Learn To Manage Late Blight Resistance In Tomatoes

Late blight is a problem for potato and tomato growers virtually every year. It’s no secret that new strains of the pathogen, Phytophthora infestans, which is Greek for “plant destroyer,” continue to emerge and are becoming more aggressive, and, in some cases, resistant to fungicides.

With that concern looming, what options do tomato growers have to keep late blight in check? One researcher says confirming the origin of the pathogen is the place to start.

Erica Goss, a University of Florida plant pathology assistant professor, wanted to clear up the confusion about the origin of the pathogen. For years it was thought that the pathogen originated in Mexico, but a 2007 study indicated that it came from the South American Andes. After analyzing four sequenced genes from more than 100 strains of the pathogen, Goss found relationships among them that lead to Mexico as the pathogen’s origin.

An Aggressive Organism
“The pathogen is very good at overcoming our management strategies,” Goss said in a recent University of Florida news release. “To come up with better solutions to late blight, we need to understand the genetic changes that allow it to become more aggressive. By understanding past changes, we can design new strategies that are more likely to be robust to future genetic changes.”

In addition to the pathogen becoming resistant to chemical control, it has a history of overcoming single-gene resistance bred into potatoes, and new, aggressive strains are showing up in the field, she says. “Because it is difficult to predict future changes, we have to look at its past evolution,” she adds.

Multiple Options
According to Pam Roberts, a plant pathologist at the University of Florida, tomato growers currently have several fungicides — with different active ingredients — available to them that are specific to this oomycete pathogen.

She agrees with Goss that overcoming fungicide resistance is critical to growers. Citing the chemical mefenoxam as an example, Roberts says the danger occurs when a grower doesn’t realize that the pathogen has become resistant to the chemical, which can occur after multiple applications or if the population that occurs in the field is already resistant.

“It is a matter of monitoring the population, knowing what is in the field, and making sure the fungicides being used are effective,” she explains. This is also why rotating different modes of action is so important with this disease.

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