P-644 - Identification and genotyping of Phytophthora nicotianae and other Phytophthora species found in floriculture crops in North Carolina

Phytophthora spp. are known to impact floriculture crop production in NC and globally. To better understand the Phytophthora species diversity in NC, 32 greenhouses were surveyed from 2021 to 2023 and eight isolates of Phytophthora spp. from floriculture samples submitted to the NC State Plant Disease and Insect clinic from 2017 to 2023 were also included. Eighty-five isolates of five species of Phytophthora were recovered from 6 greenhouses and 14 different hosts. Phytophthora nicotianae was the predominant species and was recovered from 5 of the 6 greenhouses and 9 of the 14 hosts. P. heterospora, P. pseudocryptogea, P. drechsleri, and P. tropicalis were recovered from snapdragon and Verbena, Sedum, Chrysanthemum and English ivy, respectively. Analysis of P. nicotianae isolates using microsatellite markers revealed similar genotypes among some greenhouses and hosts which points to pathogen introduction through movement of infected plants. All species were sensitive to oxathiapiprolin (0.00058 ppm) and mefenoxam (100 ppm) except two (4%) isolates of P. nicotianae were resistant to mefenoxam. Sensitivity to cyazofamid varied by species: P. nicotianae and P. pseudocryptogea were sensitive (EC₅₀ < 1 to 186 ppm), P. heterospora and P. tropicalis were moderately sensitive (EC₅₀ = 705 to 820 ppm), and P. drechsleri was resistant (EC₅₀ = 1127 ppm). Resistance to commonly used fungicides among these Phytophthora species is low in NC. Our results emphasize the importance of clean plant material and the value of genotyping Phytophthora spp. to understand pathogen movement.