Angular Leaf Spot of Cucumber Caused by Pseudomonas syringae pv. lachrymans in Kurdistan

During the spring of 2004 and 2005, angular leaf spot was observed on cucumber (Cucumis sativus L.) in some areas of Kurdistan Province in Iran for the first time. Disease incidence in affected fields was approximately 100%. Symptoms were initially small, round or irregular, water-soaked spots on leaves ranging from 3 to 5 mm in diameter. These spots were limited by the leaf veins that gave them an angular appearance. Under humid conditions, tiny, white exudates formed on the undersides of the leaves and severely infected leaves turned yellow. A fluorescent pseudomonad was consistently isolated from lesions on King's medium B and characterized. Twelve strains were selected from Marivan, Dehgolan and Kamyaran in western Iran. When compared with previously identified strains, (1,2) on the basis of phenotypic, biochemical, and physiological properties, isolates were identified as Pseudomonas syringae pv. lachrymans. This was confirmed with data from whole-cell protein pattern analysis, which indicated that the strains were highly similar to reference strain 4963^T (International Collection of Microorganism from Plants [ICMP]). Isolates produced round, white colonies that were 1 to 2 mm in diameter. All strains were gram negative, aerobic, levan positive, oxidase negative, potato soft rot negative, arginine dihydrolase negative, and induced a hypersensitive response on tobacco leaves. The strains were positive for catalase, urease, and 4% NaCl tolerance and negative for nitrate reduction, methyl red production, acetoin and indole production, phosphatase, gas from glucose, reducing substances from sucrose, and ketolactose tests. All strains hydrolyzed Tween 80, esculin, casein, and gelatin, but failed to hydrolyze starch and lecithin. Results for growth at 41°C and production of hydrogen sulfide from cystein and peptone were negative. In Ayers' medium, all strains produced acid from d-galactose, citrate, sucrose, raffinose, fructose, d-xylose, glucose, inositol, mannitol, sorbitol, glycerin, mannose, ribose but not from trehalose, maltose, salicin, l-rhamnose, adonitol, cellobiose, ethanol, l-sorbose, inulin, dulcitol, starch, lactose or melibiose. All strains used l-asparagine, l-lysine, aspartate and l-arginine but did not use l-tartrate, propionate, ornithine, l-tyrosine, borate, benzoate, l-tryptophan, or acetate as carbon sources. Pathogenicity of four strains was confirmed by injecting bacterial suspensions (10⁸ CFU/ml) into the undersides of 3- to 4-week-old cucumber leaves using a sterile syringe. Sterile water was injected into cucumber leaves as a negative control. Inoculated plants were maintained in the greenhouse at 25 to 28°C with 90 to 98% relative humidity until symptoms were assessed 4 to 7 days after inoculation. Angular leaf lesions developed on inoculated cucumber. Bacterial strains were reisolated from infected tissues and confirmed as P. syringae pv. lachrymans by biochemical characterization as previously described. This disease has been observed in other areas of Iran, but to our knowledge, this is the first report that characterizes the phenotypic and biochemical properties of the bacterium and disease in Kurdistan Province. References: (1) D. J. Brenner et al. Bergy's Manual of Systematic Bacteriology. 2nd ed. Springer, New York, NY, 2005. (2) D. C. Sands et al. J. Bacteriol. 101:9, 1970.