S01 - Session O8 - Polyploid GWAS identifies loci associated with phenology-related traits in Southern Highbush Blueberry

Authors: Kyoka Nagasaka *, Soichiro Nishiyama, Mao Fujikawa, Hisayo Yamane, Kenta Shirasawa, Ebrahiem Babiker, Ryutaro Tao

Phenology-related traits are major determinant factors of crop production areas. Southern highbush blueberry (SHB) is a tetraploid blueberry group adapted to warmer climates and has been developed by multiple interspecific hybridizations between elite Northern highbush blueberry (NHB) ( Vaccinium corymbosum L.) and low-chill Vaccinium species native to the southern United States. In this study, we aimed to explore the genomic regions associated with five phenology-related traits (chilling requirement, flowering date, ripening date, fruit development period and continuous flowering) in a SHB population, which was anticipated to be key to adaptation to warmer climates. Phenology-related traits evaluated in this study showed moderate to high heritability and correlation coefficients for between-year replications. Genome-wide association studies (GWAS) based on genetic models that included polygenic additive and simplex/duplex additive marker effects were conducted using continuous/discrete allele dosage genotypes. Overall, continuous allele dosage was superior to discrete allele dosage in terms of detectability, probably because of genotyping errors when assigning one of five genotype states in the discrete genotyping. Among the variants detected by GWAS, a novel single peak associated with chilling requirement was located at the same region on Chromosome 4 using two years data. Comparison of genotypes at the GWAS peaks between NHB and SHB revealed the putative introgression of low-chill, late-flowering and late-ripening alleles into the highbush genetic pool. In addition, genotype variations associated with phenology-related traits were largely correlated with the climates of thebreeding locations. Collectively, our results provide basic insights into the diversity of phenological traits in blueberry and the genetic establishment of current highbush cultivar groups.