Tomato Brown Rugose Fruit Virus (ToBRFV) update Webinar

A newly emerging virus, Tomato brown rugose fruit virus (ToBRFV), has been confirmed in mainland Europe which poses a potential and significant risk to UK tomato and pepper crops. As part of AHDB's response to this threat we hosted a webinar with Adrian Fox (Senior Plant Virologist, Fera), Heiko Ziebell (Senior Scientist, Julius Kühn-Institut for Epidemiology and Pathogen Diagnostics), and Sharon Matthews-Berry (Plant Health Consultant, Defra) to update the industry with the latest information on this virus, alongside recommendations for growers.

Please see below for answers to some of the questions that were posed during and after the ToBRFV webinar held on 30th April 2019.

Please get in touch with nathalie.key@ahdb.org.uk for any further questions and information.

FAQs 

As far as we know, they were reported at about the same time. Within North Rhine-Westphalia where the virus was initially reported, the growers work closely together so the outbreaks seemed to be detected at about the same time.

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 being the risk, 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.

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.

This is possible, but without knowledge of presence or incidence in natural populations this is not a known risk. These were experimental infections, so show the possibility that the virus could go into a plant, rather than the specific risk posed by that plant or other wild species.

There have been infections in S. Nigrum and Chenopodiacea, but these have plants have been infected for experimental purposes and are not natural infections.

Heiko: This factsheet will be released in German initially (hopefully by mid-May), but there are plans to translate this into English and this will be made available on the Julius Kűhn Institute website for public access.

Heiko: For the samples we received at the time, 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 the question is if it is ToBRFV, we start straight away with the RT-PCR protocol.

Generic primers can produce result 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 very difficult because of the risk of cross-contamination. This is especially true for the tobamoviruses, so you need to be very careful when handling samples, otherwise it may be possible to have a wrong result.

However, the sequencing should help give confidence and specifically identify the type of tobamovirus it is.

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, so it doesn't matter if you have a virus from Jordan or from Israel or Germany, they are all very similar.

This is possible, but nanopore sequencing is still in development and validation and not yet ready to deploy as a frontline 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.

Heiko: This should be possible, but is not currently available here. We haven't tested any young plants or seedlings yet, but the diagnostic protocols should be sensitive enough to detect the virus in low titre.

This should work/be possible in theory, but the test just needs some validation.

Not yet, no. We are assuming that seed transmission is part of the picture, as it is for other tobamoviruses, but without published evidence (peer-reviewed) we can only say that seed is implicated, not demonstrated. It is likely that EU emergency measures would include some form of seed testing and growers should take every possible precaution in their transport/trade of seeds.

Heiko: Not currently, no. Young plants and seedling have not yet been tested, only samples from known sites of outbreak.

Menno Florades was used on the outbreaks in Germany. Currently only licensed product for this use in Germany. Some reports are available that you can use skimmed milk or other soapy products, but none of them are licensed or have been tested to produce data on the efficiency/efficacy of these products, so we do not recommend using these measure, as we have no hard data supporting the efficiency/efficacy of these products. If you use skimmed milk you do not have batch continuity, so please use only licenced products. We do not have any experiments at the moment where alternatives have been tested.

There have been other reports that skimmed mild is not effective for disinfection against this virus.

We have no specific data for the efficacy of Virkon S on ToBRFV, but it has been shown to have efficacy on other stable plant viruses

The proposed work by Fera to test the survival and best disinfection methods for this virus will test different available viricides for efficacy. These results will be shared when they are available.

Heiko: I can only provide the advice that has been given in the instructions for the commercial disinfectant, where they investigated the time you need to successfully inactivate Tobacco Mosaic Virus. There have not yet been experiments to test it specifically with ToBRFV.

There is currently no specific information about this for ToBRFV. We have the thermal deactivation point for TMV in sap which is around 90˚C for 10 minutes, which may be a useful starting point. Unfortunately we are not yet sure how this compares to surface sterilisation.

Bumblebees are also used as an integral part of the pollination and production process in glasshouse tomatoes. If the virus is not present in the crop, or exposure to inoculum is otherwise minimised, then the movement of bees within a crop will present no greater risk than other contact related transmission events.

In Israel there have been reports of a 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), via 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 3000 (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.

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.

Given 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. 

There is no information specific to ToBRFV on this. This is advice by analogy to other tobamoviruses. We know that some tobamoviruses are resistant to denaturing even in composting, but this will also depend on specific conditions including moisture content, temperature, length of time and so on.

As things currently stand, we would take statutory action against this virus and so it would be under a Plant Health Notice. Although not listed anywhere as a regulated organism, we would be treating it as such at the moment.

Within the UK plant health regulations 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 a sufficient threat.

Within the legislation there is a line somewhere which mentions "plants not normally present within the territory" that you can take action on. Action would be taken under that piece of legislation.

Sharon: Highly unlikely that Plant Health Inspectorate would order total crop destruction, but this is usually considered on a case by case basis. To clean this up, likely be relying on a crop break at some point, which I know for some growers is not the normal production method. In general do not think we would be requiring total crop destruction.

Again, this would probably be considered on a case by case basis. Haven't specifically considered organics yet. Will need to consider remainders of roots left in the soil after removal.

Adrian: We have proposed some work to look at survival and disinfection for the virus. Series of different disinfectants and plan to test how effective they are on the virus across different surfaces. Look at survival of the virus on different surfaces and on hands. Some basic work on things like the best hand washing protocol so that we can add into that hygiene best practice advice.