Tomato brown rugose fruit virus: FAQs
Read the FAQs we have received about ToBRFV.
If you have further questions or queries, please contact Nathalie.Key@ahdb.org.uk.
The virus is not vectored in a traditional sense through insects. Contact transmission, most likely through humans (hands/clothing) and equipment, trolleys, crates, etc. is the most likely method of spread. Major risks are via seed transmission and bringing in infected plants.
This is difficult to answer at this stage because most of what we know is based on warm climate crops (primarily Israel). Heat stress has been linked to ToBRFV symptom severity. In Israel, symptoms are more severe during the hottest months. In Turkey, where tomato crops may experience very cool temperatures ~5°C, this has also been linked to triggering symptoms. No information is currently available on the impact of temperature extremes on European varieties, or how lit crops are affected.
Given that in Northern Europe this is a glasshouse pathogen, outbreaks are in a controlled environment and prevailing conditions are probably unrelated to the spread of the pathogen.
We know that tobamoviruses are transmissible through water (e.g. recirculating irrigation systems). And it is likely that ToBRFV will also be transmissible through this pathway. Rather than the molasses product, it is more likely the risk would be the water source, if free flowing/recirculating.
Irrigation, especially recirculating irrigation, could present a route for spread of infection within a crop, once the virus is present within a glasshouse system.
If outbreak is suspected, you should close the hives in the potentially affected glasshouse/ compartment. If the presence of the virus is confirmed, destroy the hives.
To limit the risk of spread, you should make efforts to reduce the movement of bees between areas, where possible – e.g. careful closing of doors. However, it is difficult to control their movement.
Some nurseries have been using mesh to cover openings to limit the movement of bees, but the efficacy of this intervention is not proven.
They are all susceptible, but the symptom development is different (some just display fruit symptoms, some leaf symptoms). Some infected varieties may even be asymptomatic, but capable of spreading the virus. We have not heard of a single resistant variety yet.
Yes, the virus has been found on the seed coat, but not inside the seed. Although it is likely that the rate of transmission via seed is relatively low, growers should take every possible precaution in their transport/trade of seeds.
Because of the way varieties are bred and produced in a monoculture cropping environment, natural immunity will not develop.
Breeding programmes tend to develop resistance and then breed those resistant genes into existing varieties, rather than their developing naturally.
As mentioned, resistance breeding work is currently ongoing, and resistant/tolerant genes are likely to be found but these are not at market yet.
Currently, the main two options are by incineration or deep burial.
Disposal by anaerobic digestion or composting may be possible options but need to be reviewed to check efficacy. This can be determined on a case-by-case basis and Defra is open to considering other measures.
Take care when removing organic material from production sites. Avoid storing material outside of site entrances and have all waste material removed by covered trucks.
Generic primers can produce results within a day, but you won't know what type of tobamovirus is in your plant. Depending on your commercial sequencing provider, it takes another day or two to receive the sequences that need to be analysed. We say you will get results and confirmation within a week.
ToBRFV is difficult to analyse because of the risk of cross-contamination. This is especially true for the tobamoviruses, so you need to exercise caution when handling samples, otherwise it is possible to obtain a wrong result.
However, the sequencing should help give confidence and specifically identify the type of tobamovirus.
The risk with specific primers is that there might be variations of the virus around that might be detected with this specific primer sequence, so we prefer to use the generic tobamovirus primers. The published sequences are very similar, whether you have a virus from Jordan or from Israel or Germany.
This is possible, but nanopore sequencing is still in development and validation, and not yet ready to deploy as a front-line tool. This will likely be of greater use as a research tool for studying populations of the virus. ELISA and PCR-based methods will be of greater immediate use for routine detection of the virus.
For the samples we received at the time (in the German outbreak), it was an unknown virus. Tomatoes can be infected by 40 or 50 different viruses. We do not have the capacity to do 40–50 specific tests, but electron microscopy can be used as the first line of diagnosis to give an initial indication of what the virus might be. This narrows down the second line of testing, where we can then use specific tests, for example, PCR protocols. This is decided on a case-by-case basis. If it is ToBRFV, we start straightaway with the RT-PCR protocol.
Lateral flow devices are antisera-type diagnostics, which work in a similar way to an ELISA – you have an antibody specific to the virus that’s coating a membrane, the sap in a buffer is dripped on, and would work its way up the membrane. If positive for a virus, the line would go darker.
Not currently aware of an LFD for this virus. Other tobamoviruses can easily cross-react so this type of diagnostics may not be accurate for ToBRFV.
Visit the outbreak pages on our website for up-to-date information on UK and international outbreaks.
All we have heard from them is that when outbreaks are found, they are put under eradication measures.
To confirm a virus is eradicated, you must go through a full cropping cycle after clean-up to show there is no carryover of the disease. Therefore, it is too early to confirm whether eradication has occurred.
It is difficult to determine that information as we need to differentiate between crop loss from disease versus loss from crop destruction due to eradication action.
In most situations in Europe, because eradication action has been taken, impact will effectively be total crop loss in most cases. In most places in Europe, we are not letting the crops run with this disease, so it is difficult to say what the impact of ToBRFV would be under Northern European conditions if the virus ran its course.
The Israeli approach to growing is very different compared with European production. In Israel, where ToBRFV is widespread, original crop losses were 100%, due to plant death. Changes to practices, including growing two crop cycles a year, splitting heads and careful variety choice have reduced this to about 20% of the yield loss compared with what was achieved when growing one crop cycle, pre-ToBRFV emergence.
No research has been done into what, if any, is the current level of infection in UK supermarkets. It is important to note, however, that ToBRFV has been intercepted on imported tomato and pepper seed, and on imported fruit destined for retail.
The variability of symptoms (i.e. sometimes symptoms do not occur on fruit) mean that, in theory, infected fruit could come through unnoticed.
On most production sites, tomato fruit originating from other producers are not allowed on site as a precaution.
We would take statutory action against this virus, if found, and so it would be under a Plant Health Notice.
Within the UK, plant health regulations state that any disease that’s deemed to be injurious to a plant is liable for action to be taken, if it is deemed to be of sufficient threat.
Within the legislation, there is a line that mentions ‘plants not normally present within the territory’ that you can act on. Action would be taken under that piece of legislation.
This is unlikely but is usually considered on a case-by-case basis. To clean this up, the likelihood would be a crop break at some point, which, for some growers, may not be the normal production method.
Presently, there are no changes expected to existing measures. The UK will be following the European guidance during the transition period to December 2020 and will be transposing into our own legislation at the end of the period. These measures will be under ongoing consideration as the situation develops.
Menno florades, Jet 5, sodium hypochlorite, Virkon S, Huwa San TR 50, TSOP.
So far, the disinfectants we have tried at short exposure times appear to be relatively ineffective. The practicalities of actually being able to disinfect a whole wheel within a rotation need to be considered – i.e. does your wheel dip allow for coverage over the entire wheel?
It is likely that wheel dipping will be less than one minute in terms of actual exposure. There will also likely be issues of how you clean down, as well as crevices in wheels posing a problem. Spinning wheels can repel the disinfectant.
We would like to look at tyres in further development of the Survival and Disinfection Project and are currently working out the practicalities of this.
The need to continue to test for this virus diligently, at different stages of production, is clear. A diagnostic ‘gold’ standard for the virus is currently being drafted by EPPO, which will determine the reliability of diagnosing from seed and from leaves, and the best protocols to follow in both cases.
Further information on the relative susceptibilities of European varieties, including the typical ToBRFV symptom profiles for the common varieties would enhance crop monitoring, enabling earlier identification of ToBRFV outbreaks.
Further work needs to be done to identify host weed species to clarify the level of risk.
Firmer disinfection advice is needed on the shortest possible contact time to allow better integration of these methods into production routines. It also needs to include information on the more difficult surfaces and challenges that come with that, e.g. wheel treads.
Another practical consideration is how early in the infection cycle can we detect the virus? If we are performing testing of plants early in the cycle, can we be sure that when we are not actually seeing symptoms, we are still able to detect the virus? Knowing this will enable us to better advise growers on when is the best time to test, how many samples should be tested, etc. This work is under development.
It is also important to note that resistance work is under development in other countries.
Not that we know of. The virus that has been tested from different locations has been found to be very similar – not much sequence difference. We only know that different tomato varieties have a differential response in terms of symptom expression.
Unfortunately, there were no practical recommendations specific to organic production coming out from the trip. It does need to be an avoidance strategy. The advice comes back to doing your best to stay clean, and track where your plants are coming from.
In Israel, there have been reports of a 20–50% reduction in yield, with the tomato fruit symptoms reducing likelihood of sale. Growers have been forced to grow short cycle crops, reducing the yield dramatically as well as fruit quality.
Infected plants should be isolated, carefully removed and destroyed, ideally by incineration, but avoiding airborne debris.
As other tobamoviruses can be transmitted via seed (TMV and ToMV), seed propagation materials and graft operations; to reduce the risk of initial infection, there are recommendations that growers seek seed companies and nurseries to test each lot of seeds for the virus – a sample of 3,000 (12 repetitions of 250 seeds).
As the virus is spread mechanically/via contact, only preventative crop management and sanitation practices will aide in preventing an outbreak. As has been recommended already, strict best practice hygiene protocols should be implemented as standard – including clean clothing, tools, implements, etc. use of disposable protective clothes and gloves, and preventing/limiting visitors or movement of workers and tools between pack houses and glasshouses, and in between different glasshouses.
If there is a suspected outbreak, you should seek professional diagnosis for confirmation as soon as possible.
Yes, you can download it here. Other resources and information that you may find useful are in our Useful Links section on the main ToBRFV page.