Inducible Volatile Chemical Signalling Drives Antifungal Activity of <scp> <i>Trichoderma hamatum</i> GD12 </scp> During Confrontation With the Pathogen <scp> <i>Sclerotinia sclerotiorum</i> </scp>

The use of beneficial soil fungi or their natural products offers a more sustainable alternative to synthetic fungicides for pathogen management in crops. Volatile organic compounds (VOCs) produced by such fungi act as semiochemicals that inhibit pathogens, with VOC production influenced by physical interactions between competing fungi. This study explores the interaction between the beneficial soil fungus Trichoderma hamatum GD12 strain (GD12), previously shown to antagonise crop pathogens such as Sclerotinia sclerotiorum, to test the hypothesis that its antagonistic effect is mediated by volatile chemical signalling. In dual-culture confrontation assays, co-inoculation of GD12 and S. sclerotiorum led to fungistatic interactions after 7 days. VOCs collected from individual and co-cultures were analysed by gas chromatography-flame ionisation detector (GC-FID) analysis and coupled GC-mass spectrometry (GC-MS), revealing significant differences in VOC production between treatments, with VOC production notably upregulated in the GD12 + S. sclerotiorum co-culture. Peak VOC production occurred 17 days post-inoculation. Synthetic VOC assays revealed several compounds inhibitory to S. sclerotiorum, including 1-octen-3-one, which also arrested the growth of other fungal crop pathogens (Botrytis cinerea, Pyrenopeziza brassicae, and Gaeumannomyces tritici). Structural insights into 1-octen-3-one's antifungal activity against S. sclerotiorum are also presented. These findings support the hypothesis that the antagonistic properties of T. hamatum GD12 against crop fungal pathogens can, in part, be attributed to VOC production. Further research is needed to assess the potential of these semiochemicals as tools for pathogen management in agriculture.