Reaction of sugar beet, pepper and bean plants to co-infection with Cucumber mosaic virus and beet curly top viruses

Mixed infections of plants with viruses is a common phenomenon occurring in nature. In the present study, interactions between Beet curly top virus (BCTV-Svr), Beet curly top Iran virus (BCTIV) and Cucumber mosaic virus (CMV) were investigated in resistant cultivar (BST853) of sugar beet (Beta vulgaris) to curly top disease at 20°C and 26 °C; pepper (California Wander cultivar) and bean (Akhtar and Goli cultivars) at 26 °C. Experiments were performed in a completely randomized design. Plants were inoculated with infectious clones of BCTV-Svr and BCTIV and also mechanically with the sap of the Fars isolate of CMV infected Cucumis sp. leaves. The intensity of the bands of PCR products was evaluated by Totallab software. The viruses did not induce any symptoms at 20 ± 1 °C on sugar beet plants, except vein clearing observed in some treatments. In the case of BCTV-Svr + CMV and BCTV-Svr + BCTIV treatments, plants showed symptoms one week earlier than single infection treatments at 26 ± 1 °C. Similar results were obtained in treatments using pepper and bean plants. Analysis of PCR data showed that BCTV-Svr accumulation in BCTV-Svr + CMV and BCTIV + BCTV-Svr treatments increased compared to single treatment of the virus. Results of this study showed that co-infection of BCTV-Svr and BCTIV with CMV leads to breakdown of resistance and induction of severe symptoms in sugar beet, pepper and bean plants. Hence, it seems that the host plant, does not affect interaction of these viruses.