Relative quantities of antifungal metabolites produced in resistant and susceptible soybean plants inoculated with <i>Phytophthora megasperma</i> var. <i>sojae</i> and closely related nonpathogenic fungi

Abstract

Resistant Harosoy 63 plants produced 7 times as much fungal inhibitor as susceptible Harosoy when both were inoculated with the soybean pathogen, P. megasperma var. sojae. When the challenging fungus was a nonpathogenic variety of P. megasperma, Harosoy 63 produced only twice as much inhibitor as Harosoy. A closely related fungus, P. cactorum, also nonpathogenic on soybean, stimulated equal amounts of inhibitor in both varieties. The three Phytophthora isolates did not differ significantly in their ability to stimulate inhibitor in Harosoy 63, but in Harosoy, both isolates of P. megasperma stimulated significantly less inhibitor than did P. cactorum. Inhibitor from the interaction of P. megasperma var. sojae × Harosoy 63 was most inhibitory to P. megasperma and least inhibitory to P. cactorum.