Submitted to: Pesticide Management Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/4/2010
Publication Date: 3/3/2010
Publication URL: http://www3.interscience.wiley.com/journal/117935712/grouphome/home.html
Citation: Ahonsi, M.O., Banko, T.J., Doane, S.R., Demuren, A.O., Copes, W.E., Hong, C. 2010. Effects of hydrostatic pressure, agitation and CO2 stress on Phytophthora nicotianae zoospore survival. Pesticide Management Science. 66(7):696-704. Interpretive Summary: Shear forces generated from agitation and pressurized carbon dioxide are used to kill food-borne microorganisms. These factors were tested to see if they would kill zoospores of Phytophthora nicotianae which is a serious plant pathogen spread in nursery and greenhouse irrigation systems. These factors were tested individually in a laboratory system using both pressurized carbon dioxide and breathable air as a comparison. It was shown that only exposure to carbon dioxide and not pressure or agitation killed Phytophthora species zoospores in water. While carbon dioxide alone can kill zoospores, zoospores die at a faster rate when the carbon dioxide is delivered under pressure. The use of sub-critical carbon dioxide levels delivered under low pressure may still be useful as a alternative method to the use of chlorine for killing micro-organisms in irrigation systems. This information will benefit the food preparation industries and research scientists working to rid irrigation systems of harmful micro-organisms.
Technical Abstract: Phytophthora nicotianae Breda de Haan was used as a model pathogen to investigate the effects of hydrostatic pressure, agitation, and aeration with CO2 or breathable air on the survival of Phytophthora zoospores in water. Injecting CO2 into 2 liters of zoospore-infested water for 5 min at 110.4 ml (0.2 g) CO2/min resulted in zoospore mortality of 66 - 81% (P=0.001). That same level of mortality (78 - 87%) was achieved in 30 sec when CO2 was injected under a gauge pressure of 630 kPa (16.3 g CO2). Reducing the CO2 injection pressure to 70 kPa (3.85 g CO2) resulted in as much zoospore mortality as at 630 kPa. In contrast, when breathable air was used in place of CO2 under similar pressure conditions as with CO2, there was no reduction in zoospore survival. Aerating zoospore-infested water with CO2 longer than 5 min at 0.2 g/min or increasing exposure time over 30 sec when CO2 was injected under pressure did not result in an increased mortality of zoospores. Likewise, agitating zoospore-infested water during CO2 injection did not increase mortality of zoospores. Exposing zoospore-infested water to mechanical treatments such as hydrostatic pressure at 840 kPa for 8 min or agitation with a mixing intensity of G=6483 1/s for 4 min did not result in a reduction of viable zoospores. Similarly, hydrostatic pressure at 840 kPa combined with agitation by forcefully releasing zoospore-infested water under pressure through a fine (size 8) spray nozzle did not reduce zoospore survival. We conclude that only exposure to CO2 and not pressure or agitation results in the mortality of Phytophthora spp. zoospores in water. While CO2 alone apparently caused zoospore mortality, the application of pressure and CO2 increased the rate at which zoospores were killed. The use of sub-critical CO2 at pressure magnitudes < 1 MPa as a possible alternative to the use of chlorine for water decontamination is promising.