Abstract

The pathogenicity of Alternaria alternata, A. tenuissima, Stemphylium botryosum, Cladosporium cladosporioides and Ulocladium atrum commonly associated with diseased foliage of pyrethrum (Tanacetum cineariifolium) was characterised by inoculating glasshouse-grown pyrethrum plants in three replicated experiments. In the first experiment only one cultivar was used, whilst in the remaining two experiments the susceptibility of cultivars was evaluated. Inoculation with A. alternata, C. cladosporioides and U. atrum failed to induce disease in any cultivar. Inoculation with A. tenuissima resulted in the development of necrotic spots which coalesced to cover large areas of the leaves in all cultivars, whereas foliage of those inoculated with S. botryosum developed necrotic halos surrounded by a pink/brown margin. No significant differences were detected in disease severity following inoculation with A. tenuissima or S. botryosum between the four cultivars commonly grown in Tasmania. However, some significant differences were noted between cultivars in the number of lesions per leaf following inoculation with S. botryosum.