THE INFECTION OF POTATOES BY PHYTOPHTHORA-INFESTANS DURING SIMULATED WASHING AND ITS CONTROL USING A HOT-WATER TREATMENT

A single blighted tuber released on average 1.39 mg of P. infestans my celia and sporangia during simulated washing. In subsequent experiment s up to 100% of tubers were infected when healthy tubers were washed i n a suspension of P. infestans equivalent to a concentration of 1.65 m u g ml(-1), i.e. that calculated to be in a commercial washing plant a fter washing a potato stock with approximately 1% of tubers infected w ith bright for 4 hours. Immature tubers were more prone to infection d uring washing than mature tubers. Damaging tubers, irrespective of the ir maturity, increased the incidence of tuber infection. The viability of P. infestans isolates was significantly reduced by in vitro immers ion in water at 44 degrees C for 5 minutes. The infection of daughter tubers dipped in a suspension of P. infestans for 3 minutes was preven ted when the suspension temperature was 44 degrees C. There was no ind ication of tuber damage at this temperature.