CHARACTERISTICS OF STATIONARY-PHASE VARIATION AFFECTING VIRULENCE IN XANTHOMONAS-ORYZAE PV. ORYZAE

Xanthomonas oryzae pv. oryzae is the causal agent of bacterial leaf bl ight, a serious disease of rice. Spontaneous loss of virulence in X. o ryzae pv. oryzae is associated with mutants that produce reduced level s of extracellular polysaccharide. Evidence is presented that these mu tants accumulate in long-term stationary phase cultures but are not ob tained from exponentially growing cultures. A number of independent sp y (stationary-phase variation) mutants have been isolated and characte rized. These mutants differ from each other with respect to the stabil ity of the mutant phenotype, extent of loss of virulence, ability to o utcompete wild type cells in stationary-phase cocultures, and hypersen sitivity to hydrogen peroxide.