Detection of Phytophthora ramorum Blight in Oregon Nurseries and Completion of Koch's Postulates on Pieris, Rhododendron, Viburnum, and Camellia

Phytophthora ramorum, the cause of sudden oak death in California and Oregon coastal forests and ramorum blight in European nurseries and landscapes (1), was detected in six Oregon nurseries in Jackson, Clackamas, and Washington counties from May to June 2003. The pathogen was isolated from: Viburnum bodnantense ‘Dawn’, V. plicatum var. tomentosum ‘Mariesii’, Pieris japonica × formosa ‘Forest Flame’, P. japonica ‘Variegata’ and ‘Flaming Silver’, P. floribunda × japonica ‘Brouwer's Beauty’, Camellia sasanqua ‘Bonanza’ and other cultivars, C. japonica, and Rhododendron × ‘Unique’. Samples of symptomatic tissues were plated on a Phytophthora-selective medium (PARP) and tested by polymerase chain reaction (PCR) (3). All samples positive for P. ramorum with PCR yielded P. ramorum isolates in culture. The isolates have the European genotype, mating type A1, except for the Camellia spp. isolates, which have the North American genotype, mating type A2 (2). Isolates are deposited in the American Type Culture Colle...