Heat treatments for sustainable control of soil viruses

Food contamination by toxic pesticides has induced intense research for alternative methods to control pests and diseases. For instance, the phasing out of methyl bromide used for soil disinfection has led to a reconsideration of heat-based methods to control soil-borne pathogens. Techniques such as soil steaming and soil solarization have been applied successfully. However, traditional steaming and solarization are unable to control viruses such as the Tobacco mosaic virus. Thus, methods for sustainable control of virus in soil are not available. Here, we tested the effect of short-duration soil steaming enhanced by the addition of exothermically reacting chemicals-potassium hydroxide or calcium oxide-and soil solarization. These methods were tested against three viruses having different stability: the highly stable Tobacco mosaic virus and the medium stable Potato virus Y, and the Cucumber mosaic virus as non-persistent control. Steaming was done in laboratory and open-field conditions after incorporation of exothermically reacting chemicals. Soils were solarized for 20 days using transparent polyethylene, ethylene-vinylacetate and high-effectiveness infrared films. Our results show that steaming with exothermic chemicals decreased the infectivity of the Tobacco mosaic virus below 3.0 %. We also found that the Tobacco mosaic virus was not controlled by solarization. The Potato virus Y was totally controlled by steam treatments and by soil solarization with ethylene-vinylacetate or high-effectiveness infrared films. Overall, our findings evidence promising ways to control soil viruses.