Etiology of Phytophthora drechsleri and P. nicotianae (=P. parasitica) Diseases Affecting Floriculture Crops

Phytophthora nicotianae and P. drechsleri isolates (n = 413) recovered from eight floricultural hosts at 11 different production sites were described according to compatibility type, resistance to mefenoxam, and amplified fragment length polymorphism (AFLP) profiles. Sample sizes ranged from 2 to 120. In all cases, isolates recovered from a single facility had the same compatibility type and resistance to mefenoxam. AFLP analysis indicated that six clonal lineages of P. nicotianae and two clonal lineages of P. drechsleri were responsible for the 11 epidemics and that isolates recovered from the same facility were identical. A single clone of P. nicotianae was recovered from snapdragons at two field production sites in the southeastern United States receiving seedlings from the same source. This clone persisted at one site from 2000 to 2001. Another clone was recovered from verbena at three separate greenhouse facilities where one facility was supplying verbena to the other two. These results suggest that asexual reproduction of these pathogens plays an important role in epidemics and spread may occur between distant facilities via movement of plants.