Daily Fluctuations of Chlorophyll Efficiency of Dark-adapted Rhododendron and Kidney Beans

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. 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). However, to determine the most effective time of day for replicate measurements of chlorophyll activity, we designed this study to determine if daily circadian rhythm impacts chlorophyll activity as measured by Fv/Fm values in dark-adapted Rhododendron and kidney bean plants. Data were collected using a LI-COR 6400 Leaf Chamber Fluorometer (LI-COR, Lincoln, NE). Chlorophyll activity for Rhododendron foliage resulted in no measurable differences (P < 0.05) in Fv/Fm of 0.800 at 0700 hours to 0.785 at 1930 hours. Chlorophyll activity for kidney bean decreased linearly from Fv/Fm of 0.800 at 07300 hours to 0.780 at 1930 hours. These results indicate that the time of day does not significantly influence chlorophyll activity for dark adapted Rhododendron and kidney bean plants.