Physiological Studies on Mycorrhizal Fungi Production

Abstract

Micro-organisms are present in large numbers on and near the feeder roots of trees, and they play vital roles in numerous physiological processes. Pelmont (1993) stated that these dynamic processes are mediated by associations of micro-organisms participating in symbiotic root activities as nitrogen fixation and phosphorus mobilization. Mousain (1993) and Strullu (1991) confirmed that the major symbiotic associations on tree roots have been bacterial with Rhizobium or fungal in mycorrhizas. Mycorrhizas are defined as durable unions based in reciprocal exchanges between plant roots and fungi (Marx and Cordell, 1994). Each one optimizes its development due to this association. Mousain et al. (1998) opined that ectomycorrhizal fungus such as Lactarius Pers., Pisolithus Alb. Schwein. and Suillus P. Karst. should be considered as fundamental micro-organisms for qualitative improvement of the trees and reforestation programs. De Araújo et al. (1008) studied the effect of culture media, initial pH, and salt concentration on the apical growth of four ectomycorrhizal fungi. However, not much information is available about ectomycorrhizal fungi biomass production and their metabolites. Because of this, a non-destructible technique was development to evaluate biomass production and analyse metabolites as pigments, enzymes, sugar, and organic acids present in agar. Baar et al. (1997) determined mycelium biomass by dissolving agar media in hot water and filtering the solution before drying (100°C, 24 h) and determining dry weight as described by Oort (1981). As discussed by Jongbloed and Borst-Pauwels (1990), this method could cause loss of water-soluble compounds amounting to approximately 35% of biomass with little variation between isolates and no effect of age of cultures and composition of media on the amount of loss. Dry weight loss of biomass of L. bicolor as estimated by Jongbloed and Borst-Pauwels (1990) was approximately 19%. Gibson and Deacon (1990) described mycelium development of ectomycorrhizal fungi in vitro by radial growth and biomass production. Jongbloed and Borst-Pauwels (1990) hypothesized that radial growth reflected exploitation of resources, whereas biomass production was a measure of accumulation of carbon and nutrients.