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Golden Nematodes Are Anything But

ARS nematologist Bill Brodie (left) and Cornell University plant breeder Robert Plaisted assess the merits of new nematode-resistant varieties. (K3364-4)

Just as all that glitters is not necessarily gold, all that's golden is not necessarily good—as any long-time potato farmer on New York's Long Island will attest.

That's because a Hicksville, Long Island, potato farm was unhappily the setting in 1941 of the United States' first known infestation of the golden nematode, Globodera rostochiensis. The tiny worm's enormous appetite for potato plant roots can wipe out entire crops.

To make matters worse, each female nematode can produce hundreds of eggs capable of lying dormant in the soil for decades, just waiting for the right soil conditions and a vulnerable potato crop.

Bill B. Brodie can’t do anything about soil conditions, but he's spent more than a quarter of a century steering potato producers away from the second half of the nematode’s wish list—vulnerable potato varieties.

A plant pathologist in ARS' Plant Protection Research Unit at Ithaca, New York, Brodie's collaborated there with Cornell University researchers Robert L. Plaisted, Edward D. Jones, Donald E. Halseth, Steven A. Slack, and H. David Thurston on nonchemical control strategies to defeat the golden nematode.

The ARS-Cornell team has developed nematode-resistant potato varieties, as well as a crop rotation plan to stymie the pest and halt its spread. Since 1966, scientists with USDA and Cornell and other universities have brought forth 31 potato varieties that resist golden nematode attacks. Among them is the ARS-bred Atlantic, a leading chipping potato and the country's most widely grown nematode-resistant potato.

"The first 40 years of golden nematode control depended on fumigating infested fields with as much as 90 gallons per acre of chemicals," Brodie points out.

"During the years when the greatest number of golden nematode-infested fields were being found, federal regulatory agencies spent more than $2 million annually to survey the soil for nematodes and for other activities. And the State of New York was spending more than $250,000 a year for the soil fumigants to treat infested fields."

Chemical use against the pests came to a halt after traces of the chemicals were detected in Long Island groundwater in the early 1980's. To fill the protection gap, Brodie and colleagues provided convincing evidence that 2 consecutive years of growing a nematode-resistant variety of potato controlled the pest as effectively as the chemicals.

Besides, fumigants wouldn't wipe out all the live nematode eggs lurking in the soil, Brodie notes. But, resistant potato varieties' roots naturally fend off nematode infection, starving the hatching nematodes and slashing nematode totals by about 90 percent each year.

The watershed event in the war against the golden nematode was the 1954 discovery of a single gene whose presence could gird potatoes against the pest’s attacks. That gene, called H-1, was the cornerstone of the first nematode-resistant potato varieties—Cornell's Peconic in 1966, and ARS' own Wauseon, released at Beltsville, Maryland, in 1967.

But growers beyond nematode-besieged Long Island were slow to trade in their favorite spuds for an unfamiliar, though resistant line, Brodie recalls.

"In 1944, New York State quarantined portions of Nassau and Suffolk Counties on Long Island where the nematode was first found. Then, in 1969, the federal government again quarantined portions of those counties—plus Steuben County in New York and New Castle County in Delaware, where the nematode had also been discovered," says Brodie.

"Because those quarantine measures prevented the spread of golden nematodes, growers outside those areas never experienced any losses to the nematode and they weren't interested in switching varieties."

But, as the years passed, science and market demands finally converged, with development of resistant varieties such as Atlantic, Allegheny, and Kanona that combine nematode-blocking ability with the quality traits growers demand.

"Potato breeders throughout the United States need parent plants to make crosses," Brodie explains. "They've begun using resistant varieties as parents because these potatoes happen to have other traits that they like. Last year, I found three newly released potato varieties that no one even knew were resistant,"

In a stroke of scientific serendipity, the ARS-Cornell team's persistent pursuit of better nematode-fighting tubers has put them ahead in a contest they didn’t know they'd entered.

"There are five races of golden nematodes around the world, but in this country we'd always had just one of those races, Ro1," Brodie reports. “Then, in 1994, we found a race of golden nematodes on our experimental farm that was increasing, instead of decreasing, on our resistant varieties! Tests showed we now had race Ro2 of the golden nematodes in the United States."

Fortunately for American potato farmers, Brodie and the Cornell researchers had, for the past decade, kept the fire going under a small project on pinpointing potato lines that would also resist exotic races of golden nematode—races other than their longstanding enemy, Ro1.

"Bob Plaisted and I knew that we'd been relying too much on the H-1 gene for our nematode resistance. So we had begun developing different germplasm here and sending it to Peru for testing, since they have other races of the golden nematode there." Brodie explains. "Our objective was to develop germplasm that would be resistant to the other races and also adapted to our growing conditions in the United States.

"We had some germplasm that was really good at resisting several races of the golden nematode, and we thought we'd simply make it available to other countries that already had those races," says Brodie.

"But call it chance, or serendipity, or whatever—when we were developing germplasm with resistance to exotic races, some of that same germplasm showed resistance to Ro2, as well. Since we had incorporated resistance to Ro1 into this germplasm, we're more than 5 years closer to having a potato variety that's resistant to both races and ready for release to growers. So this little project has turned out to be a good value for our farmers."

Studies are under way at Cornell University to pinpoint the basis of the new germplasm's resistance to Ro2. "We don't know if it's one gene, like the H-1 gene, or several." Brodie says.

Meanwhile, he continues to check all the new varieties from potato breeding programs at Cornell, the Universities of Maine and Minnesota, Agriculture Canada, and Frito Lay, Inc.—as well as ARS potato breeding programs at Beltsville, Maryland, and Aberdeen, Idaho—in search of fresh weapons against the golden nematode.

"We consider the golden nematode the most serious pest threatening the U.S. potato industry," Brodie concludes. "Federal, state, and local governments have come together on this program to protect our potato crop." — By Sandy Miller Hays, ARS.

USDA-ARS Plant Genetic Resources Unit, Cornell University, Ithaca, NY

"Golden Nematodes Are Anything But" was published in the April 1996 issue of Agricultural Research magazine.