ANSES warns of an emerging virus affecting vegetable plants
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News of 03/02/2020
ANSES is issuing an alert about a new emerging virus threatening tomato, chilli pepper and sweet pepper crops in France. Tomato brown rugose fruit virus (ToBRFV) is particularly hazardous to susceptible plants. This virus can be transmitted through infected seeds, plants and fruits, as well as by simple contact. It can survive for a long time without losing its infectivity, and there are currently no treatments or varieties resistant to this virus. Identified for the first time in the Middle East in 2014, reports have been increasing since 2018, first in Mexico and the United States, then in Europe and Asia. Following its expert appraisal, ANSES confirmed the high risk of introduction and spread of the virus in France and the potentially major impact on crops, both in professional sectors and in household production, which represents significant volumes. The Agency reiterates the importance of complying with European regulations on seed and seedling imports, with special requirements applying to fruit imports. It recommends implementing a suitable surveillance plan and ensuring that the virus's presence in any production area is reported promptly, with the aim of eradicating the virus from these structures. Lastly, private individuals and professionals need to be informed of the risk posed by ToBRFV and the preventive measures to be taken.
Following the health monitoring carried out by its Plant Health Laboratory and the work of its specialised experts, ANSES is issuing an alert about the emerging ToBRFV tomato virus. This virus affects tomato, chilli pepper and sweet pepper production throughout the world. The first reports date from 2014 in Israel and 2015 in Jordan, then in 2018 the virus was reported in Mexico, the United States, Germany and Italy. Since then, the geographical distribution of ToBRFV has spread with confirmed reports in China, Turkey, Greece, the Netherlands, the United Kingdom and Spain. It has now been eradicated in Germany and the United States. In 2019, emergency measures were adopted at European level to respond to this emerging threat. This led the Agency to conduct a risk assessment for metropolitan France.
An emerging virus that is destructive to tomatoes
Tobamoviruses, the genus to which ToBRFV belongs, can enter a plant through microdamage caused by physical contact with any virus-carrying medium: plants, hands, work tools, handlers' clothing, pollinating insects, birds or irrigation water. Once inside, the virus spreads from cell to cell and invades the entire plant. Seeds, plants and fruits remain infectious and can carry ToBRFV over long distances, especially through trade.
The damage observed on tomato plants in greenhouse production includes leaf symptoms (chlorosis, mosaic and mottling) and necrotic spots on peduncles, calyces and flower stalks. The fruits show discolouration resulting from irregular ripening, with yellow or brown spots, deformations and sometimes characteristic rugose symptoms, making them non-marketable. The virus can infect up to 100% of plants on a production site, making it a formidable threat to high-density crops such as those in greenhouses. Nevertheless, all types of tomato crops can be affected: conventional and organic agriculture, crops using integrated pest management, and both greenhouse and open-field production.
These viruses are highly stable and can survive for several months on inert media without any loss of infectivity. Moreover, tomato varieties have not developed resistance to ToBRFV, as they have to other viruses of the same family (through the Tm-2 and Tm-22 genes). In addition, there are currently no chemical, genetic or biocontrol solutions to tackle this virus. As a tomato-producing country, France is at risk of significant economic consequences, affecting not only professional sectors but also household production, in which the area under cultivation is estimated to be similar to that of industrial open-field production.
Actions to prevent entry and to eradicate ToBRFV in the event of introduction
Following its expert appraisal, ANSES confirmed the high risk of introduction and spread, and the impact on crops in France. The Agency therefore recommends that management measures be put in place. To prevent the entry of ToBRFV, it is vital to comply with the emergency measures for seeds and seedlings intended for planting that have been put in place at European level. In addition, fruit imports should come from production sites declared free of ToBRFV.
The Agency believes that the likelihood of virus transfer from imported fruits to crops is greater in household production than in the professional world, due to the proximity between culinary and production activities and the movement of handlers on production sites, compared to professional holdings with more structured activities. There is also a risk of entry via the market for seeds purchased by private individuals on the Internet, and ANSES therefore recommends that private individuals be informed of this new risk.
To increase the likelihood of eradicating ToBRFV in the event of its entry and establishment in France, the Agency recommends measures on two levels:
- introduction of a national plan to ensure structured surveillance and early detection of ToBRFV, which will enable rapid application of control measures;
- removal of symptomatic and asymptomatic plants from contaminated production units and destruction by fire after regulatory authorisation, coupled with strict prophylactic measures including the implementation of an appropriate fallow period on the production site.
Only rapid and determined action involving communication efforts targeting both professionals and amateurs will enable the eradication objective to be achieved. The Agency stresses the critical importance of reporting the presence of the virus in production areas as rapidly as possible. Indeed, the Agency has doubts about the success of a containment strategy aimed solely at limiting its spread through the application of hygiene measures and restricted movement of contaminated plant material.
Since it is a new emerging pathogen, the Agency also points to the need for research to reduce uncertainties regarding assessment of the rate of seed transmission, effectiveness of seed treatments and characterisation of the host range (particularly the role of relay plants), and to provide long-term control strategies such as the breeding of resistant varieties.