Phytophthora Species Recovered From Irrigation Reservoirs in Mississippi and Alabama Nurseries and Pathogenicity of Three New Species

From a survey for Phytophthora spp. in containment basins at one nursery each in Alabama and Mississippi, eight species and one taxon were recovered, with Phytophthora gonapodyides dominant in cooler months and P. hydropathica in warmer months, accounting for 39.6 and 46.6% overall recovery, respectively. Among the recoveries were P. macilentosa, P. mississippiae, and P. stricta, three new species recently described from a small lake (labeled M4) that serves as a primary water source for irrigation and to feed another irrigation pond (M5) at the Mississippi nursery. Neither of ponds M4 and M5 directly receives runoff from any production area. The three new species were tested for pathogenicity with Catharanthus roseus, Gardenia jasminoides 'August Beauty,' Hydrangea quercifolia 'Semmes Beauty,' Ilex magland 'Oakland,' Pieris japonica 'Mountain Snow,' and Rhododendron x 'Brandi Michele Raley.' None of the three species infected any of the test plants or became established in peat or pine bark growing media. Based on the result of pathogenicity trials as well as the field observation that none of the nine Phytophthora taxa recovered from irrigation reservoirs have caused episodic disease in the nurseries, they appear to not present a high risk to ornamental plants at those nurseries.