Screening fluorescent Pseudomonas bio-inoculants for cultivar-dependent growth promotion and root phenomics in soybean (Glycine max (L.) Merrill)

Abstract

Plant growth-promoting rhizobacteria (PGPR) offer a sustainable means of enhancing crop productivity, but their efficacy often varies with host genotype. This study evaluated twenty-four fluorescent Pseudomonas isolates for their ability to promote growth and modify root system architecture in two soybean cultivars, JS 335 and RKS 113. Isolates were applied by seed bacterisation and assessed under glasshouse conditions against an uninoculated control, using pot-culture biomass parameters and root image analysis (WinRHIZO). Growth promotion was strongly cultivar-dependent: most isolates significantly improved growth in JS 335, whereas only a subset were effective in the more vigorous RKS 113, and several reduced growth relative to the control. Only three isolates, P5, P161 and P167, significantly enhanced all six growth parameters in both cultivars, identifying them as broadly compatible candidates. Root analysis indicated that the most effective isolates reallocated biomass toward the root system and increased the proportion of fine, absorptive roots, a response consistent with auxin-mediated stimulation of root development. Root and shoot dry weights were positively correlated, indicating that enhanced root development translated into coordinated whole-plant growth. A composite index integrating growth efficacy, cross-cultivar consistency and fine-root quality ranked P5, P161 and P167, together with P124, as the leading isolates overall. These findings demonstrate that the benefit of a Pseudomonas inoculant cannot be assumed to transfer between soybean genotypes and that effective candidates are best identified by combining growth performance with root-architectural quality. Isolates P5, P161 and P167 are promising candidates for development as soybean biofertilisers and merit field evaluation.