Downy mildew, caused by Peronospora manshurica (Naoum.) Syd. is a relatively common disease of soybeans. First symptoms appear as indefinite lighter green areas on the upper surface of the leaf. Later, these areas become more chlorotic and appear angular, being delimited at the edges by small veins. During periods of heavy dew, the fungus sporulates profusely from the underside of these chlorotic areas. Later in the season, these areas change to well-defined greyish brown lesions with chlorotic borders. Large numbers of oospores of the fungus may be found in the necrotic tissue of these lesions. Oospores in overwintered leaf debris or oospore encrusted seed are sources of initial infection, and conidia are responsible for secondary spread in the field.
Geeseman, Lehman, and Grabe have reported several physiological races of downy mildew in the United States. Grabe applied this physiologic specialization when he developed a laboratory technique for the identification of morphologically similar varieties of soybeans.
Proceedings of the Iowa Academy of Science
©1958 Iowa Academy of Science, Inc.
Pederson, Vernyl D.
"A New Method of Obtaining Systemic Infection of Soybeans by Peronospora manshurica (Naoum.) Syd.,"
Proceedings of the Iowa Academy of Science, 65(1), 146-149.
Available at: https://scholarworks.uni.edu/pias/vol65/iss1/18