Commodity PRA for Agaricus bisporus - Defra

4. Discussion
Commodity PRA for Mushrooms
CSL/Warwick HRI, December 18th 2007; revised 24 February 2009
CSL Registered File No. PPP 12011A
This analysis has shown that the majority of the mushroom pathogens, weed
moulds and pests recorded in the literature are present in the UK.
Nevertheless, several species are not found in the UK that could potentially
affect mushroom production if introduced. They are discussed in part below.
There are also a number species that have been recorded in other habitats or
on other hosts in the UK but have not recorded in UK mushroom crops. These
species include several species of weed mould and nematode, and one
species of fungal pathogen, Verticillium fungicola var. aleophilum. Of these
species, the most significant threat is the fungal pathogen. This organism has
been recorded affecting mushrooms in North America, where it is the main
cause of dry bubble disease, causing a variety of symptoms on mushroom
caps such as lesions, distortion and discolouration. However, in Europe, dry
bubble is associated with Verticillium fungicola var. fungicola, therefore
mushroom growers already deal with dry bubble caused by a related species.
Nevertheless, mushroom growers are advised to remain vigilant against
species that are already present in the UK and have the potential to affect
mushroom production, but have not yet been officially recorded in mushroom
production environments.
4.1 Pathogen risks
Paecilomyces penicillatus. This fungus has not been recorded in the UK.
There is only one report of it affecting mushrooms (found on a decaying
mushroom in Belgium). As this was an isolated report it may have been an
opportunistic infection. If P. penicillatus were an aggressive pathogen of
mushrooms then it is likely that the disease would have been more widely
reported. Therefore the risk this pathogen presents to UK mushrooms is likely
to be low.
Pseudomonas species. Pseudomonas costantinii and Pseudomonas
‘reactans’ have never been recorded in the UK. However, little is known about
their current distribution. Pseudomonas costantinii was originally considered a
strain of Pseudomonas tolaasi (Munsch et al., 2002). Both P. tolaasi and P.
costantinii can cause brown blotches on mushroom caps. P. tolaasi is known
to be common in the UK on mushrooms. Since many Pseudomonas strains
already occur in UK mushrooms, many uncharacterised, it is possible that
these species are also present but have not been formally reported. UK
mushroom growers already manage diseases caused by several other
Pseudomonas species. Therefore, it is likely that these Pseudomonas species
present little additional risk to UK mushrooms.
4.2 Weed mould competitor risks
Trichoderma aggressivum forma aggressivum. This species is an
aggressive coloniser of mushroom composts in North America but is not
present in Europe. An HDC-funded Project undertook a survey of
Trichoderma species present in UK mushroom production on 15 farms, over a
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