Identification and mefenoxam sensitivity of oomycete root pathogens recovered from ornamental plants in Georgia

Mefenoxam is a fungicide widely used in the greenhouse and ornamental industry to control Pythium and Phytophthora diseases. Mefenoxam insensitivity was reported in several states in the USA. The objectives of this study were to identify oomycete root pathogen species recovered from ornamental plant nurseries in Georgia, and to determine if any isolates were insensitive to mefenoxam fungicide. Isolates were collected from 42 plant species and identified based upon morphological characteristics and rDNA ITS region sequencing. The 117 isolates recovered included seven species of Phytophthora, nine species of Pythium, and four species of Phytopythium. Mefenoxam sensitivity screening was conducted in vitro. Mefenoxam insensitivity was identified in 45.3% of the 117 isolates corresponding to 7.7%, 54.3%, and 70% of the Phytophthora, Pythium, and Phytopythium spp. isolates, respectively. This is the first report of Phytopythium spp. recovery from ornamental plants and of mefenoxam insensitivity in Pythium spp. and Phytopythium spp. in Georgia.