Inter-specific hybridization of Alnus rubra and Alnus rhombifolia : preliminary report of a new taxon and DNA marker resources for bioenergy feedstock production

Exploratory hybridization of red alder ( Alnus rubra Bong.) and white alder ( Alnus rhombifolia Nutt.) was conducted to initiate a long-term investigation into the inter-specific taxon’s potential for biomass production. Red alder selections originated in stands west of Oregon’s Cascade Mountains, while white alder came from provenances west and east of the Cascades. White alder’s heretofore unknown chromosome number was determined equal to red alder (2 n = 2 x = 28) and included a pair of satellite chromosomes. An experimental crossing technique was proven, establishing the species’ reproductive affinity for the first time. Hybridization was substantially more productive when red alder served as the female parent as opposed to white alder. Hybridity was confirmed using four species-specific SSR markers developed from transcriptome resources for identifying sib relationships in domesticated populations. To begin a description of the inter-specific taxon, hybrids and their open-pollinated siblings were assessed at ages four through six for morphological and phenological traits and carbon and nitrogen isotopic ratios in a field planting in western Washington, USA. Principal component analysis of quantitative leaf and internode morphologies showed that red alder and hybrid alder are relatively comparable and both are distinct from white alder. Qualitative differences in leaf morphology are more diagnostic with inter-specific hybrids often intermediate to red and white alder. Principal coordinate analysis of molecular data cleanly separated the three taxa. Plans for continued investigation of the taxon as a biomass crop species are discussed including a potential role for inter-specific hybrids in adapting red alder to the effects of climate change.