EVOLVING STRATEGIES FOR BIOLOGICAL-CONTROL OF WEEDS WITH PLANT-PATHOGENS

Current biological control strategies involve the use of exotic or nat ive biocontrol agents, proven to be host-specific and lethal. This is a successful field of endeavor, attractive to a large cadre of entomol ogists and a few plant pathologists. The main limitation is that each weed species must be attacked by a separate host-specific agent and th ese organisms are not always lethal. Only by using a radical paradigm shift can we reach a new strategy of biocontrol. In this strategy, let hal, broad host-range pathogens are genetically modified to permit the ir safe release. Either they are rendered host-specific or they are gi ven a chemical dependency that prevents their spread or long-term surv ival. This genetic-manipulative approach offers numerous and diverse s cenarios for biocontrol. Host-specific promoters or toxins, host-depen dency by multiple auxotrophy, or mutants dependent on specific environ mental conditions are all approaches that lend themselves to genetic m odification. Such self-delimiting pathogens may have the advantage of repeated marketability, environmental safety and multiple target weeds .