The farmers of the world, harvesting the abundant crops of the Green Revolution, have so far defied Malthusian predictions that population growth would outrun agricultural production and consign much of humanity to chronic famine.
But scientists say the diverse varieties of traditional crops and wild plants they need to breed more productive new strains are in jeopardy.
In the field, farmers are abandoning them in favor of the new high-yield varieties.
Wild strains of agricultural plants are disappearing as development destroys their habitat. And lack of funds, lack of care, and political upheaval threaten the collections of seeds, in "banks" around the world, in which much of the remaining genetic diversity is stored.
The prospect of losing this genetic capital would be alarming under any conditions, scientists agree, but it is particularly threatening because of the way Green Revolution crops have changed the world's agriculture.
In the first phase of the revolution, high-yield strains of wheat and rice bred especially to accommodate and thrive on large amounts of synthetic fertilizer enabled harvest yields to double and triple in much of the Third World.
Famine caused by underproduction has largely disappeared; hunger today is mostly a product of political upheaval, bad administration of food supplies or the inability of the poor to buy food.
But this historic achievement has exacted a price: while the new crops are vastly more productive than traditional varieties, they are also much more vulnerable to catastrophic destruction by insects, fungi, bacteria and viruses.
Genetically uniform crop strains have been adopted across wide stretches of the earth. As a result, pests or diseases that used to be local problems can race across nations and continents, cutting a destructive swath through the world's food production.
To counter this threat, plant breeders must continually add new resistance traits to crops by crossing them with traditional and wild varieties.
The same genetic techniques also allow scientists to confer on crops characteristics that contribute to higher yields -- tolerance to drought, heat or cold, for instance. And they offer a benign alternative to synthetic pesticides and fertilizers and the environmental harm these can cause.
Some of the most recent results have been dramatic:
* Scientists at Cornell University under contract to the International Potato Center in Lima, Peru, combined a nonedible wild potato from the Peruvian Andes with a conventional edible potato. Their offspring inherited a highly desirable characteristic from the wild plant: tiny hairs on the leaves and stem that entrap insect pests. The hairs exude a substance that adheres to the insect's feet, immobilizing it. The trait also prevents egg-laying and feeding and makes the plant highly resistant to all major potato pests, eliminating the need for pesticides. The pests cause major crop losses annually, and eliminating them would boost productivity. Cornell plans to test the potato in New York State fields this year.
* In another advance, scientists at the International Maize and Wheat Improvement Center in Mexico City are breeding wheat resistant to the Russian wheat aphid, an insect that costs the United States $300 million a year in lost production and %o insecticides. The scientists are crossing the modern wheat with traditional agricultural forms found in Turkey. Five more years' worth of breeding cycles should achieve resistance, scientists say.
* Researchers at the International Center for Tropical Agriculture at Cali, Colombia, have identified wild bean plants containing antibiotics that keep bruchid bean weevils from reproducing. The weevils infest stored grains and destroy up to 15 percent of the total bean harvest of Latin America and 25 percent of the harvest in Africa. Insecticides cannot be used because they would poison the beans. The wild beans have been crossed with cultivated beans and are now being field-tested in Latin America and Africa.
The advances were described, and alarms about the loss of genetic diversity were sounded last week by scientists at a symposium in Washington sponsored by the Washington-based Consultative Group on International Agricultural Research.
This is a broadly based consortium that supports a worldwide network of research centers and gene banks in the forefront of the enterprise.
A similar warning was sounded earlier this month in Oslo, where an international group representing research organizations, foundations, governments and seed producers resolved to launch a global initiative aimed at heading off the danger.
If the erosion and deterioration of genetic resources continues, the group said in a statement of consensus, "genetic options for needed changes in agricultural production in the future will be lost forever."
The group advocates a five-fold increase, to $300 million a year, in financing for the preservation and development of genetic resources.