Many farmers have stopped growing traditional crops, such as millet

Over the last century about 75% of the world's crop varieties have been lost, data from the UN Food and Agriculture Organization (FAO) suggests.

UN researchers say that we now rely on just three crops: wheat, rice and maize.

The fact that poorer nations are almost twice as dependent on these cereals as richer nations has led to the question: are we now too reliant on too few crops?

The Kolli Hills in Tamil Nadu, southern India, is home to about 40,000 people.

Scientists have visited the area to see if ancient traditions offer any clues to finding a way out of a future global food crisis.

Changing landscape

"First of all, I think the environment is going to be more unpredictable," Sayed Azam-Ali, professor of tropical agronomy at the University of Nottingham, UK, tells the Television Trust for the Environment's Earth Report programme.

"So we need crops that are going to be safe," he said.

For centuries, farmers of the Kolli Hills harvested millet

"We can't rely on importing and moving crops around the world indefinitely.

"I think we have to be more reliant on locally sourced food."

Until the first road was built in the 1960s, the Kolli Hills were cut off from the outside world.

Farming families had been harvesting millet for centuries, and it was their main source of nutrition.

"This was the only food crop they could depend on," explained Dr S Bala Ravi, a researcher from the Swaminathan Research Foundation.

"There was no communication system; there was no public distribution system, so this was the only dependable crop for them which could be grown in the hills."

However, the construction of the road presented an opportunity for some farmers to switch to more profitable crops.

One such crop is cassava, also known as tapioca.

One farmer explained that until 20 years ago he used to grow millet, but tapioca offered a better return and a better standard of living.

Growing demand

The demand for relatively few crops has left experts worried that traditional knowledge of how to harvest millet will die out; something they have called "cultural erosion".

A project to reintroduce the crop has begun to have some success.

Researchers believe the high nutritional value and its resilience means millet offers a more secure future for farmers, rather than growing cash crops and buying cheap rice to eat.

Thirty-two of the 250 villages in the hills are growing millet again, but Professor Bala Ravi knows more is needed; farmers need to be able to sell it for cash too.

The farmers' millet products are finding their way into more stores

"We want the farmers, instead of selling the raw harvest at a low rate, to enhance its value by various processing methods.

"We are supplying the various machineries and increasing the capacity for processing," he added.

"We have created a market line so that they can bring out their own entrepreneurship and enhance it."

Kolli Hills millet products are now on sale in 34 stores in the region, and sales have increased by 300% over the past year.

Mixing minor crops, such as millet, into the major farming system could be the future for food, locally and globally.

But researchers warn that the success of this type of venture still hangs in the balance.

The Television Trust for the Environment's (TVE) Earth Report - Forgotten Fruit - will be broadcast on BBC World on 15-20 February 2008. Please check schedules for further details