Isolation and characterization of bacterial agents associated of wetwood disease on elm trees in Iran

Elm trees (Ulmus spp.) are one of the most widespread landscape plants, widely used as ornamental trees to embellish parks and streets of different countries including Iran. Elm trees cultivation is seriously limited by biotic factors such as bacterial pathogens. Recently, bacterial wetwood has been identified as a common disease on elm trees in Northwest Iran. In present study, in order to identify bacterial pathogens associated with elm trees, wetwood infected samples were collected from elm trees showing wetwood symptom across Tabriz city and immediately transferred to the lab. After isolation and purification of isolates, hypersensitive reaction (HR), pathogenicity, biochemical and molecular tests were used to characterize the isolates. In total of 92 isolates obtained, 32 and 10 isolates were able to induce HR and wetwood symptoms on tobacco leaves and young branches of elm, respectively. Based on biochemical and molecular tests, the identity of the isolates studied were determined as Brevundimonas bullata, Paracoccus alcaliphilus, P. marcusii and Luteimonas aestuarii. To the best of our knowledge, this study shows that these four bacterial species here reported are responsible for the causal agent-complex of wetwood disease on elm trees for the first time in the world.