Specific elicitors of plant phytoalexin production: detenninants of race specificity in pathogens?

Race 1 cultures of the phytopathogenic fungus Phytophthora megasperma var. sojae produced a specific elicitor of the soybean phytoalexin hydroxyphaseollin that resulted in higher production of the phytoalexin on disease-resistant Harosoy 63 soybeans than in the near-isogenic susceptible cultivar Harosoy. Race 3 of the fungus, which gives susceptible reactions on both soybean cultivars, did not produce the race I specific elicitor.