Archivio Journal of Plant Pathology

Abstract:

In October 2016, bacterial leaf spots on onion (Allium cepa L.) were observed in fields with rainy irrigation of Eghlid, Fars province in Iran with the rate of occurrence varying from 90 to 100% of the plants. Symptoms on leaves comprised leaf blight and water soaked, irregular, white and brown spots on the leaf surface. Bacterial isolates were obtained on nutrient agar (NA) from leaf spot and blight lesions that were surface disinfected in 70% ethanol for 45 s. The isolates were fluorescent on King's B agar, gram-negative and strictly aerobic. All isolates belonged to P. syringae (LOPAT) group Ia (+, −, −, −, +) (Lelliott et al., 1996). Isolates were deposited in the Culture Collection of the Bu-Ali Sina University of Iran. DNA was extracted from the representative isolate (YMAO17) by the alkali lysis method and the 16S rRNA, gyrB and rpoD regions were partially sequenced using fD1/rP2 (Weisburg et al., 1991), gyrB-Fpsc/gyrB-Rpsc, and rpoD-Fpc/rpoD-Rpsc (Sarkar and Guttman, 2004) primers, respectively. PCR product were sequenced and their sequences were aligned and compared with those deposited in GenBank. Sequences of the 16S rRNA (Accession No. KY684039), gyrB (KY684037) and rpoD (KY684038) of a representative isolate showed 100% identity with those of Pseudomonas syringae pv. porri. To confirm Koch's postulates, leaf spot symptoms were reproduced on onion leaves inoculated with bacterial suspensions (1 × 106 CFU/ml) and the same bacterial isolate was reisolated from artificially infected leaves as confirmed by LOPAT. To our knowledge, this is the first report of bacterial leaf spot of onion caused by P. syringae pv. porri in Iran.