Patch surrounded by off-white mushrooms, a first clear sign of MVX.


countries contacted me due to problems with MVX. So this article is another call to action for the problem to be taken seriously and for a consolidated, sector-wide approach!


What is Virus X? History


In 1996, inexplicable symptoms were seen on various mushrooms farms in the UK, such as bare patches, stripes and off-white to brown mushrooms. By 1998, this had developed into a major problem nationwide, with production being disrupted and causing yield losses of 20- 60%. Growers were unable to pinpoint the cause so finding a solution was impossible. Many mushroom farms were unable to survive and were forced to close down. In 2000, this ‘new’ disease was named Mushroom Virus X (MVX), because it was possible to show a high concen- tration of a complex of multiple virus particles in these mushrooms. The disease rapidly spread in Ireland too. In 1997 it only reared its head occasionally, but five years later some 50% of growers had already been affected. The first reported cases of Virus X in the Netherlands came from seven farms in 2000. Four years later, this figure had already risen to 38. So what is MVX?


The virus has the mysterious letter X because no one actually knows precisely what it is. What is certain is that 18 different virus particles have been identified in infected mushrooms. Three of these virus particles are associated with die back disease (La France disease), one particle is associated with the browning symptoms and another to the bare patches. Higher concentra- tions of these viruses can be identified in mushrooms that exhibit these symptoms. However, a large number of ‘unknown’ virus particles are also found in the mushrooms. It is unknown what or whether they do anything, or if and when they might do something, and which factors potentially trigger a response. Interac- tion between the different strains of virus par- ticles is also a possibility.


Severe Virus X infection in the 1st flush.


Another unknown is whether the typical symp- toms we see are caused by the viruses, or whether the symptoms are a protective response of the mushrooms to create a barrier that inhibits a further outbreak of the viruses. What are the symptoms? Brown Cap


One of the milder symptoms is Brown Cap, which is associated with virus particle AbV16. Off-white mushrooms occur between the white mushrooms. The initial response of the grower is that some spawn or compost from chestnut mushrooms has ended up among the white mushrooms. There is no notable loss of production. However, the number of off-white mushrooms can increase to as much as 60%. Despite being of good quality, they are rejected as the market for fresh mushrooms does not want these ‘discoloured’ mushrooms. This causes a financial drama for the grower in question. Patches/Swirls


In my opinion, the AbV6 virus particles associated with the occurrence of bare patches are the most dangerous. All the signs are encouraging, the compost is nicely spawned and smells good, the mycelium has colonised the casing soil well and pinhead formation looks normal. So, you expect to be able to harvest a normal 1st flush three to four days later. However, patches start to develop on the bed where the pinheads don’t grow out. These patches expand in size during the 2nd and 3rd flushes and can even cover half the bed surface. Swirls devoid of mushrooms also appear across the beds.


The problems often start with a small “innocent” patch, which is frequently mistaken for mummy disease. This acts like a red herring and sends you searching for the cause of the problem in the wrong place: an area of the room with sub-optimal evaporation, over-compacted casing soil, compost that is too wet etc. So, as a consultant, you always recognise the real culp- rit too late. But the problem just keeps getting bigger as the cropping cycles progress and the ultimate result is up to 60% lower yields.


The virus has the mysterious letter ‘X’ because no one actually


knows precisely what it is.


 MUSHROOM BUSINESS 9


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48