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United States Department of Agriculture

Agricultural Research Service

Title: Evaluation of Infection Potential and Sporulation of Phytophthora Ramorum on Five Rhododendron Cultivars

item Grunwald, Niklaus
item Linderman, Robert

Submitted to: Phytopathology
Publication Type: Abstract Only
Publication Acceptance Date: April 6, 2006
Publication Date: June 1, 2006
Citation: McDonalad, V., Grunwald, N.J., Linderman, R.G. 2006. Evaluation of infection potential and sporulation of Phytophthora ramorum on five Rhododendron cultivars. Phytopathology. 96:S75.

Technical Abstract: The epidemiology of Phytophthora ramorum, the cause of sudden oak death (SOD) in trees and Ramorum blight on many ornamentals, is poorly understood. Measurements of various fitness parameters of P. ramorum on ornamental nursery crops would increase understanding of how this pathogen spreads in the commercial nursery industry and assist in developing management practices. An evaluation of the susceptibility of five Rhododendron cultivars to P. ramorum was performed using a detached leaf assay. Leaves were wounded on the adaxial side, inoculated with a 20 µl drop of a zoospore suspension and incubated for 10 days in a moist chamber. Measurements of total sporangia per lesion, percent lesion area and incubation period showed significant differences in susceptibility among the five cultivars. In the first trial, ‘Catawbiense boursault’ and ‘Cat. album’ were more susceptible than ‘Lee’s Dark Purple’ and ‘Scintillation’. ‘Minnetonka’ was moderately susceptible. A second experiment confirmed these results with slight differences. Total sporangia produced per lesion under growth chamber conditions ranged from 15 to 1471, and lesion area ranged from 1% to 20% of total leaf area, on moderate to highly susceptible cultivars, respectively. Incubation periods for wound-inoculated leaves ranged between 24-48 hrs.

Last Modified: 4/21/2015
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