Identification and Fine-Mapping of qPH15 for Plant Height in Sunflower (Helianthus annuus L.)

Plant height is a key component of sunflower (Helianthus annuus L.) plant architecture. It strongly influences lodging resistance, mechanized harvestability, and yield stability. However, the genetic basis of plant height in sunflowers remains underexplored. This study aimed to develop an F₂ population consisting of 715 individuals from a cross between the dwarf inbred line 150A and the tall inbred line PT326. Bulked segregant analysis coupled with whole-genome resequencing was employed to identify loci associated with plant height. Using three complementary analytical methods, a major quantitative trait locus, qPH15, was identified on chromosome 15. This locus was subsequently fine-mapped, using Kompetitive Allele Specific PCR (KASP) markers and recombinant screening in F₂ and F₃ populations, narrowing it to a 64.66-kb region containing three annotated genes. Among these, HanXRQr2_Chr15g0707451, which encodes an NAC transcription factor designated HaNAC7, was identified as the most promising candidate gene. Haplotype analysis of HaNAC7 across 148 sunflower accessions revealed 4 polymorphic sites defining 6 haplotypes with substantial differences in plant height. The shortest haplotypes, Hap2 and Hap3, were associated with reduced plant height and were predominantly found in Asian germplasm. These findings suggest that HaNAC7 is a strong candidate gene underlying qPH15 and provide useful molecular markers and favorable allelic resources for improving sunflower plant architecture.