Tomatoes & TMV

The 'wilty gene' causes upward curling of tomato leaves

By: Sandy Feather 2009
Penn State Extension

Q. I am growing several types of tomatoes in my garden this year. I have noticed that the tomato leaves are tightly curled on some of them, while other plants look normal. Is this a problem with tomatoes this year?

A. Our office has received a lot of questions about tomato leaf roll due to the wet weather most areas have experienced recently. Leaf roll on tomatoes is a physical symptom specific to certain cultivars of tomatoes. Those that contain a specific gene known as the wilty gene- will develop lengthwise, upward curling of the leaves in response to certain environmental conditions or infection by tobacco mosaic virus - TMV.

Growth Habit

Leaf roll caused by environmental factors is not a serious problem, and affected plants should produce a normal crop of fruit. They will even develop a more normal growth habit if the weather dries out. Favorable environmental conditions for leaf roll include high temperatures, drought, and prolonged periods of wet soil and we have experienced all of those during the current growing season. The symptoms often appear when the plants are carrying a heavy load of fruit. It is common for the lowest, oldest leaves on susceptible plants show rolling more than newer leaves higher on the plant.


Leaf Roll Symptom

Leaf roll may also indicate that plants carrying the wilty gene are suffering from tobacco mosaic virus (TMV). Plants suffering from TMV usually will show light-and-dark-green mottling on the leaves in addition to leaf roll. The mottling may also appear on green fruits. Affected plants may appear stunted compared to uninfected plants of the same variety. TMV is very infectious and may be spread by simply brushing up against plants as you work in the garden. Plants suspected of virus infection should be pulled from the garden and sent out with the trash to avoid infecting clean plants. There is no treatment for virus infections in plants.

Virus Indexing

The only sure way to confirm that a suspicious-looking tomato plant is infected with a virus is by virus indexing through a certified laboratory. This can be expensive, and is really meant for commercial growers rather than home gardeners. Penn State's Disease Diagnostic Lab does not perform virus indexing.


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