Scientists say they\'re close to producing \'super varieties\' of wheat that will resist a virulent fungus which leaves behind fields of withered black stems. They added that the new crop could boost yields by up to 15 per cent while averting the deadly threat to the world\'s food supply. Researchers from the Durable Rust Resistance in Wheat project at Cornell University have developed wheat in Mexico that shows resistance to all three kinds of wheat rust. We are facing the prospect of a biological firestorm, but it\'s also clear that the research community has responded to the threat at top speed, and we are getting results in the form of new varieties that are resistant to rust and appealing to farmers,\' said Cornell project leader Ronnie Coffman. But significant obstacles must be overcome before the resistant new varieties of wheat can replace the susceptible varieties that make up as much as 90 percent of the wheat now in production, the researchers said. They called for more investments by wealthy countries and international institutions to continue developing the varieties and develop the infrastructure needed to put the new varieties in the hands of poor farmers in developing countries. The new varieties mark a huge advance, said Marty Carson, research director at the U.S. Department of Agriculture\'s Cereal Research Laboratory at the University of Minnesota. \'Anytime you can talk about a 15 per cent boost in yields from existing varieties, I mean that\'s phenomenal. And to get combined resistance to all three rusts, that\'s also a very big deal,\' he said. The new varieties will be planted in several countries for yield trials in the coming growing season in hopes they can enter widespread use in a few years. The latest research will be presented next week at a conference in St Paul, Minnesota.