Ireland, K., Hüberli, D., Dell, B., Smith, I., Rizzo, D. and Hardy, G.E.St.J. (2010) Australian native plant susceptibility to Phytophthora ramorum. In: 5th IUFRO Phytophthora Diseases in Forests and Natural Ecosystems, 7 - 12 March, Auckland and Rotorua, New Zealand.
Phytophthora ramorum causes considerable and widespread damage in nurseries, gardens and natural woodland ecosystems of the USA (where it causes Sudden Oak Death) and Europe, and is classified as a Category 1 plant pest in Australia. It is of particular interest to Australian plant biosecurity as, like P. cinnamomi, it has the potential to become a major economic and ecological threat in areas with susceptible hosts and conducive climates. Research was undertaken in California to assess the pathogenicity of P. ramorum on Australian native plants. Sixty-nine plant species within 24 families were sourced from established gardens and arboretums, and selected based upon provenance from areas of climatic suitability for P. ramorum as well as ecological and economical importance. Foliar, branch and log susceptibility were tested using detached leaf, branch and log inoculations. Sporulation potential and chlamydospore production was also tested on detached foliage of a select mid to upper storey species. All species demonstrated some level of foliar susceptibility, and some asymptomatic infection was recorded. Disease incidence and severity were greater during the summer, and when the leaves were wounded. Branch inoculations indicated some species may be affected by branch dieback. However, only juvenile branches of Eucalyptus leucoxylon displayed symptoms more severe than the positive control, Rhododendron ‘Colonel Cohen’. Sporulation was recorded for a few species, particularly on juvenile foliage, while putative bole canker hosts in the Eucalyptus have been identified. Results of the studies will be discussed in relation to their implications for disease entry, spread and development of an epiphytotic within an Australian biosecurity framework.