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A review is given about the morphological and ultrastructural characters of Piriformospora indica. The morphology of hyphal cells, mycelial, and chlamydospores are described in detail. Piriformospora is able to form different types of interactions with plant groups mosses, ferns, and gymno- and angiosperms. A survey of the tested host plants is given. The morphology of interacting hyphae and root cells depends on the plant species. Besides the mutualistic mode of life, Piriformospora indica is able to live as an endophytic fungus; under specific conditions, this species can behave as a necrotrophic fungus. All these different characters of the plant growth-promoting fungus, Piriformospora indica, indicate that this species is very valuable for basic research and a wide spectrum of applications in agriculture and horticulture.

Soil microflora influence plant growth and health both beneficially and adversely. The microorganisms used as biofertilisers stimulate plant growth response by providing necessary nutrients as a result of their colonisation of the rhizosphere (Azotob acter, Azospirillum, phosphate-solubilising bacteria and cyanobacteria) or by symbiotic association (Rhizobium, mycorrhizae fungi and Frankia). They may also regulate the physiological processes in the ecosystems by involvement in the decomposition of organic matter, fixation of atmospheric nitrogen, secretion of growth-promoting substances, increase in the availability of mineral nutrients, immobilisation of these assimilable nutrients and protection of plants from pathogens (Mukerji et al. 1998). Thus, rhizosphere effects through microbial activities, modify the plants by providing plant growth substances and increasing the availability of nutrients at the root zone. Plant root anatomy and tissue articulation play a significant role in the symbiotic processes (Lynch 1995).