Assess suitability of hydroaeroponic culture to establish tripartite symbiosis between different AMF species, beans, and rhizobia

BACKGROUND: Like other species of the Phaseoleae tribe, common bean (Phaseolus vulgaris L.) has the potential to establish symbiosis with rhizobia and to fix the atmospheric dinitrogen (N(2)) for its N nutrition. Common bean has also the potential to establish symbiosis with arbuscular mycorrhizal fungi (AMF) that improves the uptake of low mobile nutrients such as phosphorus, from the soil. Both rhizobial and mycorrhizal symbioses can act synergistically in benefits on plant. RESULTS: The tripartite symbiosis of common bean with rhizobia and arbuscular mycorrhizal fungi (AMF) was assessed in hydroaeroponic culture with common bean (Phaseolus vulgaris L.), by comparing the effects of three fungi spp. on growth, nodulation and mycorrhization of the roots under sufficient versus deficient P supplies, after transfer from initial sand culture. Although Glomus intraradices Schenck & Smith colonized intensely the roots of common bean in both sand and hydroaeroponic cultures, Gigaspora rosea Nicolson & Schenck only established well under sand culture conditions, and no root-colonization was found with Acaulospora mellea Spain & Schenck under either culture conditions. Interestingly, mycorrhization by Glomus was also obtained by contact with mycorrhized Stylosanthes guianensis (Aubl.) sw in sand culture under deficient P before transfer into hydroaeroponic culture. The effect of bean genotype on both rhizobial and mycorrhizal symbioses with Glomus was subsequently assessed with the common bean recombinant inbreed line 7, 28, 83, 115 and 147, and the cultivar Flamingo. Significant differences among colonization and nodulation of the roots and growth among genotypes were found. CONCLUSION: The hydroaeroponic culture is a valuable tool for further scrutinizing the physiological interactions and nutrient partitioning within the tripartite symbiosis.