Molecular characterization of pythium populatins in ornamental greenhouse and nursery crops

Description: Pythium species are ubiquitous pathogens that cause root rots, black leg of cuttings, and damping-off of seedlings in ornamentals and forest nurseries. Pythium inoculum can be present in plant materials, water, and soilless potting mixes used in floricultural operations. Epidemiological studies of Pythium diseases in ornamentals are challenging because of the diversity of crops involved, the multitude of potential sources of inoculum, and the difficulty of species identification. Overlapping morphological characteristics and the existence of cryptic species make species identification an arduous process, even for experienced diagnosticians. This study identified species and characterized Pythium populations fluctuation in floricultural greenhouses and forest nurseries, additionally the phylogeny of the Pythium irregulare species complex was studied. Isolates were collected from diverse plant hosts. Species morphological identifications were verified by DNA sequencing of the ITS region, including the 5.8S rDNA. DNA sequence analysis of Pythium isolates P. irregulare sensu lato as the most prevalent species. Phylogenetic analysis of P. irregulare s.l. complex revealed four discrete clades within the complex, supporting the species status of P. irregulare s.s. and P. cryptoirregulare and provide additional support for the designation of P. ?vipa? as species distinct from P. irregulare s.s..

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