Go bananas while you still can. The world's most popular fruit and the fourth most important food crop of any sort is in deep trouble. Its genetic base, the wild bananas and traditional varieties cultivated in India, has collapsed.

Virtually all bananas traded internationally are of a single variety, the Cavendish, the genetic roots of which lie in India. Three years ago, New Scientist revealed that the world Cavendish crop was threatened by pandemics of diseases such as that caused by the black sigatoka fungus. The main hope for survival of the Cavendish lies in developing new hybrids resistant to the fungus, but this is a difficult and time-consuming task because the seedless modern fruit does not reproduce sexually and has to be bred from cuttings.

Now the UN Food and Agriculture Organization (FAO) has warned that wild banana species are rapidly going extinct as Indian forests are destroyed, while many traditional farmers' varieties are also disappearing. It could take a global effort to save the bananas' gene pool.

In fact many of the genes that could save the Cavendish may already have been lost, says NeBambi Lutaladio, a plant scientist at the FAO's headquarters in Rome, Italy. One variety that contains genes that resist black sigatoka survives as a single plant in the botanical gardens of Calcutta, he says.