Isolation and characterization of rhizosphere bacteria with potential for biological control of weeds in vineyards

Aims: Deleterious rhizosphere inhabiting bacteria (DRB) have potential to suppress plant growth. This project focuses on the isolation of DRB with potential for development as commercial products for weed control. Methods and Results: Bacteria were isolated from the rhizosphere, rhizoplane, and endorhizosphere of seedlings and mature plants of wild radish (Raphanus raphanistrum), annual ryegrass (Lolium rigidum) and capeweed (Arctotheca calendula) growing in vineyards in the Swan Valley, Western Australia. A majority (81.5%) of the 442 strains was obtained from either rhizospheres or rhizoplanes. Rapid screening techniques were developed to evaluate in the laboratory and glasshouse the effects of bacteria on plants. Strains were screened in the glasshouse for deleterious effects on annual ryegrass, wild radish, grapevine rootlings (Vitis vinifera) and the legume cover crop subterranean clover (Trifolium subterraneum). Three strains were identified using the Biolog system and 16S rRNA gene sequencing as two strains of Pseudomonas fluorescens (WSM3455 and WSM3456) and one strain of Alcaligenes xylosoxidans (WSM3457). One of the P. fluorescens (WSM3455) strain produced hydrogen cyanide, an inhibitor of plant roots and a broad-spectrum antimicrobial compound. Conclusions: Three strains specifically inhibited wild radish but had no significant deleterious effects on either grapevine rootlings or subterranean clover. Significance and Impact of the Study: This study suggested manipulation of the weed seedling rhizosphere using identified DRB as a potential biocontrol agent for wild radish.