MVX transmission during bulk handling
transmit MVX, so it is still wise to minimise sporulating mushrooms when there is an MVX outbreak.
Airborne transmission during Bulk Handling of Phase 3 MVX had emerged as a problem in the late 1990’s and early 2000’s at a time when there was rapid expansion of bulk phase 3 production in Britain, Ireland and the Netherlands. A set of experiments were done to explore the potential for MVX trans- mission by the microscopic airborne compost/ mycelial fragments that are generated during the bulk handling of phase 3 compost (HDC report M39a). In these experiments, MVX-infected phase 3 compost (1283) was bulk handled in the same room as uninfected phase 3 compost (Con- trol +) but well separated from each other. The air was sampled during this process to see if com- post/mycelial fragments were detectable. A second control batch of uninfected phase 3 was bulk handled and grown in isolation for compari- son (Control). The results were stark. The two controls yielded similarly, showing no virus symptoms, while the MVX-infected com- post showed crop delay and reduced yield as expected (Figure 1 and 2). Despite showing no symptoms, the 1st flush ‘Control +’ mushrooms showed extra viral elements, and the 2nd flush mushrooms showed the presence of AbV6, simi- lar to the MVX-infected mushrooms, while the ‘Control’ mushrooms, cropped in isolation, remained free of MVX viral elements (Figure 3). The air samples showed around 3,000 microsco- pic compost and mycelial fragments/m3 of air during the bulk handling operation, indicating they were the most likely source of MVX trans- mission to the control compost. Of great interest is the fact that 7 microscopic mycelial fragments/ m3 of air were still detectable four hours after the bulk handling had finished!
Compost fragment transmission at spawning and end of spawn run Another research trial with strain 1283 looked at infecting Phase 2 compost with three different rates of MVX-infected compost (0.0001%, 0.01% and 1%) either at the start of spawn run or at the end of spawn run during bulk handling of Phase 3 (HDC report M39c). These rates equate to 1g, 100g and 10 kg of infected compost per tonne. One gram (0.0001%) per tonne of compost is a tiny amount - literally a few straws of compost in an 18 kg bag. The results were again stark. When compost was infected at the start of spawn run, all three rates caused significant crop
100 150 200 250 300 350
50 0
18 20 22 24 26 28 30 32 34 36 38 40 42 Days after casing
Figure 1. Yield from Phase 3 compost bulk handled in isolation or bulk handled in the presence of MVX-infected Phase 3.
Control (bulk handled in isolation) Control + (bulk handled in presence of 100% infected) 100% infected (bulk handled in presence of Control +)
Figure 2. A ‘Control +’ plot on the left and a ‘100% infected’ plot on the right, showing crop delay and patchiness.
AbV6
Figure 3. MVX test on mushrooms from Phase 3 compost bulk handled in isolation (C), or in presence of MVX infected compost (C+), in comparison with mushrooms from MVX infected compost (Inf).
MUSHROOM BUSINESS 21
Yield kg / tonne
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