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Ash Dieback Chalara fraxinea Alistair McCracken & Louise Cooke Applied Plant Science & Biometrics Division November 2012 Ash (Fraxinus excelsior) Chalara dieback of ash Chalara fraxinea (asexual) Anamorph of new species called: Hymenoscyphus pseudoalbidus (sexual) Ash Dieback • The causal agent of dieback of European ash (Fraxinus excelsior) was first (2006) described as Chalara fraxinea. • Study of the teleomorph of C. fraxinea revealed a species complex but that the strain causing ash dieback should be reassigned to Hymenoscyphus pseudoalbidus (2011). Chalara fraxinea hosts • Fraxinus excelsior (European Ash) • F. angustifolia (Narrow-leaved Ash) • F. nigra (Black Ash) • F. ornus (Manna Ash / South European Flowering Ash) • F. pennsylvanica (Green Ash) • F. americana (White Ash / American Ash) • F. mandschurica (Manchurian Ash) Impact “The disease is particularly prevalent in Denmark where up to 90 per cent of trees in many locations are infected and all are expected to die. Chalara ash dieback has the capacity to inflict on common ash what Dutch elm disease did to English elm in the 1970s. That is to essentially wipe out the species as forest, woodland, amenity and landscape tree in the UK.” (British and International Greenkeepers Association Ltd. Sept. 2012) Pathways • Movement of soil, plants for planting or wood are possible pathways for longdistance transmission • Wind-borne spores can move up to 30 km/year • Plants for planting from known infected areas are considered to be the likely means of entry Spread from plant to plant • Aerial spread – Asexual spores are not thought to be an important means of dissemination Sexual spores • Sexually formed spores (Hymenoscyphus psaudoalbidus) can be dispersed by wind and would appear to be the more important means of dispersal Dispersal rate • Evidence from Norway has suggested a potential dispersal rate of 20-30 km/year. • There is evidence of insect (flies; sapfeeders) dispersing other Chalara spp. Symptoms • Symptoms of Chalara fraxinea can be visible on leaves, shoots and branches of infected trees • In severe cases the entire crown shows leaf loss and dieback intensive dieback of ash (Chalara fraxinea) on European ash (Fraxinus excelsior) Andrej Kunca, National Forest Centre - Slovakia, Bugwood.org intensive dieback of ash (Chalara fraxinea) on European ash (Fraxinus excelsior) Andrej Kunca, National Forest Centre - Slovakia, Bugwood.org intensive dieback of ash (Chalara fraxinea) on European ash (Fraxinus excelsior) intensive dieback of ash (Chalara fraxinea) on European ash (Fraxinus excelsior) intensive dieback of ash (Chalara fraxinea) on European ash (Fraxinus excelsior) intensive dieback of ash (Chalara fraxinea) on European ash (Fraxinus excelsior) intensive dieback of ash (Chalara fraxinea) on European ash (Fraxinus excelsior) intensive dieback of ash (Chalara fraxinea) on European ash (Fraxinus excelsior) Canker caused by Chalara fraxinea on Fraxinus Prof. H. Solheim, Norwegian Forest and Landscape Institute, Aas, Norway Times of year when symptoms are most likely to be observed Jan Leaf necrosis Shoot lesions Stem lesions Fruiting bodies Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Detection and Diagnosis • Culturing Difficult to culture Very slow growing – could take 5 – 8 weeks to get a colony Molecular (PCR) • Molecular lab is fully set up to examine plant samples and / or cultures Thank you
