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In order to evaluate the inhibitory effect induced by gamma interferon (Hu g IFN) on plant viruses, pre‐inoculation treatments (brushing the leaves) were carried out in two different plant‐virus systems: D. stramonium* TMV and G. globosa* PVX. Results showed that Hu g IFN induced a higher inhibitory effect (IP = 90%) in D. stramonium* TMV system (Table 1). Comparing the antiviral effect of the three IFNs: gamma, alpha and beta‐like interferons, it was verified that Hu g IFN was more effective than the other two (Table 2). Hu g IFN was also used for post‐inoculation treatments (incubation of tobacco leaf‐discs) and using different dilutions a dose response curve could be obtained (Fig. 1). Hu g IFN inhibitory effect was confirmed by the neutralization of its inhibitory effect using monoclonal antibody (Table 3). Results suggest that although the three IFNs differ in their composition, they present similarities in their biological activities probably triggering an antiviral state in plants.

Virazole (1, beta-D-ribofuranosyl-1,2,4-triazole-3-carboxamide = Ribavirin), a synthetic nucleoside analogue, has been successfully used against tomato spotted wilt virus (TSWV) in tomato and tobacco plants. In tomato, the most efficient concentration to control TSWW was 500 mg/l while in tobacco, concentrations of 100 mg/l were sufficient to control systemic infection. When the plants did not show a systemic reaction virus could not be recovered from inoculated and treated tomato and tobacco plants by means of the local lesion assay. The results point out the response of a new plant virus to Virazole and indicate a possibility of controlling TSWW systemic infection.

Tomato plants (Lycopersicon esculentum Mill.) inoculated with tomato white necrosis virus (VNBT) and treated with Virazole (1-beta-D-ribofuranosyl--1, 2, 4-triazole-3-carboxamide) at a concentration of 500 mg/l developed systemic virus symptoms in only 40 per cent of the plants in which a remarkable reduction in virus concentration was also observed. From inoculated and Virazole-treated plants which had produced no symptoms, no virus could be recovered. This result suggests that Virazole may inhibit replication of VNBT in tomato.