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New strain of tomato spotted wilt virus on cucumber in Fukushima Prefecture, Japan

A ProMED-mail post
http://www.promedmail.org
ProMED-mail is a program of the
International Society for Infectious Diseases
http://www.isid.org

Date: May 2022
Source: European Journal of Plant Pathology [summ. Mod.DHA, edited]
https://doi.org/10.1007/s10658-022-02515-9

[ref: T Kon et al (2022): Occurrence and characterization of tomato spotted wilt orthotospovirus isolated from cucumber. Eur J Plant Pathol 163, online; DOI: 10.1007/s10658-022-02515-9]

In 2019, leaf necrosis was observed on cucumber plants in Fukushima Prefecture, Japan. TSWV infection was identified in the diseased plants by molecular methods. Complete genome sequencing of the isolate showed highest identity with previously characterised TSWV isolates. Phylogenetic analyses of the cucumber-infecting variant (named TS-FC19) based on the intergenic regions revealed that it clustered with other TSWV isolates collected from the same area in a distinct clade.

Cucumber plants inoculated with TS-FC19 produced symptoms of leaf necrosis, whereas other TSWV strains did not induce severe symptoms in this host. Our findings indicate that the cucumber leaf necrosis disease in Fukushima Prefecture is caused by a new strain of TSWV that appears to have evolved locally. This is the first detailed report on the biological characteristics of a cucumber-infecting TSWV.

So far, TS-FC19 has been detected only in a few locations, no regional spread has been confirmed. Several other tospoviruses are known to occur in cultivated cucumbers in Japan, and it will be important to evaluate the risk of new viruses arising from multiple infections with TSWV.

--
Communicated by:
IBIS (International Biosecurity Intelligence System)
https://ibisbiosecurity.org/

[_Tomato spotted wilt virus_ (TSWV; type species of genus _Orthotospovirus_, previously _Tospovirus_) has one of the broadest host ranges among plant viruses and is one of few affecting both dicot and monocot hosts. It is regarded as one of the most economically destructive plant pathogens and has had a serious impact on many crop species worldwide, causing up to 100% yield loss in some instances. Symptoms on tomato may include purple discolouration and/or drooping of leaves; necrotic lesions on stems and fruit; and stunting of plants.

TSWV is transmitted by various species of thrips (_Frankliniella_ and _Thrips_ species). Thrips are plant pests in their own right causing considerable leaf damage. The virus is not seed transmitted, but transmission by mechanical means and grafting has been reported. Weed species can serve as pathogen reservoirs. Disease management may include vector control, use of clean planting material, control of weed hosts of virus and vectors, as well as phytosanitary measures. Breeding programmes for resistant varieties have been established for some crops, but resistance breaking strains of the virus are emerging, for example for capsicum (e.g., ProMED-mail post 20080123.0280) and tomato cultivars.

Coinfections of TSWV with other viruses have also been reported (e.g., in tomato; ProMED posts 20191029.6751082, 20200507.7307615). It is thought that respective symptoms may then be due to either virus or to synergism. Further research is needed to clarify potential roles of the different viruses in such coinfections and to determine whether the presence of the common TSWV may have led to earlier cases of misdiagnosis and delayed identification of other new viruses.

Due to their agricultural importance, research on tospoviruses has increased dramatically in recent years. As a result, many new species are being found and many more can be expected to exist. The above reported information on a new strain in its region of origin, before it had opportunities for further recombination with other strains or viruses elsewhere, is a valuable contribution to the epidemiology and evolutionary potential of this important group of viruses.

Maps
Japan:
https://www.nationsonline.org/maps/japan-map.jpg and
https://promedmail.org/promed-post?place=8703234,12184
http://toursmaps.com/wp-content/uploads/2016/08/political-map-of-japan.gif (with prefectures)

Pictures
TSWV symptoms on capsicum:
https://bugwoodcloud.org/images/768x512/1573188.jpg and
http://www.hort.cornell.edu/livegpath/images/pepper_tswv5x1200.jpg
TSWV symptoms on tomato:
http://garden.org/pics/2014-01-14/farmerdill/6f17df.jpg,
http://www.tomatonews.com/maj/phototheque/photos/Images_TN/6239_00.jpg, and
http://sistemasdeproducao.cnptia.embrapa.br/FontesHTML/Tomate/TomateIndustrial/Image43.jpg (affected field)
TSWV on potato:
https://bugwoodcloud.org/images/768x512/1578136.jpg,
https://c8.alamy.com/comp/A55ABA/tomato-spotted-wilt-virus-symptoms-on-potato-leaves-A55ABA.jpg,
https://nwdistrict.ifas.ufl.edu/phag/files/2013/06/tomato-wilted-virus.jpg, and
https://ephytia.inra.fr/en/I/30297/TSWV5
TSWV photo galleries:
http://www.forestryimages.org/browse/TaxImages.cfm?Area=62&fam=652&genus=Tospovirus and
http://vegetablemdonline.ppath.cornell.edu/PhotoPages/Tomatoes/Tom_SpWilt/Tom_SpWiltPhotoList.htm
TSWV particles, electron microscopy:
https://ephytia.inra.fr/en/Images/view/18124
Western flower thrips:
http://www.insectimages.org/images/768x512/4387048.jpg

Links
Information on TSWV and tospoviruses:
https://pnwhandbooks.org/plantdisease/host-disease/tomato-solanum-lycopersicum-tomato-spotted-wilt,
https://aces.nmsu.edu/pubs/_h/H242/welcome.html,
http://www.ipm.ucdavis.edu/PMG/r783102211.html,
http://vegetablemdonline.ppath.cornell.edu/factsheets/Virus_SpottedWilt.htm, and
https://www.daf.qld.gov.au/__data/assets/pdf_file/0007/58777/Thrip-viruses-veg-crops.pdf
Review on tospoviruses, impact, and global crop risks:
https://doi.org/10.1146/annurev-virology-100114-055036
Virus taxonomy via:
https://talk.ictvonline.org/taxonomy/
Thrips information:
https://projects.ncsu.edu/cals/course/ent425/library/compendium/thysanoptera.html,
http://www.cals.ncsu.edu/course/ent425/text18/plantvectors.html, and
https://www2.ipm.ucanr.edu/agriculture/onion-and-garlic/thrips/
- Mod.DHA]