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Enabling recycled water use: The diversity and management of cryptic oomycete pathogens in recycled irrigation water in Mid-Atlantic nurseries

Justine Beaulieu: University of Maryland

<div>While recycling irrigation water can reduce constraints and costs in nurseries, there is an increased risk of recirculating and spreading waterborne pathogens. Culture-based analysis revealed diverse Oomycetes (16 species) present in recycled pond water at two Mid-Atlantic nurseries in 2015, 2016, and 2017. Of these, <em>Pythium oopapillum</em>, <em>Pythium aff. diclinum,</em> <em>Phytophthora cryptogea </em>and<em> Phytopythium helicoides </em>were all pathogenic in seedling trials (90% damping off). <em>Pythium oopapillum</em>, <em>Ph. cryptogea </em>and <em>Ph. helicoides</em> increased root rot severity in chrysanthemum trials (although differences were not significant<em> P</em> = 0.06), and reduced stem growth (<em>P</em> < 0.05); the latter two species also increased wilt severity (<em>P</em> = 0.03). Similar results were obtained in geranium trials (analyses underway). Slow sand filtration of pond water (site 1) reduced oomycete recovery from 100% of baits in the holding pond to 0%, based on monthly analyses (April-November 2017), although recovery increased to 50% following transport to the greenhouse (species were primarily non-pathogens). Chlorine treatment (site 2) reduced oomycete recovery from 100% of baits in the pond to 33% in the spring and summer, and to 0% in the fall (2017). These results indicate that recycled water is a source of many pathogens which have not been previously described in Mid-Atlantic nurseries, and that slow sand filtration appears to be more effective than chlorine treatment in reducing pathogen load.</div>