2019 ASHS Annual Conference

Hydrangea macrophylla is one of the most important floral and nursery crops worldwide. However, breeding of new hydrangea varieties has been hampered by its long breeding cycle and lack of genetic resources. The goal of this research was to employ genotyping-by-sequencing (GBS) for single nucleotide polymorphism (SNP) marker development and genome-wide association study of inflorescence shape, a key horticultural trait of hydrangea. This study investigated genetic diversity of 83 hydrangea cultivars using (GBS). A total of 5,805 high quality SNPs were identified and used for genetic diversity and genome-wide association study of inflorescence shape. Diversity studies confirmed the taxonomic classification of H. macophylla ssp. serrata as a subspecies of H. macrophylla. Population structure revealed a second gene pool within H. macrophylla ssp. macrophylla group. GWAS was performed with three models: general linear model (GLM), general liner model with Q (structure) as covariates, and mixed linear model (MLM) with Q as covariates. 93 shared SNPs were detected under two GLM models with one more additional SNP identified in GLM+Q model using the Bonferroni threshold (8.7E-6). Only the lead SNP in two GLM models was identified in MLM+Q model under the same threshold. The lead SNP explained 65.51% and 36.12% of phenotypic variation in GLM and MLM, respectively. This SNP was converted to a cleaved amplified polymorphic sequence (CAPS) marker that was able to accurately identify inflorescence shape in a validation panel. The accurate categorization of hydrangea germplasm is essential to capture available genetic diversity for hydrangea breeding improvement, and the development of CAPS and other molecular markers will reduce time-to-market for improved hydrangea varieties.