Infected seed is the primary source of tomato (Lycopersicon esculentum) bacterial spot causing a rapid development of the disease with severe yield losses under favorable environmental conditions. The present work was undertaken to evaluate the effect of heat treatment (70 ºC for 96 h) on germination and seed structure, as well as to determine the efficiency of heat therapy to prevent bacterial growth and disease establishment. Two experiments were carried out using tomato seeds inoculated by vacuum with Xanthomonas campestris pv. vesicatoria strain ENA 4463 adjusted to 10(7) cells.ml-1 followed by air-drying. In the first assay, four treatments were designed as follows: (1) inoculated seeds; (2) inoculation followed by heat treatment (70 ºC/96 h); and two controls, uninoculated seeds without (3) and with (4) heat treatment. In the second assay, three treatments: (1), (2) and (3) were compared. Samples from different treatments were evaluated for the physiological status of the seeds and presence of the bacteria. The latter was tested by recovering the bacteria by vacuum extraction, isolation in semi-selective medium and visualizations though scanning electron microscopy (SEM). The efficiency of the heat treatment as a method to control the disease ranged from 99,96 to 100% for the second and first assay, respectively. Furthermore, there was no significant effect of the heat on seed germination. However, under SEM, heat treated seed showed some superficial structural changes, characterized by a greater number of broken trichomes, and a deposition of trichomes randomly or organized in plates over the seed surface and morphological changes in the bacterial cell shape.
