Xanthomonas citri pv. malvacearum Genome sequencing

Cotton bacterial blight (CBB), caused by Xanthomonas citri pv. malvacearum (Xcm), significantly limited cotton yields in the early 20th century but has been controlled by classical resistance genes for more than 50 years. In 2011, the pathogen re-emerged with a vengeance. The Xcm pathovar can be further divided into at least 19 races according to virulence phenotypes on a panel of historical cotton cultivars. Historically, the most common race observed in the U.S. has been race 18, which was first isolated in 1973. This race is highly virulent, causing disease on all cultivars in the panel except for 101-102.B. Thirteen Xcm strains were sequenced using Illumina technology to determine the phylogenetic relationship between recent isolates of Xcm and historical isolates. Isolates designated as race 1, race 2, race 3, race 12 and race 18 have been maintained at Mississippi State University with these designations. Additional isolates were obtained from the Collection Française de Bactéries associées aux Plantes (CFBP) culture collection. Together, these isolates include nine strains from the US, three from Africa, and one from South America and span collection dates ranging from 1958 through 2014. In this study, we compare diverse pathogen isolates and cotton varieties to further understand the virulence mechanisms employed by Xcm and to identify promising resistance strategies.