Tomato brown rugose fruit virus (ToBRFV) is an emerging tobamovirus. It was first reported in 2015 in Jordan in greenhouse tomatoes and now threatens tomato and pepper crops around the world. ToBRFV is a stable and highly infectious virus that is easily transmitted by mechanical means and via seeds, which enables it to spread locally and over long distances. The ability of ToBRFV to infect tomato plants harboring the commonly deployed Tm resistance genes, as well as pepper plants harboring the L resistance alleles under certain conditions, limits the ability to prevent damage from the virus. The fruit production and quality of ToBRFV-infected tomato and pepper plants can be drastically affected, thus significantly impacting their market value. Herein, we review the current information and discuss the latest areas of research on this virus, which include its discovery and distribution, epidemiology, detection, and prevention and control measures, that could help mitigate the ToBRFV disease pandemic.

Tomato brown rugose fruit virus (ToBRFV), belonging to the genus Tobamovirus, is a highly virulent emerging virus, causing disease outbreaks and significant crop losses worldwide. The growing number of ToBRFV epidemic episodes prompted the investigation of the role of seeds in the dissemination of the virus as an important aspect in the overall disease management. Therefore, the objectives of this study were to determine the localization of ToBRFV within tomato seeds and to evaluate its seed transmission characteristics. Seeds extracted from naturally ToBRFV-infected tomato fruits were tested for the presence of the virus using serological, molecular, and biological assays. Three immunolocalization techniques were used to determine the localization and distribution of ToBRFV within the different tissues and parts of tomato seeds. To evaluate seed transmission of ToBRFV, two grow-out experiments were conducted to assess the rate of both vertical (seeds to progeny seedlings) and possible horizontal transmission (plant to plant) based on serological and molecular assays. Seeds extracted from ToBRFV-infected fruits had a 100% contamination rate. The localization of ToBRFV in tomato seeds is only external on the seed coat (testa). Seed transmission rate from seeds to their seedlings was very low (0.08%), while no transmission was recorded from plants to plants in a small-scale greenhouse experimental setup. In conclusion, ToBRFV is a seedborne virus located externally on tomato seed coat and transmitted mechanically from ToBRFV-contaminated tomato seeds to seedlings, which could initiate a disease foci and eventually drive further dissemination and spread of the disease in a new growing area.

Pepper (Capsicum annuum L.) is one of the major vegetable crops in Jordan. During winter growing seasons of 2015 and 2016, virus symptoms including stunting of young plants, puckering and yellow mo...

Tomato brown rugose fruit virus (ToBRFV; genus, Tobamovirus, family, Virgaviridae) was first reported in 2015 infecting tomatoes grown under protected cropping in the Jordan Valley. Since then, ToBRFV has been detected in tomatoes grown in both protected and open fields across Jordan. The increased incidence of ToBRFV prompted this investigation of the potential role of natural weed hosts in the dissemination of ToBRFV. A survey was conducted in the Jordan Valley and highlands to determine possible reservoir hosts of ToBRFV in fields and greenhouse complexes in which tomatoes were grown. Detection of ToBRFV infection was made by double-antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) and further confirmation by reverse-transcription polymerase chain reaction (RT-PCR), followed by DNA cloning and sequencing, and bioassays. Thirty weed species belonging to twenty-six genera from sixteen families were tested. Twelve species belonging to eight families were infected of which ten species are newly reported hosts for ToBRFV. Seed transmission of ToBRFV in Solanum nigrum was confirmed in a grow-out experiment. To our knowledge, this is the first report of the natural occurrence of ToBRFV on weed hosts. Identification of natural reservoirs of ToBRFV can help to develop management practices focused on weed plant species to prevent ToBRFV transmission. The extent to which ToBRFV survives in diverse alternate weed host species outside tomato growing seasons in different world regions requires further research in order to establish the risk associated with the possible contribution of weeds as a reservoir for primary infections in tomato crops.

Tomato (Solanum lycopersicum L.) is an important vegetable crop worldwide. In spring and autumn 2017, virus-like symptoms were observed on greenhouse grown tomato plants in the east of Akkar plain (south of coastal region, Tartous governorate, Syria). These symptoms were: mild to severe mosaic on the apical leaves, brown necrosis on sepals, receptacle and flower’s cluster carrier, and severe symptoms of brown rugose and discoloration on fruit. During next growing seasons, disease spread was observed in most of Syrian coastal region with disease incidence ranged from 40% to 70% by 2020. Tomato brown rugose fruit virus (ToBRFV) was suspected as a main causal agent of the disease, especially since its first report in Jordan, a neighboring country (Salem et al. 2016), Palestine (Alkowni et al. 2019), Turkey (Fidan et al. 2019), Germany (Menzel et al. 2019), Italy (Panno et al. 2019), America (Camacho-Beltrán et al. 2019), Egypt (Amer and Mahmoud, 2020), and recently in Spain (Alfaro-Fernandez et al. 2021). In November and December 2020, seventy-one leaf samples from symptomatic plants (59 from Tartous and 12 from Lattakia governorates) and seven from asymptomatic ones (5 from Tartous and 2 from Lattakia) were collected and tested for the presence of ToBRFV by double-antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA), using ToBRFV-commercial kit (LOEWE® Biochemia, Germany) following the manufacturer’s instructions. Results showed, forty-three of symptomatic samples reacted positively (38 in Tartous and 5 in Lattakia) and none of asymptomatic ones. On the other hand, sap mechanical inoculation of 10 tomato cv. Mandaloun F1 (Enza Zaden, the Netherlands) plants using a positive tomato isolate gave systemic mosaic symptoms in all plants identical to those observed in the original plants in the field, after 13 days of inoculation, and necrotic local lesions on 10 plants of Nicotiana tabacum after 5 days, indicating the presence of a tobamovirus in general. ToBRFV infection was confirmed in all mechanically-inoculated plants by DAS-ELISA. Further tests were necessary to investigate ToBRFV presence, because of its serological relationships with another tobamoviruses. Six representative symptomatic samples (ELISA-positive) and two asymptomatic (ELISA-negative) samples were subjected to total RNA extraction using the SV-Total RNA Extraction kit (Promega, U.S.A.) following the manufacturer’s instructions. The samples were tested by two-step reverse transcription-polymerase chain reaction (RT-PCR) using species-specific primers and protocols for most common tomato-infecting viruses, including: tomato chlorosis virus and tomato infectious chlorosis virus (Dovas et al. 2002), pepino mosaic virus (PepMV) and tomato torrado virus (Wieczorek et al. 2013), alfalfa mosaic virus (Parrella et al. 2000), tomato spotted wilt virus (Salem et al. 2012) and a pair of primers: ToBRFV-F2 (5’-CATATCTCTCGACACCAGTAAAAGGACCCG-3’) and ToBRFV-R2 (5’-TCCGAGTATAGGAAGACTCTGGTTGGTC-3’) targeting a region of the RNA dependent RNA polymerase (RdRp), of the ToBRFV genome (KT383474; Salem et al. 2016). First-strand cDNA synthesis was carried out using Moloney murine leukemia virus reverse transcriptase (M-MLV RT; Promega) and random primer according to the manufacturer's protocol, then followed by PCR with the seven species-specific primers. Only ToBRFV was detected among all tested viruses in symptomatic samples (ELISA-positive), and none of the tested viruses was detected in the asymptomatic plants. To confirm the presence of ToBRFV, two selected RdRp-specific PCR amplicons (872 bp) were purified and ligated into pGEM T-Easy Vector (Promega), and three clones were sequenced (GenBank accession nos. MZ447794 to 96). BLASTn analysis showed that the nucleotide sequences are 99.77-100% identical and shared around 99% identity to RdRp of ToBRFV isolate (MT118666) from Turkey available in the GenBank. Accordingly, the presence of ToBRFV was confirmed by bioassays on indicator plants, DAS-ELISA, RT-PCR, and further sequencing. To our knowledge, this is the first report of ToBRFV infecting tomato in Syria, and this requires special emphasis for further investigations because of the virus severity, easy transmission ability and absent of commercial resistance varieties till now.