Tomato Brown Rugose Fruit Virus (ToBRFV)
Tomato Brown Rugose Fruit Virus (ToBRFV) is an emerging disease issue in greenhouse tomato crops worldwide. First identified in Israel in 2014, a number of outbreaks have since occurred in North America, Europe, and Asia. The pathogen is known to be present in greenhouse tomatoes in Mexico, and has occasionally been found in field tomatoes there as well. An outbreak in a California greenhouse in early 2019 is currently the only confirmed incidence of this virus in the USA and it was successfully contained. Natural infection of pepper has also been reported.
ToBRFV is a member of the tobamovirus family along with tobacco mosaic (TMV), tomato mosaic (ToMV), and tomato mottle mosaic (ToMMV). ToBRFV is especially worrisome for tomato growers because it has overcome the Tm-22 gene that confers resistance to tobamoviruses in many tomato cultivars. Like TMV, ToBRFV is very stable and easily transmitted by mechanical means; in a highly managed crop such as greenhouse tomatoes, this means that human activity is the primary vector. It may also be transmitted mechanically by bumblebees employed to pollinate greenhouse crops. The virus is also seedborne; however, research indicates that it is associated with the seed coat, not the embryo. This means that treatments such as hot water or steam should be effective in removing the virus from seed.
In peppers, the L genes that confer resistance to TMV and PMMoV (Pepper mild mottle virus) appear to be stable and confer resistance to ToBRFV as well. Pepper cultivars lacking these genes are highly susceptible to ToBRFV. The virus may be transmitted from peppers to tomatoes or vice versa. Infection of other Solanaceous crops has yet to be reported, but caution and vigilance are encouraged.
Foliar symptoms of ToBRFV on tomato and pepper include deformed, crinkled leaves, mosaic, mottling, flecking, chlorosis, and/or necrosis. Fruit symptoms include discoloration and rough brown patches or ringspots. Irregular fruit shape and maturation patterns may also occur. Browning of the veins in the fruit calyx in the early stages of fruit ripening may also be observed. Symptom expression can vary widely among tomato cultivars: some may be infected but remain asymptomatic.
Management practices for ToBRFV include planting of disease free seed and seedlings, scouting plants regularly for symptoms, and isolating symptomatic plants. Disinfect tools and workers’ hands frequently. Recent research has demonstrated that the most effective disinfectants include 10% bleach, 50% Lysol, and 20% nonfat dry milk. If you have reason to believe that ToBRFV is active in your tomato or pepper crop, please contact the UMass Extension Plant Diagnostic Lab at 413-545-3208 or see our website for instructions for vegetable sample submissions: http://ag.umass.edu/diagnostics
On November 15th, 2019, USDA/APHIS issued an emergency federal order that calls for pre-export testing of tomato and pepper propagative material (plants, seeds, grafts, and cuttings) and fruit produced in any country where ToBRFV has been detected; to date, this list includes Israel, Jordan, Turkey, Greece, Italy, the United Kingdom, the Netherlands, China, and Mexico. Countries where ToBRFV has not been reported may state this fact by providing a letter from the nation’s plant protection organization: propagative material and fruit exported to the USA will then be exempt from the testing requirement. Tomato and pepper fruit from Canada will also be subject to inspection prior to export, because Canada imports these crops from Mexico and re-exports them to the US. US Customs and Border Protection will also increase inspections at U.S. ports of entry to ensure imported tomato and pepper fruit from Mexico, Israel, the Netherlands, and Canada are free from symptoms of ToBRFV. This federal order is similar to the one passed in August 2019 concerning several viroids known to infect tomato.
The tobamoviruses infecting tomato are closely related and many, including ToBRFV, will elicit a positive reaction from a TMV immunostrip test.
Mechanically transmitted viruses are typically more problematic in greenhouse crops than in the field. While an outbreak in the Northeast is not expected, it is important to be aware of the signs and symptoms of ToBRFV. See the references below for photos and further information.
University of Florida: http://blogs.ifas.ufl.edu/pestalert/2019/07/23/tomato-brown-rugose-fruit-virus/
American Seed Trade Association: https://www.betterseed.org/wp-content/uploads/ToBRFV-QA.pdf