Genetic Range of Xanthomonas phaseoli pv. phaseoli as Revealed by Phylogeographic Analyses

Common bacterial blight of common beans caused by various Xanthomonas species is considered a significant threat to bean production worldwide. In this study, common bean-associated xanthomonads in Iran were investigated using a multilocus phylogeographic approach. Majority of the bacterial strains investigated in this study were isolated in 2023-2024, while a number of 1990s and 2000s Iranian strains were also included in the analyses. Phylogenic analyses using the sequences of four housekeeping genes showed that among 45 strains isolated from common bean across nine Iranian provinces, 44 strains belonged to Xanthomonas phaseoli pv. phaseoli, while one strain was identified as Xanthomonas citri pv. fuscans. Multilocus sequence analysis showed that all strains collected in 2023-2024 in Iran along with four strains isolated in 1999, 2006, and 2020 clustered into a monophyletic clade. Multilocus sequence typing of the Iranian strains along with 29 worldwide strains retrieved from the NCBI GenBank revealed low genetic diversity within the global population of X. phaseoli pv. phaseoli. Majority of the worldwide X. phaseoli pv. phaseoli strains belonged to the same haplotype. However, a distinct haplotype containing only the strains isolated in Iran was observed, with no members from the worldwide population. Our analysis provides novel insight into the population structure of common bacterial blight pathogen on a global scale. Emergence of a novel lineage of X. phaseoli pv. phaseoli in Iran raises concerns about further expansion of the pathogen and highlights the need for strict quarantine measures in a global scale.