Interaction of turnip mosaic virus or cauliflower mosaic virus with Phoma lingam in canola

Plant infections to several pathogens at a same time are expected in nature. In most cases, plant mixed infections with viruses and fungi could result in increased susceptibility in plant host. In the present study, the interaction between turnip mosaic virus or cauliflower mosaic virus with Phoma lingam in canola (Brassica napus L.) was investigated. Experiments were carried out using a completely randomized design. Plants were mechanically inoculated with virus-infected turnip leave saps and by medium plug of fungal causal agent. To evaluate the interactions, in addition to recording the type and severity of symptoms, enzymatic (catalase and guaiacol peroxidase) and non-enzymatic (carotenoids and flavonoids) defense responses of treated plants were measured. The results showed that the severity of Phoma symptoms significantly increased in primary infection with turnip mosaic virus and then phoma inoculation, but no significant changes of Phoma symptoms were observed in initial infection with cauliflower mosaic virus. All treatments infected with case studied pathogens compared to the control treatment (no pathogen infection) showed a significant decrease in chlorophyll content, quantity of carotenoids, and flavonoids. While, catalase and guaiacol peroxidase content in the treatments infected with case studied pathogens showed a significant increase compared to the control treatment. Due to the synergistic effect of Phoma lingam and turnip mosaic virus in mixed infection of canola and reporting the incidence of both causal agents in canola cultivated areas in Iran, it is recommended to select canola cultivars that are resistant to both pathogens.