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New Zealand Plant Protection 67 (2014): 330

The search for "white tip" of Californian thistle in New Zealand

M.G. Cripps, K.L. Bailey, C.N. Merfield, S.D. Jackman and G.W. Bourd˘t


Phoma macrostoma is a cosmopolitan fungus, pathogenic to a wide range of herbaceous and woody plant species, but non-pathogenic to most grasses. Recently, a strain of P. macrostoma pathogenic to Californian thistle (Cirsium arvense) and other broadleaf weeds was registered as a bioherbicide in Canada for use in turf grass and arable cropping systems.This strain causes a condition known as "white tip" disease that is characterised by symptoms of yellow to white chlorosis, commonly referred to as photobleaching. Symptoms characteristic of white tip disease have been observed on Californian thistle in New Zealand, but it is uncertain if the causal agent is P. macrostoma. The aim was to determine if strains of P. macrostoma that cause white tip disease and are genetically similar to the Canadian bioherbicide strain are present in New Zealand. The presence of such strains would facilitate the registration of this pathogen as a bioherbicide since most safety requirements will have been satisfied by overseas research. People in the agricultural industry are encouraged to look for Californian thistle with white tip symptoms and send samples to AgResearch for identification.

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