Control of viruses in soil by steaming and exothermic reaction

Experimental trials were carried out in open-field conditions to assess the effectiveness of steam and chemical exothermic reaction (potassium hydroxide) against three widespread plant viruses: Tobacco mosaic virus (TMV), Potato virus Y (PVY) and Cucumber mosaic virus (CMV). In addition to crop residues, native flora is known as an important virus reservoir, thus a pre- planting treatment by steam/potassium hydroxide could be useful not only for fungal, bacterial and weed control, but also against viruses in the soil. Treatments were carried out with a self-propelled soil-steaming machine designed for steam release after incorporation into the soil of a substance that causes an exothermic reaction characterized by a thermal peak, capable of providing a satisfactory control of various soil-borne pathogens up to a 20 cm depth. Purified preparations of the three viruses were thoroughly mixed with air–dried soil samples taken from each experimental plot. The resulting mixtures were placed in nylon screen bags. Three bags per treatment were buried in each plot at depths of 14-16 cm 24 h before treatments with steam or steam/KOH. Significantly lower amounts of each virus were recovered from treated than untreated soil, in particular from soil samples that had been exposed to steam/KOH. Following mechanical inoculation of tobacco plants, no PVY and CMV infectivity was recovered from soil samples exposed to steam/KOH, whereas a significant reduction of infectivity was observed for TMV. These results show that this method can be useful for wide-spectrum control of soil-borne pathogens