Application of some plant growth-promoting rhizobacteria to enhance plant growth and protection against Cucumber mosaic virus in cucumber

The current study evaluated Pseudomonas fluorescens VUPf5 and three isolates of Bacillus subtilis (GB32, GB12, and VRU1) for induction of resistance against Cucumber mosaic virus (CMV) in cucumber Cucumis sativus L. (cultivar Sultan) plants. Seed treatment with plant growth-promoting rhizobacteria (PGPR) strains significantly reduced the number of symptomatic plants when CMV was mechanically inoculated. Serological analysis using double-antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) also showed a significant reduction in the CMV accumulation in plants treated with PGPR strains. In every treatment, growth indices, leaf chlorophyll content, leaf carotenoid content, leaf, and root Iron, Zinc, Copper, and Manganese concentration of virus-infected plants were significantly increased. The highest reduction in CMV concentration was observed in plants treated with VRU1. The maximum chlorophyll concentration, leaf Iron, copper, and manganese were observed in plants treated with GB32.
Nevertheless, the highest carotenoid content was measured in the VUPf5 treatment. In the case of growth indices, the best results were obtained by VUPf5 compared to untreated control. In addition, the production of lipase, siderophore, protease, cellulase, HCN, auxin, and phosphate carbonate was determined under in vitro conditions. All four strains were positive for siderophore and auxin production. These results suggest that P. fluorescens and B. subtilis should be further evaluated for their potential to contribute to CMV management under in vivo and in situ conditions.