Alternaria infectoria and Stemphylium herbarum, two new pathogens of pyrethrum (Tanacetum cinerariifolium) in Australia.
Perithecia at the base of dead flower stems of pyrethrum (Tanacetum cinerariifolium) plants in yield-decline affected fields of northern Tasmania were identified as Alternaria infectoria and Stemphylium herbarum. Identification was based on morphological description of cultures established from single ascospores; and conidiospores; ascospore shape and septation; and multigene phylogenetic analyses using the internal transcribed spacer (ITS) region, translation elongation factor 1-α (EF1), polymerase II second largest subunit (RPB2) and glyceraldehyde 3-phosphate dehydrogenase (GAPDH) genes. Stemphylium herbarum produced necrotic leaf lesions on both sides of the spray inoculated pyrethrum leaves which coalesced to encompass the entire leaf in in vivo and in vitro experiments. Alternaria infectoria produced small necrotic leaf lesions on both sides of the leaves two weeks after inoculation which did not expand and hence, was considered as a minor pathogen of pyrethrum. This is the first report of A. infectoria and S. herbarum as pathogens of pyrethrum in Australia. The role of A. infectoria and S. herbarum in pyrethrum yield-decline in northern Tasmania needs to be evaluated.