Bacterial spot is an economically important disease of tomato worldwide. Tomato (Solanum lycopersicum L.) is the world’s second most important vegetable crop, after potato, due to its nutritional value and culinary properties. Bacterial spot causes losses in field-grown tomatoes throughout the eastern US. In Florida, bacterial spot of tomato has been shown to reduce expected yields by up to 50%, while also reducing the quality and market value of fruits, resulting in an estimated $100 million in annual crop losses in Florida.
CAUSE and GEOGRAPHIC DISTRIBUTION
Bacterial spot of tomato is cause by four species of the bacterial genus Xanthomonas. In Florida, X. perforans is the pathogen responsible for bacterial spot of tomato. In cooler regions, X. gardneri causes this disease. Both X. gardneri and X. perforans have recently been replacing the pathogens historically responsible for this disease.
Some of the strains of Xanthomonas responsible for bacterial spot of tomato can often also infect peppers. While these pathogens do not cause disease on other plants, they can survive on the surface of leaves which aids survival between growing seasons.
The disease starts as dark brown leaf spots on leaves. X. perforans produces what look like shot holes in leaves. Leaf spots can run together to affect whole leaves and cause defoliation. The defoliation can cause sun scalding of tomatoes, which are no longer protected by the leaf canopy. Lesions may form on tomato fruits, which reduces marketability and prevents peeling of processing tomatoes.
SPREAD of PATHOGEN and CONTROL OPTIONS
There are no disease resistant tomato varieties available commercially. The extensive use of copper-based bactericides has led to the spread and establishment of copper-tolerant Xanthomonas strains in most production areas. Although alternatives to copper-based bactericides are commercially available, the cost is prohibitive and they are not effective when weather conditions favor rapid disease development. A team led by UF are currently studying ways to expand management strategies to include critical periods of seed and transplant production.
Prepared by Erica Goss and Mustafa Jibrin, UF/IFAS Department of Plant Pathology; and Gary Vallad, UF/IFAS Gulf Coast Research and Education Center.