Tomato Brown Rugose Fruit Virus

BY DR. OLUFEMI J. ALABI, Associate Prof. & Extension Specialist, Department of Plant Pathology & Microbiology, Texas A&M University AgriLife Research & Extension Center Weslaco, TX 78596, (956) 969-5624; alabi@tamu.edu

Tomato brown rugose fruit virus (TBRFV) is an economically damaging viral pathogen of tomatoes and peppers and a new threat to the tomato and pepper industry. The virus was first discovered in in 2014 and its occurrence has since then been reported in several countries including China, Greece, Israel, Italy, Jordan, Mexico, the Netherlands, Saudi Arabia, Spain, Turkey and the United Kingdom, according to the European and Mediterranean Plant Protection Organization (EPPO). More recently, ToBRFV was also detected in isolated outbreaks in greenhouse tomato crops in California and Germany and the virus has been eradicated in both cases. Over the years, scientists have developed improved varieties of tomatoes and peppers with genetic resistance to tobamoviruses. Unfortunately, these improved varieties are susceptible to infection by ToBRFV, indicating that the virus can overcome the resistance.

What do disease symptoms look like? Like its other tobamovirus relatives such as tobacco mosaic virus (TMV) and tomato mosaic virus (ToMV), leaf symptoms of TBRFV on tomato include chlorosis, mosaic and mottling with occasional leaf narrowing (Figures 1A-1C). The leaf petiole, fruit peduncles and calyx may also show necrotic (dead) spots (Figures 1D-1E). Perhaps more importantly are symptoms induced by the ToBRFV infection on the fruits of disease-affected plants (Figures 1F-1I). Such symptoms include yellow and/or brown spots or blotchiness, uneven ripening, and rugosity (deformed or corrugated surface) (Figures 1F-1I) from which the virus derives its name. Disease symptoms on peppers include leaf deformation, yellowing and mosaic. Affected pepper fruits may also become deformed, with yellow or brown areas or green stripes. Though ToBRFV does not pose a health risk to people or animals, symptomatic tomato and pepper fruits are rendered unmarketable, resulting in severe economic losses.

ToBRFV and other tobamoviruses are mechanically transmitted, which means that they can be transmitted through contact including via contaminated tools, hands, clothing, and direct plant-to-plant contact. The virus can also be transmitted through grafting or spread through movement of infected plant materials such as transplants and via fruits from infected plants. Contaminated seeds are also primary means through which the spread of tobamoviruses occur. Thus, movement of infected plant materials (transplants and seeds) by humans constitutes a major pathway for the spread of tobamo viruses across local, national and international boundaries. Though not vectored by an insect, insects such as pollinators may facilitate mechanical spread of ToBRFV as they forage between infected and healthy plants. The virus can remain viable in seeds, plants debris and contaminated soil for months.

It is difficult to distinguish between foliar and fruit symptoms due to ToBRFV infection and those due to other tobamoviruses based on visual observation. With seeds, it is impracticable to determine their health status based on visual inspection. In addition, asymptomatic virus infections are not unusual, with the infected but symptomless plants serving as continuous source of virus spread. Consequently, accurate and reliable detection of the virus can only be performed by trained personnel using approved antibody- or DNA-based techniques. There are antibody-based tests such as enzyme-linked immunosorbent assay (ELISA) and ImmunoStrips that can detect tobamoviruses in infected plant samples. Unfortunately, these tests cannot distinguish between the different tobamovirus species conclusively. The definitive identification of ToBRFV relies on DNAbased tests such as reverse transcription polymerase chain reaction, complemented by DNA sequencing. Such assays can only be performed in a well-equipped diagnostic laboratory.

What is being done to prevent ToBRFV spread in the U.S. Due to its economically damaging nature, and to safeguard the United States against the introduction of this virus while facilitating the safe trade of healthy tomatoes, the United States Department of Agriculture Animal and Plant Health Inspection Service has put in place a ToBRFV Federal Import Order effective November 22, 2019. The Federal Order applies to imports of tomato (Solanum lycopersicum) and pepper (Capsicum spp.) seed lots and transplants from all countries and imports of tomato and pepper fruit entering the United States from Mexico, Canada, Israel, and the Netherlands. The Order requires that all tomato and pepper seed lots and transplants imported from countries where the virus exists should be officially tested and certified free of the disease. That all tomato and pepper fruit imported from Mexico, Israel, and the Netherlands should be inspected at the point of origin to ensure it is free of disease symptoms. And that Canada should inspect all tomato and pepper fruit prior to export to the United States to ensure it is free of disease symptoms. Obscured seeds (seeds that are coated, pelleted, or embedded in tape or another substrate that obscures visibility) and small seed lots are also subject to the Federal Import Order. In addition, U.S. Customs and Border Protection (CBP) will increase inspections of tomato and pepper seed, plant, and fruit imports from countries where the virus is known to occur and will take action to keep any infected products out of the country. Further information about the Federal Order can be found at https://www.aphis.usda.gov/aphis/ourfocus/planthealth/ import-information/federal-import-orders/tobrfv/tomato-brown-ru gose-fruit-virus

However, there are steps that can be implemented to prevent spread of ToBRFV. In addition to complying with federal and state regulations on the safe movement of plants and plant materials, ToBRFV spread can be limited through proper sanitation such as the use of disinfectants to sanitize surfaces and implements. It is recommended that farm workers should wash their hands regularly during the day, ensure their clothing are disinfected daily, and wear disposable shoe covers when entering greenhouses where the risk of contact spread is extremely high. Farm tools and implements should also be disinfected regularly. Some of the recommended disinfectants include household bleach (10% chlorox), Virkon® S (2%), and nonfat (skimmed) milk (3.5% protein). Direct seeding or transplanting of plants into soils with debris from previous tomato and pepper crops should be avoided. In general, it is a good practice to practice rotation with non-host crops in-between season.

It is important to ensure compliance with federal and state regulations on the safe movement of plants and plant materials, including transplants, seeds and fruits. These measures are meant to safeguard our agriculture because once an infected plant material is introduced into an area, it could serve as source of virus spread. If you suspect an infected plant based on its appearance, check to see if the symptoms match which those described for tobamoviruses. Immediately isolate the suspect plant from others, taking precautions to avoid mechanically contact between it and other host plants. Although inconclusive for diagnosis, the observation of the described symptoms on a tomato or pepper varieties that carry known tobamovirus resistance genes heightens the likelihood of ToBRFV infection. While keeping the suspect plant isolated, contact the nearest diagnostic laboratory for guidance on how to send a sample for testing and confirmation of ToBRFV infection. The lab would also

Figure 1. Naturally infected tomato plants with tomato brown rugose fruit virus. (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 typi cal 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: Neta Luria et al./ PLOS https://creativecommons.org/licenses/by/4.0/

provide guidance on how to notify the relevant agencies to contain further spread of ToBRFV. In the event of positive ToBRFV detection, affected plants and plant parts should be destroyed by burying or incineration.

Sources Levitzky N, Smith E, Lachman O, Luria N, Mizrahi Y, Bakelman H, et al. (2019) The bumblebee Bombus terrestris carries a primary inoculum of Tomato brown rugose fruit virus contributing to disease spread in tomatoes. PLoS ONE 14(1): e0210871. https://doi. org/10.1371/journal.pone.0210871 Luria N, Smith E, Reingold V, Bekelman I, Lapidot M, Levin I, Elad N, Tam Y, Sela N, Abu-Ras A, Ezra N, Haberman A, Yitzhak L, Lachman O, Dombrovsky A (2017) A new Israeli Tobamovirus isolate infects tomato plants harboring Tm-22resistance genes. PLOS One 12:e0170429. doi: 10.1371/journal.pone.0170429 Tomato brown rugose fruit virus (ToBRFV): Q&A on the new Tomato brown rugose fruit virus (ToBRFV). American Seed Trade Association; https://www.betterseed.org/wp-content/ uploads/ToBRFV-QA.pdf. Assessed on March 02, 2020. Tomato brown rugose fruit virus Federal Import Order; United States Department of Agriculture Animal and Plant Health Inspection Service; https://www.aphis.usda.gov/aphis/ourfocus/planthealth/import-information/federal-import-orders/tobrfv/tomato-brown-rugose-fruit-virus-faqs. Assessed on March 02, 2020. Tomato brown rugose fruit virus. Agronomic Spotlight, Seminis; https:// seminis-us.com/resources/agronomic-spotlights/tomato-brown-rugose-fruit-virus/. Assessed on March 02, 2020.

Kerry was born and raised in the great state of Texas. She graduated from the University of Texas at Austin with a BA in communications, and built a successful career in investment banking and corporate communications for NYSE and NASDAQlisted oil and gas companies. Once Kerry realized that the olive oil business was her true passion, she chose to leave the business world and focus on a different kind of oil instead.

Her family’s ranch in Asherton, Texas inspired her to first consider the idea of producing and creating her own brand of olive oil. Asherton is a town that has an abundance of history for her family; her grandparents had owned the town’s first general store as far back as 1923, and it seemed to be the ideal spot to continue her family’s local legacy.

Eventually, the perfect plot of land was purchased in 2012, and Kerry’s journey began. She now lives on her ranch full time, managing the orchard and advocating for the Texas olive industry. In her efforts to support and educate growers, Kerry holds active leadership roles in the Texas agricultural community, including Secretary of the Texas Association of Olive Oil (TXAOO). In 2018, she was nominated and voted in as the first female Director to the Soil and Water Conservation District Board (Dimmit County, TX) , Subdivision 1.

ater is always on the mind in the Lower Rio Grande Valley. It seems like there is either too much or not enough. This spring, factors are pointing more toward the latter for the coming growing season.

“Over the last month, drought conditions have crept into the Lower Rio Grande Valley. In mid-January, only the western extent of Hidalgo County was in moderate drought,” said Dr. Lucas Gregory, senior research scientist at the Texas Water Resources Institute, College Station. “Now moderate and severe drought conditions cover most of Hidalgo County and W

parts of Cameron and Willacy counties.”

As of mid-February, Amistad and Falcon reservoirs sat at a combined storage capacity of about 54 percent, about 10 per cent less than this time last year. According to an early-February Associated Press news release by Mark Stevenson, “Mexican farmers take over dams to stop water payments to U.S.,” farmers in Mexico attempted to take control of two dams west of Big Bend to prevent water releases to meet water delivery requirements outlined in the 1944 U.S.-Mexico Water Treaty. Pair this with the dryer than normal conditions currently in place and the National Weather Service (NWS) outlook for warmer than normal tempera tures forecasted for the coming year, and the water supply situa

tion could look better. “In times when water supplies are tight, irrigation conservation pays off,” Gregory said. “In these types of situations, water that is available needs to be better used and more effectively delivered to the crop where and when it is needed.”

Dr. Shad Nelson, dean of the Dick & Mary Lewis Kleberg College of Agriculture and Natural Resources at Texas A&M UniversityKingsville, said a number of planting and irrigation practices have been developed and are being implemented across the citrus industry that conserve water. Board are cohosting the free program. Registration and light breakfast begin at 8 a.m. with the program starting at 8:30 a.m. Presentations that focus on water conservation practices in mature orchards, novel field planting designs for new orchards and sustainable water reuse options in agriculture and cities will begin the day. The program will then shift locations to Lance Neuhaus’ property (formerly Pawlik Farms) for further discussion on these topics with researchers and growers.

Content also includes discussion on pest and fertility manage

“In existing groves, converting traditional pan flood irrigation to narrow-border flood, drip or micro-spray applications have all been shown to save water. In newly planted groves, raised beds paired with drip irrigation and plastic mulch not only save water, but have also proven effective in managing certain pests,” Nelson said.

These practices and more will all be discussed at the “Novel Citrus Management Practices for Sustainable Water Use” workshop and field day being held Wednesday, March 25 in Mission. The program will be 8 a.m.–noon at Texas Citrus Mutual, 901 Business Park Drive #300.

In mid-January, only western Hidalgo County was in moderate drought. Now moderate and severe drought cover most of Hidalgo County and parts of Cameron and Willacy counties.

Photo by U.S. Drought Monitor.

ment allowing Texas Department of Agriculture pesticide applicator license holders to secure three continuing education units. This program is being hosted as a part of the “Lower Rio Grande Valley Irrigation Education and Outreach” project funded by the Texas Water Development Board through an Agricultural Water Conservation Grant to the Texas A&M AgriLife Extension Service.