EFFECT OF A CONTINUOUS HOT WATER-TREATMENT OF POTATO-TUBERS ON SEED-BORNE FUNGAL PATHOGENS

The viability of five pathogens was decreased by treatment with hot water when tested in vitro. Polyscytalum pustulans was most sensitive and Rhizoctonia solani least sensitive. Potato tubers were exposed to 55-degrees-C for 5 min in a commercial continuous hot water treatment plant using naturally contaminated seed tubers and tubers which had been inoculated by dipping in comminuted cultures. The frequency of eyes colonised by P. pustulans, Helminthosporium solani, and R. solani was reduced to virtually zero and the effect persisted on tubers subsequently stored at 4-degrees-C and at 15-degrees-C for up to 16 wk. Results with Colletotrichum coccodes were inconclusive. Treatment suppressed Penicillium spp. which, however, rapidly recolonised the eyes during storage, leading to higher contamination levels in the treated than in the untreated tubers. With tubers inoculated with Phoma foveata, good control was achieved when the incubation period before treatment was 10 d but not when the period was 42 d.