Using SSR markers to estimate diversity among hydrangea germplasm and improve breeding of new cultivars

Authors: Rinehart, Timothy - Tim; Reed, Sandra

Submitted to: International Symposium on Woody Ornamentals of the Temperate Zone
Publication Type: Abstract Only
Publication Acceptance Date: 5/26/2008
Publication Date: N/A
Citation: N/A

Interpretive Summary: Hydrangea macrophylla is widely grown as both a landscape and florist plant. In the landscape, it is valued for its large, long-lasting inflorescences that are produced in early summer. Only H. macrophylla subsp. macrophylla is used in the florist’s trade, but both H. macrophylla subsp. macrophylla (bigleaf hydrangea) and H. macrophylla subsp. serrata (mountain hydrangea) are sold as garden plants. The two subspecies are differentiated by the larger leaves and inflorescences of H. macrophylla subsp. macrophylla (McClintock, 1957). Out of the other Hydrangea species that are commercially available, the most popular landscape plants include H. paniculata, H. arborescens, and H. quercifolia. Our SSR markers have also been used to generate DNA fingerprints for more than 200 H. macrophylla cultivars. Results indicate that 30 loci are enough to uniquely identify all cultivars that are sexually derived. Cultivars produced by sport mutations have identical DNA fingerprints as their source plants. These markers have been used to make taxonomic distinctions between subspecies, unambiguously identify cultivars, and look for mislabeled plants in the trade. We recently expanded our search for mislabeled plants and data presented here confirm that plants labeled ‘All Summer Beauty’ include two different DNA fingerprints. We also present DNA fingerprint data confirming the parentage of ‘Blushing Bride’, and identifying the paternal contribution for Midnight Duchess and Queen of Pearls, which were selected from open pollinated populations. Also presented is evidence that that a new cultivar ‘Hopcorn’ is not a rename of a similar-looking, pre-existing cultivar called ‘Ayesha’. The same technology can be applied to "true to name" guarantees, plant labeling disputes, and plant patent protection.

Technical Abstract: Hydrangea popularity and use in the landscape has expanded rapidly in recent years with the addition of remontant varieties. Most cultivars in production belong to the species Hydrangea macrophylla but H. paniculata, H. arborescens, H. anomala, and H. quercifolia are also widely cultivated. In addition to species diversity there is high intraspecies variation, particularly in H. macrophylla which includes two cultivated subspecies, mophead and lacecap inflorescence forms, French, Japanese, dwarf, and variegated varieties. Relatively little is known about the genetic background or combinability of these plants. We recently established a molecular key for Hydrangea species and used it to resolve taxonomy at the species level. We used the same SSR markers to verify interspecific hybridization within Hydrangea and confirm intergeneric hybrids between Dichroa and Hydrangea. Here we use microsatellite markers to determine the parentage of new H. macrophylla cultivars such as 'Midnight Duchess', 'Blushing Bride' and 'Queen of Pearls', to identify mislabeled cultivars, to confirm the renaming of cultivars, and to demonstrate that some similar-looking cultivars are actually genetically unique. The same technology can be applied to "true to name" guarantees, plant labeling disputes, and enhance plant patent applications.