Xanthomonas citri pv. malvacearum Can Disseminate Similarly from Both Cotton Bacterial Blight–Resistant and –Susceptible Cultivars Under Field Conditions

Cotton bacterial blight, caused by Xanthomonas citri pv. malvacearum (Xcm), reemerged in U.S. cotton production without evidence of new pathogen races. To test whether resistant cotton can act as an inoculum source, we conducted replicated field trials over two seasons using Xcm strains with distinct spontaneous antibiotic resistance markers facilitating source tracking from inoculated resistant and susceptible seed embedded within rows of susceptible and uninoculated plants. Xcm was recovered from uninoculated susceptible plants in both years, originating from both resistant and susceptible sources, with recovery highest early in the season and declining over time. Most isolations were from asymptomatic leaves, and rare seed-to-seed transmission from resistant plants was confirmed (0.13%). These findings provide field-based evidence that resistant cotton can asymptomatically harbor Xcm and potentially contribute to pathogen persistence.