The AMF spores in soil are not known to compete for nutrients as spore reserves are utilized for survival until root contact is achieved. Following root entry, competition can occur for infection sites, host photosynthates, and root space (Smith and Read 1997). Competition between AMF and pathogens can be used for physical exclusion of pathogen (Davis and Menge 1980; Hussey and Roncadori 1982; Smith 1988), if the host is preinoculated with AMF. Simultaneous colonization of AMF and the pathogen may not provide a competitive edge for AMF for inoculum build-up (Daniels and Menge 1980) because of its relatively slow growth rate compared with the pathogen. In contrast, some others have noted that competition may not occur between AMF and other organisms (Sempavalan et al. 1995). Competition, as a mechanism of suppressing pathogens by AMF did not receive much consideration, because in some cases pathogens were suppressed even in noncolonized root portions that was later described as induced resistance by AMF (Pozo et al. 1999). In addition, inconsistencies with regard to prerequisites and AMF effects on pathogens have contributed to a lack of interest.
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