Efficacy of Rhizobacteria as biological control agents of grassy weeds
Deleterious rhizobacteria (DRB) associated with the roots and rhizosphere of weeds have tremendous potential as biological weed control agents. Screening and evaluation of the efficacy of DRB for biological control of downy brome (Bromus tectorum), green foxtail (Setaria viridis), and wild oats (Avena fatua) was conducted and methods for optimizing biocontrol activity were determined. Several hundred isolates of DRB were screened, with more than 100 isolates with 280% suppression of root growth in laboratory bioassays showing weed inhibitory properties. An increase in root growth suppression was demonstrated when unfiltered bacterial broth was incorporated into agar, compared to cell-free culture filtrate alone. Nutritional factors also played a role in enhancing biocontrol activity. Increases in root and shoot suppression were demonstrated when selected DRB isolates were grown in a nutrient broth, compared to a minimal salts broth. Specific requirements in the nutritional environment of the bacterial culture medium and the effect these changes have on propagule yield, efficacy and stability will have a significant impact on the potential of a biological control agent and its success as a commercial product.
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