Elucidating the patterns of seed-to-seedling transmission ofXanthomonas citripv.malvacearum, the causal agent of cotton bacterial blight

ABSTRACT Cotton bacterial blight (CBB) was a major disease of cotton in the United States in the early part of the 20 th century. The recent reemergence of CBB, caused by Xanthomonas citri pv. malvacearum ( Xcm ) revealed many gaps in our understanding of this important disease. In this study, we employed a field isolate of Xcm from Georgia USA (WT) to generate a non- pathogenic, hrcV mutant lacking a functional Type III Secretion System (T3SS-). We tagged the WT and T3SS- strains with an auto-bioluminescent Tn 7 reporter and compared colonization patterns of susceptible and resistant cotton seedlings using macroscopic image analysis and bacterial load enumeration. Wildtype and T3SS- Xcm strains colonized cotton cotyledons of resistant and susceptible cotton cultivars. However, Xcm populations were significantly higher in susceptible seedlings inoculated with the WT strain. Additionally, WT and T3SS- Xcm strains systemically colonized true leaves, although at different rates. Finally, we observed that seed-to-seedling transmission of Xcm may involve systemic spread through the vascular tissue of cotton plants. These findings yield novel insights into potential Xcm reservoirs for CBB outbreaks.