Characterisation of Trichoderma isolates as agents for engineering disease suppressive composted growing media

Six isolates of Trichoderma were assessed for suitable attributes for potential inoculation into composted material to develop disease suppressive growing media. Each isolate had previously been shown to possess in vitro suppressive properties against root-rot diseases via the production of inhibitory secondary metabolites. In the present study, isolates were further investigated for in vitro mycoparasitic properties and in vivo suppression of the pathogens Pythium ultimum and Fusarium oxysporum. Mycelial growth of each isolate was also tested in vitro on potato dextrose agar (PDA) against ranges of abiotic properties found in composted materials, such as electrical conductivity (EC), pH and temperature. Four of the six isolates displayed no reduced growth on PDA medium with EC values of 9.45 mS cm‑1, with two isolates showing slightly reduced growth. pH was found to have a much more influential effect on mycelia growth, with only two of six isolates displaying uninterrupted in vitro growth across a range of pH6 to pH10. The Trichoderma isolate CS30-01 was found to be the sole isolate with identifiable mycoparasitic properties in vitro. Isolate CS30-01 also displayed no reduced growth at the EC and pH ranges tested. Temperature tests found isolate CS30-01 to possess the highest tolerance at 37°C, while also displaying good growth across a temperature range of 15-35°C. Inoculation of a peat based growing medium with a suspension of CS30-01 spores had no negative effects on plant germination or growth, and indicated co-incubation of CS30-01 and P. ultimum significantly reduced disease severity (P=0.005) on Brassica rapa seedlings. Evidence of suppression of F. oxysporum disease severity on Allium cepa was observed, but not found to be statistically significant. The results from this study indicate that the isolate CS30-01, identified as a strain of T. harzianum, possesses suitable biocontrol and growth properties for developing disease suppressive growing media.