Sm gene confers tolerance to ToBRFV in tomato

Tomato brown rugose fruit virus (ToBRFV) infection significantly reduces plant vigor, fruit size, and quality, and in the long term affects international seed trade. Several genes have been reported to restrict the systemic spread of ToBRFV in tomato, thereby conferring partial tolerance. We hypothesized that the SmRR gene, an incomplete dominant resistant gene against Stemphylium sp. in tomato, may also contribute to tolerance against ToBRFV infection. To test this, tomato varieties containing the SmRR or Smrr genes were mechanically inoculated with ToBRFV. Symptom severity on leaves was recorded at one, two, and three weeks post-inoculation using a standardized disease rating scale, and viral presence was confirmed by RT-PCR. Results showed that the Smrr (susceptible) variety exhibited the highest disease severity (maximum score= 3), while the SmRR variety had a lower average severity score (1.5) and no visible fruit symptoms, indicating tolerance. Future studies should employ functional assays, such as gene knockdown or overexpression, to validate the role of SmRR in ToBRFV tolerance.