Identification and characterization of Pythium, Globisporangium, and Phytopythium species present in floricultural crops from Long Island, New York

Several Pythium, Globisporangium and Phytopythium species cause Pythium diseases in greenhouse floricultural crops, resulting in significant seasonal losses. Four hundred eighteen Pythium, Globisporangium and Phytopythium isolates from flowering crops, growing media, or bench and floor debris were collected from Long Island greenhouses or clinic samples between 2002 and 2013. Isolates were identified to species based on morphology and ITS barcoding. Twenty-two species of Pythium, Phytopythium and Globisporangium were identified, with Globisporangium irregulare sensu lato being the most common. To determine the origin of inoculum during the 2011 cropping season, eleven microsatellite loci were analyzed in 124 G. irregulare s.l. isolates collected in four greenhouses and six previously collected from clinic samples. Cluster analyses grouped G. irregulare s.l. isolates into four groups: G. irregulare sensu stricto, plus three G. cryptoirregulare clusters. Population structure defined by greenhouse and host was found in two clades. Additionally, the population dynamics of G. irregulare s.l. isolates associated with Pelargonium spp. from 2011 to 2013 were examined using 85 isolates and nine informative microsatellite loci, to assess inoculum survival over multiple cropping seasons. Although most isolates had unique genotypes, closely related genotypes were found in the same locations over different years. Our results indicate that G. irregulare s.l. inocula have local as well as remote origins. Isolates may be initially brought into ornamental operations from common sources, such as infected plant materials or infested potting mixes. Our results support the hypothesis that established strains can serve as inocula and survive in greenhouse facilities over multiple seasons.