Effect of Rhizoglomus irregulare symbiosis on reducing disease severity in tomato plants infected with Tomato bushy stunt virus with emphasis on the expression of methylation- related genes

Tomato bushy stunt virus (TBSV), a member of the genus Tombusvirus is one of the causal agents for curly disease in tomato plants. In this study, the interaction between a mycorrhizal fungus, Rhizoglomus irregular, and TBSV in tomato plants was investigated. In a completely randomized design experiment, tomato seedlings were inoculated with R. irregular and after four weeks they were inoculated with TBSV. Four treatments were included: control plants (C), TBSV -infected plants (V), mycorrhizal plants (M), TBSV -infected mycorrhizal plants (MV). Nineteen days after inoculation the infected plants were tested for symptom production and virus accumulation. Results of symptoms evaluation based on the disease severity index showed a lower disease severity in MV plants compared with V plants. Supporting this result, a lower level of virus accumulation was observed in V plants which was more significant at long-term infection. The expression of methylation-related genes including ADK, HEN1 and MET1 was tested by Real-time PCR. Results showed that the expression of these genes was significantly higher in MV plants as compared with V plants. An increase in the expression of methylation-related genes in MV plants indicates that resistance to the virus is likely to occur through methylation and also supports the lower level of virus accumulation in MV plants.