The modern plant protection system has involved the new means that act not directly on fungi and bacteria, but activate the natural defense mechanisms of the plant and enhance the same physiological and biochemical changes in plants as does the biological systemic activated resistance. In 1999–2000, the role of the plant activator Bion (benzothiadiazole) in the resistance of tomato against early blight (Alternaria solani) and late blight (Phytophthora infestans) was investigated at the Lithuanian Institute of Horticulture. Physiological and phytopathological observations were carried out on greenhouse tomato Aušriai exposed to Bion. The data showed that the plant activator Bion and the fungicide Euparen (tolylfluanid) reduced early blight incidence by 10.35% and late blight by 34.5% in comparison with untreated plants. Application of the plant activator and the fungicide increased tomato yield by 4.5 kg/m2 and exhibited a rather high biological efficiency (42–63%).

Tomato sprayed with Bion accumulated insignificantly more pigments in leaves at a normal temperature. Under these conditions other physiological processes were similar. At a high temperature the physiological processes were more intensive in tomatoes sprayed with Bion than in non-sprayed ones.

Keywords: Solanum lycopersicum L., Alternaria solani, Phytophthora infestans, benzothiadiazole, tolylfluanid, pigments, phytomonitoring, photosynthesis