Evaluation of Wetland Plants for Potential Susceptibility to Phytophthora Spp. Found In Irrigation Water At Ornamental Plant Nurseries

Increased water consumption by both producers of agricultural commodities and the urban community currently is causing a rise in the demand for water.  Growers eventually will need to adopt water conservation and retention technology to ensure an adequate water supply for irrigation purposes.  The use of constructed wetlands is an ecologically-based option for collection and re-use of irrigation runoff. This technology also limits export of agrichemicals in runoff water to off-site surface waters.  A major concern with using recycled irrigation water is the potential to recirculate propagules of oomycete pathogens through the irrigation system.  The goal of our proposed study is to assess the potential susceptibility of plants used in constructed wetlands to infection by species of Phytophthora commonly found at ornamental plant nurseries.  Initially, we will evaluate five wetland plant species (Canna flaccida, Hydrocotyle umbellata, Pontederia cordata, Sagittaria latifolia, and Typha latifolia) to determine the potential for infection by five species of Phytophthora (P. cinnamomi, P. citrophthora, P. cryptogea, P. nicotianae, and P. palmivora).  Tissue culture-grown plant liners will be placed into modified 3.8-liter aquatic plant containers filled with a simulated nursery effluent solution.  Plants will be challenged independently by zoospores of each species of Phytophthora, and the persistence and viability of these zoospores will be monitored throughout the experiment.  Susceptibility of each wetland species will be determined using several techniques.  Plants will be rated for symptom severity over time, and root and shoot weights of treated plants will be compared to those of non-treated control plants at the end of each experiment to determine the impact of Phytophthora spp. on plant growth.  Excised root pieces also will be embedded in PARPH-V8 selective medium in an attempt to isolate Phytophthora spp.  Our results could have important implications for the re-use of nursery runoff water for irrigation.  Constructed wetlands or vegetated channels should be established using plant species that are not susceptible to infection by species of Phytophthora to ensure that these plants do not contribute to the inoculum supply in the irrigation system.  The next step in this project will be to determine if wetland plants can serve as biological filters to help remove propagules of Phytophthora spp. from irrigation water.