VIEW ARTICLE

Resistance

Hypocotyl Reactions and Glyceollin in Soybeans Inoculated with Zoospores of Phytophthora megasperma var. sojae. E. W. B. Ward, Agriculture Canada, Research Institute, University Sub Post Office, London, Ontario, Canada N6A 5B7; G. Lazarovits(2), C. H. Unwin(3), and R. I. Buzzell(4). (2)(3)Agriculture Canada, Research Institute, University Sub Post Office, London, Ontario, Canada N6A 5B7; (4)Agriculture Canada, Research Station, Harrow, Ontario, N0R 1G0. Phytopathology 69:951-955. Accepted for publication 14 February 1979. Copyright 1979 The American Phytopathological Society. DOI: 10.1094/Phyto-69-951.

Soybean (Glycine max L.) cultivars were tested for resistance or susceptibility to races of Phytophthora megasperma var. sojae by placing droplets of zoospore suspensions on hypocotyls of etiolated seedlings. Within 24 hr, resistant, hypersensitive interactions produced brown necrotic lesions, whereas susceptible tissues were soft, water-soaked, and rotted. Up to four races were evaluated on a single hypocotyl, and the method could be of value for screening cultivars and typing races and, especially, for genetic studies. The concentration of the phytoalexin glyceollin (determined from absorption measurements at 285 nm of ethyl acetate extracts of diffusates) was consistently higher in resistant reactions than in susceptible ones. However, because of considerable quantitative variation and the fact that visual ratings were entirely reliable, glyceollin determination did not appear to provide information of critical value for screening purposes.