First Report of Phytophthora ramorum Infecting Camellia Flower Buds in North America

isolate used for inoculation was recovered locally from an infected rhododendron near Felton, CA. Beginning 20 December 2005, after several rain events, necrotic flower buds on many camellia plants were observed. The flower bud disease became widespread and severe by mid-January 2006 following another extensive rainy period. Infection began on the lowest sepals attached near the flower bud receptacle. Infected sepals contained relatively large areas of necrotic tissue and the lesions were often surrounded by diffuse necrosis (Fig. 1). The infection progressed from the sepals into the receptacle and then further into the flower bud. The petals eventually became completely necrotic within the flower bud. At this stage of disease development, the male flower parts initially appeared unaffected (Fig. 2). Most infected buds never opened, eventually abscised at the receptacle, and were shed. When flower buds fell to the soil, they often broke into many light parts that were observed moving readily with wind gusts. In some cases, the necrosis developed into adjacent vegetative and flower buds via stem tissue but the growth in stem tissue was generally very limited, and was only detected internally about 1 cm from the receptacle of an infected flower bud or vegetative bud (Fig. 3).