Characterization and biocontrol of oomycetes recovered from a phytoremediation plant for the treatment of farmhouse wastewaters

The reuse of wastewater for crop irrigation after treatment in constructed wetlands (CWs) represents an eco-friendly strategy to enhance agricultural sustainability. This study aimed to detect oomycete plant pathogens in wastewater from an agritouristic farm treated in CWs and reused for irrigation, and to evaluate antagonistic filamentous fungi as potential biocontrol agents (BCAs) of waterborne oomycetes. Three predominantly aquatic species, Phytophthora gonapodyides, P. inundata, and Phytopythium litorale, were isolated from CW water, whereas only terrestrial species, including P. citrophthora, P. nicotianae (the most frequent), and Phytopythium vexans, were recovered from soils of citrus orchards irrigated with reclaimed water. This difference suggests CW water is not a primary inoculum source for terrestrial pathogens under tested conditions. Among candidate BCAs, Trichoderma asperellum, T. atroviride, T. harzianum, and Epicoccum nigrum significantly inhibited in vitro mycelial growth of the isolated oomycetes, with T. harzianum showing the strongest inhibition (69.17% against P. nicotianae). However, these BCAs were ineffective in controlling P. nicotianaeinfections on tomato seedlings when applied individually. Conversely, treatments either with the mixture of the three Trichoderma species or with the chitosan- and nosodes-based bioproducts Ascoma® and Verde® significantly reduced disease severity, indicating a synergistic effect among Trichoderma species in the soil rhizosphere.