Methodological Framework to Evaluate Entomopathogenic Fungi and Rhizobial Co-Inoculation Effects on Plant Growth and Root Morphology.

Entomopathogenic fungi are increasingly recognized as multifunctional bioinputs, but robust methodological approaches are needed to evaluate their compatibility with established microbial inoculants and their effects on plant performance. Our study proposes an integrative framework to assess Metarhizium-Bradyrhizobium interactions in soybean (Glycine max), combining laboratory compatibility screening with greenhouse assessment. First, Metarhizium anisopliae LCM S04 and Metarhizium brunneum LCM S11 were tested against Bradyrhizobium diazoefficiens BR 85 (=SEMIA 5080) and Bradyrhizobium japonicum BR 86 (=SEMIA 5079) using dual-culture assays in a medium that supported the growth of both fungal and bacterial partners, allowing direct evaluation of intermicrobial compatibility. Subsequently, the microorganisms were evaluated in soybean under greenhouse conditions through direct seed inoculation. Each seed received bacterial culture, fungal suspension, or both (including absolute and nitrogen-fertilized controls). Plants were maintained under controlled conditions for 47 days. Plant height, leaf production, branching, nodulation, biomass, and root morphology were assessed. No inhibition zones were observed in vitro, and co-inoculation did not impair nodulation. The combination BR 86 + LCM S04 improved fine root number in soybean. This framework provides a reproducible approach for evaluating microbial compatibility and functional bioinput benefits and can be adapted to crops other than soybean.