The plant growth-promoting fungus Fusarium equiseti and the arbuscular mycorrhizal fungus Glomus mosseae induce systemic resistance against Cucumber mosaic virus in cucumber plants

Aims: The aim of this study was to elucidate the effects of the interactions between the arbuscular mycorrhizal fungus Glomus mosseae (Gm) and Fusarium equiseti GF18-3 on cucumber growth and the biocontrol of the yellow strain of Cucumber mosaic virus (CMV-Y). Methods: Cucumber plants were pre-inoculated with Gm and GF18-3 for 4 weeks before the leaves were inoculated with CMV. CMV accumulation in cucumber leaves was determined using an indirect enzyme-linked immunosorbent assay (ELISA) at 1, 2, and 3 weeks post-inoculation (WPI). An RT-PCR analysis was performed to evaluate the expression levels of defence-related genes. Results: The co-inoculation of cucumber plants with Gm and GF18-3 or GF18-3 alone resulted in effective control of CMV disease severity, though no significant reduction was observed in the Gm-alone treatment. CMV accumulation was significantly decreased in cucumber plants treated with combined inoculation or with GF18-3 alone at 1, 2, and 3 WPI. The RT-PCR results revealed higher expression levels of SA-inducible genes in all treatments, while only Gm treatment of plants induced JA-inducible genes. Conclusion: The dual inoculation treatment and inoculation with GF18-3 alone have the potential to reduce disease severity and increase plant growth. Moreover, modulation of plant defence responses in the shoots may contribute to this protection.