Biological Properties of the Agent of Soryz Bacterial Spot in Ukraine

Soryz is a new promising agricultural crop. Sorghum leaf spots are one of the most common and harmful diseases of these crops. Improving the technology of growing agricultural crops requires the development of methods of controlling their pathogens, based on data on their distribution and properties. There is no information on the taxonomic status and properties of the causative agents of soryz bacterial spot in Ukraine. The aim of the work was to identify the causative agent of bacterial spots of a new sorghum crop — soryz in Ukraine and to study its biological properties. Methods. Identification of the causative agent of soryz bacterial spots was carried out in the Cherkasy and Kyiv regions of Ukraine in 2019-2023. Isolation of the pathogen and study of its morphological-cultural, physiological-biochemical properties were carried out by classical microbiological methods using the NEFERMtest24 (MikroLaTEST®, ErbaLachema, Czech Republic) and API 20NE (Biomerieux, France) test systems. Electron microscopy, chromatographic separation, and identification of fatty acids were conducted at the Center for Collective Research of the Zabolotny Institute of Microbiology and Virology of the National Academy of Sciences of Ukraine (IMV). The antigenic properties of isolated bacteria were investigated by the agglutination reaction with antisera to five serological groups of Pseudomonas syringae strains. Identification of the obtained bacteria was carried out on the basis of their phenotypic properties and the results of MALDI-TOF mass spectrometry on a VITEK MS mass spectrometer. Results. Affecting by spotting was noted in 2—27% of soryz plants, and the development of symptoms of damage was 1—4 points. Bacteria with sorghum disease symptoms were isolated, from which ten virulent isolates were studied in detail. According to the phenotypic properties, 9 isolates that were similar to the characteristics of the typical strain of P. syringae UCM B-1027T, were identified as P. syringae van Hall 1902. One isolate belongs to phytopathogenic bacteria of the genus Pseudomonas according to its main properties, but its taxonomic status within the genus needs to be clarified. In the cellular lipids strains isolated from affected soryz plants, as well as in the type strain of P. syringae UCM B-1027T, such fatty acids as dodecanoic, tetradecanoic, hexadecanoic, octadecanoic, cis-9-hexadecenoic, cis-11-octadecenoic, cis-9,10-methylene hexadecanoic, cis-9,10-methylene octadecanoic acids were identified. In the cellular lipids of strains from soryz, fatty acids with an even number of carbon atoms predominate, the total content of which is more than 60% of all detected fatty acids. Isolates from soryz also contain 3-hydroxydecanoic, 2-hydroxydodecanoic, and 3-hydroxydodecanoic fatty acids, the presence of which confirms the belonging of the isolated bacteria to the species P. syringae. According to the antigenic properties, nine strains of P. syringae isolated from soryz are homogeneous and belong to serogroup I. One strain of Pseudomonas sp. does not belong to any of the studied serogroups that parasitize grain crops. Belonging to the causative agent of soryz bacterial spots to the species P. syringae was confirmed by the MALDI-TOF mass spectrometry method. Conclusions. Therefore, on the base of our results, it has been established that the main causative agent of soryz bacterial spots in Ukraine is P. syringae. According to antigenic properties, the population of the causative agent of soryz bacterial spots is homogeneous, which makes it possible to develop serological rapid tests for the detection of the causative agent. By comparing the biological properties of collection strains from sorghum, a species of Pseudomonas holci, which does not exist in modern taxonomy, with the properties of strains from soryz, the typical strain of P. syringae UCM B-1027T, we established that P. holci bacteria isolated in the Department of Phytopathogenic Bacteria of the IMV in 1968-1971 belong to the species P. syringae.