Reassessment of the occurrence and distribution of Xanthomonas arboricola on fruit trees in Iran

Abstract

AbstractBacterial canker and spot of stone fruits and bacterial blight of walnut, caused by different pathovars of Xanthomonas arboricola, namely X. arboricola pv. pruni and X. arboricola pv. juglandis, respectively, are considered among quarantine or regulated (nonquarantine) agents in different countries. The two pathogens were initially reported in Iran in 2005 and 1977, respectively. However, the precise identity, pathogenicity status and geographic distribution of these pathogens have been questioned. In this study, we have employed a series of comprehensive field surveys and samplings over a course of 5 years (2015–2019) across 16 provinces to reassess and clarify the occurrence and distribution of X. arboricola on fruit and nut trees in Iran. Besides dozens of non‐Xanthomonas and nonpathogenic bacterial strains, 27 X. arboricola strains were isolated from stone fruits (n = 13) and walnut (n = 14). Except for the strains Peh35, Peh78 and Peh79, the stone fruit strains were nonpathogenic on their host of isolation as well as several other plant species, while the walnut strains were pathogenic on their host of isolation. Multilocus sequence analysis (MLSA) of four housekeeping genes, atpD, dnaK, gyrB and rpoD, revealed that among the stone fruit strains only Peh78 and Peh79 could be assigned into X. arboricola pv. pruni, while the walnut strains were identified as X. arboricola pv. juglandis. Based on the results of pathogenicity assays and phylogenetic analyses, we confirm the occurrence of X. arboricola pv. juglandis in Iran, while X. arboricola pv. pruni was absent in the plant samples evaluated in this study.