Molecular Divesity of Arbuscular Mycorrhizal Fungi and their Influence on Micropropagated Medicinal Pants

Abstract

Mycorrhizas are mutualistic symbiotic associations formed between many plant roots and certain fungi. The association is characterized by the movement of plant produced carbon to the fungus and fungal acquired nutrients to the plant. The term mycorrhiza, which literally means fungus root, was first applied to fungus tree associations described in 1885 by the German forest pathologist A.B. Frank. Available fossil and molecular evidence, supports the concept that this symbiosis is of ancient origin, implying a very long period of co-evolution of plants and fungi with a possible integral part in establishment of a land flora around 450 million years ago (Simon et al., 1993 ; Remy et al., 1994). Bidirectional nutrient transfer is the main basis for mutualism. The fungi depend on a supply of photosynthate from the plants and at the same time increases uptake of mineral nutrients particularly phosphorus from the soil (Harrison, 1997 ; Smith and Read 1997). Hence both members of the association can benefit, but whereas symbiosis is obligate for the fungi, this is not the case for the plants, which vary in their responsiveness to fungal colonization. Two types of mycorrhizae are known today : ecto and endomycorrhizas. The ectomycorrhizas are characterized by an extracellular fungal growth in the root cortex. They are more common in temperate and boreal forest trees and number over 5000 species mainly within the Basidiomycetes (Siverding, 1991).