Phenotypic Validation of the Cotton Fiber Length QTL, qFL-Chr.25, and Its Impact on AFIS Fiber Quality

Advances in spinning technology have increased the demand for upland cotton (<i>Gossypium hirsutum</i> L.) cultivars with superior fiber quality. However, progress in breeding for traits such as fiber length is constrained by limited phenotypic and genetic diversity within upland cotton. Introgression from <i>Gossypium barbadense</i>, a closely related species known for its superior fiber traits, offers a promising strategy. Sealand 883 is an obsolete upland germplasm developed through <i>G. barbadense</i> introgression and is known for its long and fine fibers. Previous studies have identified a fiber length quantitative trait locus (QTL) on Chromosome 25, designated <i>qFL</i>-<i>Chr</i>.25, in Sealand 883, conferred by an allele introgressed from <i>G. barbadense</i>. This study evaluated the effect of <i>qFL</i>-<i>Chr</i>.25 in near-isogenic introgression lines (NIILs) using Advanced Fiber Information System (AFIS) measurements. Across four genetic backgrounds, NIILs carrying <i>qFL</i>-<i>Chr</i>.25 consistently exhibited longer fibers, as reflected in multiple length parameters, including UHML, L(n), L(w), UQL(w), and L5%. Newly developed TaqMan SNP diagnostic markers flanking the QTL enable automated, reproducible, and scalable screening of large populations typical in commercial breeding programs. These markers will facilitate the incorporation of <i>qFL</i>-<i>Chr</i>.25 into commercial breeding pipelines, accelerating fiber quality improvement and enhancing the competitiveness of cotton against synthetic fibers.