Distribution and diversity of Phytophthora species in nursery irrigation reservoir adopting water recycling system during winter months

Irrigation water recycling is an increasingly important practice in agriculture in the context of diminishing water supply and the regulatory requirements in some parts of the world. This practice potentially accumulates and disseminates plant pathogens including Phytophthora species that pose a great threat to agriculture and forest ecosystems. Despite a high economic importance of Phytophthora species, the current understanding of their aquatic ecology is very limited. Therefore, a study was conducted to investigate the distribution and diversity of Phytophthora species in an irrigation reservoir of a commercial nursery in eastern Virginia over two consecutive winters. Multiple baits were deployed in surface water at a run-off entrance, 20, 40, 60 and 80m from the entrance and near the pump inlet and at various depths at the 20-m station. Ten different Phytophthora species were detected in this study that included P. citrophthora, P. gonapodyides, P. hydropathica, P. inundata, P. irrigata, P. megasperma, P. pini, P. polonica, P. syringae and P. tropicalis. Phytophthora recovery declined through the winters from November to March. It also declined with distance from the run-off entrance. These results suggest that water decontamination during winter irrigation events is required at this nursery and possibly in the nurseries from the southern part of the United States. The placement of the pump inlet away from run-off entrance may be a viable strategy to reduce the crop health risk.