Tomato brown rugose fruit virus (ToBRFV): A new concern for tomato and pepper producers

Tomato brown rugose fruit virus (ToBRFV) is making headlines and eliciting USDA action. Growers need to learn more about ToBRFV biology, symptoms and control.

ToBRFV fruit symptoms
Figure 1. ToBRFV fruit symptoms. (A-C) Symptomatic mosaic pattern on leaves of cluster tomato plants cv. Mose. (C) Narrowing leaves of cluster tomato plants. (D) Dried peduncles and calyces on cherry tomato plants cv. Shiran leading to fruit abscission. (E) Necrotic symptoms on pedicle, calyces and petioles cv. Ikram. (F) Typical fruit symptoms with yellow spots cv. Mose. (G-I) Variable symptoms of tomato fruits cv. Odelia. (G) The typical disease symptoms. (H) Symptoms of mixed infections by the abundant TSWV and the new tobamovirus isolate. (I) Unique symptoms of the new tobamovirus isolate found at a single location at Sde-Nitzan village. Photos by Neta Luria et al./PLOS

Tomato brown rugose fruit virus (ToBRFV) is a newly identified virus affecting tomato, pepper and possibly their relatives. ToBRFV first appeared in Israel in 2014. Since then, it has shown up in several other countries, including eradicated greenhouse outbreaks in 2018 and 2019 in Arizona and California. These back-to-back U.S. outbreaks indicate ToBRFV will probably be something that without good diligence has a high probability of happening again.

An added concern for the U.S. industry is ToBRFV is present in countries exporting tomato and pepper fruit to the U.S.; these include Mexico (where it was widespread in 2018) and the Netherlands. The virus has not been found in Canada, but some fruit imported into the U.S. goes through Canada. The U.S. Department of Agriculture (USDA) is tightening restrictions on imports effective Nov. 22, 2019. These actions include seed lot and transplant testing for countries where the virus exists, and inspection of tomato and peppers from these countries and Canada.

ToBRFV belongs to the same group as tobacco mosaic virus (TMV) and tomato (ToMV) mosaic virus. However, tomato plants tolerant to these two viruses are not tolerant to ToBRFV. Currently, no commercial tomato varieties are tolerant to ToBRFV. Peppers with tolerance to TMV and pepper mild mottle virus (PMMoV) have shown some tolerance.

Leaf symptoms of ToBRFV include wrinkling and bubbling with an accompanying mosaic pattern. Fruit has a browning calyx and is undersized with a rough surface (rugose means wrinkled). Fruit abortion may occur while remaining fruit will be blotchy, pale and may have brown, necrotic spots (Figure 1). Plants infected early will be stunted with poorly formed fruit. Plants infected later may not express fruit symptoms until the fruit turns red. To observe leaf and fruit symptoms, check out “Q&A on the New Tobamovirus: Tomato Brown Rugose Fruit Virus” from the American Seed Trade Association.

Since ToBRFV is related to TMV and ToMV, its spread and control are similar. All viruses spread mechanically through people and equipment touching infected plants and transferring it to a healthy plant. ToBRFV is very stable and very infectious. It has high mechanical infectivity, which is concerning since tomato and pepper plants are highly manipulated through transplanting, staking, tying, pruning and harvesting. ToBRFV’s high stability allows it to stay infectious in the soil, in plant debris and on stakes for long periods—up to 20 years by some accounts. There are reports of spread by bumble bee pollinators in greenhouse situations. However, there are no reports of plant-to-plant transmission by aphids, leafhoppers or white flies.

Just as with TMV and ToMV, a high degree of sanitation is the key to avoidance. There are no sprays that can be applied that are effective in reducing the virus’s spread. Seed and transplant production are the most critical steps since contamination at these steps creates a risk of contaminating hundreds, if not thousands, of plants. Recommended actions include:

  • Start with certified seed from a reputable dealer. Do not plant seed from unverified sources, especially if they come from restricted areas.
  • Have greenhouse workers wash and sterilize hands and tools often.
  • Supply single-use gloves that are discarded between greenhouse ranges.
  • Provide protective clothing that stays in that range or is well washed before going to another range.
  • Dispose of symptomatic plants and plants within 5 feet of infected plants. Also, dispose of plants, trays and media through incineration—DO NOT spread it out on your fields!
  • Monitor movement of equipment and workers between fields. Thoroughly wash equipment and possibly have workers bring a change of clothes.
  • Rogue and incinerate symptomatic plants and conduct activity last in that field followed by good sanitation.

Suspected plant material can be tested for ToBRFV by submiting samples to Michigan State University’s Pest & Plant Diagnostics. As with any pest, the best way to deal with ToBRFV is to never get it. To do that, you will have to pay special attention to sanitation, something most do already. How severe of a problem this becomes remains to be seen.

Summary: Key points about ToBRFV

Developed by the American Seed Trade Association in “Q&A on the New Tobamovirus: Tomato Brown Rugose Fruit Virus.”

  • ToBRFV is a highly virulent very aggressive virus that can cause severe infection on tomatoes with resistance genes including Tm-22, and susceptible peppers that lack the L resistance genes.
  • This virus can spread quickly and easily by mechanic transmission, especially under intensive production practices.
  • Symptoms may vary by variety, and in some cases, infected varieties may be asymptomatic. Typically, infected plants have fruit with severe symptoms.
  • Leaf symptoms include distortion, shoestring and fern leaf; calyx symptoms include browning of the veins. Affected fruit may be aborted or small with blotching or brown spots.
  • The virus behaves similarly to other tobamoviruses such as TMV or ToMV, but the symptoms (especially in the fruit) may be much more severe.
  • The virus can very easily be moved from plant to plant by workers or even from root to root contact. Personnel coming from an infected greenhouse can introduce the virus if proper sanitation measures are not in place.
  • ToBRFV is very stable and can survive for long periods in infected debris, in the soil or on contaminated surfaces.
  • Do not rely on genetic resistance to tobamovirus to provide control, especially with tomato. Strict sanitation measures must be implemented including using clean clothing, tools and implements, stakes, etc.
  • Symptomatic plants can be removed and destroyed but only very carefully, being sure not to touch any other plants or surfaces. Do not move from infected to clean greenhouses. Approach each production as if there is no resistance to this highly transmittable and damaging tobamovirus.
  • If you find plants with tobamovirus symptoms, especially if the variety has genetic resistance, obtain a professional diagnosis for confirmation.
  • Overall, best practices for prevention are essential. Workers should wear protective clothing when moving between greenhouses, especially disposable coats and gloves. Even if the virus has not been detected, this should be standard procedure.

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