ToBRFV, a Tobamo virus like TMV and ToMV, was discovered in 2014 in Israel and then in 2015 in Jordan. Since then, it has been found in Mexico, the United States (Southern California), Germany, Italy, Turkey, the Netherlands and Saudi Arabia. Countries like Mexico, Japan, Turkey and Australia have begun to implement restrictions on tomato and pepper seed imports. This virus can overcome the known resistance genes in tomato varieties that have protected field and greenhouse productions from Tobamo viruses for many years. In peppers, the L gene that confers resistance to TMV and PMMoV seems to be holding up against ToBRFV. Varieties without the gene are highly susceptible. As t its name suggests, it causes yellow to brown colored wrinkled, necrotic spots on the fruit. Like the other Tobamo viruses, it is seed borne and can be readily spread from plant to plant mechanically in tomato/pepper productions, whether commercial productions or seed increases.
The Mexican government has instituted a regulatory seed testing program for tomato and pepper seed being imported into Mexico. There is concern in the seed industry that the testing method being used by SENASICA labs produces a high percentage of false positives. Research is underway in the United States to evaluate the Mexican protocol along with other publically available methods in an effort to harmonize a standard protocol that can be used across countries. This will help the tomato and pepper seed companies from being unduly punished or restricted based on inaccurate testing. Various sets of PCR primers have been developed and are in use to specifically detect this virus in seed and plant tissue. However, these primers have not been fully validated against a range of ToBRFV isolates. There are also commercial ELISA reagents available but they are not specific and will detect ToBRFV along with TMV and/or ToMV. Additional testing such as bioassay and sequencing is required to specifically determine which of the Tobamo viruses are present in samples that test positive by ELISA
It will take a concerted effort from the seed industry to slow the impact of this virus. This is why various companies (both seed companies and third-party testing labs like Eurofins BioDiagnostics) as well as universities are intently interested in solving this issue. Accurate and reliable seed testing is one of the main keys and is why Eurofins BioDiagnostics has actively participated in screening primer sets, tested ELISA reagents and duplicated the Mexican protocol.
* TMV – Tobacco Mosaic Virus, ToMV – Tomato Mosaic Virus, PMMoV – Pepper Mild Mottle Virus.