Effect of environmental conditions and lesion age on sporulation of Phytophthora ramorum on California bay, rhododendron, and camellia.

Author , ,
Date 2011.
Publication Phytopathology 101:S177.
Key Words
AbstractPhytophthora ramorum is the causal agent of the disease known as Sudden Oak Death (SOD). The objective of our research was to determine the environmental conditions and lesion age favorable for Phytophthora ramorum sporulation under field conditions. For two years, new camellia, rhododendron, California bay (Umbellaria californica) nursery stock were seasonally inoculated (every 3 months) on foliage. They were covered overhead to prevent rainfall from falling on the plants, but otherwise the plants were completely open to the natural environment. Consistent leaf wetness periods were produced with overhead misting systems and controlling sensors to simulate rainfall, fog, dew, or other conditions that might be supportive of sporulation in an irrigated nursery or landscape. For each season, these wetness conditions began when leaf lesions were 3, 6 and 9 weeks old and, at each of these time points, the wetness conditions were maintained for 8 days. Sporulation was evaluated by washing leaf lesions before the wet period began and at 1, 2, 4 and 8 days during the wet period. Leaf wetness and temperature were measured near the plants. For rhododendron, a Poisson regression model demonstrated that sporulation decreased with increasing lesion age. Sporulation increased with increasing consecutive hours of leaf wetness up to about 48 hours. Sporulation decreased with higher maximum temperatures. Sporulation often occurred when leaves were coated with naturally forming dew.
Full Citation Tjosvold, S.; Chambers, D.; and Mori, S. 2011. Effect of environmental conditions and lesion age on sporulation of Phytophthora ramorum on California bay, rhododendron, and camellia. Phytopathology 101:S177.