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United States Department of Agriculture

Agricultural Research Service

Research Project: EXOTIC, EMERGING, RE-EMERGING, AND INVASIVE PLANT DISEASES OF HORTICULTURAL CROPS Title: Susceptibility in Viburnum to Phytophthora ramorum

Authors
item Grunwald, Niklaus
item Kitner, M - OREGON STATE UNIVERSITY
item Mcdonald, V - OREGON STATE UNIVERSITY
item Goss, Erica

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 24, 2007
Publication Date: January 15, 2008
Citation: Grunwald, N.J., Kitner, M., Mcdonald, V., Goss, E.M. 2008. Susceptibility in Viburnum to Phytophthora ramorum. Plant Disease. 92:210-214.

Interpretive Summary: Phytophthora ramorum, the plant pathogen responsible for causing sudden oak death disease on oak and tanoak and Ramorum blight or Ramorum shoot dieback on ornamentals, is a recently emerged pathogen. Viburnum are commonly grown ornamental shrubs known to be susceptible to P. ramorum. The whole genus has been placed on the P. ramorum host list. The range of susceptibility to P. ramorum of Viburnum cultivars is currently not understood. We evaluated whether Viburnum cultivars differ in susceptibility to P. ramorum. The genus Viburnum shows remarkable differences in susceptibility to infection by P. ramorum. Viburnum genotypes differed significantly in susceptibility to P. ramorum in detached leaf inoculations. V. x burkwoodii was consistently the most susceptible host genotype, followed by V. plicatum ‘Mariesii’ and V. lentago. Most cultivars evaluated for resistance to P. ramorum were not susceptible or developed only small lesions as determined under controlled conditions in the laboratory.

Technical Abstract: Phytophthora ramorum, the causal agent of sudden oak death on oak and tanoak and Ramorum blight or Ramorum shoot dieback on ornamentals, is a recently emerged pathogen. Viburnum is a genus of commonly grown ornamental shrubs known to be susceptible to P. ramorum. The whole genus has been placed on the P. ramorum host list. The range of susceptibility of genotypes in the genus is currently not understood. We evaluated whether cultivars in the genus Viburnum differ in susceptibility to P. ramorum in controlled, detached leaf inoculations using two isolates belonging to the two clonal lineages found in Oregon. The genus Viburnum shows remarkable differences in susceptibility to infection by P. ramorum. Viburnum genotypes differed significantly in susceptibility to P. ramorum in detached leaf inoculations. V. x burkwoodii was consistently the most susceptible host genotype, followed by V. plicatum ‘Mariesii’ and V. lentago. Most cultivars evaluated for resistance to P. ramorum were not susceptible or developed only small lesions as determined here with a detached leaf assay. Our work only provides information on leaf based resistance and inferences on epidemic development in whole canopies and under field conditions cannot currently be made.

Last Modified: 10/21/2014
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