The total area of stone fruit trees in Spain is 764,000 ha and producing 1,5 tons of fruit in 1994 (Anuario de estadística agraria, 1994). Very different viruses that can cause important losses affect some fruit trees. The diseases associated with these viruses show symptoms that can range from a slight disorder such as mosaic, shot-hole, and distortion of leaves to more serious disorders of canker, precocious flowering, alterations in ripening date, fruit abnormalities, and even tree death
