VIEW ARTICLE

An Inducer of Soybean Phytoalexin and its Role in the Resistance of Soybeans to Phytophthora Rot. J. A. Frank, Research Assistant, Department of Plant Pathology, University of Illinois, Urbana 61801; J. D. Paxton, Associate Professor, Department of Plant Pathology, University of Illinois, Urbana 61801. Phytopathology 61:954-958. Accepted for publication 10 March 1971. DOI: 10.1094/Phyto-61-954.

A material capable of inducing phytoalexin production in soybean plants was isolated from Phytophthora megasperma var. sojae. This inducer is soluble in methanol, and has a paper chromatographic R_F of 0.23 using a butanol:acetic acid:water solvent (4:1:5, v/v). The molecular weight of the inducer is in the range of 10-30,000, and chemical tests indicate that it is a glycoprotein. The production of this inducer is the key reaction attributed to the Rps gene for resistance in soybeans. The amount of inducer produced by the fungus was greatly increased when the fungus was placed in contact with the resistant (Harosoy 63) host tissue for 8 hr. This same increase in the amount of inducer could be stimulated by placing the fungus in the filter-sterilized juice of the resistant host for 8 hours. When the same procedures were carried out using the susceptible (Harosoy) host as the stimulator, there was no increase in the amount of inducer present in the fungus. Other soybean varieties carrying the Rps gene reacted in a manner similar to the resistant Harosoy 63 variety.