ABSTRACT
Disease resistance is commonly considered a highly effective and satisfactory means of control because it is inexpensive, easy to apply, and not harmful to other biological components of our ecosystem. It is used on a world-wide scale in cultivated herbaceous and arboreous species to control the most destructive diseases. The use of resistant cultivars constitutes the main factor for yield increase in tomato. For instance, in the 1940s tomato yields ranged between 10–20 tons per hectare on the average. Regarding tomato, in the past 50 years great progress has been made in the study of: the mechanism of pathogen variability, the distribution and identification of physiological races of pathogens, and the use of techniques for screening and evaluating germplasm collected in many parts of the world and in the center of origin of this species.
