Effects of hydrostatic pressure,agitation and CO2 stress on Phytophthora nicotianae zoospore survival

BACKGROUND: Phytophthora nicotianae Breda de Haan is a common pathogen of ornamental plants in recycled irrigation systems. In a previous study, annual vinca (Catharanthus roseus Don) inoculated with zoospore suspensions using a CO₂‐pressurized sprayer had less foliage blight than plants inoculated using a hand sprayer. Here, the impact of hydrostatic pressure, agitation and aeration with CO₂ on the survival of P. nicotianae zoospores was examined. RESULTS: Exposure of zoospores to 840 kPa hydrostatic pressure for 8 min or agitation at a mixing intensity (G) of 6483 s^?1 for 4 min at 22–23 °C did not kill zoospores, but resulted in viable cysts. Motile and forcefully encysted zoospores of P. nicotianae were equally infectious on vinca or lupine (Lupinus polyphylus Lindl.). Bubbling CO₂ into zoospore‐infested water at 110.4 mL (0.2 g) min^?1 for 5 min caused 81% reduction in the number of germinated zoospores. Pressure at 630 kPa (16.3 g CO₂) or 70 kPa (3.85 g CO₂) facilitated CO₂ injection and shortened the zoospore inactivation time to 30 s. When air was bubbled through the suspension, germination was similar to the control. CONCLUSIONS: Exposure to CO₂ killed P. nicotianae zoospores in water. Neither pressure nor agitation had an effect on zoospore viability or infectivity. Based on results of this study, the authors designed a recycling CO₂ water treatment system that is currently under evaluation. Copyright © 2010 Society of Chemical Industry