During spring and summer 2004 and 2005, a new disease of Christ’s thorn (Paliurus spina-christi P. mill.) was observed in Iran, in some areas of the Kurdistan province. Symptoms were initially yellow areas on the leaves, in which irregular water-soaked spots 3-5 mm in diameter developed. A non-fluorescent bacterium was consistently isolated from lesions on King’s medium B. Fifteen bacterial isolates were obtained from different locations of west Iran. According to phenotypic, biochemical and physiological properties all bacterial isolates were identified as Acidovorax avenae subsp. citrulli. They produced round white colonies 1-2 mm in diameter, were all aerobic, gram-, levan-, arginine dihydrolase-, catalase- and potato soft rot-negative, but oxidase- positive, and induced hypersensitivity reaction in tobacco leaves. Pathogenicity of selected isolates was confirmed by injecting bacterial suspension into the underside of leaves. This is the first report of a bacterial disease on Christ’s thorn in Iran.
