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International Society for Infectious Diseases
Date: Thu 2 Sep 2021
Source: Plant Disease [summ., edited]
[Citation: Hasan ZM, Salem NM, Ismail ID, et al. First Report of _Tomato brown rugose fruit virus_ on tomato in Syria. Plant Dis. 2021. doi: 10.1094/PDIS-07-21-1356-PDN
In 2017, virus-like symptoms were observed on glasshouse grown tomato plants in the Tartous governorate, Syria, including leaf mosaic, necrosis and discolouration on fruits. During the next growing seasons, disease spread was observed in most of the Syrian coastal regions. Disease incidence ranged from 40% to 70% by 2020. _Tomato brown rugose fruit virus_ (ToBRFV) was suspected, especially due to its presence in neighbouring countries such as Jordan and Turkey.
59 leaf samples from symptomatic plants from Tartous and 12 from Lattakia governorates, as well as 5 asymptomatic samples from Tartous and 2 from Lattakia, were tested for the presence of ToBRFV by DAS-ELISA. 43 symptomatic samples were positive (38 from Tartous, 5 from Lattakia) but none of the asymptomatic ones. Mechanical inoculation with leaf sap from infected plants to tomato (_Solanum lycopersicum_) resulted in the same symptoms as the source plants. Inoculation of tobacco (_Nicotiana tabacum_) as indicator species resulted in necrotic lesions, confirming the presence of a tobamovirus.
Sequencing of amplicons from ToBRFV specific RT-PCR showed a nucleotide sequence similarity of around 99% to a ToBRFV isolate from Turkey. _Tomato chlorosis virus_, _Tomato infectious chlorosis virus_, _Pepino mosaic virus_, _Tomato torrado virus_, _Alfalfa mosaic virus_, and _Tomato spotted wilt virus_ were not detected by respective specific RT-PCR tests. ToBRFV was further confirmed by bioassays on indicator plants, DAS-ELISA, RT-PCR, and additional sequencing. This is the first report of ToBRFV in Syria, further investigations are needed.
[_Tomato brown rugose fruit virus_ (ToBRFV) was recently identified as a new member of the genus _Tobamovirus_ (type member _Tobacco mosaic virus_, TMV) in Jordan and soon after in Israel (see links below). Since then, it has also been reported from a number of other countries in Europe and the Mediterranean region, where it appears to be spreading, as well as from North America and China. It was shown to affect also capsicum and has been detected in both plants and seeds of both crops. ToBRFV symptoms on tomato vary depending on host cultivar but may include chlorosis, mottling, mosaic, crinkling (rugosis) on leaves; necrotic spots on petioles and calyces; yellowish mottling, brown spots, rugosis on fruit, making them unmarketable. On capsicum, leaf symptoms are similar; fruits may be deformed with yellow mottling or green stripes. Almost 100% incidence was reported for some outbreaks in tomato but not every fruit on an infected plant may show symptoms.
ToBRFV (like many tobamoviruses) is seed transmitted and can also be spread by mechanical means, contaminated equipment, as well as with plant or other materials. It is very stable and can remain infectious for months outside a host. Recently, bumblebees which are used widely as commercial pollinators in glasshouse tomato production, have been shown to be effective vectors of ToBRFV (see link below). Volunteer crop plants and solanaceous weed species are likely pathogen reservoirs. The Tm-22 resistance gene used in some tomato cultivars to protect from other tobamoviruses (such as _Tomato mosaic virus_) does not appear to be effective against ToBRFV. Disease management relies mainly on exclusion but may include phytosanitation (disinfecting tools, removing crop debris) and control of virus reservoirs. Use of certified clean seeds or tomato transplants is crucial. Research on possible seed treatments to eliminate the virus is being carried out (see link below). Tomato seeds are traded widely and are known to pose a risk for spreading viruses and other pathogens internationally (for example, ProMED post 20140122.2222560).
Coinfection of ToBRFV with _Pepino mosaic virus_ (genus _Potexvirus_) and _Tomato spotted wilt virus_ (genus _Orthotospovirus_) have been found (ProMED posts 20191029.6751082, 20200507.7307615). It is thought that the respective symptoms on tomatoes may be due to either virus or to synergism. Further research is needed to clarify a potential role of ToBRFV in coinfections and to determine whether its presence in coinfections may have led to earlier cases of misdiagnosis and delayed identification of this new virus.
https://www.ezilon.com/maps/images/asia/political-map-of-Syria.gif (with governorates)
Middle East region:
ToBRFV symptoms on tomato:
Information and characterisation of ToBRFV:
https://gd.eppo.int/taxon/TOBRFV (with distribution map),
https://www.ndrs.org.uk/article.php?id=041020 (in capsicum) and via
ToBRFV spread by pollinators:
Tomato resistance breeding:
ToBRFV seed treatment:
International spread of tobamoviruses by seeds (review):
Virus taxonomy via: