Abstract
Background and Aims Phosphorus (P) deficiency limits crop productivity. Root hairs are crucial for P acquisition and may influence plant–microbe interactions. We investigated how root-hair defects affect plant responsiveness to beneficial bacteria under low-P conditions, using maize, rice and barley as cereal screening contexts. Methods A greenhouse screen was conducted in sterile low-P soil using three cereal species, 12 genotypes, including root-hair mutants and corresponding wild types, and selected bacterial inoculants. Maize was further analyzed for shoot biomass, shoot P concentration, total shoot P content and root traits. A 7-d agar plate assay assessed root-hair traits and early root system architecture (RSA) in the maize mutant rth5 , complemented by in vitro bacterial characterization. Results A consistent genotype-dependent growth response was observed mainly in maize, with the root-hair mutant rth5 responding most strongly to Kribbella and Nocardioides . Inoculation mitigated the lower shoot P concentration of rth5 and increased its total shoot P content and biomass. While Kribbella also increased root biomass and RSA traits, Nocardioides primarily enhanced shoot P accumulation and RSA. Agar plate assays revealed that bacterial inoculation did not restore the defective root-hair phenotype of rth5 but remodeled early RSA, including root length, surface area and branching. In vitro assays confirmed genus-level differences in plant growth-promoting traits. Conclusion Kribbella and Nocardioides promote maize growth under low-P conditions in a genotype-dependent manner. In rth5 , improved performance was associated with RSA remodeling and improved P acquisition rather than morphological restoration of root hairs. Graphical Abstract Created in BioRender. Huang, X. (2026) https://BioRender.com/mdwnd2b