Susceptibility of Australian Plant Species to Phytophthora ramorum

Phytophthora ramorum is an invasive plant pathogen causing considerable and widespread damage in nurseries, gardens, and natural woodland ecosystems of the United States and Europe, and is classified as a Category 1 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 pathogenicity of P. ramorum on Australian native plants. Sixty-eight test species within 24 families were sourced from established gardens and arboretums. Foliar and branch susceptibility were tested using detached leaf and branch assays. The experiment was repeated to account for seasonality. Initial results indicate the majority of species tested were susceptible to varying degrees. Of particular interest are the high levels of variability within the eucalypts, low levels of susceptibility within the Pittosporaceae family, and a concerning number of latent or asymptomatic infections.