Management of Stemphylium Blight of Onion by using Biological Agents and Resistance Inducers

Onion, (Allium cepa L.) is one of the main important and oldest vegetable crops grown in Egypt. The Egyptian onion is famous allover the world for its superior quality and early appearance in European markets. Onion although primarily is grown for food, it is also used as traditional medicine. During the last years the international cultivated area with onion profoundly has been decreased because of the serious damage of the crop yield due to infection by several diseases that attack onion during the growing season (Schwartz and Mohan, 1996). Stemphylium blight disease, incited by different species of Stemphylium is one of the serious diseases that attacks onion leaves causing apical choler spots which become necrotic and covering the leaves. It can cause severe damage, especially to the onion seed crop and losses of about 80-85% on the crop by affecting leaves and seed stalk (Tomaz and Lima, 1988). In 2004, onion plants (Allium cepa) cv. Giza 6 grown in several commercial fields in Upper Egypt (Assiut Governorate) exhibited symptoms of blight on the leaves and seed-stalks. Initial symptoms on leaves consisted of tip necrosis followed by small white and/or large purple spots. Such observed symptoms resembled Stemphylium blight symptoms on onion leaves, which are caused by S. vesicarium (Wallr.) Simmons. The disease is widespread in Asia and Europe and has been recorded previously on onion plants in South Africa (Verwoperd and Du