As a University of Florida plant pathologist, Gary Vallad likes to call himself and his colleagues “sleuths of the plant world.” These detectives find out what ails plants and crops, hopefully before the disease gets out of control.
Most recently, scientists with the UF Institute of Food and Agricultural Sciences discovered some novel pathogens that may damage Florida tomatoes. Their findings could be critical to keeping Florida’s $437 million-a-year tomato industry strong. Thanks to their early findings, the industry faces no immediate threat.
However, Vallad said early and accurate pathogen diagnosis is key to crop protection.
“There are numerous microorganisms capable of impacting crop production in Florida; some are just more prevalent than others,” Vallad said. “We don’t always understand all the conditions related to some disease outbreaks. In this case, we had some novel pseudomonads causing symptoms similar to some common pathogens.”
According to Vallad, misidentifying a pathogen can be problematic for disease control.
“Without proper identification, it is easy to misdiagnose a disease based on symptoms alone, which could lead to an improper treatment, most likely an improper or unnecessary pesticide application,” Vallad said. Using the wrong pesticide can result in unsatisfactory disease control, or even worsen the disease.
A team of researchers led by Vallad, a UF/IFAS associate professor, identified two pathogens. Scientists knew one of the pathogens, Pseudomonas cichorii, could cause bacterial leaf spot in lettuce and other food crops in Florida. However, this was the first time it was ever associated with tomato in Florida. Interestingly, the researchers discovered that the P. cichorii strains from tomato, lettuce and other crops in Florida are 
genetically distinct, compared to other strains of P. cichorii from around the world. The second identified pathogen is quite novel and was only found on tomato.
Researchers first saw evidence of the pathogens in Hillsborough and Manatee counties, associated with some unusual disease outbreaks that occurred in 2011 and 2012. Although researchers realized early that the isolated bacterial strains were unusual, additional tests at the UF/IFAS Gulf Coast Research and Education Center in Balm, Florida, were required to properly identify the pathogens and confirm their ability to cause disease on tomatoes, Vallad said. In addition to the distinct group of Pseudomonas cichorii, they also identified a novel pseudomonad-causing disease on the tomato that they named Pseudomonas floridensis sp. nov.
Based on other similar pathogens, both are likely spread by wind and rain. Control methods include:
- Use clean seeds and healthy transplants
- Avoid overhead irrigation if possible
- Avoid handling plants when foliage is wet
- Apply pesticides labeled for bacterial pathogens preventatively.
The findings about Pseudomonas cichorii are published in the journal Plant Disease, while the findings about Pseudomonas floridensis sp. nov., have been accepted for publication in the International Journal of Systematic and Evolutionary Microbiology.
by Brad Buck, University of Florida Institute of Food and Agricultural Sciences