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Understanding the mechanisms of infection and survival of the maize pathogen Xanthomonas vasicola pv vasculorum

Mary Carmen Ortiz-Castro: Colorado State University

<div>Bacterial leaf streak of corn, caused by <em>Xanthomonas vasicola </em>pv.<em> vasculorum </em>(<em>Xvv</em>), is an emerging disease of maize in North and South America. The disease has been found in Argentina and the United States affecting sweet corn, popcorn, and grain corn. Based on the combined $52.4 billion value of the maize industry, early reports of <em>Xvv</em> disease severity, and lack of management methods, this emerging pathogen represents a serious economic threat to U.S. maize production. The primary goal of this research is to provide a basic understanding of the mechanism of infection and survival of the maize bacterial leaf streak pathogen. Through genetic transformations of the bacteria with fluorescent proteins, several inoculation strategies, and confocal microscopy, we were able to describe the mode of entry of this pathogen into the corn plant. In addition, we found that there is a significant phenotypic diversity between <em>Xvv</em> isolates across different regions. Strains from Colorado and Nebraska, where the disease was first reported, showed the highest and lowest levels of virulence. Finally, through litter studies at multiple locations, we demonstrated that infected residue left on the soil surface harbored significantly greater quantities of <em>Xvv</em> than infected residue buried 10 cm below the surface. These findings provide a more complete understanding of the bacterial leaf streak disease cycle and will aid in the development of management strategies that may limit <em>Xvv</em>’s distribution within corn fields and prevent further spread to other corn producing regions.</div>