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

## TL;DR

This study validates a gene region in cotton that improves fiber length and quality, which could help breed better cotton varieties.

## Contribution

The study validates the qFL-Chr.25 QTL and develops diagnostic markers for its efficient use in cotton breeding.

## Key findings

- NIILs with qFL-Chr.25 showed longer fibers across multiple genetic backgrounds.
- TaqMan SNP markers flanking qFL-Chr.25 enable scalable screening for breeding programs.
- Introgression from G. barbadense enhances fiber quality in upland cotton.

## Abstract

Advances in spinning technology have increased the demand for upland cotton (Gossypium hirsutum 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 Gossypium barbadense, a closely related species known for its superior fiber traits, offers a promising strategy. Sealand 883 is an obsolete upland germplasm developed through G. barbadense 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 qFL-Chr.25, in Sealand 883, conferred by an allele introgressed from G. barbadense. This study evaluated the effect of qFL-Chr.25 in near-isogenic introgression lines (NIILs) using Advanced Fiber Information System (AFIS) measurements. Across four genetic backgrounds, NIILs carrying qFL-Chr.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 qFL-Chr.25 into commercial breeding pipelines, accelerating fiber quality improvement and enhancing the competitiveness of cotton against synthetic fibers.