VIRUS X A15-A15 A15-CWH A15-ARP23
Figure 1. Hyphal compatibility interactions: (A) compatible, A15-A15; (B) competitive, A15-CWH and (C) antagonistic, A15-ARP23.
Strain A Strain B Strain C Strain D Strain E
Rep 1 Rep 2 Rep 3 Rep 1 Rep 2 Rep 3 Rep 1 Rep 2 Rep 3 Rep 1 Rep 2 Rep 3 Rep 1 Rep 2 Rep 3
MVX-1153 @Sp
@Ca
- - - - + -
- - - - + -
- - + - - -
- + + + + +
- - - - - +
Figure 2. Hyphal anastomosis between Strain D (left) and MVX-1153 (right).
Figure 3. Detection of AbV16 virus (-/+) in five different mushroom crops following infection with MVX-1153 either at spawning (@ Sp) or at casing (@ Ca).
Virus-Agaricus interaction studies Five strains of A. bisporus were used in the virus interactions studies; Strain D: a modern mid-range hybrid strain and strain A, B, C & E, which were considered to be not very compati- ble with Strain D. All strains (‘acceptors’) were grown in dual culture with strain MVX-1153 (‘donor’), a culture which had been isolated in October 2016 from commercial mushrooms showing MVX brown-cap disease symptoms. Presence or absence of the MVX AbV16 virus was determined by a molecular PCR test once hyphal interactions had taken place between the dual cultures.
There was a high level of anastomosis between Strain D and MVX-1153 in laboratory cultures as expected, as both are standard commercial mid-range hybrid strains that are compatible (Figure 2). Low levels of anastomosis were recorded between MVX-1153 and Strains A, B, C & E, but these were enough to allow MVX AbV16 to be detected in the mycelium of all of them. Under cropping conditions, the AbV16 virus was
34 MUSHROOM BUSINESS
less effectively transmitted to the Strains A, B, C & E, with only an occasional mushroom being positive. Nonetheless, positive results were obtained for ALL strains, indicating that trans- mission had nonetheless taken place (Figure 3). Thus virus transmission between different A. bisporus strains, irrespective of their compati- bility status, would appear to be difficult to pre- vent. These results again show the challenges associated with developing an effective A. bisporus ‘virus breaker’ strain.
Despite the fact that viruses were shown to be transmitted between different, apparently ‘incompatible’ A. bisporus strains, the good news is that each strain responded differently to infection with MVX viruses at a genetic and protein level. In Strain D, representative of currently grown A. bisporus strains worldwide, this was reflected in heightened cellular stress responses, upsetting normal processes in the mycelium. Strain C fruit bodies, which were less susceptible to MVX, demonstrated a variety of antiviral activities when AbV16 was present, including high levels of antiviral proteins and
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