Updated May 15, 2023
Virus alert [5-12-2023]: Tomato seed and plants potentially contaminated with tomato brown rugose fruit virus (ToBRFV)
All growers with tomatoes need to know about Tomato brown rugose fruit virus (ToBRFV), a new tobamovirus. Import restrictions now in place are expected to decrease the risk. Federal Order effective since 22 November 2019 imposes restrictions on imports of tomato and pepper seed lots, transplants, and fruit from all countries where ToBRFV exists. Concern remains for seed imported beforehand in 2019 from these countries and seed from other countries. Some seed companies are testing all tomato and pepper seed for tobamoviruses. ToBRFV is mechanically transmitted therefore greatest concern is with greenhouse tomato crops due to frequency of handling.
Facts about ToBRFV:
- It is seed-borne. This most likely is how this virus has been moved globally. While virus could get on hands from handling infected fruit, likelihood is very low that someone is going to get ToBRFV on their hands by handling infected fruit purchased in a store and then handle tomato plants without having washed their hands. Furthermore, workers at tomato production greenhouses, where ToBRFV is of greatest concern, typically are required to wash hands when entering.
- The outer layer of the viral particle (the coat protein which protects the viral RNA inside) is tough and thus impervious to standard chemical treatments for viruses. An effective seed treatment has not been found yet, but research on this is on-going. Concern is that trisodium phosphate (TSP) itself may not be sufficient.
- Transmission is mechanical. This virus can be moved very easily by workers handling plants. Consequently, ToBRFV is expected to primarily be a problem in greenhouse tomato crops due to the frequency that plants are handled by workers. Tomatoes in high tunnels are at greater risk than those outdoors.
- It can be moved by pollinators, in particular bumblebees which are commonly used in greenhouses. This was documented through research conducted in a greenhouse. (See article.)
- Tobamoviruses may be able to be spread in irrigation water.
- It overcomes all known genetic resistances in tomato to other tobamoviruses.
- Affected tomato plants could produce fruits with brown discoloration symptoms rendering them unmarketable.
- Pepper is also a natural host. Petunia, tobacco, European black nightshade, and several species of Chenopodium and Chenopodiastrum may also be hosts based on demonstrated susceptibility through artificial inoculation; however, while helpful, this procedure is notorious for identifying potential hosts that are never found naturally infected. Eggplant and potato were found to not be susceptible.
- In general, tobamovirus can remain infectious in infested plant debris, in soil, and on surfaces for more than 20 years, which may also be the case for ToBRFV. This degree of stability is unusual for viruses.
Symptoms
Yellowing, bubbling, mosaic and mottling, fern leaf and leaf narrowing are all symptoms of ToBRFV on leaves. Symptoms most commonly develop on upper leaves. Affected fruit may have rough surface; blotchy, pale, or yellow-brown spots; be undersized, deformed, and mature irregularly. Calyx veins can be brown and tips necrotic. Brown lesions also sometimes form on peduncles and pedicels. Flower abortion also occurs. Infected plants often are stunted. Symptoms of ToBRFV resemble those caused by related viruses including tobacco mosaic virus (TMV). Symptoms tend to be more severe during times of stress. Some varieties can remain symptom-free when infected. Photographs are posted at an MSU webpage and in brochure prepared by the American Seed Trade Association.
Known Occurrences
ToBRFV was first described in Israel in 2014. Since then, it has been confirmed in Canada, China, Germany, Greece, Italy, Jordan, Palestine, Saudi Arabia, and Turkey plus unconfirmed occurrences in Belgium, Chile, Ethiopia, the Netherlands, Peru, Sudan, Thailand, and United Kingdom. To date in the USA ToBRFV has been detected in imported tomatoes in Florida and California, in a tomato plant within a community garden in Florida, in greenhouse tomato production greenhouses in California and Arizona in 2018 and in New Jersey in fall 2019, and in seed of 2 varieties marketed by 2 companies to gardeners and growers in 2023 (this seed was produced in a greenhouse in California). ToBRFV has been found in field crops but only in Mexico. It is now considered eradicated from the USA greenhouses where detected and from Germany. There likely have been occurrences in other countries not publicized and additional cases in the USA not reported due to ToBRFV being a regulated pathogen.
Management:
- Select seed that has been tested free from tobamovirues, including ToBRFV.
- Minimize touching plants with hands, clothing and tools. Brushing plants to obtain sturdier stems can move viruses like ToBRFV, as well as bacterial pathogens. Watering seedlings is not considered to have enough force to transfer ToBRFV.
- Require workers wash hands and use hand sanitizer before handling tomato plants.
- Have workers wear disposable gloves and routinely disinfect them and tools while working.
- Disinfectants currently recommended are Virocid at 0.5 – 2%, Clorox 10%, and Lactoferrin 0.5%. These were very effective in a recent study. While significantly less effective, Virex 2% was highly effective and Virkon 2% and Lysol disinfectant 50% were both less effective. Several other products were tested and found to be ineffective.
- Regularly inspect plants for symptoms.
- Submit samples with suspect symptoms promptly to a diagnostic laboratory that has expertise to detect ToBRFV, which in New York is the Cornell Plant Disease Diagnostic Clinic in Ithaca. Contact staff before submitting. Take photographs to document symptoms before sampling.
- When plants are confirmed to have ToBRFV, wear disposable gloves while carefully removing them plus adjacent plants in contact, then destroy by burying, incinerating, or double bagging for trash disposal. Dispose of seedling trays and soil.
Additionally for greenhouse tomato crops:
- Disinfect hands and equipment between each plant worked on is recommended. Ideal is for each worker to have 2 sets of tools so that one can be sitting in disinfectant solution while other is in use. ToBRFV can also be moved on clothing that rubs against plants. Disinfect shoes at least once daily.
- Routinely disinfect carts and other equipment that rubs against plants.
- Use UV to treat recirculated water.
- Promptly remove and destroy leaf clippings.
- Discontinue irrigation for a day before removing affected plants to decrease risk of moving ToBRFV in sap. Remove some adjacent non-symptomatic plants. Extent of rogueing needed depends on situation including plant age.
More information
- Tomato brown rugose fruit virus: An emerging and rapidly spreading plant RNA virus that threatens tomato production worldwide. Review article published in Molecular Plant Pathology in 2022.
- The bumblebee Bombus terrestris carries a primary inoculum of Tomato brown rugose fruit virus contributing to disease spread in tomatoes. Research conducted in greenhouse. Published in PLOS ONE in 2019.
- Tomato Brown Rugose Fruit Virus: What is it and why should we be concerned? – Capital Area Agricultural and Horticultural Program podcast
Prepared by:
Margaret Tuttle McGrath
Associate Professor
Long Island Horticultural Research and Extension Center (LIHREC)
Plant Pathology and Plant-Microbe Biology Section
School of Integrative Plant Science
College of Agriculture and Life Sciences
Cornell University
mtm3@cornell.edu