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This study was carried out to characterize a virus causing severe mosaic, yellowing, stunting and leaf deformation on melon (Cucumis melo L.), and evaluate the capacity of Pseudomonas fluorescens as biofertilizer to improve plant growth and restrict the accumulation of the virus in the plant. The virus was identified as an isolate of Cucumber mosaic virus (CMV) by means of symptoms on indicator plants, serological characteristics using double antibody sandwich-enzyme linked immunosorbent assay (DAS-ELISA) and immunochromatography, and molecular weight of coat protein on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The source of the virus infection was also determined by the same means. P. fluorescens was used as seed treatment and soil applications. The seedling grown from bacterial treated seeds in non-treated soil and those grown from non-treated seeds in bacterial treated soil were mechanically inoculated with CMV extract at the primary leaf stage. Two proteins representing CMV coat protein appeared on 10% SDS-PAGE of 24 and 26 kD. It has been found that 9 of 35 weed plants harbor CMV. Treatment seeds and soil with P. fluorescens suspension induced significant reduction in virus accumulation in the plants as proved by absorbance values of ELISA- reactions. Minimum absorbance values of ELISA reactions at 405 nm were found to be 0.160 and 0.298 for seed and soil treatments, respectively when compared with 1.190 for samples from CMV-inoculated plants (control). The inhibition activity of P. fluorescens against CMV continued to be significant up to 20 days of virus inoculation with absorbance values of ELISA-reactions (0.460 and 0.930) for seed and soil treatment, respectively. The results indicate that P. fluorescens is able to induce systemic resistance against CMV in the plants.
Key words: Cucumber mosaic virus (CMV), Cucumis melo, melon, plant growth promoting microorganisms (PGPM), Pseudomonas fluorescens, viral diseases management.