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New Mexico State University

New Mexico State University

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Some Transgenic Cotton Vulnerable to Plant Disease

LAS CRUCES -- A cotton disease is cropping up in some new genetically altered varieties planted to fight insect and weed problems in the Mesilla Valley, a New Mexico State University plant pathologist said.

Some fields of transgenic cotton have been infected with Verticillium wilt, one of the most important and devastating diseases in cotton, said Natalie Goldberg with NMSU's Cooperative Extension Service . The disease reduces lint and seed yields and diminishes fiber quality.

About 75 percent of New Mexico's cotton fields have the soilborne fungus that causes Verticillium wilt, Goldberg said. Usually, the disease is kept in check by growing tolerant cotton varieties.

"Some of the transgenic varieties that are being grown because of our insect problems have not maintained the tolerance to Verticillium wilt," Goldberg said. "What we're seeing is that growers who have planted certain Paymaster varieties have fairly heavy infections of Verticillium wilt, whereas growers who have gone with the traditional Acala 1517 lines or new Deltapine Bollgard lines are not seeing that."

Many growers are switching to transgenic varieties to fight increasing weed and insect problems. Insect-resistant cotton lines have been genetically altered to deter pests like pink bollworm. Other transgenic cottons are herbicide-resistant, allowing growers to spray weeds without killing cotton. Varieties with "stacked" genes offer a combination of the two.

Some transgenic cotton lines have been developed in other parts of the Cotton Belt, where Verticillium wilt is not as prevalent as it is in New Mexico, Goldberg said.

In cooperation with Mesilla Valley growers, NMSU has been testing transgenic cotton in large-scale field trials. In 1997, Paymaster varieties were among the top yielding in the tests.

The fact that disease problems did not surface until this year underscores the need for caution when switching varieties, Goldberg said.

"I think it's important when we look at some of these alternative varieties, which are exciting, that we make sure we haven't lost the traits we've been building on for years," she said. "We always recommend that varieties be thoroughly evaluated through variety trials and that growers do their own small-scale variety trials on a few acres before they make large-scale changes."

Cotton infected with Verticillium wilt is stunted, often with yellow-mottled leaves. Some infected plants fall over, exposing opened bolls to soil.

Once plants are infected with Verticillium wilt, no effective treatment is known, she said. Losses vary widely depending on the level of infection.