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One stunt tomato growers don't want to see.

One Stunt Tomato Growers Don't Want To See

A silent killer lurks in tomato fields of southern California's Imperial Valley. Last year's victim: 20,000 tons of tomatoes - fresh-market harvests that never made it to the produce section of your supermarket and cannery-type processing tomatoes that never saw the inside of a catsup bottle or salsa jar.

Scientific sleuthing by ARS plant pathologists James E. Duffus, James S. Gerik, and co-researchers revealed several years ago that the mysterious affliction was caused by tomato bushy stunt virus.

And although the virus and disease are known to occur in tomato fields in North Africa and Europe, they were never before found here, says Adolph F. Van Maren, former Imperial County farm adviser who helped identify the culprit virus.

So now, Duffus and Gerik in their labs at Salinas, California, are seeking a fast, simple test that tomato breeders can rely on to judge tomato varieties' natural ability to shrug off the debilitating virus.

"Resistance is the cheapest and most practical weapon against bushy stunt," says Duffus. Their outdoor tests of processing tomatoes, planted in soil infected with the virus, showed that among eight leading commercial varieties, Centurion and H-100 are much more resistant than strains such as UC-82 or P-95.

Now, in laboratory tests of those varieties, they're looking for a convenient market or early sign of resistance. The discovery of a marker might speed selection of the most promising new tomato types.

"A fast indicator may be what's known as titer - the abundance of virus particles in tomato tissue," says Gerik. "You find the titer by checking sap a week after infecting plants with the virus."

Raising naturally resistant varieties will likely prove to be a more desirable option than costlier tactics such as fumigating soil with methyl bromide or covering vacant tomato beds with plastic sheets so the desert sun can superheat the ground and kill the microorganisms.

Another option - to abandon tomato production on infected soils and move to other sites in the valley - offers a stop-gap remedy but not a long-term solution.

The virus got its name from the stunted, unnaturally bushy appearance of infected plants. A healthy tomato plant's low-growing vines sport lots of healthy green leaves that shelter fruit from the sun.

But plants stricken with the virus become malformed, spiky bushes. Their yellowed, unnaturally curled leaves expose the tomatoes to the sun. Sunburnt tomatoes look bad, taste funny, and aren't marketable. The virus can affect whole fields and reduce yields by as much as 80 percent.

A problem in the valley since 1977, the bushy stunt virus lives in the soil and flourishes in the cool weather of late winter, when young tomato seedlings are struggling to get established. When temperatures climb in early spring, the virus all but disappears. By the time the virus begins to fade, however, it's too late for infected plants to recover.

At Donbee Farms, owner Donald Cox has lost about $400,000 worth of tomatoes in four different bouts with the virus. His was the first farm in the valley to be attacked by the troublesome disease. Symptoms appear only after the virus has already taken hold, he says. And fields "seem to go down overnight.

"There are always problems with tomatoes, because they're so delicate," Cox says. "But almost everything else that can happen to tomatoes is more manageable than bushy stunt - it's the worst deal ever."

Even though the Imperial Valley's tomato production is dwarfed by that of the San Joaquin Valley to the north, Imperial offers something no other California region can, that is, the earliest possible start to the processing-tomato harvest.

Imperial-grown tomatoes are ready 4 weeks earlier than those in any other part of California, the nation's leading tomato-growing state. Early harvest offers canners a longer season, which in turn makes better use of their equipment.

The virus not only imperils profits of Imperial growers but also worries their counterparts to the north, even though the virus hasn't attacked tomatoes outside the desert. Duffus and Gerik hope to pinpoint the virus' source, and may at the same time allay the fears of tomato growers elsewhere in the United States.

PHOTO : Tomato plants at left reflect damage from the soilborne tomato bushy stunt virus. Healthy plants at right are growing in soil that was covered with plastic.
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Title Annotation:research to combat tomato bushy stunt virus
Author:Wood, Marcia
Publication:Agricultural Research
Date:Jan 1, 1991
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