Identification and Fine-Mapping of qBr10, a Major-Effect Locus for Shoot Branching in Sunflower (Helianthus annuus)

Shoot branching, as an important architectural trait, influences the number of flower heads and the pattern of flowering in sunflowers (Helianthus annuus L.). However, the main genetic factors leading to extensive branching throughout the plant were not clearly understood. In this study, we analyzed branching inheritance and identified a significant locus using an F2 population (n = 660) from a cross between the non-branched line 150A and the highly branched line PT326. The branching phenotypes varied from having no branches to complete plant branching, with segregation fitting a 3:1 ratio (χ2 = 2.916, p > 0.05), suggesting that a single major gene controls this trait, with the non-branched phenotype being dominant. Using bulked segregant analysis (BSA) and whole-genome resequencing, a strong and consistent signal was identified on chromosome 10 across three separate statistical analyses, pinpointing a primary candidate interval of approximately 3.40 Mb, named qBr10. Through the use of 10 developed Kompetitive Allele-Specific PCR (KASP) markers and recombinant screening, qBr10 was restricted to a 388.5 kb (Chr10:13,422,378–13,780,875). Analysis of this interval identified 21 genes, among which WRKY21 and MTB3 were prioritized as candidate genes for further functional validation. Our findings identified qBr10 as a strong candidate for cloning and offer closely associated markers to aid in marker-assisted improvement of branching and capitulum number in sunflower breeding.