Mycorrhizal Plants in Response to Adverse Environmental Conditions

Abstract

Plant roots provide an ecological niche for many of the microorganisms that abound in soil. In natural ecosystem mycorrhizal fungi occur in nearly all soils on the earth and forms a symbiotic relationship with root of most terrestrial plants (Bagyaraj, 1991). The two major types ofmycorrhizae are the ectomycorrhizae (EM) and the endomycorrhizae (Vesicular-arbuscular mycorrhizae, VAM), so named and distinguished by the anatomical nature of the symbiotic relationship. VAM fungi are known to be associated with most agricultural crops and appear over a wide range of ecological zones; they have 1000 genera ofplants representing some 200 families (Bagyaraj, 1991). There are atleast 30,000 receptive hosts in the world flora (Kendrick and Berch, 1985), and about 150 species of VAM fungi(Schenck and Perez 1985). If the hosts are divided up evenly among the fungi with no overlap in host range, each fungus would have more than 2500 potential partners (Bagyaraj, 1991). The beneficial effects of VAM fungi on plant growth have long been recognized. Increased growth and yield of many plants owing to infection with VAM fungi has been attributed to enhance nutrition status, especially of phosphorous (Rhodes and Gerdemann, 1978; Safir, 1980; Safir and Nelson, 1981), and to improve water relations (Hardie and Layton, 1981; Levy and Krikun, 1980; Safir et al. 1972; Sievertding, 1979).