Submitted to: Biocontrol Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/6/1997
Publication Date: N/A
Interpretive Summary: Farmers are adopting more sustainable practices such as crop rotations and reduced use of pesticides to protect and maintain our environment. As pesticide use decreases, nonchemical methods of controlling pests must be developed to assure economic production of agricultural goods. Biological control, consisting of naturally occurring organisms (insects, fungi, bacteria) is an alternative to chemicals for managing weeds in crops and pastures. The numerous organisms in nature with potential for biological control must be tested rapidly and efficiently in order to select the most effective organisms, to verify their weed control ability in the field, and to supply them in the shortest time possible to farmers using sustainable practices. We developed a rapid method for evaluating large numbers of bacteria for effectiveness in injuring leafy spurge, a serious weed pest infesting millions of acres of cattle-grazing and recreation lands in the United States. The method uses tissue grown from the plant and reacting this with the biological control organism. The method reduced evaluation by 20 times compared to standard methods, saved labor costs, and made more efficient use of expensive laboratory space. Ultimately, the results of this research could impact the practical implementation of biological control of weeds by drastically reducing the time from initial assessment to selection of superior organisms for use on lands infested with leafy spurge.
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 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 at 27C for 48 h. 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. A high proportion nof isolates found to be phytotoxic in tissue culture bioassays were similarly effective in standard leafy spurge seedling bioassays. 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.