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A bacterial leaf blight of Christ's thorn plants (Paliurus spina-christi) observed in the Kurdistan province of Iran is described for the first time. Main symptoms of the disease are foliar water-soaked, irregular spots with yellow halo, 5-8 mm in diameter, which eventually turn brown. Due to it is relatively recent detection in Iran, very little is known about the pathogen. Yellow, non-mucoid colonies consistently isolated from leaf lesions were produced by a Gram-negative, catalase positive and oxidase negative bacterium, 15 isolates of which showed more than 90% similarity. Comparative 16S rDNA gene sequence analysis positioned this bacterium in the genus Sphingomonas with the highest sequence similarity (97%) to Sphingomonas melonis. Chemotaxonomically, fatty acid methyl ester analysis revealed that the bacterial isolates contained C16:0 (9%), C18:1 ω 9 (51%) as predominant fatty acids and C14:0 2OH (25%) as a major 2-hydroxy fatty acid, confirming their belonging to the genus Sphingomonas. [ABSTRACT FROM AUTHOR]