Submitted to: North Central Weed Science Society US Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 4/3/2000
Publication Date: N/A
Technical Abstract: Deleterious rhizobacteria (DRB) are under considerable investigation as potential biological control agents of weeds. Plant growth suppressive activity of DRB presumably results from secondary metabolites absorbed through plant roots. Harmful metabolites include hydrogen cyanide, high concentrations of auxin-like compounds, and many complex metabolites. Besides phytotoxic metabolites, DRB also produce secondary metabolites suc as exopolysaccharides and siderophores that, although not phytotoxic, are involved in establishment and competition in the complex rhizosphere environment. Previous studies have demonstrated that DRB are present in the rhizospheres of weeds found in various cropping systems. Objectives of this study were to determine possible mechanisms responsible for phytotoxicity of DRB isolated from various crop management systems and to relate growth inhibitory effects to physiological properties associated with the DRB. Seedling bioassays confirmed the phytotoxicity of detectable DRB using either lettuce as a standard indicator or the host weed seedling. In summary, the most active DRB produced more than one class of secondary metabolites presumably involved in phytotoxicity. This suggests that more than one mechanism may be involved in suppression of weed seedling growth. DRB with these properties may be detected in all cropping systems; however, the relative proportions of DRB detected in weed rhizospheres will vary among these systems.