Interactions between the vesicular-arbuscular mycorrhizal fungus Glomus fascicuhtum and Aphanomyces euteiches root rot of peas

Interactions between Glomus fasciculatum and Aphanomyces euteiches root rot of peas (Pisum sativum), were studied in pot experiments using irradiated soil. Infections with the pathogen were suppressed by VAM when plants were challenge inoculated after two weeks. No reduction of the pathogen was detected when the plants were inoculated with both fungi at the same time. The suppression of the pathogen, obtained by preinoculation with G. fasciculatum, was not reduced when the inoculum level of the pathogen was increased thirty times. The induced resistance to A. euteiches in VAM plants was partially a systemic effect. When root systems were split into two halves, one with mycorrhiza and one with A. euteiches, the oospore production was reduced in both root systems. The infection with the pathogen was only suppressed when both fungi were present in the same pot. The background for the induced resistance is discussed.