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Growing high-quality spuds is no small potatoes.

Growing High-Quality Spuds Is No Small Potatoes

Last year, Americans chowed down about 5 billion pounds of french fries. Most of those fries came from Northwest-grown Russet Burbanks, the favorite potato of fast-food restaurants.

Characterized by their oblong shape and dark-tan skin, Russet Burbanks also make good baked potatoes. Nearly all the potatoes grown in Idaho, our number one spud-producing state, are Russet Burbanks. Idaho, Washington, and Oregon together produced half of the nation's $2 billion potato crop last year.

Growing high-quality potatoes is no easy matter. Farmers must contend with everything from virus-carrying aphids to soilborne fungi attacking their crop, while facing increased scrutiny for using chemical controls. They must also meet processor demands for large, unblemished potatoes that make golden fries and crunchy chips.

To help farmers please french-fry aficionados, ARS researhcers are breeding better spuds - ones that look and taste as good as the classic Russet Burbank yet withstand environmental assaults.

One of North America's largest potato breeding programs is at Aberdeen, Idaho. Another is in Beltsville, Maryland, at the ARS Vegetable Research lab, headed by Kathleen G. Haynes.

At the Aberdeen facility, ARs breeders Joseph J. Pavek and Dennis L. Corsini have released three promising new potatoes in the past 2 years.

Two are russets, Ranger and Frontier, both for sale in supermarket produce sections or for processing into fries. The third is the smooth, round, white-skinned Gemchip, used for making potato chips.

ARS, university, and cooperative extension scientists throughout the West conducted years of field trials on the new varieties. University of Idaho horticulturist Stephen Love, who works closely with Pavek and Corsini, has coordinated the trials with the Tri-state Potato Development program of Idaho, Oregon, and Washington.

Further testing involves trials with processors like J.R. Simplot Co. in Caldwell, Idaho, and Carnation Processed Potato Division in Moses Lake, Washington. Simplot is one of the nation's largest potato processing companies.

Glenn Vogt, manager of agricultural services at Simplot, praises Ranger Russet for its high solids content and good size, top priorities for french-fry processors.

When a potato is high in solids, or dry matter, it won't soak up as much oil during frying as lower-solids potatoes. That's a bonus for both processors and consumers, since oil is costly and adds calories.

Too much oil makes for a flaccid fry. "When you pick up a french fry, it shouldn't droop," asserts potato-expert Pavek.

One drawback to Ranger, which was just released this spring, is its susceptibility to blackspot bruising - grey or black spots found just under the skin.

But future breeding work, using potatoes that resist bruising, could remedy that problem for tomorrow's new varieties. Potatoes with higher protein levels, Corsini found, don't bruise as readily, so he hopes to boost protein content through genetic engineering of existing varieties.

Early Harvest a Plus

Frontier, which was made available to growers in April 1990, matures earlier than Russet Burbank. That's good for growers, who get higher prices for early-season spuds.

Curtis Stoddard, a farmer near Grace, Idaho, says he harvests his Frontier Russets starting in mid-August, about a month before the Burbanks. "We can dig early and finish while the weather's still good," he says. Stoddard's family grew 200 acres of Frontiers last year on their southern Idaho farm.

Although Frontier makes good fries if processed shortly after harvest, it doesn't fry out of storage as well as Russet Burbank. About 80 percent of each year's crop goes into storage, some of it for up to 11 months.

But Frontier could capture a large share of the fresh market, he speculates, because of its smooth skin and attractive appearance.

Many fresh-market potatoes will end up in potato salads, soups, and pancakes, or they simply might be baked. While baked potatoes are often topped with a dollop of sour cream or a pat of butter before they're eaten, not so for those served to volunteer tasters who judge unadulterated spuds on their sensory appeal. They rate flavor, texture, and appearance - deeming the vegetables mealy or watery, sweet or earthy tasting, white, gray, or greenish looking.

The ideal baked potato has white flesh and fluffs easily with a fork, says Mary Lou Ruby, one of the extension home economists who heads the taste tests in Blackfoot, Idaho. Ruby serves each of the dozen or so tasters two potato halves. Once half, usually a Russet Burbank, serves as a reference for comparison. The testers - who can't drink coffee or smoke an hour before the test - then grade the potatoes on a scale of one to nine. Frontier and Ranger got high marks - usually sixes and sevens - on par with Russet Burbanks.

What makes a good chipping potato? One with high solids and a very low sugar content, like Gemchip, because hot oil can turn chips brown if sugar content is high.

In Western regional trials, Gemchip, which was released in 1989, gave 30 percent higher yields from the field than Norchip, the industry's main chipping potato. Gemchip was initially selected at Presque Isle, Maine, by R.V. Akeley, as ARS researcher, and C.E. Cunningham, of the Campbell Institute for Agriculture Research and later field-tested in Washington and then by the Aberdeen group.

The new chipper could be a boon to the snack food industry, since Americans eat more than a billion pounds of potato chips each year, according to the National Snack Food Association. Besides their demands for high-solids, low-sugar potatoes, processors also want them large and well-formed so less goes to waste when they're sliced or chipped. But the farmer faces challenges way before potatoes ever get that far - while they're still in the field.

Verticillium wilt is one of the major potato diseases facing growers in warm, arid regions of the western United States. The soilborne fungus contributes to early dying, which cuts yields, says Corsini. Both Frontier and Ranger are less susceptible to Verticillium wilt than older varieties.

At the ARS Vegetable and Forage Crop Production Research Unit in Prosser, Washington, geneticist Mark W. Martin has been developing potato varieties with strong resistance to Verticillium wilt and other fungal diseases, like early blight and powdery mildew, as well as two viruses - serious problem faced by potato growers.

Martin collects potato germplasm from home and abroad for his breeding projects. Top contenders come from Argentina, Germany, Great Britain, Poland, and Peru's International Potato Center in Lima.

Some of these potatoes are a far cry from our commercial varieties. "When we grow them, we're amazed at how ugly they look - some are lumpy, others are the size of chicken eggs, and many have yellow flesh," says Martin, who has been breeding potatoes at the Prosser station for over 14 years.

From an original population of about 1 million plants, he has identified 40 lines that grow successfully without insecticides, fungicides, or soil fumigants. And that's using virus-infected seed in fields with rampant soil and virus diseases.

In contrast, "if you grow Russet Burbank or any of our western commercial varieties in such a field, using infected see, not a single potato will be marketable," says Martin. "Of course, we don't advise farmers to use infected seed; this technique is exclusively used as a research tool."

These clones could reduce risks and costs for growers, he says. That's especially crucial because western potatoes often grow on sandy soil under irrigation - ideal conditions for excess chemical to seep toward groundwater. To protect their valuable crops, farmers sometimes apply high levels of insecticides, fungicides, and fumigants.

Several of the new multi-resistant lines also look promising in terms of other criteria such as yield, type, solids, storability, handling, and cookability, adds Martin.

Ever cut into a potato that looked perfectly fine only to see dark brown veins running through the white flesh? The problem, known as net necrosis, is caused by a virus that is carried to potato fields by tiny, flying aphids.

Their wingless progeny crawl from plant to plant, spreading virus within the fields as they probe potato plants with their stylets. "The stylet is like a soda straw the aphid sticks into the leaves or stems to suck out sap," says Peter Thomas, a pathologist who specializes in potato viruses.

In the process, the bugs - who may pick up the virus from weeds or other plants - infect potatoes they feed on, with devastating results.

Viruses are a very serious problem for western potato growers. Farmers in Idaho, Washington, and Oregon spend about $112 million each year to control them, especially potato viruses X and Y and leaf roll virus.

Not all potatoes infected with leaf roll develop net necrosis. But those that do will produce dark, discolored french fries, and major fry producers won't accept the unsightly potatoes. Russet Burbank is particularly susceptible to both the virus and net necrosis, says Thomas, who works at the Prosser research station with Martin.

"When I first began working here, in the mid-70's, 38 percent of the potatoes harvested had potato leaf roll virus," says Thomas. By the 80's, the rate was down to 1 percent.

Improved techniques to detect the virus, developed by Thomas and his colleagues, helped bring about the reduction. The screening techniques are now used by seed-certification agencies, which provide virus-free seed to growers.

The widespread use of aldicarb, a powerful, soil-applied, systemic insecticide that kills the aphid vectors of potato viruses, also helped reduce the rate.

But public concern about ground-water contamination with aldicarb and the potential for aldicarb residues in potatoes led manufacturers to withdraw the product from the market. That lends an even greater urgency to finding nonchemical means to stop the virus.

One option is giving potato plants a way to fight off infection - through genetic engineering. The advantage to such an approach, says Thomas, is that the new, added gene only changes one characteristic and leaves the other characteristics intact. That's not possible with conventional breeding because every cross results in new and different offspring that may be close, but not exactly the same, as the parent.

Scientists can add new genes to many broadleaf plants like potatoes, tomatoes, and tobacco with help from the commonly used vector Agrobacgerium tumefasciens. The bacterium contains a plasmid, a tiny piece of DNA, that enters a plant's chromosomes during the infection process. Because the DNA actually becomes integrated into the plant's DNA, it's a perfect carrier for introducing foreign genes into plants. A tumefasciens itself half been genetically altered so it doesn't cause they typical infection signs - galls, or swellngs, in the plant's leaves or stems.

The desire gene in this case is one that gives the potato the ability to resist viral infections.

Thomas is collaborating with Monsanto Co. scientists, led by molecular biologist Nilgun Tumer, in field evaluations of Russet Burbank potatoes that contain the viral coat protein gene of potato viruses X and Y.

Last year's results were promising, says Thomas. One Russet Burbank line containing the two genes was highly resistant to both viruses. Tubers from those plants will be planted this spring to confirm their resistance.

The scientists will also field-test 200 lines of Russet Burbanks containing a gene for the coat protein of potato leaf roll virus this year.

Potatoes may harbor not only the troublesome viruses but also a problematic worm, the Columbia root knot nematode. Female nematodes burrow into potatoes and lay their eggs under the skin. These show up as black spots when potatoes are peeled.

Controlling the nematodes with fumigants costs growers between $200 and $400 per acre and may be an environmental risk.

Certain wild varieties of Mexican potatoes, however, possess strong resistance to nematodes. Charles R. Brown, also a geneticist at Prosser, crossed one of these strains with a cultivated potato. The hybrids are long, russetted tubers that can fend off both races of nematodes found in the Northwest.

Other wild species are so genetically different that they can't be crossed with cultivated potatoes, so Brown and colleague Sandra Austin-Phillips, at the University of Wisconsin, are using protoplast fusion to make hybrids of the two.

In the laboratory, scientists strip walls off cells of the two parent potato lines and place them together in a petri dish. This allows the cells to fuse together and recombine into one cell. The cell then divides repeatedly and grows into a clump of cells called a callus.

The callus sprouts a tiny plant that can later be transplanted to the field.

Austin-Phillips has already produced a potato plant by protoplast fusion that can be used in breeding nematode resistance.

Brown has produced genetically engineered potatoes that contain a gene from Bacillus thuringiensis (Bt). Bt is a naturally occurring soil organism that is toxic to Colorado potato beetles. The peanut-sized, march over the plant's leafy canopy, leaving scraggly, chewed leaves in their wake.

When a beetle larva consumes the Bt, the protein disrupts its gut, causing it to slowly starve to death. Used by organic farmers and others for insect control. Bt is harmless to bees, other beneficial insects, animals, and people, says Brown. Various strains of Bt are already sprayed on a variety of crops and trees to control beetles and caterpillar pests.

"Getting the plant to make its own Bt toxin would save growers time and money," says Brown. "They wouldn't have to continually apply insecticides."

Brown's collaborators at the University of Washington - Helen R. Whitely, Gene W. Nester, and Douglas Bradley - cloned the Bt genes used in the experiments.

Potatoes grown in last summer's field trial contained the gene but didn't produce enough beetle-killing toxin to ward off attacks. Next year's expirements will test plants with a pumped-up version of a new gene that has beetle-battling powers but has never been tried before in plants.

PHOTO : At the J. R. Simplot potato-processing plant, ARS breeders Joseph Pavek (left) and Dennis Corsini, University of Idaho horticulturist Steve Love, and Simplot employee Jess Lewis inspect potato strips for defects before french frying. (K-4018-12)

PHOTO : Gemchip, Ranger Russet, and Frontier Russet have been released within the past 2 years. (K-4016-5)

PHOTO : Colorado potato beetle. (K-1291-2)

PHOTO : Plant geneticist Joseph Pavek (right) and technician Feliks Pazdan examine a new hybrid family of potatoes to be tested in the field this spring. (K-4019-14)

PHOTO : Plant pathologist Dennis Corsini compares ARS-developed storage-rot-resistant potato in his right hand with a normal susceptible variety. (K-4017-13)
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Title Annotation:includes other articles; potato research
Author:Corliss, Julie
Publication:Agricultural Research
Article Type:Cover Story
Date:Apr 1, 1991
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