| dc.description.abstract | Trichoderma hamatum GD12 is a beneficial soil fungus attracting agricultural interest due to its ability to promote plant growth and elicit biocontrol against a range of fungal pathogens. Evidence suggests volatile organic compounds (VOCs) produced by beneficial fungi can play a role in these biological activities. Two previously generated mutants of T. hamatum GD12 demonstrate enhanced plant growth promotion and antagonism against a range of pathogens, respectively, for which differences in VOC production could be responsible. The N-acetyl-β-D-glucosaminidase deficient mutant of T. hamatum GD12 (ΔThnag::hph) showed enhanced growth promotion of lettuce, relative to T hamatum GD12. Moreover, ΔThnag::hph demonstrated a loss of biocontrol activity against the fungal pathogen Sclerotinia sclerotiorum. Deletion of Heterochromatin Remodelling Protein 1 (ΔThhepA::hph) showed enhanced antagonism against a range of fungal pathogens, showing chemical zones of antibiosis against the pathogens, suggesting enhanced production of inhibitory compounds. However, the involvement of VOCs in these biological activities is currently unknown. VOC analysis demonstrated quantitative and qualitative differences in VOC production across the three strains of T. hamatum, which could relate to their unique biological activities. Moreover, during the physical interaction of T. hamatum with S. sclerotiorum, significant changes in VOC production were observed relative to controls, including the de novo production of VOCs which were absent in controls, indicating ordinarily silent secondary metabolite clusters in T. hamatum GD12 are activated by the presence of S. sclerotiorum. To date, studies investigating microbial VOC production sample VOCs from fungi inoculated in vitro, which does not reflect the heterogenous environment where soil fungi usually reside. Here, plastic tubing coated in a sorptive fibre (polydimethylsiloxane (PDMS)) was effective at capturing T. hamatum VOCs directly from peat microcosms. During the interaction of T. hamatum with S. sclerotiorum in soil microcosms, PDMS tubing detected quantitative changes in VOC production, showing increases in the production of VOCs in co-cultured microcosms relative to axenic microcosms. Finally, a novel VOC is overproduced by the ΔThnag::hph mutant relative to GD12 and ΔThhepA::hph, potentially playing a role in the enhanced plant growth promotion observed. Taken together, this thesis provides a clearer understanding of the VOCs involved in the enhanced biocontrol and plant growth promoting capabilities of T. hamatum GD12. | en_GB |
