Identification, Mefenoxam Sensitivity, and Compatibility Type of Phytophthora spp. Attacking Floriculture Crops in North Carolina

Phytophthora isolates were collected from floriculture crops grown in commercial greenhouses in North Carolina for species identification, compatibility type determination, and mefenoxam sensitivity tests. Isolation from 41 symptomatic plant species at 29 production locations resulted in 483 isolates from eight crops at seven locations. Phytophthora cryptogea (184 isolates) was recovered from dusty miller and gerbera daisy. All isolates of P. cryptogea were insensitive or intermediate in sensitivity to mefenoxam at 1 μg a.i./ml and were A1 compatibility type. P. nicotianae (273 isolates) was isolated from African violet, lavender, pansy, petunia, and vinca. Of these isolates, 21% were insensitive to mefenoxam at either 1 or 100 μg a.i./ml. Isolates of P. nicotianae from five locations were A2 compatibility type, whereas isolates on pansy at one location were A1 compatibility type. English ivy grown at two locations was infected with P. palmivora. All 26 isolates of P. palmivora were sensitive to mefenoxam and were A1 compatibility type. Mating type and mefenoxam sensitivity were uniform among isolates of P. nicotianae and P. palmivora from a given crop at a given location, suggesting that epidemics within a location may have originated from a single source of inoculum.