Host Range of Australian Phoma ligulicola var. inoxydablis Isolates from Pyrethrum

Ray blight, caused by Phoma ligulicola var. inoxydablis is one of the most damaging diseases of pyrethrum (Tanacetum cinerariifolium [Trevir.] Sch. Bip.) in Australia. The pathogenicity of P. ligulicola var. inoxydablis to a range of ornamental and other plant species was tested to determine potential sources of inoculum into pyrethrum crops. Differences were identified in the host range of P. ligulicola var. inoxydablis isolates in this study in comparison with isolates reported from garden chrysanthemum (Chrysanthemum morifolium L.), most likely to be P. ligulicola var. ligulicola. Australian P. ligulicola var. inoxydablis isolates were unable to infect and cause disease following repeated inoculation to zinnia (Zinnia elegans L.), sunflower (Helianthus annuus L.), dahlia (Dahlia variabilis Desf.), and several cultivars of crisphead lettuce (Lactuca sativa L.). French marigold (Tagetes patula L.) was recorded as a susceptible host for this pathogen for the first time. Moreover, the susceptibility of annual chrysanthemum (Chrysanthemum carinatum L.) to infection by P. ligulicola var. inoxydablis was confirmed. Implications for disease management in Tasmanian pyrethrum fields are discussed. © 2008 Blackwell Verlag.