Parasitism of arbuscular mycorrhizal fungi: reviewing the evidence

In order to understand the functioning of mycorrhizal fungi in ecosystems it is necessary to consider the full suite of possible biotic interactions in the soil. While a number of such interactions have recently been shown to be crucially important, parasitism is a highly neglected feature in the ecology of arbuscular mycorrhizal fungi (AMF). A number of studies have classified some interactions between populations of bacteria and fungi with AMF as parasitism, generating discussion about its consequences at both 'parasite' and host population levels. This paper reviews these various publications, and based on a set of criteria that are necessary to demonstrate parasitism, it was concluded that parasitism has not been conclusively shown to exist in AMF, even though some data are highly suggestive of such a relationship. The difficulties in gathering data supportive of parasitism were discussed, and hypotheses for defense were offered. This paper concludes by presenting potential consequences of AMF parasitism at the population/community levels and by discussing applied aspects.