Screening Trichoderma species for biological control activity against Phytophthora ramorum in soil

• Trichoderma spp. were screened in vitro for antagonism towards Phytophthora ramorum.
• Soil bioassays showed two isolates remediated soil infested with P. ramorum.
• Potential to commercialize T. asperellum for biological control of P. ramorum.

Despite efforts of eradication and sanitation, Phytophthora ramorum persists in the United States and abroad. Fungicides have limited effectiveness, but there are concerns that they may only inhibit pathogen growth and hasten resistance development after repeated fungicide applications. Biological control is an active control measure that can work continuously as long as the agent is alive and active. The goal of this study was to examine whether Trichoderma spp. have the potential as a biological control agent against P. ramorum. Sixteen Trichoderma spp. isolates were screened for mycoparasitism of P. ramorum in a dual culture assay. The different Trichoderma spp. isolates demonstrated variable mycoparasitic activities with some isolates showing no activity while others completely eliminated the pathogen after 4 weeks. Seven isolates of T. asperellum were consistent among replicated trials in eliminating recovery of P. ramorum from the exposed agar plugs and preventing leaf disk necrosis. Further testing of six T. asperellum isolates against two different P. ramorum isolates (A1 and A2 mating types) resulted in the same high level of mycoparasitic activity. Soil assays involving P. ramorum-infested potting mix and selected Trichoderma spp. isolates demonstrated that two isolates (04-22 and 02-64) were consistent among the repetitions to eliminate P. ramorum propagules to non-detectable levels. Based on these results, specific T. asperellum isolates have the potential to remediate P. ramorum-infested soil and have the potential to be developed into a commercially-viable product.

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