CHARACTERISING THE VIRAL AGENTS CAUSING BROWN CAP MUSHROOM DISEASE OF AGARICUS BISPORUS. Double stranded RNA elements from the mushroom Agaricus bisporus

The symptoms of viral infections of fungi range from cryptic to severe but there is little knowledge of the factors involved in this transition of fungal/viral interactions. Brown Cap Mushroom Disease of the cultivated Agaricus bisporus is economically important and represents a model system to describe this transition. Differentially expressed transcript fragments between mushrooms showing the symptoms of Brown Cap Mushroom Disease and control white non-infected mushrooms have been identified and sequenced. Ten of these RNA fragments have been found to be up-regulated over a thousand-fold between diseased and non-diseased tissue but are absent from the Agaricus bisporus genome sequence and hybridise to double-stranded RNA’s extracted from diseased tissue. We hypothesize these transcript fragments are viral and represent components of the disease-causing agent, a bipartite virus with similarities to the Partiticlass. The virus fragments were found at two distinct levels within infected mushrooms, at raised levels in infected, non-symptomatic, white coloured mushrooms and between 3,500-87,000 times greater in infected mushrooms exhibiting brown colouration. In addition, differential screening revealed 9 up-regulated and 32 down-regulated host Agaricus bisporus transcripts. Chromametric analysis was able to distinguish colour differences between white non-infected and white infected mushrooms at an early stage of mushroom growth. This method may be the basis for an ‘on-farm’ disease detection assay.