explore the genetic composition of oil content (OC) and seed index (SI) is helpful for utilizing the cottonseed. Under multiple environmental conditions, the genetic structures of OC and SI were explored using two recombinant inbred lines (RILs) and corresponding backcross (BC) populations in Upland cotton. Twenty-four and 31 quantitative trait loci (QTLs) for OC and SI, respectively, were detected using composite interval mapping, in which 9 QTLs for OC and 18 QTLs controlling SI were simultaneously identified in more than two environments or two populations. Forty-seven and 37 QTLs with main effects (M-QTLs) for OC and SI and 114 and 74 QTLs involved in digenic interactions (E-QTLs), respectively, identified by inclusive composite interval mapping. On average, the E-QTLs explained a larger portion of the phenotypic variation than the M-QTLs did. It was concluded that additive effects of single-locus and epistasis derived from complementary loci with few detectable single-locus effects played an important role in oil content and seed index in Upland cotton.