Identify the plant pathogenic fungi present in recycled irrigation water in nursery and glasshouse facilities, including analysis of the propagule forms present and seasonal fluctuations in species composition .|
Determine the numbers and types of fungal propagules that actually reach plants via recycled irrigation water.
Establish realistic treatment targets for selected fungal pathogens in recycled water.
Determine the effectiveness of various water treatment procedures in killing or removing fungal propagules from recycled water.
Develop procedures allowing nurserymen to monitor water supplies for the presence of common pathogens and assess the effectiveness of water treatments.
Many nursery and glasshouse growing facilities in California have been required to sharply limit discharges of irrigation wastewater. Regulations limiting effluent runoff have been adopted primarily to prevent nitrate-laden leachates from contaminating surface or groundwater resources, and also to force greater water conservation. While the need to conserve water and prevent the pollution of drinking water resources is clear, wastewater recirculation introduces a significant risk of spreading plant pathogens within affected nurseries. |
In surveys of recirculating systems at several commercial nurseries, we found that irrigation effluents contain large numbers of fungal propagules. Some of the fungi in recirculated water are known to be plant pathogens, and we have detected them in the irrigation water being applied to crops. In effect, plants are being inoculated with pathogenic fungi each time they are irrigated with recycled water. Experiments showed that daily irrigation of healthy plants with artificially- or naturally-infested water caused substantial root infections within 10 weeks.
Experiments with two root-infecting fungi frequently detected in irrigation water showed that spores suspended in distilled water were killed following relatively brief exposure to UV radiation, or low concentrations of chlorine or ozone. However, when spores were suspended in nursery effluent water, which contains soil particles and organic impurities, treatment efficacy was significantly reduced. Treatment dosages or contact times had to be increased by a factor of 2-10, depending upon water quality. Under such conditions, we found a UV-emitting excimer laser to have greater efficacy at high throughput capacity than a commercial UV water purifier. A simple baiting-ELISA method, utilizing commercially-available test kits, was developed to help growers detect one of the most common and important root pathogens in irrigation water.