Pathogenicity of Sclerotinia sclerotiorum to Chrysanthemoides monilifera ssp. rotundata (Bitoubush) and Selected Species of the Coastal Flora in Eastern Australia

Chrysanthemoides monilifera spp. rotundata (bitoubush) is an invasive, noxious weed of coastal ecosystems in eastern Australia. Bushes infected by Sclerotinia sclerotiorum were sampled at nine locations along the New South Wales coast. All isolates of the fungus were pathogenic but there were significant differences in the virulence of isolates and in the resulting disease severity in bushes inoculated with fragmented mycelium. The most virulent isolate was chosen for pathogenicity testing on 45 species of plants in 21 families that are members of the common coastal native flora. Nine species developed lesions and Kennedia, Pandorea, Scaevola, and Westringia were the most susceptible genera, although their reaction to inoculation was variable and disease progression ceased on removal of plants from a humid environment. Only one plant (Carpobrotus sp.) died as a result of inoculation but no sclerotia developed on the diseased tissue of any native species. As no disease caused by S. sclerotiorum has been observed in the native flora, it is considered that this pathogen should be studied further as a biocontrol agent for bitoubush.