By David Brough ROME, Sept 18 (Reuters)

Breeds of farm animals are dying out and types of plant disappearing at an alarming rate, threatening long-term food security and depriving the world of their ability to resist disease and harsh climates. The United Nations world food body says two breeds of farm animals disappear each week, and 1,350 breeds face extinction. Over the past 15 years, 300 out of 6,000 breeds of farm animal identified by the Rome-based U.N. Food and Agriculture Organisation (FAO) have become extinct. Latest information suggests that 30 percent of the world's farm animal breeds are at risk of disappearing, and their valuable traits, such as their ability to adapt to harsh conditions, disease, drought and poor quality feed, could be lost too. "Once you lose a genetic resource, it's gone forever," said Ricardo Cardellino, the FAO's senior officer for animal genetic resources. "We don't know what we will need in future in terms of genetic resources."

PLANTS

Plant varieties are also disappearing fast. The FAO estimates that over time 10,000 plant species were used for human food and agriculture. Now no more than 120 cultivated species provide 90 percent of human food supplied by plants. More than 90 percent of the agricultural diversity that existed at the start of the 20th century has been lost. Given the expected doubling of food needs in the next three decades as the world's population grows, biodiversity will be essential to food security, the FAO says. The risk of depending on just a few varieties of plants and animals is great because they could fall victim to disease or drought. "Farmers depend upon this diversity to raise animals able to respond to unpredictable changes in the environment, threats of disease, or changing market conditions," an FAO document said. "Further erosion of animal diversity invites disaster as options for long-term productivity and sustainability are lost." Hartwig de Haen, an FAO assistant director-general, said: "Insofar as biodiversity makes ecosystems more resistant to the vagaries of climate..., it contributes to alleviating hunger." Over the past decade, the FAO has helped collect data from some 170 countries on domesticated mammals and birds: cattle, goats, sheep, buffalo, yaks, pigs, horses, rabbits, chickens, turkeys, ducks, geese, pigeons, even ostriches. The greatest threat to domestic animal diversity is the export of animals from developed to developing countries, which leads to cross-breeding or even replacement of local breeds. Many indigenous breeds are being replaced in both developed and developing countries by a few high production breeds which, to be successful, require costly feed and maintenance, skilled management and benign environments. High-production Holstein cows now provide much of the milk drunk in northern Europe and North America. As for plants, industrial farming and globalisation have contributed to dwindling diversity. "If you want tomatoes that can be taken to the market and remain hard, are the same size and don't mature rapidly, then you could end up with just a few varieties," Cardellino said.

RISKS

Shrinking biodiversity is bad news for mankind because it puts too much reliance on too few crops and farm animal species. "If biodiversity continues to shrink, we are increasing the risks of producing a large percentage of our food based on few varieties or breeds," Cardellino said. "If anything goes wrong -- say, a variety is susceptible to a disease -- then we could lose a lot." FAO believes that using agricultural diversity is the best way to conserve it. "We cannot have a zoo where we have all the breeds in the world," Cardellino said. "They have to be used."