Evaluation of several commercial biocontrol products on European and North American populations ofPhytophthora ramorum

Abstract

Five commercially available biological control products were tested in vitro with seven isolates of Phytophthora ramorum from North American (NA1, NA2), and European (EU1) populations. The in vitro tests included dual culture methods and detached leaf assays on wounded Rhododendron and Camellia leaves. Variability in response to biocontrol agents among isolates of P. ramorum from North American and European populations was examined. In dual culture tests, both Bacillus subtilis products (Companion † and Serenade † ) resulted in better inhibition of the NA1 group than NA2 and EU1. Actinovate † (Streptomyces lydicus) was the least effective of the three bacterial biocontrol agents and there was no difference in percent inhibition among P. ramorum lineages. Two products containing Trichoderma spp. were tested: Plant Helper † (T. atroviride) caused 100% inhibition of all lineages of P. ramorum, while SoilGard TM (T. virens) was only about 30% effective. There was great variability among P. ramorum isolates in their response to biocontrol agents. All treatments reduced P. ramorum lesion size on both Rhododendron and Camellia. Combined treatments of Actinovate † with one other BCA did not perform as well as either treatment used individually. Best results were obtained with Serenade † on Rhododendron and Camellia foliage, especially against the NA1 group. Lack of a linear relationship between percent inhibition of P. ramorum by BCAs in vitro and foliar treatments on detached Rhododendron and Camellia leaves indicates that in vitro testing is a poor predictor of BCA performance on plant material.

Scientific Opinion on the Pest Risk Analysis onPhytophthora ramorumprepared by the FP6 project RAPRA

“…A study by Elliott et al (2009a) on the biocontrol options for P. ramorum reports that control of P. ramorum on Rhododendron foliage with BCAs was comparable to the one obtained with some contact fungicides, although it was lower than with systemic fungicides tested in the study by Wagner and colleagues, which was cited in the RAPRA report. Nevertheless, Elliott et al (2009a) point out that with fungicides there is an issue of resistance development, as well of course as environmental and toxicity considerations.…”

“…On this point, it is interesting that the majority of Belgian P. ramorum isolates have become resistant to metalaxyl One problem in adopting BCAs as a control strategy for P. ramorum may be that there was great variability among P. ramorum isolates in their response to the commercial Biocontrol Agents (BCAs) tested (Elliott et al, 2009a). However, there is certainly some potential as all treatments reduced P. ramorum lesion size on both Rhododendron and Camellia (Elliott et al, 2009a).…”

“…However, there is certainly some potential as all treatments reduced P. ramorum lesion size on both Rhododendron and Camellia (Elliott et al, 2009a). The study also tested various BCAs in combination but compared the combinations with the most effective treatment.…”

“…Nevertheless, Elliott et al (2009a) point out that with fungicides there is an issue of resistance development, as well of course as environmental and toxicity considerations.…”

In vivostudies evaluating commercial biofungicide suppression of blight caused byPhytophthora ramorumin selected ornamentals

“…In Canada only fosetyl-Al (Aliette † ; Bayer CropScience Inc., Canada) was registered for control of P. ramorum at the time of this study. Elliott et al (2009) conducted in vitro tests (dual culture and detached-leaf assays) using commercially-prepared biological control products. They found that biofungicides containing Trichoderma spp.…”