The 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.

Item Type:	Refereed Article
Research Division:	Biological Sciences
Research Group:	Plant Biology
Research Field:	Plant Pathology
Objective Division:	Plant Production and Plant Primary Products
Objective Group:	Horticultural Crops
Objective Field:	Horticultural Crops not elsewhere classified
Author:	Pethybridge, SJ (Dr Sarah Pethybridge)
Author:	Jones, S (Dr Suzie Jones)
Author:	Hay, FS (Dr Frank Hay)
Author:	Wilson, CR (Associate Professor Calum Wilson)
ID Code:	49634
Year Published:	2008
Funding Support:	Australian Research Council (LP0560562)
Web of Science® Times Cited:	10
Deposited By:	Agricultural Science
Deposited On:	2008-08-01
Last Modified:	2015-03-31
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