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United States Department of Agriculture

Agricultural Research Service

Title: Evaluation of Viburnum Cultivars for Susceptibility to Phytophthora Ramorum

Authors
item GRUNWALD, NIKLAUS
item Kitner, M - OREGON STATE UNIVERSITY
item Larsen, M - OREGON STATE UNIVERSITY
item Linderman, Robert

Submitted to: Biological and Cultural Tests for Control of Plant Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 9, 2006
Publication Date: April 13, 2006
Citation: Grunwald, N.J., Kitner, M.L., Larsen, M.M., Linderman, R.G. 2006. Evaluation of viburnum cultivars for susceptibility to phytophthora ramorum. Biological and Cultural Tests for Control of Plant Diseases. 23:O006.

Interpretive Summary: The relative susceptibility of 17 Viburnum species and cultivars to the pathogen Phytophthora ramorum causing Ramorum blight on Viburnum was evaluated in detached leaf assays in the laboratory. Because P. ramorum is a regulated pathogen, these experiments currently can only be conducted in detached leaf experiments. Leaves obtained from field-grown Viburnum were detached from cut shoots. Leaves were wound-inoculated with the pathogen. Treatments were incubated in a containment growth chamber at room temperature with a 14-hour light cycle for 8 days. Percent lesion areas were averaged over both isolates and statistically analyzed. Ramorum blight developed on all Viburnum species and cultivars evaluated. All cultivars had less than 30% lesion area in the experiment. Of the 17 cultivars evaluated, 8 had percent lesion areas less than 10% and appear to be the most resistant in detached leaf experiments. Ideally all these plants should be evaluated under field conditions to validate the detached leaf data.

Technical Abstract: The relative susceptibility of 17 Viburnum species and cultivars to Phytophthora ramorum was evaluated in a detached leaf assay in the laboratory. Because P. ramorum is a regulated pathogen, these experiments currently can only be conducted in detached leaf experiments. Leaves were inoculated on 21 Sept 05 with six replications per treatment and isolate. Two isolates, namely D12A (A1 mating type isolated in OR) and 4123 (A2 mating type isolated in OR), were grown on V8 agar for two weeks prior to inoculation. Leaves obtained from field-grown Viburnum were detached from cut shoots and stored overnight at 4°C. Leaves were placed in plastic containers with 300 ml moistened vermiculite. Plants were wound-inoculated with 5mm V8 agar plugs with fresh mycelium or control agar plugs without mycelium and placed upside down on the wound site. Treatments were incubated in a containment growth chamber at 20°C with a 14-hour light cycle for 8 days. Percent lesion areas were averaged over both isolates and subjected to analysis of variance. Ramorum blight developed on all Viburnum species and cultivars evaluated. The factor cultivar had a significant effect on percent lesion area (P < 0.05). All cultivars had less than 30% lesion area in the experiment. Of the 17 cultivars evaluated, 8 had percent lesion areas less than 10% and appear to be the most resistant in detached leaf experiments. Ideally all these plants should be evaluated under field conditions to validate the detached leaf data. The data from this experiment were developed under quarantine containment conditions for this pathogen and will be repeated at other times of the year using sporangia or zoospores as inoculum.

Last Modified: 9/29/2014
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