The time course of inhibition of potato virus X ( PVX ) synthesis by the newly developed antiphytoviral compound 2,4- dioxohexahydro -1,3,5-triazine (DHT) was determined in mechanically inoculated leaves of Nicotiana tabacum L. cv. ' Samsun '. At the permissive temperature (22 +/- 3 degrees) DHT