Coffee is the world's most popular drink. But coffee plants are being threatened by coffee leaf rust, a fungal disease found in virtually all coffee-producing countries. The IAEA, together with the FAO and co-sponsored by OFID, is training scientists how to use a nuclear technique, known as plant mutation breeding, to develop coffee plant varieties that are resistant to this disease. Experts mainly from Central America, the region most affected by the disease, came to the IAEA's laboratories to learn more about this method.