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Bacterial blight disease on cotton caused by Xanthomonas citri pv. malvacearum (Xcm) is one of the most important factors determining cotton production in the world, including Syria. A field survey was conducted to investigate the spread of bacterial blight disease on cotton in the North-Eastren Region of Syria during the 2021 agricultural season. The incidence and severity of infection in the studied fields were determined; Isolation and identification of the causal pathogen was also realized on different cultivated varieties. The results of the bacterial blight disease survey of 70 fields showed it spread in 97% of the studied fields. The incidence of disease on cotton plants ranged between (0-76)% and the severity between (0-40)%. The most susceptible variety to Xcm is Aleppo 90 with an infection rate of 29.82% (means of all fields cultivated by Aleppo variety) and an infection severity of 10.97%. The results also demonstrated that seed contamination play the greatest role in the spread of the disease with the presence of favorable conditions of humidity, increased nitrogen fertilization, using a high seed rate, and early planting. Also, 56 bacterial isolates possessed tested characteristics of Xcm were obtained. Molecular identification by using colony-PCR and a pair of specific primers which a amplify the rpfB segment of Xcm (288bp), demonstrate that the isolated bacteria from the dried samples of fields with severe infection belonged to Xcm. In addition, we were studied the effect of 1mM Salicylic Acid (SA) solution and chitosan 0.1% on development of cotton bacterial blight disease Aleppo 90 variety under natural infection conditions. The results indicate that chemically delinting seeds with sulfuric acid and soaking with of chitosan 0.1% solution or soaking with of SA 5mM solution reduced the Xcm infection rate in the field as compared to the control (2.39, 4.27, 14.46%), respectively, while for undelinting seeds (5.75, 13.64, 23.59%), respectively. The results show a decrease in the severity of infection in the field for the role of chemically delinting seeds and soaking the seeds with of chitosan 0.1% solution or soaking with of SA solution 5mM as compared to control (0.2, 0.37, 1.55%), respectively, while for undelinting seeds (0.56, 1.67, 3.65%), respectively, and the highest incidence and severity of injury were at the end of the season (86.83, 56.2%) respectively; Spraying with 1mM SA solution reduced the severity of infection over time. The best treatments at the end of the season for the infection rate were for the chemically delinting, sprayed twice with 1mM SA solution, followed by soaking with 5mM SA solution followed by a spray of 1mM SA solution, then soaking with chitosan 0.1% solution, then sprayed once with 1mM SA solution, followed by soaked with 5mM SA solution as compared to the control (61.84, 69.61, 72.5, 73.43, 78.8, 84.11%), respectively. While for undelinting, the best treatment was sprayed twice with 1mM SA solution, followed by soaking with 5mM SA solution followed by a spray of 1mM SA solution, followed by soaked with 5mM SA solution, then soaking with chitosan 0.1% solution, then sprayed once with 1mM SA solution as compared to the control (67.33, 74.05, 77.38, 79.19, 80.34, 86.83%), respectively. The best in reducing the infection severity at the end of the season was for the delinting with two sprays of 1mM SA solution, followed by soaking with 5mM SA solution followed by a spray of 1mM SA solution, then sprayed once with 1mM SA solution, followed by soaked with 5mM solution, then soaking with chitosan 0.1% solution as compared to the control (36.56, 41.15, 44.6, 46.05, 46.24, 56.2%) respectively, while for the undelinting sprayed with two sprays of 1mM SA solution, then soaking with chitosan 0.1% solution, followed by soaking with 5mM SA solution followed by a spray of 1mM SA solution, followed by soaked with 5mM SA solution, followed by soaking with acetic acid 1% solution, then sprayed spray with 1mM SA solution, as compared to the control (40.5, 43.75, 45.5, 46.9, 49.2, 51.35, 51.2), respectively. The Chitosan was found to have an inhibitory effect on germination (without significant differences) and height (with significant differences), and there were no significant differences and weight of ten bolls. There were a clear significant differences in the number of bolls, the productivity of 100 plants, and the productivity of area unit in tons/ha as compared to the control. The results show the significant role of SA in increasing cotton production, as it reached the highest for the plants twice with a solution of SA 1mM, followed by soaking with 5mM SA solution followed by a spray of 1mM SA solution, then sprayed spray with 1mM SA solution, then soaking with chitosan 0.1% solution, followed by soaked with 5mM SA solution, followed by soaking with acetic acid 1% solution as compared to the control (7.53, 7.33, 6.48, 6.02, 5.47, 5.11, 4.21) tons/ha, respectively. The increase was (78.8, 74.1, 53.91, 42.99, 29.93, 21.38, 0%) respectively; this increase leads to an increase in the economic return of the crop per area unit.
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