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Tan spot: a new disease of pyrethrum caused by Microsphaeropsis tanaceti sp.nov
journal contribution
posted on 2023-05-16, 20:52 authored by Pethybridge, SJ, Suzanne JonesSuzanne Jones, Shivas, RG, Hay, FS, Calum WilsonCalum Wilson, Groom, TThe isolation frequency of Microsphaeropsis sp. in spring in association with necrotic lesions on leaves in Tasmanian pyrethrum (Tanacetum cinerariifolium) fields has increased substantially since first identification in 2001. Examination of morphological features and sequencing of the internal transcribed spacer region (ITS) resulted in the identification of a new species, herein described as Microsphaeropsis tanaceti sp. nov. The pathogenicity of three M. tanaceti isolates to two pyrethrum cultivars was confirmed by inoculating glasshouse-grown plants in three experiments. No significant differences in the susceptibility of the two cultivars to infection by M. tanaceti were found. Symptoms were tan-coloured spots which coalesced around the margins of the leaves. Therefore, the name 'tan spot' is proposed for this new disease of pyrethrum. The sensitivity of seven M. tanaceti isolates to difenoconazole and azoxystrobin, commonly used fungicides for the management of foliar diseases in spring, was assessed under in vitro conditions. Sensitivity testing for difenoconazole was conducted using a mycelial growth assay on potato dextrose agar, whilst testing for sensitivity to azoxystrobin used a conidial germination assay on water agar. Microsphaeropsis tanaceti was found to be more sensitive to azoxystrobin than difenoconazole, with complete inhibition of conidial germination at concentrations above 0.625 μg a.i. mL-1. By comparison, concentrations of 50 μg a.i. difenoconazole mL-1 or greater were required for significant inhibition of mycelial growth. It therefore appears likely that there is currently some control of tan spot as a result of the use of azoxystrobin and to a lesser extent, difenoconazole, for the control of other diseases. © 2008 The Authors.
Funding
Australian Research Council
Botanical Resources Australia Pty Ltd
History
Publication title
Plant PathologyVolume
57Issue
6Pagination
1058-1065ISSN
0032-0862Department/School
Tasmanian Institute of Agriculture (TIA)Publisher
Wiley-Blackwell Publishing LtdPlace of publication
United KingdomRepository Status
- Restricted
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