Aiming to explore some epidemiological aspects of bacterial spot of tomato incited by Xanthomonas spp., a field experiment was carried out in Caçador, SC. Tomato plants were inoculated with a bacterial suspension before transplanting. At seven-day intervals the bacterial population on leaf surface and disease severity were monitored during 19 weeks. Daily weather records were registered during the crop season. It was observed that epidemic onset coincided with physiological maturation of the first fruit clusters. Leaves were symptomless until 77 days before harvest. It was observed that even under a dry period the bacterial leaf spot continued to develop. It is possible that the leaf wetness from dew deposits favored disease development. Weather records showed an average of 13 hours with relative humidity e"90%. The bacterial population on leaf surface varied during the first 10 weeks after planting, according to the weather conditions, however, it remained stable after the fists symptoms of the disease. The disease curve progress was fitted to the logistic model y = 0,99964/(1+exp (10.35989-0.69762*x)), where y is disease severity and x the time in days. Disease severity on fruits was high, reaching 30.22%, with total productivity of 117.88 ton.ha-1. The results will be used to estimate disease onset in a forecast system.
epidemiology; bacteria; Lycopersicon esculentum
