An unusual postharvest spotting disease of the comercial mushroom, Agaricus bisporus, caused by a novel pathovar of Pseudomonas tolaasii

摘要

An unusual postharvest spotting disease of the commercial mushroom, Agaricusbisporus, which was observed on a commercial mushroom farm in Ontario, was found tobe caused by a novel pathovar of Pseudomonas tolaasii.Isolations from the discoloured lesions, on the mushroom pilei, revealed the presenceof several different bacterial and fungal genera. The most frequently isolated genus beingPseudomonas bacteria. The most frequently isolated fungal genus was Penicillium. Ofthe bacteria and fungi assayed for pathogenicity to mushrooms, only Pseudomonastolaasii was able to reproduce the postharvest spotting symptom. This symptom wastypically reproduced 1 to 7 days postharvest, when mushroom pilei were inoculated with101 to 105 cfu. Of the fungi tested for pathogenicity only a Penicillium sp. andVerticillium fungicola were shown to be pathogenic, however, neither produced thepostharvest spotting symptom.The Pseudomonas tolaasii strain isolated from the postharvest lesions differed from atype culture (Pseudomonas tolaasii ATCC 33618) in the symptoms it produced onAgaricus bisporus pilei under the same conditions and at the same inoculumconcentration. It was therefore designated a pathovar. This strain also differed from thetype culture in its cellular protein profile. Neither the type culture, nor the mushroompathogen was found to contain plasmid DNA. The presence of plasmid DNA is thereforenot responsible for the difference in pathogenicity between the two strains.