Dual inoculation with seleted rhizobium and arbuscular mycorrhizal isolates in unsterile soils

Nursery pot experiments were conducted in Senegal and Kenya using rhizobial and arbuscular mycorrhizal inoculants singly and in combination. Growth responses of Calliandra calothyrsus seedlings were examined in unsterilised local soils using Flores and San Ramón provenances. The experiments also examined the effects of using single- and multi-isolate inoculants and soil solarisation on seedling growth. Results showed that dual inoculation with rhizobial and mycorrhizal inoculants gave better results than single inoculation with either microsymbiont, and that rhizobial and mycorrhizal inoculants were more effective in promoting seedling growth than microsymbionts occurring naturally in the soils. Responses varied according to the fertility of the soils. Rhizobial and mycorrhizal inoculation tended to benefit different aspects of plant growth, with rhizobial inoculation increasing leaf dry mass and mycorrhizal inoculation increasing stem and root dry mass. Solarisation of two Kenyan soils produced contrasting effects on seedling growth, which may have been related to changes in soil chemistry or populations of naturally occurring microsymbionts and soil pathogens. For both rhizobia and mycorrhizas, single isolate inoculants performed better than mixed isolate inoculants. (Résumé d'auteur