Evaluating Oomycete Pathogen and Community Responses to Chemical- and Slow Sand Filtration-Based Water Treatment Strategies to Enable Water Recycling in Nursery Production Systems.

Although recycling irrigation water can reduce water use constraints and costs in nurseries, adoption is hindered by the associated risk of recirculating and spreading waterborne pathogens. To enable regional water reuse, this study assessed oomycete recirculation risks and recycled water treatment efficacy at organismal and community scales. In culture-based analysis of recycled pond water at two Mid-Atlantic nurseries across 3 years, diverse oomycetes (12+ species) were detected using culture-based analysis, with Phytopythium helicoides as the dominant species; MiSeq analysis detected eight of these species, plus 24 additional taxa. Oomycete contamination risk and detection abilities in recycled water was highest in fall and/or spring based on species richness (P = 0.001). Four species, Pythium oopapillum, Pythium aff. diclinum, Phytophthora cryptogea complex, and Phytopythium helicoides, were pathogenic to seedlings (90% damping off) and mature chrysanthemum plants, causing decline in more plants than negative controls (P = 0.025)-these species thus represented the known pathogen targets for recaptured water treatment. Slow sand filtration (SSF) of recaptured water resulted in an 85% or greater reduction in oomycete recovery from baits across months, although detection in greenhouse water following treatment indicated reintroduction challenges. MiSeq analysis indicated that SSF altered relative species abundances, which decreased for two species and increased for three species, including one putative pathogen, after SSF (P < 0.05). Chlorine treatment reduced recovery of oomycetes from baits by at least 75%, although diversity increased, as did relative abundance of several species, including one putative pathogen (P < 0.05). Together, these results indicate that SSF and chlorination have potential efficacy in enabling irrigation water recycling in nursery production, although system modifications are needed to improve treatment efficacy and prevent pathogen reintroduction after treatment.