In the summer and autumn of 2019-2020, young walnut orchards were monitored for the presence of bacterial diseases. Diseased walnut samples comprising trunks and branches with symptoms of vertical oozing canker (VOC), walnut bacterial blight (WBB) and superficial bark necrosis were collected from eight locations in Serbia. Based on phenotypic features, pathogenicity, and molecular assays using PCR with specific primers, 49 isolates obtained from samples showing VOC and WBB symptoms were identified as Xanthomonas arboricola pv. juglandis, while further two isolates obtained from bark necrosis were identified as Brenneria rubrifaciens. One tested X. a. pv. juglandis isolate obtained from a VOC sample produced deep cankers in the bark of inoculated trunks of young walnut trees (cultivars Chandler, Franquette and Sejnovo). Therefore, this is the first report of an association between X. a. pv. juglandis and VOC symptom in Serbia. Considering that X. a. pv. juglandis significantly endangers walnut production, the presence of this pathogen in walnut transplant imports needs to be assessed by an authorised laboratory. Furthermore, as this is also the first report of B. rubrifaciens on walnut trees in Serbia, it is noteworthy that this pathogen is not particularly harmful to young walnut trees.
Pseudomonas strains originating from symptomatic (bacterial spot) leaf tissues of sweet cherry (Topola, Sumadija) and plum (Krusedol Selo, Srem) were isolated during 2016 and 2020, respectively. Based on the findings yielded by classical microbiological methods, LOPAT (+---+), GATTa (--++) and pathogenicity tests performed on detached fruitlets (sweet and sour cherry) and pods (bean pods), all strains were confirmed to belong to P. syringae pv. morsprunorum. The detection of cfl gene allowed strains that belong to race 1 to be identified. The DNA fingerprinting patterns obtained with four rep-PCR (BOX and ERIC), RAPD-PCR (M13), and IS50-PCR (IS50) methods revealed that the seven tested sweet cherry and plum P. s. pv. morsprunorum strains, as well as comparative KBNS71 and the reference strain CFBP 2119, were genetically heterogeneous. Conversely, MLSA based on the four-gene-based scheme (gapA, gltA, gyrB, and rpoD) indicated genetic homogeneity among all tested Serbian sweet cherry and plum strains, as well as P. s. pv. morsprunorum race 1 strains from the NCBI. Although the MLSA findings indicate that the sweet cherry and plum strains used in this study are 100% identical, as they might have different virulence genes, genome sequencing should be performed to eventually find the strain sub-clades based on the host.
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