It was a ghastly image Ken Deahl saw under his microscope in Beltsville that day. In the slice of a rotten potato was a direct descendant of the blight that caused Ireland's An Gorta Mor -- the Great Hunger. And it was in the United States.
The potato from Washington state arrived on his desk at the U.S. Agricultural Research Center in the fall of 1990 with a note saying no pesticides had been able to save it.
On the 150th anniversary of the first reports of the blight in the Irish press -- September 1845 -- the potato blight is back. The new strain is threatening to cause famine in underdeveloped countries and raise potato prices in the United States, where it already has cost farmers at least $200 million.
This summer, it struck in Maryland. Glenn Holland, who raised 140 acres of potatoes on his farm a mile north of the Virginia line on the Eastern Shore, said he lost about an acre of his potato crop to the blight. The dry weather helped confine it, Mr. Holland said, and agriculture officials say most of Maryland's handful of potato farmers have avoided the scourge so far. But Mr. Holland said he is worried about next year.
It's "the worst crisis to hit the U.S. potato industry ever," said Dr. Deahl, an Irish-American who has been researching potato blight since 1980.
"Internationally, it's the worst to hit since the blight that hit Ireland back in the 1840s," he said. "In a lot of ways, it seems to be a case of history repeating itself."
The blight appeared in Ireland about the same time landlords were clearing peasant farmers off lands to make way for dairy farms, according to Robert J. Savage, a professor of Irish history at Boston College. An estimated 1 million died of starvation and another 1.5 million fled, most to the United States and Canada. Ireland's population dropped from 8.5 million in 1845 to 6 million in 1851. Among the immigrants was Dr. Deahl's great-great-grandfather.
Dr. Deahl and his staff of 10 at the vegetable lab at the Beltsville Agricultural Research Center have been searching for a sort of "silver bullet seed" by cross-breeding potato seedlings from around the world in hopes of finding a combination that would be resistant to the blight.
When he sliced a piece of the potato from Washington and put it under his microscope, it was as if he had seen a ghost. "I thought, 'Oh boy, it's really here,' " he recalled. "I was astounded."
Before that, he and other plant pathologists believed that crops could be protected by spraying with Ridomil, a fungicide that had been effective. The strain of blight resistant to the spray, known as A2, was thought confined to Central Mexico.
But the evidence they were wrong is everywhere in Dr. Deahl's lab -- from the autopsylike photos of infected potatoes in a file drawer to the mortuary of sorts he has set up.
On the lab's shelves are 1,400 test tubes, each filled with samples of the fungus that destroyed a potato farm somewhere in North America.
The new strain of blight first appears as a small, yellow lesion that infects the potato plant, transforms quickly into a cottony growth and produces spores that become airborne and may travel hundreds of miles. One infected potato plant can quickly spoil thousands of others, turning a field of potato plants into rotting foliage in a few days.
No one is sure how the new strain escaped from Mexico. Most scientists believe it probably came north on a potato or a tomato plant, which also can be infected. They are sure of one thing, however. It is spreading.
In 1985, the new strain was found only in isolated pockets of Pennsylvania and in British Columbia. By 1993, it turned up in Minnesota and North Dakota.
Last year, it had spread to farms throughout the Middle Atlantic states. This year, it was reported in the key potato-producing states of Idaho, Washington and Oregon, where it was spread inadvertently to thousands of acres through irrigation systems. It also has spread to Europe, Africa and South America. Experts at the International Center for Potato Production, in Lima, Peru, predict it may cause a famine.
"Developing countries in Africa and South America could face real problems because of this," said William Fry, a plant pathologist and potato expert at Cornell University.
Dr. Deahl, who has researched the blight in South America, Mexico and in several states, was to speak at a conference sponsored by the European Potato Association at Trinity College in Dublin to mark the 150th anniversary of the potato famine.
The anniversary is being marked in Ireland by political speeches, television programs and seminars.
Dr. Deahl believes that some relief may be in sight. His lab should be able to offer a breed of potato seeds resistant to the fungus to growers and seed producers in the next two to three years.
The new breed will alleviate the damages caused by the fungus, but never will eradicate it, Dr. Deahl said. "It's an awesome fungus, just awesome. It's here to stay."