Surveys of nurseries, forests and waterways in Minnesota revealed the presence of 14 new records of Phytophthora species

Many Phytophthora species are plant pathogens with the capacity to inflict extensive damage and economic losses in nurseries, forest stands and other urban and natural landscapes. This survey aimed to study the Phytophthora species present in Minnesota, USA, and assess the potential damage these Phytophthora could cause to Minnesota’s urban and natural environments. From 2020 to 2023, soil, plant biomass and water were collected from managed and natural forests, nurseries and natural and manmade waterways from 15 counties in Minnesota. Forest sampling was done on stands of trees that had visible signs of stress with some canopy defoliation, canopy chlorosis or tree mortality. Soil and water samples were baited with rhododendron leaves or pears to isolate Phytophthora. Necrotic plant tissue from baits and symptomatic plant tissue collected in the field were cultured on PARPH, a selective medium for Phytophthora. Genetic sequencing was performed to ascertain the presence and specific identities of Phytophthora species. The survey identified 22 Phytophthora species across 15 counties in Minnesota. Of note, 14 species were identified that had not been previously recorded in Minnesota. Several of the species found may have the capability to cause serious damage to woody plants. Additional studies will determine their potential threat.