Ash trees (genus. Here we sequence the genome of a low-heterozygosity Fraxinus excelsior tree from Gloucestershire, UK, annotating 38,852 protein-coding genes of which 25% appear ash specific when compared with the genomes of ten other plant species. Analyses of paralogous genes suggest a whole-genome duplication shared with olive (Olea europaea, Oleaceae). We also re-sequence 37 F. excelsior trees from Europe, finding evidence for apparent long-term decline in effective population size. Using our reference sequence, we reanalyse association transcriptomic data 3 , yielding improved markers for reduced susceptibility to ash dieback. Surveys of these markers in British populations suggest that reduced susceptibility to ash dieback may be more widespread in Great Britain than in Denmark. We also present evidence that susceptibility of trees to H. fraxineus is associated with their iridoid glycoside levels. This rapid, integrated, multidisciplinary research response to an emerging health threat in a non-model organism opens the way for mitigation of the epidemic.

-It is difficult to purify DNA from mature tree leaves at the end of the growing season, because of their thick cell wall, and high content in polysaccharides, phenolic compounds and endonucleases. A simple, fast and efficient method for DNA purification from 100 mg fresh weight leaf samples is described here. It has been developed for extracting DNA

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BackgroundSalix caprea is a cold-tolerant pioneer species that is ecologically important in Europe and western and central Asia. However, little data is available on its population genetic structure and molecular ecology. We describe the levels of geographic population genetic structure in natural Irish populations of S. caprea and determine the extent of gene flow and sexual reproduction using both chloroplast and nuclear simple sequence repeats (SSRs).ResultsA total of 183 individuals from 21 semi-natural woodlands were collected and genotyped. Gene diversity across populations was high for the chloroplast SSRs (HT = 0.21-0.58) and 79 different haplotypes were discovered, among them 48% were unique to a single individual. Genetic differentiation of populations was found to be between moderate and high (mean GST = 0.38). For the nuclear SSRs, GST was low at 0.07 and observed heterozygosity across populations was high (HO = 0.32-0.51); only 9.8% of the genotypes discovered were present in two or more individuals. For both types of markers, AMOVA showed that most of the variation was within populations. Minor geographic pattern was confirmed by a Bayesian clustering analysis. Gene flow via pollen was found to be approximately 7 times more important than via seeds.ConclusionsThe data are consistent with outbreeding and indicate that there are no significant barriers for gene flow within Ireland over large geographic distances. Both pollen-mediated and seed-mediated gene flow were found to be high, with some of the populations being more than 200 km apart from each other. These findings could simply be due to human intervention through seed trade or accidental transportation of both seeds and pollen. These results are of value to breeders wishing to exploit natural genetic variation and foresters having to choose planting material.

Twelve fungal isolates were obtained from roots of field-grown Rhododendron plants. One of these produced ericoid mycorrhizal roots within 5 days when reassociated with Rhododendron plantlets under aseptic conditions. The organism was identified as Oidiodendron maius. A characteristic feature of this organism was production of conidiophores in both pure culture and in association with root cells of the host. Ultrastructural observations confirmed its mycorrhizal status and showed intracellular hyphae surrounded by an interfacial zone and plasma membrane. Hyphae were found in close association with the host nucleus and cytoplasmic organelles. Pure isolates derived from diverse alternative sources were also tested for mycorrhizal formation with Rhododendron under aseptic conditions. Thus, Pezizella ericae obtained from Calluna vulgaris produced mycorrhizal infections after 10 days of culture, whereas O. maius from Sitka spruce and Oidiodendron griseum from wood pulp failed to form mycorrhizas.