Selective plant growth suppression by shoot application of soil bacteria

Selected rhizosphere bacterial isolates, previously determined as plant gro wth deleterious, were tested for their ability to suppress plant growth aft er foliar spray applications, for selectivity with regard to plant species, and in pilot field experiments for their potential as weed biocontrol agen ts. Inundative foliar applications of aqueous bacterial suspension were per formed on a range of weed and crop species. Plant symptoms after spraying r anged from rapid necrosis and wilting to an overall growth suppression or s tunting. Significant and selective reductions in biomass of up to 90% fresh weight, as well as large reductions in plant survival and plant height wer e recorded in greenhouse pot experiments. However, monocotyledonous plants were affected weakly or not at all by two isolates extensively tested. Effe cts of these were dose- and plant age-dependent, and were for some plants e nhanced by high relative humidity. For one isolate, A153, effects were also expressed in cell-free culture filtrates pointing to involvement of specif ic metabolites. In pilot field experiments, strong growth suppression was o bserved on broad-leaved plants, while barley crop plants were unaffected.