Submitted to: World Congress of Soil Science
Publication Type: Proceedings
Publication Acceptance Date: 8/19/1998
Publication Date: N/A
Technical Abstract: Leafy spurge (Euphorbia esula L.) is a perennial plant whose deep root system and vigorous plant growth make it a persistent weed problem in pastures and rangelands of the northern Great Plains of the United States and the Prairie Provinces of Canada. Relative ineffectiveness of current herbicides for controlling leafy spurge led to the investigation of biocontrol methods. Deleterious rhizobacteria (DRB), nonparasitic bacteri colonizing root surfaces and suppressing plant growth, are potentially effective biocontrol agents for leafy spurge. The objective of this study was to evaluate rhizobacteria isolated from weedy Euphorbia species for potential biocontrol activity on leafy spurge and to investigate the interaction of selected isolates with plant cells and the possible modes of action involved in plant growth reduction. A primary screening method based on leafy spurge callus tissue effectively distinguished between rhizobacteria with different levels of phytotoxicity. Selected DRB reduce seedling emergence and root development by more than 65% of controls. Electron microscopy revealed considerable alterations including membrane disruptions and cell plasmolysis in colonized plant cell surfaces, apparently caused by phytotoxins released by DRB and absorbed by plant cells which led to reduced plant growth. Thus, the primary screening method effectively selected phytotoxic DRB. The adoption of biocontrol methods based on DRB offers new strategies for managing leafy spurge.