# Fine mapping and candidate gene mining of major QTL QSL.caas-6BL.1 for spike length in bread wheat (Triticum aestivum L.)

## TL;DR

This study narrows down a key wheat gene region affecting spike length and identifies a likely candidate gene for breeding improvements.

## Contribution

The study fine-maps a major QTL and identifies a specific NAC transcription factor as a candidate gene for spike length in wheat.

## Key findings

- The QSL.caas-6BL.1 QTL was narrowed to a 3 Mb interval on wheat chromosome 6B.
- Twenty-five high-confidence genes were identified in the QTL region, with one NAC transcription factor showing strong evidence as a candidate gene.
- The candidate gene exhibited differential expression and amino acid changes between parental lines.

## Abstract

Spike length (SL) is a key agronomic determinant of wheat spike architecture and yield potential. This study focused on fine‑mapping a major SL‑regulating quantitative trait locus (QTL), QSL.caas‑6BL.1, previously identified in a Doumai (DM) × Shi 4185 population.

High‑density molecular markers were developed and used to screen recombinant families derived from the cross. Genotype–phenotype co‑segregation analysis in advanced generations was employed to delineate the QTL region.

The QSL.caas‑6BL.1 locus was delimited to a 3 Mb physical interval on chromosome 6B (IWGSC RefSeq v2.1). Gene annotation and transcriptome analysis of young spikes identified 25 high‑confidence genes within this region. Among these, the NAC transcription factor gene TraesCS6B03G1211800 emerged as the prime candidate, being the only gene that combined significant differential expression between parental near‑isogenic lines with coding‑sequence variants leading to amino acid changes.

Our work narrows a major QTL to a precise genomic interval and pinpoints a promising candidate gene, providing a valuable resource for understanding the genetic control of wheat spike development and for marker‑assisted breeding.