Genome-wide association study and transcriptome analysis reveal candidate genes for off-season flowering in blueberry

Off-season flowering in daylength-sensitive plants is an intriguing characteristic that represents an opportunity to expand crop's production timing and regions, and potentially speed up breeding. Southern Highbush Blueberry (SHB) is classified as a short-day plant, with a blooming period in the northern hemisphere ranging from late winter through spring. In Florida, some blueberry genotypes have consistently bloomed during the fall season, suggesting that flower bud initiation occurred during the summer. Such a characteristic indicates a facultative response to daylength or day-neutrality capacity, leading to the off-season flowering observed. To understand the genetic basis of off-season flowering in SHB, we performed a genome-wide association study (GWAS), followed by transcriptomic analysis of contrasting genotypes. Among the 536 genotypes evaluated, 14 % bloomed during the fall, of which seven presented consistently high scores for off-season flowering capacity. The GWAS revealed 12 single nucleotide polymorphisms (SNPs) significantly associated with the off-season flowering trait, which together accounted for 17 % of the phenotypic variance. A gene homologous to an RNA helicase and reported to modulate florescence formation and flowering time in other plant species, was identified within a genomic region associated with the off-season flowering. This gene was up-regulated in a fall-flowering blueberry genotype. Additionally, we detected down-regulation of flowering repressors and up-regulation of MADS-box transcription factors known to be involved in the fate of floral meristems. Our findings provide insights into the genetic and molecular basis of this complex trait in blueberry. These results can be useful for marker-assisted selection and further functional gene validation to accelerate the development of blueberry varieties suitable for off-season production.