Relations between rhizobial nodulation and root colonization of Acacia crassicarpa provenances by an arbuscular mycorrhizal fungus, Glomus intraradices Schenk and Smith or an ectomycorrhizal fungus, Pisolithus tinctorius Coker & Couch

The present study was initiated to (i) determine the ability of an ectomycorrhizal and an arbuscular mycorrhizal symbiont to colonize three provenances of Acacia crassicarpa root systems, (ii) to examine plant growth response to the mycorrhizal inoculation and (iii) to measure their influence on the rhizobial symbiosis with a Bradyrhizobium isolate. This study has been performed with 2 fungal symbionts: Glomus intraradices, an Arbuscular Mycorrhizal fungus, and an ectomycorrhizal fungus Pisolithus tinctorius strain GEMAS. Two experiments have been performed during two different climatic periods, hot season ( 30 degrees C day, 20 degrees C night, June to October) for ectomycorrhizal inoculation and cold season ( 25 degrees C day, 15 degrees C night, November to March) for endomycorrhizal inoculation. Moreover, Bradyrhizobium sp. strain Aus13C has been co-inoculated with each of these fungal symbionts. The results showed that ectomycorrhizal and AM fungal symbiosis clearly benefit to the growth of A. crassicarpa provenances and these fungal symbioses greatly improve the rhizobial nodulation process. However, some differences of growth were observed between the provenances tested and our results showed that both Papua New Guinea provenances produced more important total biomass than the provenance from Madagascar in both experiments However, no significant differences were observed in terms of nodulation and mycorrhization. Further research must be undertaken to identify the convenient ecological characteristics in which each kind of mycorrhizal symbiosis exerts the best effect on plant growth and nodulation formation and to identify in such environmental conditions the better rhizobial/mycorrhizal symbiosis combination.