Host-Fungus Specificity, Recognition and Compatibility in Mycorrhizae

Abstract

Susceptibility in plants to parasites (for definition see Vanderplank, 1978) is considered to be a relatively rare phenomenon in nature; a striking exception to this rule is found in mycorrhizal associations. Mycorrhizae, a term describing a range of mutualistic associations between soil fungi and plant roots, are no doubt the most frequent examples of compatibility between plants and microbes. The mycorrhizal habit has a long evolutionary history (Nicolson, 1975, Pirozynski and Malloch, 1975, Boullard, 1979) and today more than 90% of all plant taxa, ranging from thallophytes to angiosperms, form associations of one type or another with mycorrhizal fungi. Only a small number of plant species belonging mainly to the Cuperaceae, Chenopodiaceae, Cruciferae, Juncaceae and Proteaceae are nonmycorrhizal and can be considered as incompatible towards mycorrhizal fungi. A characteristic feature of the fungi forming mycorrhizae is that, although they are generally widespread in soils, they exhibit a strong biotrophic dependence on their host plants and are rarely free-living saprophytes.