Submitted to: Sudden Oak Death Science Symposium
Publication Type: Proceedings
Publication Acceptance Date: 6/10/2009
Publication Date: N/A
Technical Abstract: 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 resistance may develop. 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 asperellum isolates are mycoparasitic on P. ramorum. Sixteen isolates of Trichoderma asperellum and other Trichoderma spp. that have demonstrated antagonism towards other Phytophthora spp., or were suspected to have mycoparasitic activity were selected. The rate of mycoparasitism was determined by overlaying a strip of Trichoderma-colonized agar on a V8 agar plate colonized by P. ramorum (A2 mating type). Every 7 days, for 4 weeks, agar plugs were removed and transferred to V8 agar amended with benomyl (V8+B) or on a wounded leaf disk of Rhododendron ‘Cunningham’s White.’ Control plugs of P. ramorum, without exposure to the Trichoderma spp., always showed growth on V8+B and produced necrosis on the leaf disks. The different Trichoderma spp. isolates demonstrated variable mycoparasitic activities. Some isolates showed no inhibition of P. ramorum growth on V8+B or reduction in necrosis even from plugs removed directly below the Trichoderma strip. Other isolates showed a reduction in growth and necrosis over time, but still did not completely eliminate the pathogen after 4 weeks. Six isolates of T. asperellum were consistent among replicated trials in eliminating growth of P. ramorum from the agar plugs and preventing leaf disk necrosis within 2 weeks exposure. Further testing of four of these six T. asperellum isolates against two different P. ramorum isolates (A1 and A2 mating types) resulted in the same high level of mycoparasitic activity. We believe the results shown here demonstrate that specific T. asperellum isolates have the potential to remediate P. ramorum-infested soil. Tests are on-going to determine whether P. ramorum soil populations can be eliminated when treated with these isolates.