Competition for Infection Between Vesicular‐arbuscular Mycorrhizal Fungi

Summary The competitive abilities of three VAM fungi were investigated. Various pairs of fungi were interacted and the amounts of infection produced by mixed and single inocula were compared. The outcome of the interactions varied according to the fungi involved. Aggressiveness appeared to be inversely related to infectivity. In the interactions examined, both Glomus fasciculatum (Thaxter sensu Gerdemann) Gerdemann & Trappe and Glomus tenue (Greenall) Hall were less aggressive than Gigaspora decipiens Hall and Abbott. No interaction occurred between Gl. fasciculatum and GL tenue. Except in the interaction between Gl. fascicidatum and Gi. decipiens, the total amount of infection formed by mixed inoculation was similar to that formed by single inoculation of the more infective fungus of the interacting pair. The outcome of the interactions were shown to be affected, in some circumstances, by inoculum frequency, time of harvest, most incubation of the inoculum, and the spatial distributions of the interacting propagules.