Submitted to: Weed Science Society of America Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 2/8/1996
Publication Date: N/A
Technical Abstract: A small proportion of the microbial population in rhizospheres of weeds possesses abilities to detrimentally affect growth of the host weed. These rhizosphere microbes can be selected, screened for bioactivity, and returned to the weed to displace other rhizosphere inhabitants via inoculation causing suppression of weed growth. Among the most promising agents for weed seedling inhibition are deleterious rhizobacteria (DRB), which aggressively colonize and establish on seedling roots. Rhizobacteria for biological control of weeds likely metabolize phytotoxins at the root surface which are readily absorbed by the plant. Known metabolites produced in the rhizosphere of plants that can be phytotoxic at higher than physiologic concentrations include the auxins and hydrogen cyanide (HCN). The prospect of using rhizobacteria that produce excessive amounts of growth-regulating substances in the rhizosphere to suppress growth of weed seedlings has not been investigated. DRB were examined for their ability to produce phytotoxic metabolites in the weed seedling rhizosphere and for host specificity. Selected DRB were applied to soil and planted to soybean (Glycine max) and green foxtail (Setaria viridis). Root growth of green foxtail was greatly suppressed by DRB when applied with tryptophan, but root growth of soybean was not affected. HPLC analyses of rhizosphere soil revealed high concentrations of indole-3-acetic acid and tryptophol. As a component in a weed management system, rhizobacteria could minimize competition of specific weeds by suppressing seedling growth through overproduction of plant growth regulators.