Submitted to: Agronomy Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 10/1/1996
Publication Date: N/A
Technical Abstract: Screening large collections of microorganisms for potential biological control activity on economically important weeds is often difficult because seeds required as indicator species are not available in large supply and are highly variable in viability and germination resulting in nonuniform seedling development. A bioassay system for rapidly assessing phytotoxic effects of rhizobacteria was developed based on leafy spurge (Euphorbia esula L.) callus tissue culture in multiple-well plates. Callus pieces (0.5g) were placed in 24-well plates containing Gamborg's B5 medium, inoculated with rhizobacterial suspension, and incubated 48h. By rating inoculated callus for cellular damage, we identified about 30% of rhizobacteria isolated from weedy Euphorbia spp. collected in Europe and North America as highly phytotoxic. Damage symptoms included growth reduction, discoloration, and extensive cellular leakage. Phytotoxicity was sclosely correlated with in vitro hydrogen cyanide production by rhizobacteria. A high proportion of phytotoxic isolates were similarly effective on intact leafy spurge plants in greenhouse tests. Several effective isolates are currently being evaluated under field conditions. The screening method based on tissue culture is rapid, host-specific, and more uniform compared to assays using seedlings. The method should be adaptable to other weed species for screening microorganisms for potential biocontrol activity.