Phytophthora spp. diversity in commercial nursery stocks shown through examination of plant health practices for growers and traders of ornamental plants

Management of Phytophthora in commercial plant nurseries is important for biosecurity of traded plants, and monitoring of incidence of this important plant pathogen is a prerequisite to prevent its spread. Potted plants showing Phytophthora spp. symptoms, and nursery irrigation and runoff water, were sampled from a commercial and a non-commercial nursery in Tuscany, Italy. The samples were processed to detect Phytophthora spp., using baiting, and molecular identification of obtained isolates. High Phytophthora incidence was shown in the commercial nursery. Twelve Phytophthora spp. were isolated from potted plants or nursery runoff water. Individual symptomatic potted plants were infected with up to four pathogenic Phytophthora spp. The water sampled from nursery drainage canals had the greatest Phytophthora species diversity, with less diversity in 'flow-through' water samples (irrigation water percolated through potted plants) and samples from water puddles inside the nurseries. This study showed high incidence of Phytophthora in the commercial nursery, and associated risk of spread of these pathogens within and outside nursery operations. Lack of appropriate disease management probably increases occurrence of these pathogens.