Archivio Journal of Plant Pathology

Abstract:

Iran is the 4th largest producer of watermelon (Citrullus lanatus) in the world. In 2012 a disease characterized by water-soaked lesions and soft rot was observed on mature and immature fruits of watermelon cv. Crimson sweet. Fruit samples with transpicuous symptoms were transferred to laboratory and bacterial colonies were isolated from these on nutrient agar. Hypersensitivity reaction (HR) assays (Bauer et al., 1994) were successfully done using 108 CFU/ml bacterial suspension into tobacco leaf epidermis. Bacterial isolates were Gram-negative, facultative anaerobes, able to soften potato slices and growing at 37°C. They were negative for oxidase, urease and sensitivity to erythromycin, positive for catalase, gelatinase and utilization of malonate and citrate. Isolates produced acid from lactose, cellobiose, raffinose and trehalose (Schaad et al., 2001). The pathogenicity of bacterial isolates was confirmed by injecting cell suspension (calibrated at 107 CFU/ml) in watermelon fruits. Symptoms developed on fruits 3 to 4 days post inoculation looking the same as those shown by naturally infected fruits. Control samples injected with sterilized distilled water remained healthy. A 16S ribosomal RNA fragment of 1100 bp was amplified from bacterial isolates and the partial 16S rRNA gene sequence was deposited in GenBank under the accession No. KF956742. Based on phenotypic characteristics and the 99.7% homology of 16S rRNA sequence to Pectobacterium carotovorum subsp. carotovorum (Pcc), the bacterium that causes water-soaked and soft rot of watermelon fruit was identified as Pcc. To our knowledge, this is the first report of soft rot caused by Pcc on watermelon from Iran.