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A BASELINE SURVEY OF FUNGAL PATHOGENS AND WEED MOULDS ON NEW ZEALAND MUSHROOM FARMS

JW MARSHALL1, M WILLIAMS1 and HM GROGAN2

1Crop and Food Research, Private Bag 4704, Christchurch, New Zealand; 2HRI, Wellesbourne, Warwick, CV35 9EF, UK

Background and objectives
The New Zealand mushroom industry was established in the 1950s and 60s and currently produces approximately 5000 tonnes of fresh produce annually, most of which supplies the home market, with the remainder being exported either canned or fresh to Australia and South-East Asia. Bacterial blotch appears to have been the most serious problem for mushroom growers to date, but occasional outbreaks of cobweb (Cladobotryum) and dry bubble (Verticillium) have also occurred. These are sporadic and appear to be largely controlled with fungicides. Unusually, Benlate-sensitive Verticillium has been recorded in New Zealand but it is not known if this is generally the case throughout the country. Fungal pathogens and weed mould species cause serious economic problems on European and American mushroom farms, and the evolution of both aggressive and resistant strains poses serious problems for growers in these areas. Very little is known about the range of mushroom pathogens and weed moulds present within the New Zealand mushroom industry. A survey was undertaken in January 1998 in order to identify the range of fungal pathogens and weed mould species present on New Zealand mushroom farms with the objectives of providing baseline information for the mushroom industry, and identifying organisms which could be potentially damaging in the future. The findings from the survey would also feed into a current research programme to develop diagnostic methods to service the mushroom industry's needs in the future.

Materials and methods
Mushroom growers around the country were asked to send in any mushrooms which demonstrated unusual symptoms. Eight farms participated in the survey and sent in from four to 26 samples for isolation and identification. Fungal isolations were obtained for between four and 18 samples per farm. Photographs were taken of all symptoms and initial isolations were made on potato dextrose agar (PDA) amended with antibiotics. All cultures were subbed onto both 2% malt extract agar and PDA and were examined and identified after 5-10 days.

Results
Verticillium fungicola was recorded from three farms, while both Dactylium (Cladobotryum) dendroides and Aphanocladium album were recorded once from two separate farms. Five species of Trichoderma were recorded from the survey, which were identified as T. harzianum, T. hamatum, T. koningii, T. viride and T. virens. Trichoderma hamatum appeared to be associated with a spotting symptom. Three species of Morteirella were isolated from three farms, of which M. bainieri has been associated with a shaggy stipe syndrome [1]. Some of the mushroom samples analysed had shaggy stipes, but further work is needed to link this symptom to M. bainieri. A number of other moulds were isolated from the samples but they were not considered to be associated with any pathology.

References
1. Fletcher JT, White PF, Gaze RH, 1989. Mushrooms: Pest and Disease Control. Intercept, Andover, UK.