Root susceptibility and inoculum production from roots of eastern oak species to Phytophthora ramorum

• Published in: Phytopathology Vol. 100; no. 6; p. S136
• Main Authors: Widmer, T L, Shishkoff, N, Dodge, S
• Format: Journal Article
• Language: English
• Published: 01-06-2010
• Subjects: Phytophthora; Viburnum tinus
• ISSN: 0031-949X

Little is known about root susceptibility of eastern tree species to Phytophthora ramorum. In this study, we examined root susceptibility and inoculum production from roots. Roots of sprouted acorns for several eastern oak species were exposed to zoospore suspensions of 1, 10, 100, or 1000 zoospores per ml at 20C. After 24 h, roots were removed, rinsed in water, planted in pots and placed in the greenhouse. After 4 weeks, the roots were surface sterilized and plated on PARPH+V8 medium. A root was recorded as positive if P. ramorum was observed on the medium. Infection of oak radicles occurred at a concentration as low as 1 zoospore per ml. Differences were observed among the species tested. To test inoculum production, the roots of oak seedlings were inoculated with sporangia, washed after 24 hr and transplanted into 2 x 2 inch pots containing Turface+. Periodically, 20-25 ml samples of runoff were collected from each pot and plated on PARPH; the resulting colonies were counted. Counts from oaks were compared to a positive control, Viburnum tinus, using regression analysis. Root segments were plated to calculate percent colonization. After 16 days, inoculum production from oak seedlings was variable and lower than V. tinus, as was colonization of roots. After 35-days, results were similar. This study shows that sprouted oak acorns are very susceptible to P. ramorum and may be important epidemiologically under natural environmental conditions.