Effect of Cucumber mosaic virus and Cauliflower mosaic virus Infections on the Resistance of Canola to Turnip mosaic virus

Turnip mosaic virus (TuMV) has frequently been reported from canola fields. Cultivation of resistant varieties is the best method to control viral diseases. However, plants that are resistant to a virus may lose their resistance in co-infection with other viruses. Therefore, in the present study the effect of mixed infection of TuMV with Cucumber mosaic virus (CMV) and Cauliflower mosaic virus (CaMV) on the resistance of a tolerant canola cultivar (Karaj 3) and a transgenic canola of RGS003spring variety with hairpin construct and high resistance to TuMV was investigated under greenhouse conditions. Canola plants were inoculated mechanically and then, relative TuMV content was assayed by semi-quantitative RT-PCR. Results demonstrated that mixed infection of TuMV and CaMV did not affect the resistance of transgenic canola plants against TuMV. Also, there was not any significant difference in TuMV content in the presence of CaMV. However, synergistic interaction between TuMV and CMV could overcome the resistance of canola plants to TuMV. The result of semi-quantitative RT-PCR indicated that TuMV accumulation was enhanced in the presence of CMV in transgenic plants, whereas TuMV levels were not affected by co-infection with CMV in Karaj 3. Therefore, it is concluded that for the introduction of TuMV-resistant transgenic plants, it is necessary to design a construct that the resulting transgenic plants would also be resistant to CMVsimultaneously.