STUDIES ON THE EFFECTIVENESS OF A MILLDY VIRULENT STRAIN IN DIMINISHING THE LOSSES CAUSED BY TABACCO MASAIC VIRUS IN GREENHOUSE TOMATOES

The considerable losses caused by Tobacco Mosaic Virus (TMV) in greenhouse tomatoes, as well as the characteristics related to the marked variability and the ready propagation of this virus, enhanced the need for effective means for its prevention and control.

Lately, in addition to breeding for TMV resistance, there is an increased interest in a method of biological control involving the use of the interference phenomenon or the reciprocal exclusion between strains of the same virus. Interesting results in the protection of tomato crops were obtained with this procedure — known as plant “vaccination” or cross-protection, using strains with heat-attenuated virulence (Gotto et al., 1966; Paludan 1968, 1973), chemical mutants induced by nitrous acid treatments (Rast, 1967), or mild strains isolated from naturally infected plants (Marrou and Migliori, 1971).

The present report deals about the effectiveness of a mild TMV strain in preventing the infection of greenhouse tomatoes by a severe strain of the same virus.