Populus × euramericana (Dode) Guinier clone (cl.) “I-214” is a fast-growing interspecific hybrid between Eastern cottonwood (P. deltoides Bartr. ex Marsh) and European black poplar (Populus nigra L.). Populus × euramericana was introduced into Serbia in the 1950s and has become one of the most widely grown poplar species. In September 2019, cankers were observed on stems and branches of P. × euramericana cl. “I-214” trees in a two-year-old poplar plantation in the province of Vojvodina, Serbia. The canker tissue was soft and watery, and a colorless fluid that smelled rotten flowed from the cracks in the bark, suggesting possible bacterial disease. After two weeks, diseased trees experienced crown die-back and oozing of foamy, odorous exudates and this study aimed to identify the causal agent of the disease. Canker margins and exudates were collected from 20 symptomatic trees. The associated bacterium was isolated and identified using biochemical characteristics, phylogenetic analyses based on 16S rRNA gene sequences, and multilocus sequence analyses (MLSA) based on partial sequencing of three housekeeping genes (gyrB, infB, and atpD). The pathogen was identified as Lonsdalea populi. Pathogenicity tests were conducted on rooted cuttings of P. × euramericana cl. “I-214” in an environmental test chamber and demonstrated that the isolated bacterial strain was able to reproduce symptoms of softened, water-soaked cankers and exudation. To the best of our knowledge, this is the first report of L. populi causing bacterial canker disease on P. × euramericana cl. “I-214” in Serbia and in southeastern Europe (SEE). It is also the first report of a bacterial disease on hybrid poplars, including P. × euramericana in this country and in SEE. If the disease spreads into new areas, selection for L. populi resistance may need to be integrated into future poplar breeding programs.

Ailanthus altissima (Mill) Swingle commonly known as tree of heaven was brought to Hungary as an ornamental tree between 1841-43 and became widespread in the country in the middle of the 20th century. Due to its ability to transform its environment and reduce biodiversity it became one of the most dangerous invasive plant species in Hungary (Udvardy and Zagyvai 2012). Verticillium wilt of A. altissima has been reported in the USA (Rebbeck et al. 2013; Snyder et al. 2013) and in Europe (Maschek and Halmschlager 2017) in the last few years. According to these studies, two Verticillium species can cause wilt symptoms on A. altissima: Verticillium nonalfalfae (formerly Verticillium albo-atrum) and Verticillium dahliae. During the summer of 2016, dying A. altissima trees were observed in Nyíregyháza (northeastern part of Hungary) and in several parts of Budapest that exhibited wilt symptoms, defoliation and yellowish vascular discoloration. To identify the causal agent, samples were collected from symptomatic ...

In Hungary, from the beginning of the 19th century, horse-chestnut trees have been planted widely and are popular ornamental trees in public parks, along streets, and in gardens. In the summer of 2015, longitudinal cracks on the trunk and branches and the intensive oozing of brown liquid were observed from a wound in a horse-chestnut tree in a park in Budapest. Some years later, in 2018 and 2019, the same symptoms were found in trees in other locations in Budapest. Several bacteria were reported that induce similar symptoms, including cracks and cankers on the bark of trunks and branches and sticky, white, red, brown, or black oozing. These pathogens belong to the genera Brenneria and Lonsdalea. Bark and exudate samples were taken with the aim of identifying the causal agent by conventional and molecular methods. Our results confirmed that the bacteria isolated from Aesculus hippocastanum trees belong to the genus Brenneria and phylogenetic analysis of the 16S rRNA gene region proved to have the closest phylogenetic relation with the Brenneria nigrifluens strains.