Induced systemic resistance in cucumber and tomato against cucumber mosaic cucumovirus using plant growth-promoting rhizobacteria (PGPR)

Plant growth-promoting rhizobacteria (PGPR) strains 89B-27 (Pseudomonas fluorescens) and 90-166 (Serratia marcescens), which previously demonstrated induced systemic resistance in cucumber against some fungal and bacterial diseases, were tested for their capacity to protect Cucumis sativus L. cv. Straight 8 from disease development of cucumber mosaic cucumovirus (CMV). Seed treatment with both PGPR strains significantly and consistently reduced mean numbers of symptomatic plants when CMV was inoculated onto cotyledons. Plants treated with PGPR did not develop initial symptoms 14 days after CMV inoculation and remained symptomless throughout the experimental period. In a comprehensive study with cucumber, no viral antigen could be detected by enzyme-linked immunosorbent assay (ELISA) in any asymptomatic PGPR-treated plants; whereas CMV was evident in every leaf of symptomatic plants. The same two PGPR strains were evaluated for effects on CMV symptom development in tomato in three experiments by measuring the disease severity at six observation dates. In all experiments, the area under the disease progress curve (AUDPC) was significantly lower with strain 89B-27 than in the nonbacterized control. The AUDPC with strain 90-166 was also significantly lower than with strain 89B-27. These results suggest that PGPR should be further evaluated for their potential to contribute toward management of viral plant diseases.