Over 130 years ago, Xanthomonas campestris pv. campestris (Xcc), the causal agent of black rot of crucifers, was identified as one of the first known plant pathogenic bacteria. Since then, research has advanced our understanding of Xcc pathogenicity, virulence, taxonomy and dissemination, but the pathogen remains a major threat to cabbage, cauliflower, and other Brassica crops around the world. Black rot is the most impactful pest of cabbage in New York, the largest cabbage producing state in the USA. This thesis begins with a description of the current state of Xanthomonas campestris research, highlighting available genomic resources. The first chapter describes replicated field trials determining the susceptibility of commercially available cabbage cultivars to Xcc strains isolated in New York. Whole genome sequences of 5 New York isolates of Xcc were completed and related to the strains virulence levels. Next, sequencing of 55 additional strains of Xc from cruciferous crops and weeds in New York and cruciferous weeds in California revealed insights on pathovar structure. Comparative genomics showed that the type III effector XopAC is a host range determinant of Xc and that a cellobiosidase, cbsA, plays a role in vascular pathogenesis. The new genomic resources were further leveraged to identify the presence of transcription activator-like effectors. The role of these effectors in virulence was investigated and members of a family of berberine bridge enzyme-like genes were implicated as potential susceptibility gene targets in Brassica oleracea.