Karyotype Analysis and Genome-size Evaluation of Native Hydrangea Taxa in China

Hydrangea is a widely used ornamental plant, with its commercial cultivars mainly derived from H. macrophylla , H. paniculata , and H. arborescens . Although China exhibits rich genetic diversity in Hydrangea germplasms, the evaluation and breeding utilization of native Chinese Hydrangea resources were limited. To evaluate the unique Hydrangea germplasms in China, the karyotype and genome size of 29 resources were initially disclosed, along with additional 11 reported hydrangeas. The results revealed remarkable differences in the 2C DNA content, with values ranging from 1.98 pg in H. arborescens to 6.89 pg in H. obovatifolia . Additionally, the karyotypes of all 40 germplasms revealed two distinct chromosomal groups: 30 taxa exhibited 2n = 2x = 36, and 10 taxa were 2n = 2x = 34. Notably, the majority of taxa with a basic chromosome number other than x = 18 belong to the Hydrangea subsection, suggesting a potentially higher level of evolutionary advancement within this group. The findings provide valuable insights for future identification and breeding using local Hydrangea germplasms.