Abstract  The potential for developing a reliable strategy for selecting rhizosphere competent bacteria, based on an improved understanding of the community diversity and population dynamics of fluorescent pseudomonads, was investigated. Isolates from a collection of over 690 fluorescent pseudomonads, obtained from sugar beet and wheat plants grown in field soils in laboratory microcosms, were genotypically and phenotypically characterised. RFLP rRNA analysis (ribotyping) revealed that the sampled population was composed of 385 related but distinct ribotypes. Most ribotypes were isolated only once and represented a transient colonising population. However, representatives of 26 ribotypes were detected more often, of which five were isolated from rhizosphere soils sampled 7 months after the first sampling. Comparative phenotypic analysis of isolates (motility, antibiotic resistance and production, adherence, fatty acid composition, substrate utilisation patterns) demonstrated that the ability to utilise organic acids as carbon sources correlated with rhizosphere competence. Single inoculum and competitive colonisation studies in planted microcosms confirmed rhizosphere competence, but also demonstrated synergistic interactions. The colonisation ability and population densities of transient strains were significantly increased when co-inoculated with rhizosphere competent isolates. These data demonstrate potential cross-feeding and combined niche exploitation, rather than direct competition, confirming the multi-factorial nature of rhizosphere competence in diverse fluorescent pseudomonad communities. They also highlight the need to consider the use of mixed inocula for plant growth promotion and the systematic selection of strains for effective biotechnological exploitation.