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Extending the forage season.

A weed that farmers and ranchers curse has proved to be a surprising ally for scientists working to breed better forage grasses.

By uncovering a secret to the weed's success, they're making progress on new forages that could thrive under the cool temperatures of early spring and late fall.

That could extend the grazing season, lessening ranchers' reliance on harvested hay. Feeding hay to livestock during the winter costs more than allowing the animals to graze, says plant physiologist N. Jerry Chatterton.

Chatterton and colleagues at the ARS Forage and Range Research Laboratory have shown that Bromus tectorum, an aggressive weed commonly known as cheatgrass, relies on special carbohydrates called fructans to help the plant grow.

"That's one reason why cheatgrass often out-competes desirable range plants," explains Chatterton, who is research leader at the Logan, Utah, based lab.

"It sprouts early in the fall, stays green during the winter, and puts on new growth earlier in the spring because it is able to use fructan as an alternative energy source," he says.

Fructans are made of chains of primarily fructose molecules--the same sugar that gives fruits their sweet taste. Other so-called cool-season plants--those that grow well under cool temperatures--include forages such as wheat-grasses, timothy, and orchardgrass.

Chatterton identified 10 unique fructans in cheatgrass. To do that, he first had to develop methods to analyze the carbohydrates, as well as purify and identify standards for the different fructans. Although standards already exist for other carbohydrates--starches (polymers made with glucose), for example--the structures of grass fructans had never been characterized.

He and colleagues hope to identify and eventually clone the genes that enable cheatgrass and other cool-season grasses to make fructans. Those genes cue plants to produce enzymes needed to convert fructans into energy for growth. "Through genetic engineering, those genes could then be enhanced in cool-season plants or transferred to warm-season plants, like bermudagrass, bahia grass, or sorghum, to give them the ability to withstand cool temperatures," says Chatterton.

With the new genes, bermudagrass--a common lawn and forage variety--might stay green instead of turning brown over the winter. And, according to Chatterton, ranchers could save up to $1 per cow for each day their cattle eat grass instead of harvested hay.

That means using the new technology on forage grasses to extend the grazing season for just 2 weeks each year could save a rancher with 200 cattle as much as $2,800 per year.

N. Jerry Chatterton is with the USDA-ARS Forage and Range Research Unit, Utah State University, Logan, UT 84322-6300. Phone (801) 750-3066.
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Title Annotation:Agnotes
Author:Corliss, Julie
Publication:Agricultural Research
Date:Feb 1, 1992
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