INFLUENCE OF MEDIA TYPE ON ANTAGONISTIC MODES OF TRICHODERMA SPP AGAINST WOOD DECAY BASIDIOMYCETES

Screening is an essential first stage in the development of any biolog ical control agent and the results presented here illustrate the need for careful selection of appropriate media for this purpose, The low n utrient medium used here is more representative of the nutritional sta tus within wood (C:N ratio is approximately 410:1 which falls within t he range found within wood 350:1 to 1250:1) in terms of being low in n utrients and therefore antagonism exhibited in such a medium might be expected to be similar to that occurring in the natural substrate. Tri choderma isolates that can inhibit growth of decay fungi and/or kill b asidiomycetes in the low nutrient media may therefore prove to be bett er biological control agents in situ. The results also stress the need for careful selection of Trichoderma isolates due to the variability that exists even within strains of the same species. Target specificit y of the antagonist also needs consideration. More effective control o f decay in creosoted electrical distribution poles may be achieved by using strains of Trichoderma that are targeted specifically to Neolent inus lepideus. Analysis of all antagonistic mechanisms of the Trichode rma isolates show that they can be antagonistic to the fungi in varyin g degrees through a multiplicity of mechanisms, i.e., inhibitory solub le metabolites. inhibitory volatiles. lytic enzymes and iron competiti on. Despite the fact that these various modes of antagonism are known, the precise mechanism by which Trichoderma species control decay fung i in wood has not been identified to date. It is essential to establis h the mechanisms that are active in situ in order that appropriate met hods can be developed for screening biological control agents. It is o bvious from the results of this study that careful selection of media will be an essential part of the developmental process particularly if screening is designed to assess the effect of individual modes of ant agonism.