Disinfecting potato tubers using steam treatments

In laboratory and packing house experiments, treatment of potato tubers with steam or organic mercury reduced the incidence of the seed-borne pathogens Erwinia carotovora (Jones) Bergey et al. and Helminthosporium solani (Dur. & Mont.), and the seed- and soil-borne pathogens Streptomyces scabies (Thaxter), Spongospora subterranae (Waller), Fusarium spp., Rhizoctonia solani (Kuhn), and Colletotrichum coccodes (Waller) in tubers. The incidence of pathogens in tubers following these treatments was 1-3% compared with 26-59% in the nontreated controls. Similar results were obtained in a commercial packing house in Israel when stream treatments were applied to tubers using a nozzle system that was fitted to a conveyor belt and attached to a diesel-powered steamer. The presence of seed-borne pathogens in the daughter tubers 120 days postplanting of steam or organic mercury treated tubers was 3-4% compared with 26-31% in the nontreated controls. The treatments were slightly more effective against pathogens that were exclusively seed-borne compared with those that were both seed- and soil-borne. The presence of pathogens that were both seed- and soil-borne in the daughter tubers following these treatments was 4-9% compared with 20-44% in the nontreated control. Neither steam nor organic mercury treatments had any adverse effects on tuber viability and on plant vigor, foliage, or mass, nor on viability or yield of daughter tubers 120 days postplanting in the field, compared with the nontreated control. These results demonstrate that steam treatment can be an efficient method for disinfecting potato tubers, easily applied in packing houses to large volumes.