2013 ASHS Annual Conference

Phytophthora ramorum is a major risk to interstate trade of nursery stock. Our work focuses on chemical oxidant chemistry as a disinfectant on nursery grown Rhododendron species. Disinfection of the plant is crucial, but the impact on plant health and phytotoxic responses are also important. To determine plant stress responses to applied chemical oxidants, we are measuring chlorophyll activity (PSII quantum efficiency) as measured by Fv/Fm values in dark-adapted camellia plants. Data were collected using a Li-Cor 6400 Leaf Chamber Fluorometer (Li-Cor, Lincoln, NE) to evaluate the potential phytotoxicity of Camellia to ClO₂ and H₂O₂ at various concentrations, with or without the surfactant sarcosinate, and consecutive sprays. Chlorophyll activity (Fv/Fm) of dark adapted camellia foliage was greater when ClO₂ and H₂O₂ were applied with the surfactant sarcosinate to camellia foliage. Chlorophyll activity decreased with increasing concentrations of ClO₂ increased when sarcosinate was not present. No differences between ClO₂ and H₂O₂ solutions at the similar concentrations were observed. Visual injury of the camellia foliage increased with each subsequent spray application; however, foliar injury did not exceed a marketable threshold for most treatments, until after four or five consecutive spray applications at 400 mg·L^-1 ClO₂, with or without surfactant.