Dichroa febrifuga (Hydrangeaceae) is an evergreen shrub with metallic blue fruit that persists throughout winter. Phylogenetic studies have indicated that D. febrifuga is closely related to Hydrangea macrophylla. The objective of this study was to produce hybrids between these two ornamental species. Reciprocal crosses were made between D. febrifuga and both diploid and triploid cultivars of H. macrophylla. Two-thirds of the seed capsules produced from these hybridizations were allowed to mature on the plant, after which time seed were collected and sown in a greenhouse. Embryo rescue was used with the remaining seed capsules. Ovules were excised from ovaries about 9 weeks after pollination and plated on Gamborg's B-5 media with 2% sucrose. Both germination techniques resulted in vigorous seedlings. Hybridity was verified in plants obtained from ovule culture using simple sequence repeat (SSR) markers. Reciprocal hybrids were obtained using both diploid and triploid forms of H. macrophylla. This study confirms the close relationship between D. febrifuga and H. macrophylla and provides valuable material for future breeding efforts.
Keri D. Jones, Sandra M. Reed and Timothy Rinehart
Phillip A. Wadl, Xinwang Wang, John K. Moulton, Stan C. Hokanson, John A. Skinner, Timothy A. Rinehart, Sandra M. Reed, Vincent R. Pantalone and Robert N. Trigiano
Cross-species transferability of simple sequence repeats (SSRs) is common and allows SSRs isolated from one species to be applied to closely related species, increasing the use of previously isolated SSRs. The genus Cornus consists of 58 species that are ecologically and economically important. SSRs have previously been isolated from C. florida and C. kousa. In this study, 36 SSRs were tested on taxa from 18 Cornus species and hybrids for cross-species transferability and genetic diversity was calculated for each locus using polymorphism information content (PIC). Cross-species transferability of SSR loci was higher in more closely related species and PIC values were high. Evidence was found for conserved primer sites as determined by the amplification of SSR loci in the taxa examined. Polymerase chain reaction products were cloned and sequenced for three SSR loci (CF48, CF59, and CF124) and all individuals sequenced contained the appropriate repeat. Phylogenetic relationships of 14 Cornus species were inferred using nucleotide sequences of SSR locus CF48. The most parsimonious tree resulting from this analysis was in concordance with phylogenies based on matK and internal transcribed spacer sequences. The SSR loci tested in this study will be useful in future breeding, population, and genetic studies within Cornus.
Phillip A. Wadl, Xinwang Wang, Andrew N. Trigiano, John A. Skinner, Mark T. Windham, Robert N. Trigiano, Timothy A. Rinehart, Sandra M. Reed and Vincent R. Pantalone
Flowering dogwood (Cornus florida) and kousa dogwood (C. kousa) are popular ornamental species commonly used in the horticultural industry. Both trees are valued for their beautiful floral display and four-season appeal. Species-specific simple sequence repeat (SSR) loci were used to genotype and assess genetic diversity of 24 flowering dogwood cultivars and breeding lines and 22 kousa dogwood cultivars. Genetic diversity was determined by allele sharing distances and principal coordinate analysis and was high in both species. Molecular identification keys were developed for cultivars and breeding lines of each species using a few polymorphic SSRs loci (four in C. florida and five in C. kousa). Most (18 of 24) of the flowering dogwood and all (22 of 22) kousa dogwood accessions could be distinguished from each other using these SSRs; those that could not were resolved using DNA amplification fingerprinting. The reliability of both keys was assessed using five anonymous cultivars for each dogwood species, which were correctly identified using the molecular keys. The genetic information presented here will be useful for identification and verification of cultivars for nurseries and as molecular markers for breeders and researchers.