Scientists say poorer populations in vulnerable countries could starve if a disease called Ug-99 hits yields hard enough to push up wheat prices.
There is already a global wheat shortage and UN agencies are concerned about the impact of high food prices.
Ug-99 is a form of black stem rust that prevents wheat taking up nutrients and can wipe out whole harvests.
Scientists at the John Innes Centre, in England, are trying to find wheat with a natural resistance to the disease.
Most wheat grown in Africa, Asia and China, has little resistance to Ug-99.
The BBC's Anna Hill says scientists at the John Innes Centre are testing a wide variety of native wheats from Asia and Africa to see if they can find natural resistance to the disease and breed new varieties from them.
But this could take more than five years, by which time Ug-99 could already be causing wide spread harvest failure.
The UN World Food Programme has warned that the rise in basic food costs could continue until 2010 because of rising energy and grain prices.
Some food prices rose 40% last year, and the WFP fears the world's poorest will buy less food, less nutritious food or be forced to rely on aid.