Submitted to: Phytopathology
Publication Type: Abstract Only
Publication Acceptance Date: 5/20/2010
Publication Date: 6/1/2010
Citation: Widmer, T.L., Shishkoff, N., Dodge, S.C. 2010. Root susceptibility and inoculum production from roots of eastern oak species to Phytophthora ramorum. Phytopathology. 100/S136. Interpretive Summary:
Technical Abstract: 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. Oak radicles of several eastern oak species were exposed to zoospore suspensions of 1, 10, 100, or 1000 zoospores per ml at 20 degrees C. After 24 hours, the radicles were rinsed in water, planted in pots and placed in the greenhouse. After 4 weeks, the roots were removed, 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 on roots, sprouted oak acorns were inoculated with sporangia, washed after 24 hours and transplanted into 2 x 2 inch pots containing Turface®. Over time, 20-25 ml 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. Colonization of roots was lower than that in V. tinus. After 35-days, results were similar. This study shows that sprouted oak acorns are very susceptible to P. ramorum under controlled greenhouse conditions and may have epidemiological significance.