They hope the summit, held in the shadow of famine in southern Africa, will galvanise a drive to protect the seeds which ensure that world food staples can be revitalised in the face of changing climate, pests or disease.

"If we value our ability to feed the world - and we're going to have to feed another two billion people in the next 25 years - we need to have options available to us, without options we'll get hammered by pests, by disease, by climate change...," Dr.Tony Simons told Reuters.

Simons, who chairs the working group on genetic resources and works at the Nairobi Future Harvest Center of the Consultative Group on International Agriculture (CGIAR), said that seeds from the world's 1,470 gene banks are distributed to farmers for propagation, when required.

But many collections are under threat, with some so underfunded they are unable to preserve the plants, keep them cool or redistribute the seeds.

"Today's crop diversity ensures tomorrow's food security and the livelihood and quality of life for billions of people. And it is in jeopardy," said a report on crop diversity prepared by Imperial College Wye.

"The problem is threefold: decreasing diversity in farmers' fields; the loss of crop wild relatives in nature; and the precarious state of the world's plant diversity collections," according to "Crop Diversity at Risk: the case for sustaining crop collections."

A Global Conservation Trust, which will raise and run the self-sustaining endowment, is being set up by the U.N. Food and Agriculture Organisation and the Future Harvest Centers of the CGIAR.

HUMAN PROGRESS ROOTED IN AGRICULTURE

"Most advances in human civilisation ...have all resulted because of advances in agricultural practice," said Chris Higgins, professor of clinical sciences at Imperial College who was to present the report.

"Domestication and breeding of crops which gives better yields have allowed civilisation to flourish....That requires diversity....If we lose it we lose it forever and agriculture will not be able to develop and mankind will suffer dramatically as a result," Higgins said.

"It is one of these things actually that is crucial to the future of mankind."

The slight genetic differences in crop diversity provide natural ways to rejuvenate crops hit by new disease, pests and environmental changes, the report said.

Although humans cultivate 7,000 plants for food, just three crops - wheat, rice and maize - together provide more than half of humanity's global food supply and are staple foods for four billion people. But varieties are fast disappearing.

In Mexico, farmers have lost some 80 percent of their traditional maize varieties in the last 70 years; in Bangladesh the promotion of high yield rice has led to losses of 7,000 traditional rice varieties.

Genebanks may soon contain almost 100 percent of the diversity of both tomato and cassava, a starchy root crop.

Fund-raising for the $260 million endowment goal is going well but is not yet complete. The sum, which can fund the genebanks in perpetuity, is the equivalent of four minutes of the world's annual gross domestic product, or the price of two jumbo jets.

"I think the world can afford that," Simons said.