Genetic Engineering Of Endophytic Bacteria: A Novel Approach For Producing Pest-Resistant Corn

Genetic engineering techniques currently permit several approaches to produce crop plants with enhanced resistance to pests. Many groups are directly introducing genes which encode for pest resistance into the plant's genome. Crop Genetics International is developing an endophyte based technology for systemic delivery of biopesticides to corn and other crops. Defined broadly, an endophyte is a plant dependent microorganism that lives protected within the tissues of its host. Among endophytic bacteria, those associated with plant disease have been the past object of study. However, nonpathogenic bacterial endophytes present an opportunity for systemic delivery of genetically-engineered biopesticides and plant growth regulators. Crop Genetics has chosen a xylem-limited endophytic bacterium, Clavibacter xyli subsp. cvnodontis (Cxc) which occurs naturally in bermudagrass and is distributed throughout the southern two-thirds of the U.S. as well as Europe and Asia. Cxc is a fastidious microorganism with precise nutritional and environmental requirements. Cxc survival is brief outside the host plant in plant debris, soil, air or water, and the endophyte is not seed transmitted. Cxc, when modified with recombinant DNA techniques, provides a systemic delivery system for biopesticides within plants. The first product under development involves Cxc producing the delta-endotoxin of Bacillus thurinqiensis toxic to European corn borer (Ostrina nubilalis). Follow-on products will deliver other insecticides, fungicides, and plant growth enhancers. Crop Genetics has developed an inoculation technology to introduce the bacterium into seeds. The protocol includes imbibition followed by pressure treatment in a buffered solution containing the bacterium. Seeds are removed from the solution, dried, and coated with conventional seed coatings. This inoculation technology does not alter seed vigor or germination and provides a satisfactory shelf life of the product.