Submitted to: Phytopathology
Publication Type: Abstract Only
Publication Acceptance Date: March 25, 2009
Publication Date: June 1, 2009
Citation: Tooley, P.W., Browning, M.E. 2009. Sporulation capacity of Phytophthora ramorum on northern red oak and chestnut oak. Phytopathology. 99:S05. Technical Abstract: Branches from six 2 to 3-year old northern red and chestnut oak seedlings were dip-inoculated with ca. 5,000 sporangia per milliliter of Phytophthora ramorum isolate Pr-6 and incubated at 100 percent relative humidity in dew chambers for 6 days. Three plants were then used to assess sporangia production, while the other three plants were used to assess chlamydospore production. Sporangia production was evaluated by incubating infected seedlings in a mist chamber and collecting sporangia produced on four misted leaves per plant suspended over 15 micron-diameter nylon mesh screens. Chlamydospore content of leaf disks (6 millimeter diameter) removed from diseased leaves following one month incubation in a greenhouse was also determined. Chestnut oak exhibited significantly greater disease incidence and severity compared with northern red oak. However, sporulation levels were observed to be much larger in northern red oak. Total sporangia production per plant was not significantly different between the two species but when adjusted by lesion area, northern red oak produced 2294 sporangia per square centimeter compared with only 259 sporangia per square centimeter for chestnut oak. Mean chlamydospore production per 6 millimeter-diameter leaf disk also was significantly greater for northern red oak compared with chestnut oak (28 versus 1 chlamydospore per disk). Knowledge of P. ramorum sporulation capacity in relation to disease incidence and severity on Eastern U.S. oak species will help determine the potential for epidemic development should the pathogen be introduced.