Effects of co-inoculation of plant growth-promoting bacteria and Rhizoglomus clarum on growth, nutrition, and root microbiome of first-season maize

Abstract

Aims Maize (Zea mays L.) is a crucial crop for global food security, and its sustainable management is essential. Inoculation with plant growth-promoting bacteria (PGPB) offers a promising strategy to enhance yield and promoting more sustainable production system. While Azospirillum brasilense is the most widely adopted nitrogen-fixing bacterium in Brazilian agriculture, other native PGPB species also exhibit potential but require further study. Furthermore, we hypothesized that co-inoculating these PGPB with arbuscular mycorrhizal fungi (AMF), such as Rhizoglomus clarum, would generate synergistic effects on plant development and nutrition, yield and modulate the root microbiome.

Methods A field experiment was conducted in the Brazilian Cerrado over two growing seasons. The design was a randomized block in an 8 × 2 factorial scheme. The first factor consisted of PGPB inoculation (seven distinct species including Az. brasilense, Bacillus spp., Burkholderia sp., and Nitrospirillum sp., plus a control). The second factor was the presence or absence of R. clarum inoculation. We evaluated crop biometrics, yield components, foliar content and grain export of macro and micronutrients, and root microbiome diversity.

Results AMF inoculation increased maize leaf copper content. The bacteria A. macrocytogenes and N. amazonense increased grain zinc content and export. Coinoculating B. aryabhattai with AMF promoted a greater ear diameter. Inoculations with Bur. vietnamiensis and N. amazonense, either alone or co-inoculated with R. clarum, modulated the community of bacteria, fungi, and AMF recruited by the roots.

Conclusion Co-inoculations of PGPB with R. clarum can promote maize growth and nutrition, with emphasis on Az. brasilense, B. amyloliquefaciens, and B. aryabhattai. However, further studies are necessary to validate the stability of these inoculations and interactions under different field conditions.