Cultivable bacteria associated with infective propagules of arbuscular mycorrhizal fungi. Implications for mycorrhizal activity

This study aimed to isolate and characterize bacteria associated with surface-sterilized germinated propagules of arbuscular mycorrhizal (AM) fungi. It also aimed to evaluate their activity as mycorrhization helper bacteria (MHB) on the AM fungus Rhizophagus intraradices, which is commonly used in the formulation of bioinoculants. Most isolated bacteria did not significantly affect the viability and subsequent growth of mycelia. Azospirillum sp., Rhizobium etli, Bacillus megaterium, Bacillus sp., and Paenibacillus rhizosphaerae significantly enhanced pre-symbiotic variables (the re-growth/germination and the mycelia formed from AM propagules). P. rhizosphaerae, Azospirillum sp., and R. etli also increased extraradical mycelial length, mycorrhization percentages and the number of newly formed spores. The isolated MHB were characterized based on their starch-degrading ability, indole acetic acid production, phosphate solubilization, and inhibition of phytopathogenic fungal growth. Results suggest that some of the MHB studied, in association with viable AM propagules, could be potentially used as complex microbial inoculants for plant growth promotion.