The soil bacterium Agrobacterium tumefaciens has the remarkable ability to transfer a portion of DNA (T-DNA), derived from its resident Tumor-inducing (Ti) plasmid, to certain plant host cells. This DNA, once transferred, integrates into the host genome, where the Agrobacterium-derived genes are then expressed. The DNA-transfer capability of A.tumefaciens has been extensively exploited, by those involved in agricultural biotechnology, to introduce useful genes (like those conferring drought or salt tolerance) into various plant species. Unfortunately, for many agriculturally important crops, including corn, soybean, and wheat, Agrobacterium-mediated plant transformation is very inefficient. The long term goal of this project is to develop a generic methodology for creating Agrobacterium strains with enhanced capacities to transform these recalcitrant crops, thus rendering them amenable to genetic manipulation and to agricultural improvement. As a first step toward this goal, a generic method to 'evolve' in the laboratory a 'super-virulent' A.tumefaciens strain, which may possess the capacity to infect these plants, was explored. Because this inefficiency of Agrobacterium-mediated DNA-transfer is thought to be genetically determined, directed bacterial genome evolution can be achieved in the laboratory by repeated rounds of chemical mutagenesis of bacterial cells followed by stringent selection for cells with enhanced DNA transfer capabilities. In this regard, attempts to develop a laboratory selection for Agrobacterium cells that not only are (1) present in small numbers among large and genetically diverse populations, but also (2) possess the capacity to transfer 'tumor-inducing' DNA to either whole plant leaf cells or the yeast Sacchromyces cerevisiae are described.