Mycorrhizal symbiosis is known since the 19th century and has been described as the coexistence of fungus with the roots of vascular plants. Root colonization by endomycorrhizal fungi causes changes in the quantity and quality of exudates produced by roots. The mycorrhiza may also affect plants’ health status, their competitiveness and succession in eco-systems, and the formation of soil aggregates. The presence of a symbiont in the roots of plants causes a direct and indirect effect on rhizosphere microorganisms, fixing free nitrogen and transforming compounds constituting nutrient substrates for plants. The physiological and morphological relations of AMF with the plant promote its vitality and competitiveness by increasing resistance to abiotic and biotic stresses. Effective activation of the plant immune responses may occur, not only locally but also systemically. Mycorrhizal fungi, through the change of the composition and amount of root exudates, have influence on the development and activity of the communities of soil microorganisms. Certain soil bio-controlling microorganisms frequently showing synergism of the protective effect on plants together with AMF. In some cases, however, no positive interaction of selected microorganisms and endomycorrhizal fungi is observed. Double inoculation with the some species of bacteria and the mycorrhizal fungus can cause a decrease in the yielding the plants. Mycoparasitism of AMF spores and hyphae is also encountered in interaction between saprophytic fungi and AMF. This phenomenon is based on the lytic abilities of some fungi species which can lower the level of colonization and the effectiveness of mycorrhizal symbiosis with plants. Good knowledge of plant symbiosis with endomycorrhizal fungi and activity of these fungi in soils is necessary for their use in plant production.

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