Asra Salari

During the survey, watermelon mosaic virus was isolated from cucumber (Cucumis sativus, L) with severe mosaic and yellowing symptoms by reverse-transcription polymerase chain reaction (RT-PCR). Isolates from plant growth-promoting rhizobacteria (PGPR) were isolated from cucumber plants rhizosphere with no virus symptoms, and morphologically and physiologically identified to be related to Pseudomonas fluorescens. The bacterial liquid cultures (72 h of age) were tested for their ability to induce systemic resistance within cucumber plants (Cucumis sativus L. cultivar 547) against WMV infection. Two types of treatment were carried out: (1) spraying of healthy cucumber plants (carrying 4–5 leaves) and mechanical inoculation of WMV at time intervals (5–10 days). (2) Healthy cucumber seeds were irrigated with liquid bacterial culture and inoculated with WMV in the two-leaf cotyledons stage. A number of plants as a control were not inoculated with WMV. 21 days after inoculation, growth indices including wet and dry weight, leaf chlorophyll and carotenoid content were measured. Data proved that best results were obtained by treatment of irrigation seeds with bacterial culture, as the number of low symptomatic plants were 14 out of 37 plants inoculated, followed by Pseudomonas treated plants which gave seven low symptomatic plants. Growth indices in treated plants with PGPR were significantly increased. The maximum chlorophyll and carotenoid concentration were observed in plants treated with P. fluorescens. These results suggest that P. fluorescens should be further evaluated for their potential to contribute to WMV management in field conditions