Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/7/2012
Publication Date: 9/6/2012
Publication URL: http://handle.nal.usda.gov/10113/56001
Citation: Bennett, R. 2012. Survival of Fusarium oxysporum f. sp. vasinfectum chlamydospores under solarization temperatures. Plant Disease. 96(10):1564-1568. Interpretive Summary: Soil solarization, a method in which sunlight is used to heat soil covered with clear plastic, can reduce the incidence of soilborne plant diseases such as Fusarium wilt of cotton. Although solarization is too expensive for widespread use in cotton, it may be economical for treating small areas of infestation if it can be optimized to provide consistently high levels of efficacy. The effectiveness of solarization depends on the relationships between temperature, soil moisture, and pathogen mortality. Therefore, the survival of spores of the fungus causing Fusarium wilt in cotton was evaluated at combinations of temperatures and soil moisture. Results indicated soil moisture had a critically important role in determining spore survival. Many spores survived under dry conditions regardless of temperature or the duration of exposure. In contrast, spore survival was more sensitive to temperature under moist conditions. Under moist conditions, spore survival was generally high at relatively low temperatures (30 and 35 degrees C), but most spores died by 5 weeks of exposure to 37 degrees C, or by 6 days of exposure to 40 degrees C. A second study using a moist environment showed that few spores exposed to temperatures of 39 to 41 degrees C remained alive after 10 days. These results will serve as useful guides in developing solarization protocols to maximize effectiveness based on monitored soil temperatures.
Technical Abstract: Solarization is an effective soil treatment against race 4 of Fusarium oxysporum f. sp. vasinfectum. Despite the lack of effective alternatives, solarization is rarely used in cotton because of its high cost. Use of solarization might be increased if soil temperatures could be used to predict reductions in pathogen inoculum levels, thereby ensuring high levels of efficacy. However, relationships between survival of race 4 chlamydospores, soil moisture, and temperatures typical of solarized soil are not known. Survival of culture- and plant-produced chlamydospores of race 4, incubated at 40 degrees C in dry or moist environments, indicated the importance of moisture in determining spore survival. Mortality of spores from either source was low under dry conditions, and much higher under moist conditions. A six-week exposure of culture-produced chlamydospores to temperatures from 30 to 40 degrees C under moist conditions indicated limited mortality at temperatures =35 degrees C. However, most spores were eliminated by day 6 at 40 degrees C. A second study using a moist environment indicated high mortality of spores by 5 weeks at 37 degrees C, or by 10 days at temperatures from 39-41 degrees C. These results should serve as useful guides in efforts to develop solarization protocols that maximize effectiveness based on monitored soil temperatures.