Fine mapping and candidate gene analysis of a major QTL for grain length on chromosome 5BS in bread wheat

Large grain is a favorable trait for appearance quality and a large sink potential in wheat breeding. The stable QTL QGl.caas-5BS for grain length was previously identified in a recombinant inbred line population from the cross of Zhongmai 871 (ZM871) and its sister line Zhongmai 895 (ZM895). Here, a BC₁F₆ residual heterozygous line was selected from the cross of a ZM871/ZM895//ZM871 population, and six heterozygous recombinant plants were identified in the BC₁F₇ population from self-pollination of the heterozygous line. QGl. caas-5BS was delimited into an interval of approximately 2.2 Mb flanked by markers Kasp_5B33 and Kasp_5B2 (25.3–27.5 Mb) by phenotyping and genotyping the secondary mapping populations derived from these heterozygous recombinant plants. Five genes were predicted as candidates of QGl.caas-5BS based on sequence polymorphism and differential expression analyses. Further mutation analysis showed that TraesCS5B02G026800 is likely the causal gene of QGl.caas-5BS. The gene-specific marker Kasp_5B_Gl for TraesCS5B02G026800 was developed, and a significant genetic effect of QGl.caas-5BS on grain length was identified in a validation population of 166 cultivars using this marker. These findings lay a good foundation for map-based cloning of QGl.caas-5BS and provide a breeding-applicable marker for the improvement of grain length in wheat.