The center of wheat domestication drives diversity of <i>Clavibacter</i> pathogens

Members of the gram-positive corynebacterial genus <i>Clavibacter</i> sp. (family <i>Microbacteriaceae</i>) are seed-borne plant pathogens causing economically important plant diseases on annual crops and vegetables. While comprehensive global-scale studies have been conducted to study the population structure of <i>Clavibacter</i> species infecting tomato, potato, and pepper, phylogenomics investigations have not yet been conducted to monitor the taxonomic diversity, pathogenicity, and origin of <i>Clavibacter</i> strains pathogenic to small grain cereals. Archaeobotanical investigations suggested that human agriculture was established ≈11,000 years ago in the foothills of the Zagros Mountains in Northwestern Iran, while wheat and barley were among the very first crops domesticated in these areas. Thus, the analyses of taxonomic diversity and population structure of <i>Clavibacter</i> strains in the Iranian Plateau would shed light on the correlation between the center of domestication of these crops and the center of diversity of accompanying bacterial pathogens. Our findings showed that most of the <i>Clavibacter</i> strains isolated from small grain cereals in Iran belonged to the two previously described species <i>Clavibacter tessellarius</i> and <i>Clavibacter zhangzhiyongii</i>, while several strains were grouped in three distinct clades, all representing hypothetical novel species in the genus.