Vascular Pathogenicity of <i>Xanthomonas vasicola</i> pv. <i>vasculorum</i> in Maize Is Modulated by Tissue-Specific Host Resistance

How host genotype shapes pathogen tissue tropism remains poorly understood. Vascular and nonvascular tissues represent distinct habitats within a plant for bacteria to colonize. Host plants often utilize different mechanisms to defend themselves against vascular and nonvascular pathogens, and mechanisms of resistance employed by the host can vary by organ. <i>Xanthomonas vasicola</i> pv. <i>vasculorum</i> (<i>Xvv</i>) is an emerging bacterial maize pathogen, and this pathosystem offers an opportunity to study how host resistance differs in response to the vascular and nonvascular lifestyles exhibited by a single bacterial phytopathogen. We used different inoculation techniques to induce vascular and nonvascular disease and evaluated maize populations using both techniques to map resistance to vascular and nonvascular disease caused by <i>Xvv</i>. <i>Xvv</i> can colonize both vascular and nonvascular tissues, depending on the genotype. Different inoculation techniques can be used to induce vascular or nonvascular colonization. Independent loci control variation in resistance to <i>Xvv</i> during vascular and nonvascular pathogenesis. We confirmed the role of those regions in resistance to vascular and nonvascular infection. This study offers insights into how host resistance shapes how bacterial pathogens adapt to both vascular and nonvascular lifestyles. We show that host genotype can dictate which tissues a pathogen can infect. This system can serve as a model to understand tissue-specific host resistance to plant pathogens and tissue specificity in pathogens.