Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 3, 2009
Publication Date: February 1, 2010
Citation: Rinehart, T.A., Scheffler, B.E., Reed, S.M. 2010. Ploidy Variation and Genetic Diversity in Dichroa. HortScience. 45:208-213. Interpretive Summary: The objectives of this study were to: examine ploidy levels of Dichroa selections; evaluate the genetic diversity within the available Dichroa germplasm; and, determine if naturally-occurring hybrids between Dichroa and Hydrangea exist and identify possible parental species. Ploidy was determined using flow cytometry, while genetic diversity and hybridity were evaluated using SSR markers.While H. macrophylla has been cultivated for over 300 years, the germplasm base used for improving this species has been limited. Wide hybridization offers potential for incorporating unique new traits into this popular ornamental species. This study has demonstrated the range of genetic and ploidy diversity available within D. febrifuga available for use in H. macrophylla genetic improvement efforts. In addition, H. indochinesis has been identified as another species that freely hybridizes with H. macrophylla and could serve as a source of ornamental traits, such as purple foliage. Finally, we have demonstrated the need for a taxonomic revision of the genus Dichroa.
Technical Abstract: Recent evidence suggests a close genetic relationship between Hydrangea macrophylla and D. febrifuga, which supports previous morphological and DNA sequence data. This relationship was confirmed by the production of fertile intergeneric hybrids. Here we characterize the genetic diversity of available D. febrifuga plants, both cultivars and wild-collected taxa, as breeding material to improve H. macrophylla. Relatively high genetic diversity is seen among D. febrifuga, which splits into two main clusters. We also document considerable differences in genome size when compared to previously characterized D. febrifuga. Dichroa versicolor plants were also included and data suggest that D. versicolor could be a hybrid between H. macrophylla and D. febrifuga, similar to the intergeneric hybrids produced by recent breeding efforts. Because native H. macrophylla plants do not overlap extensively with D. febrifuga populations, we tested Hydrangea indochinensis as a possible parent because endemic H. indochinensis populations overlap regions where D. febrifuga and D. versicolor have been collected. However, results suggest that H. indochinensis does not share genetic background with D. versicolor. Taxonomic revision of Dichroa is warranted, especially since we document several more intergeneric hybrids from self-sown, open pollinated sources.