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Spatiotemporal dynamics of Phytophthora and Pythium communities in recycled irrigation water in a container nursery

Neelam Redekar: Oregon State University

<div>Recycling of irrigation water reduces crop production costs, but increases the risk of disease from waterborne plant pathogenic oomycetes. In a year-long study, we examined oomycetes in irrigation water sources within a commercial container nursery in Oregon. We compared filtration and leaf baiting methods using a metabarcoding approach. ITS1-amplicons were amplified from DNA on filters and rhododendron leaf baits, followed by Illumina MiSeq sequencing and analysis using manually curated sequences of oomycetes. We detected high OTU abundance of <em>Phytophthora citricola</em>-complex, <em>P. syringae, P. parsiana</em>-complex, <em>P. chlamydospora, P. gonapodyides, P. irrigata,</em> <em>P.</em> taxon oaksoil-complex, <em>P. citrophthora</em>-complex, <em>P. megasperma</em>-complex, <em>Pythium condricola</em>-complex, <em>Pythium dissotocum</em>-complex, and <em>Phytopythium litorale-</em>complex. The leaf baiting method was more selective for biologically active, plant-associated <em>Phytophthora</em> and a few <em>Pythium</em> and <em>Phytopythium</em> species, but did not capture the entire spectrum of oomycetes detected by filtration. Species diversity and biological activity were highly influenced by season, with the greatest number of biologically active species detected in the winter and the fewest in the summer. The metabarcoding approach allowed spatiotemporal analysis of oomycete communities, contributing insights on pathogen load and dissemination, facilitating evaluation of disease risks associated with the use of recycled irrigation water.</div>