Resistance induction in pumpkin Cucurbita maxima L. against Watermelon mosaic potyvirus by plant growth-promoting rhizobacteria

Abstract

Watermelon mosaic potyvirus (WMV) is a serious threat to pumpkin production in Egypt. To date, few reports have examined the potential of plant growth-promoting rhizobacteria (PGPR) to induce systemic resistance against diseases of several plant viruses. The aim of this study was to determine the potential of selected PGPR strains on induction of host systemic resistance within pumpkin plants (Cucurbita maxima L.) against WMV infection. The WMV was isolated from naturally infected pumpkin and squash plants in Jeddah, Saudi Arabia. Typical symptoms of WMV were observed after mechanical inoculation. Viral identification was confirmed by double antibody sandwich enzyme-linked immuno-sorbent assay and reverse transcription polymerase chain reaction. Two PGPR strains designated as Bacillus subtilis 281 (B1) strain and Bacillus pumilus 293 (B2) were tested individually and in combination for their effectiveness against the WMV infection. The results of greenhouse experiments with pumpkin plants were challenged by mechanical inoculation, and demonstrated that separate or combined treatment with PGPR strains B1 and B2, applied at 1 × 108 colony-forming unit/ml, significantly (P < 0.05) enhanced the plant height and fresh weight, while clearly lowering the disease severity rating and virus concentrations, in all repeated greenhouse trials compared to the non-treated control. Seedlings treated with B2 strain demonstrated significantly lower levels of disease than B1 + B2 or B1, respectively, in all trials compared to control. Our findings demonstrated the potential of selected PGPR strains to induce systemic resistance for WMV infection control.