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New Test May Finger Disease-Carrying Insect

By Jan Suszkiw
June 5, 1997

A new diagnostic test is now on tap to identify the mystery insect that spreads “yellow vine.” Since 1988, sporadic but devastating outbreaks of this new disease have caused losses of up to 75 percent in watermelons, cantaloupe and other cucurbit crops grown in Oklahoma and central Texas’ Cross Timbers area.

Without knowing the insect’s identity, migration or feeding patterns, cucurbit growers there can do little to effectively protect their crops using insecticides or techniques such as staggered planting dates or repellent mulches.

In early work, Agricultural Research Service scientists and collaborators conducted lengthy greenhouse experiments to determine which cucurbit-loving insects could infect the plants through feeding. Some of these included squash bugs, leaf hoppers and aphids. But few conclusive leads surfaced.

This spring, the ARS scientists will team with colleagues at Oklahoma State and Texas A&M universities to try a different approach. They’ve devised a new molecular test for rapidly screening the insects’ tissues for the unique, genetic “calling card” of the culprit behind the disease: a bacterium-like organism, or BLO. Under a microscope, it’s little more than a rod-shaped cell, but it can seriously damage the plant’s nutrient-carrying tubes called phloem.

Yellow vine can be especially costly when it strikes melon crops that have been planted in the early spring so that their fruit can be harvested for the July 4th marketing window. That’s when melons go for a premium price of 10 cents per pound. A bumper crop yields about 40,000 pounds per acre, worth $4,000. But an outbreak can wipe out a grower’s profits in just days--wasting money spent on seed, fertilizer, and water.

Key to the researchers’ new test is a sensitive technique called polymerase chain reaction. It copies the BLO’s genetic material millions of times over so it can be detected. PCR also can determine in one or two days whether an insect--or weed--harbors the organism. If so, separate greenhouse tests would then follow to see if the insect can actually transmit it to plants.

Scientific contact: Benny D. Bruton, USDA-ARS South Central Research Laboratory, Lane, OK, (405) 889-7395;