Clinic provides insight into mushroom mould problems

Helen M. Grogan

Horticulture Research International (HRI) set up a Mushroom Diagnostic Clinic for the mushroom industry in Britain in 1994. Although HRI is primarily a research institution, the clinic has facilitated a two-way flow of information: growers have access to the most recent research findings while HRI has regular contact with the industry. Such close contact enables HRI to respond quickly to emerging problems with relevant research projects. For example, in 1995 we carried out a fungicide resistance survey of Cobweb isolates, on behalf of British growers via the Horticultural Development Council (HDC), when it became apparent that an epidemic was underway (Figure 1).

Figure 1: Cobweb on a mushroom bed

Figure 1: Cobweb on a mushroom bed

Many isolates were benzimidazole-resistant but of interest also was the fact that not all isolates were Cladobotryum (Dactylium) dendroides as expected.

Cobweb disease of mushrooms is caused by a few species of Cladobotryum, most notably C. dendroides and C. mycophilum. Both of these occur on other mushroom species growing in the wild (Rogers & Samuels, 1993, 1994). Interestingly, here in Britain C. mycophilum is regularly the cause of cobweb disease on cultivated mushrooms although C. dendroides is also isolated (Grogan & Gaze, 2000). However a third type, which was genetically similar to C. mycophilum, was associated with the mid 1990’s epidemic. These isolates regularly had 3 and 4 celled spores, which were uncharacteristic of C. mycophilum, and they also lacked its characteristic odour. In addition, the bulk of these atypical C. mycophilum isolates were also resistant to carbendazim and thiabendazole, and thus were more difficult to control. Following another HDC-funded research project, the fungicide pyrifenox has now been approved for use in Britain against these benzimidazole-resistant isolates, giving very good control. However, it can delay the first flush by a day or two or reduce the 1st flush yield, particularly at the higher rate of use, so growers need to be aware of this when using the product.

Figure 2: Aphanocladium album records from 1995 to 2000

Figure 2: Aphanocladium album records from 1995 to 2000

Not all queries to the Mushroom Diagnostic Clinic concern major pests and diseases. Analysis of data acquired over the years has provided some interesting information concerning a little-encountered pathogen, Aphanocladium album. We have isolated it on a number of occasions from mushrooms with either severe or mild spotting symptoms but also from spawn run compost. It seems to occur throughout the year but over half of the recorded cases occurred between September and November, an autumnal mould perhaps? (Figure 2). Aphanocladium is not a major pathogen by any means, but it does crop up regularly and can occasionally cause severe symptoms (Figure 3). Its occurrence is often associated with periods when external humidity is high, or when humidity control in cropping houses is difficult. There is little written on the epidemiology of Aphanocladium on mushrooms (Gaze, 2000a, 2000b) but a search of the literature has revealed a few interesting facts.

Figure 3: Severe Apharocladium spotting symptoms

Figure 3: Severe Apharocladium spotting symptoms

Apart from its occasional parasitism of mushrooms, Aphanocladium album is primarily known as a parasite of other parasites (“hyperparasite”), such as powdery mildews and cereal rusts (Koc & Defago, 1983; Verharr et al, 1999). It is not surprising therefore that it has been found in cereal-based poultry feed (Bragulat et al., 1995) and also in soil (Ellanskaya et al. 1997). It is probably likely to be more common when diseases are well established on plants, for example in wet or damp summers, or when cereals are being harvested, sown or handled in bulk. A more detailed study of the incidence and epidemiology of Aphanocladium spotting would be needed however, in order to work out where it is coming from, or what environmental conditions favour its development. Such work is probably not justified at present, but many a mould has risen from obscurity in the past to pose serious problems for unsuspecting growers. Should this occur with Aphanocladium, hopefully we will be able to respond quickly with some targeted research on the subject.

References

Bragulat, M.R. et al. (1995). J. Sci. Food Agric. 67, 215-220
Ellanskaya, I.A. et al. (1997). Microbios 92, 19-33.
Gaze, R.H. (2000a). The Mushroom Journal 600, 17-18.
Gaze, R.H. (2000b). The Mushroom Journal 604, 12-13.
Grogan, H.M. & Gaze, R.H. (2000). Mycological Research 104, 357-364.
Koc, N.K. & Defago, G. (1983). Phytopathologische Zeitschrift 107, 214-218.
Rogers C.T. & Samuels, G.J. (1993). Mycologia 85, 231-272.
Rogers C.T. & Samuels, G.J. (1994). Mycologia 86, 839-866.
Verharr, M.A. et al, (1999). J Plant Dis & Prot 106, 158-165.