Submitted to: Journal of the American Society for Horticultural Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/3/2006
Publication Date: 11/15/2006
Citation: Rinehart, T.A., Scheffler, B.E., Reed, S.M. 2006. Genetic diversity estimates for the genus Hydrangea and development of a molecular key based on SSR. Journal of the American Society for Horticultural Science. 131:787-797. Interpretive Summary: Hydrangeas are the fourth top selling deciduous flowering shrub with annual sales in excess of $32 million. Breeding efforts are targeted at developing reliable, low-maintenance plants with a wide array of desirable ornamental traits. In an effort to accelerate breeding of new cultivars we established microsatellite (SSR) markers for Hydrangea species. We used 14 SSR markers to assess the genetic diversity between different species of Hydrangea and Dichroa, Platycrater and Schizophragma genera. Data suggest that H. macrophylla, the most widely grown commercial species with over 300 named varieties, is more related to H. serrata, H. scandens and Dichroa than to any other Hydrangea species. We show that Platycrater is related to subsection Aspera and Schizophragma is associated with subsection Heteromalla. In addition to discussing the taxonomy of hydrangeas, we establish the utility of SSR markers as a rapid method of species identification using a molecular-based key.
Technical Abstract: Cultivars from at least six different Hydrangea species are commonly available in the nursery trade. Despite an increase in hydrangea breeding and interest in germplasm conservation, relatively little is known about the relatedness between Hydrangea species. The last major revision of Hydrangea taxonomy was carried out in 1957 by McClintock, who established the species designations commonly used today. Using 14 codominant microsatellite markers (SSR) that cross react with fourteen Hydrangea species, we analyzed gene diversity and genetic similarity within Hydrangea. Samples also included Dichroa, Platycrater, and Schizophragma genera to establish their relatedness to Hydrangea species since previous work suggests they may be closely related. Our results support the close affiliation between Macrophylla and Petalanthe subsections and their separation from the other Hydrangea species. Most of the Hydrangea species analyzed cluster within their designated sections and subsections; however, genetic distance between species within each subsection varied considerably. Our data suggest that morphological analyses which labeled H. serrata as a subspecies of H. macrophylla are probably more accurate than recent genome size data suggesting H. macrophylla and H. serrata are separate species. In addition to assessing the genetic diversity of Hydrangea species, we also include a molecular key for unambiguous species identification.