Evaluation of genetic diversity using simple sequence repeat markers and analysis of cross compatibility in hydrangeas

Hydrangeas with large inflorescences are widely used as cut flowers and in floral arrangements. However, the genetic diversity of commercially grown hydrangeas has been limited owing to the breeding focus on popular species. Therefore, this study was conducted to suggest interspecific breeding strategies for expanding the genetic diversity in Hydrangea L. by evaluating genetic diversity in the seven main species collected in Korea and analyzing cross compatibility via intra- and interspecific hybridization. Interspecific diversity evaluation using simple sequence repeat markers resulted in the segregation of 35 varieties accounting for seven species into five groups as follows: (1) Hydrangea paniculate group, (2) Hydrangea arborescnes group, (3) Hydrangea anomala and Hydrangea aspera group, (4) Hydrangea quercifolia group, and (5) Hydrangea macrophylla and Hydrangea serrata group. Cross compatibility was confirmed via intra- and interspecific crossing, and hybrids were obtained in 18 crossing combinations. Intraspecific hybrids tend to be easy to obtain, but interspecific hybrids are difficult to obtain due to a variety of factors. While most of the interspecific hybrids were obtained using ovule culture, the crossing between H. macrophylla and H. serrata created hybrids from seed sowing, indicating that H. serrata is a subspecies of H. macrophylla. Bilateral and unilateral incompatibilities were observed across the obtained hybrids. Particularly, weak bilateral compatibility was observed between H. serrata and H.paniculata. Accordingly, it was proposed that hybrids between H. macrophylla and H. serrata can be successfully used as parental materials in crossing with H. paniculata to improve cold tolerance. In addition, cross compatibility was improved in interspecific crossing using H. macrophylla and H. arborescens as maternal plants. It is anticipated that these finding will help improve the genetic diversity in commercial hydrangeas.