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Submitted to: Biological Control
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 8/6/2014 Publication Date: 9/7/2014 Citation: Widmer, T.L. 2014. Screening Trichoderma species for biological control activity against Phytophthora ramorum in soil. Biological Control. 79:43-48. Interpretive Summary: The pathogen that causes Ramorum blight on ornamentals is a concern to native forest species because of the potential to transport this disease throughout the United States. Findings of this pathogen in a nursery often result in the nursery to be placed under quarantine status, which restricts the sale and movement of plant material. It is known that this pathogen can survive in soil and methods to eliminate the pathogen approved by government regulatory agencies, such as chemical fumigation and paving infested areas with cement are expensive and impractical. The use of other microorganisms has been examined in other areas to control soilborne plant diseases but has not been extensively examined as to whether it can eliminate the pathogen that causes Ramorum blight in soil. This study showed that different cultures of a soilborne fungus have the ability to reduce growth of the pathogen when grown together. In addition, some of these cultures also reduced populations of the pathogen in the soil when the fungus was added to infested soil. This research is important in that it shows that remediation of soil containing the pathogen that causes Ramorum blight is possible. This information will be important to researchers, nursery managers and regulatory agencies who are looking for ways to control this disease and limit the spread of the pathogen and is the first step in producing a commercially-viable product. 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 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 their rate of mycoparasitism by overlaying a strip of Trichoderma-colonized agar on a V8 agar plate colonized by P. ramorum. Every 7 days for 4 weeks agar plugs were removed and transferred to V8 agar amended with benomyl (V8+B) or 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 did not completely eliminate the pathogen after 4 weeks. Seven isolates of T. asperellum were consistent among replicated trials in eliminating growth of P. ramorum from the 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. |
