Abstract

Several monosporal VAM cultures, raised from spores isolated from the rhizosphere soils under Acacia auriculiformis, Casuarina equisetifolia and Pterocarpus marsupium, and other VAM cultures obtained from various sources were screened under glasshouse conditions to select the most efficient ones for enhancing the growth of each of the three test tree species. Inoculation with VAM fungi was found to benefit the growth and biomass production of all three species. However, the response to inoculation varied with different isolates of VAM fungi. A significant increase in total P content was also observed in the inoculated plants. Based on overall performance and a cluster analysis of the data, the most efficient VAM selected for field studies were Glomus caledonium and Glomus mosseae for Acacia, culture M-23 and G. fasciculatum (V-10) for Casuarina, and G. intraradices and culture G. mosseae (V-8) for Pterocarpus. Several of forty cultures of Rhizobium and Frankia, isolated from the nodules of A. auriculiformis, P. marsupium and C. equisetifolia were tested for acid/alkali production and acid/aluminium tolerance, and screened for efficiency in increasing growth and nodulating the 3 test tree species in the glasshouse. The two best strains were selected for each species. In glasshouse trials on the effect of fertilizers on seedling growth with and without and symbionts, significant differences were observed between various treatments. Significant differences were also observed between treatments (VAMN2 fixing symbionts and fertilizer) in height and diameter of field planted 1-year-old A. auriculiformis. All the treatments responded favourably to nitrogen and/or phosphorus fertilizer application. The percentage increase in growth (height and diameter) with fertilizer addition was more in symbiont-inoculated plants than non-inoculated controls. Symbiont inoculation alone did not increase growth. Maximum percentage increase in height was 57.4 (G. calidonius + fertilizer) and 56.2 (G. calidonius + Rhizobium A-19 Calicut + fertilizer) whereas for diameter growth the maximum increase was 84.5 (Glomus intraradices + Rhizobium A-16 Panamaram + fertilizer), followed by 70.0 (G. calidonius + fertilizer). In control treatments the increase in height anddiameter growth was 11.5 and 41.4