QTL analysis of cotton fiber length in advanced backcross populations derived from a cross between Gossypium hirsutum and G. mustelinum

The molecular basis of cotton ber length in crosses between Gossypium hirsutum and Gossypium mus- telinum was dissected using 21 BC3F2 and 12 correspond- ing BC3F2:3 and BC3F2:4 families. Sixty- ve quantitative trait loci (QTLs) were detected by one-way analysis of variance. The QTL numbers detected for upper-half mean length (UHM), ber uniformity index (UI), and short ber content (SFC) were 19, 20, and 26 respectively. Twenty- three of the 65 QTLs could be detected at least twice near adjacent markers in the same family or near the same mark- ers across di erent families/generations, and 32 QTLs were detected in both one-way variance analyses and mixed model-based composite interval mapping. G. mustelinum alleles increased UHM and UI and decreased SFC for ve, one, and one QTLs, respectively. In addition to the main- e ect QTLs, 17 epistatic QTLs were detected which helped to elucidate the genetic basis of cotton ber length. Signi - cant among-family genotypic e ects were detected at 18, 16, and 16 loci for UHM, UI, and SFC, respectively. Six, two, and two loci showed genotype×family interaction for UHM, UI and SFC, respectively, illustrating complexities that might be faced in introgression of exotic germplasm into cultivated cotton. Co-location of many QTLs for UHM, UI, and SFC accounted for correlations among these traits, and selection of these QTLs may improve the three traits simultaneously. The simple sequence repeat (SSR) markers associated with G. mustelinum QTLs will assist breeders in transferring and maintaining valuable traits from this exotic source during cultivar development.