Investigation of the Spread of Bacterial Wheat Leaf Blight Caused by Pathotypes of Pseudomonas syringae in Some Wheat Growing Areas in Syria

Wheat is one of the most important cereal crops grown globally, which is affected by several biotic and abiotic stresses, especially in conjunction with the climatic changes that have been evident in the last decade, and among these stresses is the bacterial wheat leaf blight disease caused by the bacteria Pseudomonas syringae pv. syringae. The importance and danger of this bacterium is due to its ability to be transmitted by seed, as it negatively affects the quality of grain and the weight of one thousand grains. The study aimed to investigate the spread of bacterial wheat leaf blight caused by P. syringae and its pathotypes in the main wheat growing areas in Syria (Aleppo, Hama, Homs, Tartous and Latakia governorates) during 2022. The results obtained showed that bacterial wheat leaf blight disease was observed in 42 fields out of 59 fields surveyed (71.2%). The lowest incidence (50%) was recorded in Latakia with severity of less than 2, and highest incidence (77.8%) was recorded in Aleppo governorate with severity of 4 based on a 0-5 scale. Symptoms of bacterial wheat leaf blight was observed in all fields, which began as water-soacked leaf spots, and then turned into greenish-gray necrosis and finally a straw color. Symptoms of blackish-brown color nodes were observed only in 4 fields in Aleppo and Tartous governorates, it could be caused by the pathotype P. s. pv. japonica. In addition, the bases of wheat chaffs showed blackish-brown watery spots in 6 fields. In Aleppo and Tartous governorates these symptoms were identical to those typical of the pathotype P. s. pv. atrofaciens. Characteristics of 156 isolates, LOPAT tests and fluorescence on King B medium indicated that these isolates belong to the genus Pseudomonas, representing 87.7% of the total number of isolates, whereas 26 isolates (14.3%) were negative for Levan and fluorescence tests and their characteristics indicated that they belong to the genus Xanthomonas.