Application method affects the distribution and efficacy of rhizobacteria suppressive of downy brome (Bromus tectorum)

Rhizobacteria that are capable of suppressing plant growth in a species-specific manner have potential as bioherbicides. Three bacterial strains, Pseudomonas putida strain FH160, Stenotrophomonas maltophilia strain FH131, and Enterobacter taylorae strain FH650, have been reported to suppress the growth of downy brome (Bromus tectorum L.). These strains were evaluated in the greenhouse using various application methods for the ability to colonize the rhizosphere and to inhibit downy brome emergence or biomass production. When the biocontrol strains were incorporated into the soil profile more consistent colonization of the downy brome rhizosphere by all three strains resulted relative to that achieved by either wheat seed or soil surface applications. Downy brome emergence was reduced when any of the bacterial strains were applied as a soil surface application or a wheat seed treatment. Wheat biomass production was not enhanced when plants were grown individually in soils treated with any of the three biocontrol strains. When wheat was interplanted with downy brome, increases in wheat biomass were obtained with certain bacterial treatments relative to untreated controls suggesting that these rhizobacteria diminish the competitive ability of downy brome. Application method affects the population size and distribution of the biocontrol strain in the soil profile and downy brome rhizosphere, and thus, has a marked influence on efficacy of rhizobacteria for weed control.