1 results for Ah Chee, Annette

  • Basidiomycete wood decay fungi from Pinus radiata : biology and biological control

    Ah Chee, Annette

    Thesis
    Lincoln University

    A collection of 38 basidiomycete cultures, from New Zealand Pinus radiata and resident fruiting bodies, were screened for wood decay potential using assays of cellulolytic and ligninolytic enzymes in liquid media, wood weight loss, and growth rates on artificial and wood media. Within each assay, there was significant variation observed between the basidiomycete fungi and between isolates of the same species. Correlation analyses found that the predictors of wood weight loss were wood moisture content and external fungal biomass, rot type (brown or white tot) and the production of ligninolytic, but not cellulolytic, enzymes. Isolates of Schizophyllum commune produced high cellulolytic activities but did not cause significant wood weight losses. Although Gloeophyllum sepiarium isolates caused amongst the highest weight losses of P. radiata, they had relatively slow growth rates on artificial and wood media. The brown rot fungus G. sepiarium isolate 5 and the white rot fungi Phlebiopsis gigantean isolate 104 and S. commune isolate 3 were further characterised in growth and wood decay assays. Growth on agar was higher in darkness than in the light, with optimal temperatures of 25 to 30°C. Growth in agar and liquid medium, particularly of G. sepiarium, resulted in significant reductions in pH. Low decay hazard conditions were found to be where wood was not in contact with a moisture- or nutrient-holding substrate whereas high hazard conditions involved green wood or that in soil contact. The three fungi caused little or no weight loss of Eucalyptus regnans or Pseudotsuga menziesii. Biological control systems against basidiomycete fungi were investigated using a collection of 136 Trichoderma fungi from soils of forestry, mill and bush sites in the central North Island of New Zealand, growth media of edible fungi and a HortResearch culture collection. The Trichoderma cultures produced high cellulolytic activities and had fast growth rates on artificial and wood media, but they did not cause significant wood weight losses. Dual culture agar and Pinus radiata-agar assays identified 23 Trichoderma cultures that exhibited antagonism against G. sepiarium and gave significant reductions in Pinus radiata weight loss in wood biological control assays. Less antagonism was observed towards P. gigantea and S. commune. Bioprotection resulted in limited basidiomycete colonisation of Trichoderma precolonised blocks and neighbouring sterile blocks. Biological control resulted in the loss of basidiomycete viability in G. sepiarium-precolonised blocks. Modes of antagonism were investigated for T. crassum isolate 26, T. sp. 'viride' isolate 38 and T. viride isolate 101 cultures which had shown biological control potential against G. sepiarium. Trichoderma crassum 26 had also shown bioprotection potential against Phlebiopsis gigantea. HPLC and GC-MS analyses found that T. viride 101 and T. sp. 'viride' 38 produced 6-pentyl-α-pyrone in low nutrient liquid medium, although no significant volatile inhibition of G. sepiarium was observed in high or low nutrient agar assays. Inhibitory non-volatile compounds were produced on agar, Pinus radiata, and in solvent extracts and fractions of supernatant from Trichoderma cultures grown in low nutrient liquid medium but GC-MS analyses failed to identify any of the compounds. The presence of G. sepiarium was not required to elicit production of these compounds. Trichoderma crassum gave the greatest inhibition of G. sepiarium in bioactivity assays and there was evidence of antibiosis in mycoparasitism assays. Field and controlled temperature room trials showed that significant decay of P. radiata by G. sepiarium was possible over the period of eight months, but biological control interactions were not observed as competition by other microorganisms had limited colonisation by the Trichoderma fungi. This thesis study has shown that basidiomycete fungi from P. radiata can have varied wood decay potential, and significant antagonism can be exhibited towards basidiomycete species by New Zealand isolates of Trichoderma fungi, in artificial and wood media.

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