Volume 19 Part 1 Article 14: Growth, dispersal and impact on yield of Agaricus bisporus by Trichoderma aggressivum during bulk spawn run.

Volume 19 Part 1 Article 14
Year 2016
Title: Growth, dispersal and impact on yield of Agaricus bisporus by Trichoderma aggressivum during bulk spawn run.
Author: Mairéad Kilpatrick, Caoimhe Fleming-Archibald, David Burns, Stephen Sturgeon, Paula McPoland and Helen Grogan

Abstract:
A long and complex association between Trichoderma and Agaricus mushroom cultivation in the Irish mushroom industry began in 1985 when ‘compost green mould’ reached epidemic proportions in the Phase II bag cultivation system. The causative agent, identified as Trichoderma aggressivum f. europaeum was initially associated only with outbreaks in in-situ growing systems (bags, trays, or shelves) until spring 2006 when the disease reached the technologically advanced bulk spawn-run (Phase III) systems in Europe with devastating consequences. Sporadic outbreaks since then highlighted a knowledge gap of how T. aggressivum behaves within the Phase III system.

This work focussed on characterising the growth, dispersal and impact on yield of T. aggressivum in bulk-incubation tunnels. Experimental mini composting tunnels were subdivided along vertical and horizontal planes with Trichoderma infected spawn grains positioned in the back, lower quadrant. When compost was removed from the mini-tunnels in an artificial unmixed procedure, distances travelled by T. aggressivum within the bulk spawn-run were generally limited to just ca 0.5 -1.0 m. T. aggressivum was not generally visible at the end of bulk spawn-run. The severity of the subsequent mushroom crop yield losses was highly correlated with the position of the compost in the tunnel relative to the point of inoculation. These initial compost trials increased our understanding of how far and in what direction Trichoderma can grow during the 17 day bulk spawn-run period.

A subsequent series of trials incorporated bulk handling operations similar to those carried out at commercial premises. Yield losses were highly correlated with the degree of compost mixing and indicated that T. aggressivum can readily infect and colonise otherwise healthy, productive mushroom compost evidenced by yields of 25 – 34 kg m2-1 in the control compost. Further, the use of equipment that had handled T. aggressivum infected compost was shown to infect clean compost from adjacent newly opened tunnels, spreading the infection further. Crucially, studies have now confirmed that fully colonised phase III compost is susceptible to T. aggressivum infection.

Results indicate that the bulk spawn-run process potentially increases the risk of a small compost infection becoming a serious disease outbreak, however not as a result of significant growth within the compost during the 17 day spawn-run but as a direct consequence of the bulk handling and mixing operations that disperse and spread small infections through much larger compost masses.

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