Host-Pathogen Interactions: X. Fractionation and Biological Activity of an Elicitor Isolated from the Mycelial Walls of Phytophthora megasperma var. sojae.

An elicitor of phytoalexin production in soybean (Glycine max L.) tissues was isolated from purified Phytophthora megasperma var. sojae mycelial walls by a heat treatment similar to that used to solubilize the surface antigens from the cell walls of Saccharomyces cerevisiae. The wall-released elicitor is a discrete, minor portion of the P. megasperma var. sojae mycelial walls. The elicitor released from the mycelial walls was divided by diethylaminoethylcellulose and concanavalin A-Sepharose chromatography into four fractions, each having different chemical characteristics. The four fractions were obtained from each of the three races of P. megasperma var. sojae. The corresponding fractions from each of the three races are very similar in composition and elicitor activity. The results suggest that the elicitor activity of each fraction resides in the glucan component of the fraction. Evidence is presented to demonstrate that the elicitors are not race-specific and that the accumulation of glyceollin is not sufficient to account for race-specific resistance.