Genetic map and QTL controlling fiber quality traits in upland cotton (Gossypium hirsutum L.)

Cotton is a leading natural fiber crop in the textile industry worldwide. The improvement of cotton fiber quality has become more important because of changes in spinning technology and ever- increasing demands. Mapping quantitative trait locus (QTL) for fiber quality traits will enable molecular marker-assisted selection (MAS) to improve fiber quality and provide an access to reveal the molecular mechanism of fiber development. A high-density intraspecific genetic map is constructed based on an upland cotton recombinant inbred line (RIL) popula- tion. A total of 25,313 SSR primer pairs were used and yielded 1,333 polymorphic markers, with a polymor- phic ratio of 5.3 %, producing 1,382 polymorphic loci in the RIL population. The map comprised 1,274 loci and spanned 3,076.4 cM with an average distance of 2.41 cM between two adjacent markers. Based on the phenotypic data of fiber quality traits from five environments, a total of 59 QTL were detected. These QTL comprised 15 QTL for fiber upper half mean length, 10 QTL for fiber length uniformity, 9 QTL for fiber strength, 10 QTL for fiber elongation and 15 QTL for fiber micronaire, respectively. The genetic map constructed in this study is the most detailed upland cotton intraspecific map based on SSR markers to date, and could be used to construct consensus map or as reference genetic map for tetraploid cotton genome assembly. Stable QTL identified across multiple environments reflect some important and favorable alleles shaping fiber quality, and they are valuable candidate alleles for MAS breeding projects as well as for gene function research related to cotton fiber development and quality improvement.