Studies on Vesicular-Arbuscular Mycorrhizal Fungi of Forest Trees-1. Association of Gigasporaceous Fungi, An Important Feature of Some Acacia species

Studies were conducted to find out the composition of vesicular-arbuscular mycorrhizal fungi (VAMF) in the rhizosphere of polypot raised seedlings of Acacia nilotica, A. catechu, A. mangium, A. auriculiformis, A. tortilis, Dalbergia sissoo, Azadirachta indica, Michelia champaca, Pterigota alata, Tecomella undulate, Paulownia fortunei and P. tomentosa. In all the forest trees Glomus predominated followed by Acaulospora except M. champaca and P. alata. Gigasporaceous fungi (Gigaspora and Scutellospora) were present in some Acacia spp. in most of the locations and in D. sissoo in some of the areas whereas they were absent in other tree species except A. indica where Gigaspora was present in insignificant number. Presence of more than 80% spores of Acaulospora in M. champaca and about 65% in P. alata with majority of the spores belonging to A. scrobiculata and a few to A. spinosa, a good number of spores of Glomus clarum in T. undulata, appreciable number of spores of Scutellospora werusubiae in some locations in D. sissoo and a good number of spores of Gigasporaceous fungi in A. nilotica (S. fulgida, S. gregaria), a. catechu (Gigaspora rosea, G. margarita, S. fulgida) and A. mangium (S. heterogama) suggests a strong affinity of these fungi with the associated trees and the ability to enter into symbiotic association with the preferred host plants in case they are present in the soil. Presence of 263 spores of G. rosea/440 g of sandy substrate in the rhizosphere of about 2 m high saplings of Acacia sp. raised in a raised sand bed in a forest area in Gainesville. Florida as recorded by one of the authors (MDM) during his visit to U.S.A. in 1995 also lends support to the above contention. It is suggested that Acacia spp. which appear to be dependable source of Gigasporaceous fungi are used to prepare starter cultures of these fungi and production of VAM inoculums as any VAM inoculation programme for Gigasporaceous fungi dependant Acacia spp. will remain incomplete if these fungi do not constitute as an integral component of VAM inoculums to fortify seedlings in the nurseries particularly in areas where these fungi occur naturally.