Pseudomonas syringae Population Recently Isolated from Winter Wheat in Serbia

The aim of this study was to identify the causative agent of bacterial blight and basal glume rot of winter wheat that appeared in Serbia in 2023. To characterize the isolated bacteria (eight isolates in total), their cultural, biochemical, pathogenic, and genetic characteristics were examined. Based on the results of the LOPAT test, the isolates were classified into Pseudomonas Group Ia. The syrB and syrD genes were simultaneously detected in six wheat isolates—P0123, P0223, P0323, P0423, P0523, and P0823—while two isolates, P1123 and P1323, lacked both genes. Multilocus sequence typing (MLST) of the gapA, gltA, gyrB, and rpoD genes identified six isolates (P0123, P0223, P0323, P0423, P0523, and P0823) as Pseudomonas syringae pv. atrofaciens, whereas the remaining two isolates (P1123 and P1323) were most closely related to P. poae. Phylogenetic analysis revealed three genetically heterogeneous subgroups of P. syringae pv. atrofaciens among the wheat isolates from Serbia. Pathogenicity tests demonstrated that wheat isolates are able cause disease on wheat seedlings using three different inoculation methods: spraying the entire seedling, trimming the leaves before spraying, and wounding the leaves with multiple needles followed by spraying. Overall, isolates P0123 and P0423 were identified as the most virulent, inducing pronounced blight symptoms on wheat seedlings. In contrast, isolates P1123 and P1323 were weakly virulent and are therefore considered to be secondary or accompanying factors in plants already infected with more aggressive isolates, rather than primary pathogens responsible for disease development. This study contributes to a deeper understanding of the ecology, distribution, and pathogenic potential of bacterial communities associated with wheat blight disease in Serbia.