Volume 19 Part 1 Article 22: Characterisation of the viruses associated with Mushroom Virus X (MVX) and detecting MVX-associated viruses within the European mushroom industry

Volume 19 Part 1 Article 22
Year 2016
Title: Characterisation of the viruses associated with Mushroom Virus X (MVX) and detecting MVX-associated viruses within the European mushroom industry
Author: Caoimhe Fleming-Archibald, Angela Ruggiero, Greg Deakin, Edward Dobbs, Kerry Burton and Helen Grogan

Mushroom Virus X (MVX) is a syndrome of symptoms which were first observed in crops of Agaricus bisporus in England in 1990. One of the main symptoms has been off-colour or brown mushrooms in white strain crops. MVX symptoms have been correlated with the presence of a complex of up to 30viral dsRNAs, ranging in size from 0.6 kb to 20.2 kb. As part of an EU FP7-funded project ‘MushTV’, all the MVX viruses have been characterised and industry surveys have been undertake. Nineteen viruses have now been identified, of which 16 are new to science. We now know that the brown cap symptom is largely caused by the newly identified virus AbV16, (Agaricus bisporus Virus 16) or ‘Brown Cap Mushroom Virus’ (BCMV). Other viruses, AbV6 and MBV may also contribute to the symptoms. Each virus can contain several distinct elements, for example AbV16 contains four RNA molecules with distinct sequences, AbV16-1, AbV16-2, AbV16-3 and AbV16-4.

A survey of compost producers was conducted to determine prevalence of the viruses in industry samples. Selected mushroom growing facilities, including some that had recent or on-going experience of brown mushroom symptoms were also targeted for sampling. All samples were tested for the presence of AbV16-1 and AbV6-2. Out of a total of 249 Phase 3 compost samples tested from across Europe, the AbV16 virus was detected in 8 samples (3%) and AbV6 was detected in six samples (2%), indicating a low level of presence in European Phase 3 mushroom compost. However the AbV16 virus was found in approximately 11% of the samples taken from the mushroom growing facilities and AbV6 was found in 16%.

Some of the samples taken from industry were also used in epidemiological bioassay cropping experiments to determine if infected compost would induce symptoms in subsequent crops. Brown mushroom symptoms in these cropping experiments were determined using a chromameter to quantify the colour of the mushrooms. Compost samples from compost and grower facilities, which were positive for AbV16 and/or AbV6, were found to transmit viruses into the healthy compost and resulting mushrooms, however, brown mushroom symptoms only developed in the cases where the infected compost had been taken from underneath a crop displaying brown mushroom symptoms. Thus, MVX viruses AbV16 and AbV6 can be present in both compost and mushrooms that do not exhibit any brown mushroom symptoms. Further work is required to understand what triggers symptom expression.

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