IN order to survive, there was one thing that settlers could not forget when they set sail for colonial America - a sack of seeds. Hidden behind record crop harvests today lies a startling fact: Not one major food or fiber crop currently grown in the United States is native to her soil.
Today, the US has the world's largest plant gene bank where stores of seeds are in ready supply for farmers and breeders worldwide whose crops are threatened by insects, disease, weather, and war. The seed bank, however, the US National Seed Storage Laboratory (NSSL) in Fort Collins, Colo., is itself threatened - by lack of space.
The walk-in, deep-freeze vaults are packed and boxes of seeds overflow into the halls. The NSSL, on the edge of the Colorado State University campus, has reached its original storage capacity of 225,000 samples, each sample being a minimum of 2,000 seeds. Now its stock bulges in excess of 250,000, according to research biologist Dorris Clark.
Because seed samples come in at a rate of 20,000 a year, Mr. Clark says, ``We need a new building ... we need it bad, and we need it soon.''
Germplasm is the substance in seeds that transmits hereditary characteristics. Without proper storage, the vital germplasm that would be needed to genetically rebuild agriculture after a possible disease epidemic or nuclear disaster is critically at risk.
The growing challenge to feed the world's 5 billion people has forced farmers to rely on fewer and fewer strains of high-yield crops. Two-thirds of America's corn comes from just six species, two-thirds of its rice from four; half of its wheat from nine species; and half of its cotton from three.
This dramatic decline of genetic diversity - which is happening around the world - produces record harvests but makes crops more fragile and vulnerable to nature's threats.
In a recent book, ``Gene Banks and the World's Food,'' Donald L. Plucknett, a scientific adviser at the World Bank; Nigel G.H. Smith, professor of geography at the University of Florida; and J.T. Williams and N. Murthi Anishetty of the International Board for Plant Genetic Resources in Rome cite examples: In 1985, 12 million citrus trees were destroyed by citrus canker in Florida, where only a few strains are grown. And in 1970, American corn farmers lost one-fifth of their crop - $1 billion in damages - when leaf blight struck a handful of specialized varieties.
Historically, overdependence on too few plant varieties has triggered even greater disaster, the authors say. In 1846, the Irish potato famine killed 750,000 people and forced 1 million to migrate to America. And a fungus destroyed 90 percent of the tobacco crop in Cuba in 1980, leaving 26,000 Cubans unemployed and perhaps contributing to the exodus of 123,000 Cubans to the US in the ``Mariel boatlift.''
The value of seed storage has been spotlighted in recent years as scientifically improved plants have replaced original species in their native lands around the world. If scientists do not take seed samples from the centers of crop origins and preserve them properly, seeds may be lost forever.
A report from the General Accounting Office in 1981 warned that the genetic base of US agriculture was shrinking and that it soon might be ``difficult, if not impossible, to find needed genetic strains anywhere in the world.'' It is estimated that plant species are disappearing at the rate of two a day worldwide, and the trend of high-yield breeding in modern agriculture is only exacerbating the problem.
Botanists conclude that out of America's 25,000 native species of plants, some 3,000, or 1 in 8, are rare or endangered by loss of habitat, land development, collectors, and other causes.
Progress is being made in some areas toward solving the world's germplasm decline, however. Mr. Clark at the NSSL noted that there has been much cooperation with other countries in recent years in exchanging seeds. The NSSL is part of the USDA's Agricultural Research Service, which is part of a free, worldwide seed exchange program.
The US government has a policy of free exchange of seeds, except with those countries believed to have hostile governments, like Nicaragua, Cuba, Libya, and Afghanistan. Through its National Germplasm System in Beltsville, Md., and its laboratory in Fort Collins, the USDA supplied more than 95,800 seed samples to 123 countries in 1985.
At least 227 gene banks in 99 countries house about 2.5 million crop samples. Some scientists predict that, because of declining wild gene sources, seed collectors in the future may have to lead their expeditions to the world's seed storehouses instead of the world's fields and forests.
Deep-freeze seeds for 21st-century farmers
Can seeds stay alive for 20,000 years?
Phillip Stanwood thinks perhaps so.
Reaching his thick leather glove through the fog of liquid nitrogen gas into an 850-liter steel tank, Dr. Stanwood pulls out a crusted, frozen tube of seeds. Those seeds could be planted in another century.
By using deep-freeze tanks, stable at minus 196 degrees C., seeds can be preserved for a yet-unknown length of time, Stanwood explains.
Part of the mission at the National Seed Storage Laboratory (NSSL) in Fort Collins, Colo., is to research new ways of storing seeds for future generations of agronomists and plant breeders. Stanwood, who heads the ``cyropreservation,'' or ultracold storage, program at the laboratory said his goal is to learn how to preserve germplasm, basically, forever.
When seeds in the wild fall to the ground in autumn, they go into a state of dormancy triggered by lowering winter temperatures. Seeds lie dormant until warmer spring temperatures trigger germination.
Cyropreservation mimics this natural process, but it can extend the winter dormancy period for decades or even centuries. Seeds are living plant tissue and must either be germinated or kept in a dormant state if they are to remain viable.
Conventional seed storage usually takes place in a huge walk-in freezer, where seeds are stored at minus 18 degrees C. and a moisture level of about 8 percent. But such storage requires periodic germination and testing of seed samples, often resulting in costly seed loss.
While cyropreservation is a new technique, so far the evidence suggests that seeds remain viable almost indefinitely in ultracold conditions. In addition, once the initial equipment is installed, cyropreservation can be relatively inexpensive (less than $500 per tank, per year) and reliable.