The plant growth-promoting fungus, Penicillium simplicissimum GP17-2, was evaluated for its ability to induce resistance against Cucumber mosaic virus (CMV) in Arabidopsis thaliana and tobacco plants. Treatment with barley grain inoculum (BGI) of GP17-2 significantly enhanced fresh weight, dry weight and leaf number of A. thaliana and tobacco plants 6 weeks after planting. Two weeks after CMV inoculation, all plants treated with BGI of GP17-2 or its culture filtrate (CF) showed a significant reduction in disease severity compared with non-treated control plants, which exhibited severe mosaic symptoms by the end of the experiment. The enzyme-linked immunosorbent assay (ELISA) demonstrated that CMV accumulation was significantly reduced in plants treated with GP17-2 or its CF relative to control plants. Based on RT-PCR, plants treated with GP17-2 (BGI or CF) also exhibited increased expression of regulatory and defence genes involved in the SA and JA ⁄ ET signalling pathways. These results suggested that multiple defence pathways in A. thaliana and tobacco were involved in GP17-2-mediated resistance to CMV, although neither the transgenic NahG line, nor the npr1, jar1 or ein3 mutants disrupted the response in A. thaliana. This is the first report to demonstrate the induction of systemic resistance against CMV by GP17-2 or its CF.

Trichoderma asperellum SKT-1 is a microbial pesticide that is very effective against various diseases. Our study was undertaken to evaluate T. asperellum SKT-1 for induction of resistance against yellow strain of Cucumber mosaic virus (CMV-Y) in Arabidopsis plants. Disease severity was rated at 2 weeks post inoculation (WPI). CMV titre in Arabidopsis leaves was determined by indirect enzyme-linked immunosorbent assay (ELISA) at 2 WPI. Our results demonstrated that among all Arabidopsis plants treated with barley grain inoculum (BGI) of SKT-1 NahG and npr1 plants showed no significant reduction in disease severity and CMV titre as compared with control plants. In contrast, disease severity and CMV titre were significantly reduced in all Arabidopsis plants treated with culture filtrate (CF) of SKT-1 as compared with control plants. RT-PCR results showed increased expression levels of SA-inducible genes, but not JA/ET-inducible genes, in leaves of BGI treated plants. Moreover, expression levels of SA-and JA/ETinducible genes were increased in leaves of CF treated plants. In conclusion, BGI treatment induced systemic resistance against CMV through SA signaling cascade in Arabidopsis plants. While, treatment with CF of SKT-1 mediated the expression of a majority of the various pathogen related genes, which led to the increased defense mechanism against CMV infection.

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