INCIDENCE OF ARBUSCULAR MYCORRHIZAE AND THEIR EFFECT ON CERTAIN SPECIES OF TREES

An intensive survey for the prevalence of arbuscular mycorrhizal fungi (AMF) in tree species occurring in different ecological niches revealed that these symbionts were found to have associations with various tree species growing in different areas of the forest. High levels of mycelium, arbuscules, vesicles and spores were found in soil samples and in the roots of all the plants studied. The spores were formed in the rhizosphere of the roots. Mycelium vesicles and arbuscules were formed inside the cortical cells of the root. Colonization of AMF varied in different plant roots, and spore counts ranged between 76 to 350 spores/100 g of soil. Higher spore counts (more than 150 spores/100 g of soil) supported good growth of the trees. Four genera of fungi viz., Acaulospora sp., Gigaspora sp., Glomus sp. and Sclerocystis sp. were identified. Glomus was the most prevalent genus. Of the various species of Glomus observed during the study, G. fasciculatum and G. mosseae were most abundant. Inoculation of AMF on the roots of Azardirachta indica (Meliaceae), Polanthia longifolia (Annonaceae) and Terminalia arjuna (Combretaceae) increased the dry weight of the plants by 57.53, 43.49 and 65.10 percent respectively, over the controls. Combined inoculation of Rhizobium and AMF mycorrhiza on to Acacia nilotica (Mimosaceae) and Prosopis juliflora (Fabaceae) roots resulted in increases of mycorrhizal colonization, plant height, number of leaves, nodular weight and biomass production. The differences were significant compared to the untreated control plants, the mycorrhizal plants and plants treated with Rhizobium and AMF. Maximum growth, nodule weight and biomass were observed in plants inoculated with both Rhizobium and AMF.