Race-specific molecules that protect soybeans from Phytophthora megasperma var. sojae.

Phytophthora megasperma var. sojae (A. A. Hildebrand) is a fungal stem and root rot-causing pathogen of soybeans. Glycoproteins secreted into the medium of the aseptically cultured fungus have been partially purified by (NH(4))(2)SO(4) precipitation and by column chromatography on norleucine-substituted Sepharose 4B and on DEAE-cellulose. Glycoprotein preparations from P. megasperma var. sojae races 1, 2, and 3 have been tested on four cultivars of soybeans. The partially purified glycoproteins from incompatible races of the pathogen (races that cannot successfully infect the plant), but not those from compatible races (races that can kill the plant), protect soybean seedlings from attack by compatible races. The seedlings are protected by introducing the glycoproteins into hypocotyl wounds of seedlings either 90 min prior to or at the time of inoculation of the wounds with mycelia of one of the pathogens. The glycoprotein preparations are poor nonspecific elicitors of phytoalexin accumulation; the glycoproteins have less than 1.0% of the elicitor activity of the glucans present in the mycelial walls of the pathogen.