A ProMED-mail post
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International Society for Infectious Diseases
http://www.isid.org

Date: Mon 4 Oct 2021
Source: HortiDaily [summ., edited]
https://www.hortidaily.com/article/9360514/what-is-killing-the-world-s-salad-bowl-in-california/


In the Salinas Valley in California, one of the largest producers of leafy greens, crops are fighting _Impatiens necrotic spot virus_ (INSV) in 2021. According to the regional Grower's Association, the virus first entered their radar around 2005. But it was not a problem until 2020 when a severe outbreak moved from one field to the next. A lot of fields were never harvested in 2021 because there was too little to get. In lettuce, the virus causes necrotic tissue and stunting, making infected plants unmarketable.

There have been discussions about whether growers would have to move out of the area because of how bad the disease has become. Because the virus can also live in weeds, one of the reasons for the outbreak could have been the lack of weed management. The virus appears to have built up in the area so that there is more inoculum available in the environment than previously.

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ProMED
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[_Impatiens necrotic spot virus_ (INSV) was considered a strain of _Tomato spotted wilt virus_ (TSWV; type species of genus _Orthotospovirus_, previously _Tospovirus_) but has since been classified as a separate species in the genus. It has a wide host range and is of significant economic importance for many crop and ornamental hosts. The virus is distributed in Europe and North America and has also been identified in a few locations elsewhere. INSV is transmitted by the western flower thrips _Frankliniella occidentalis_, other thrips vectors have so far not been recorded.

Tospoviruses are an extremely important group of plant viruses able to infect a large range of crops. They are transmitted exclusively by thrips species, which are found worldwide. Weed species can serve as pathogen or vector reservoirs, tospovirus epidemiology is complex. Disease management is difficult but may include vector control (for glasshouse crops), use of clean planting material, control of weed hosts of virus and vectors, phytosanitary measures, as well as use of resistant crop cultivars. 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.

Maps
USA:
https://www.orangesmile.com/common/img_country_maps/usa-map-0.jpg and
https://free-printablemap.com/wp-content/uploads/2018/10/us-states-and-capitals-map-pertaining-to-united-states-of-america-map-with-capitals.jpg (with states)

Pictures
INSV symptoms on lettuce varieties:
https://agfstorage.blob.core.windows.net/misc/FP_com/2020/07/17/Lettuce_INSV_Greece.JPG,
https://www.growingproduce.com/wp-content/uploads/2020/06/necrosis_lettuce.jpg,
https://ucanr.edu/blogs/SalinasValleyAgriculture/blogfiles/11100.jpg,
https://ucanr.edu/blogs/SalinasValleyAgriculture/blogfiles/11105.jpg and
https://www.tricaldiagnostics.com/wp-content/uploads/2018/07/INSVGrnLf1.jpg
Thrips:
http://www.insectimages.org/images/768x512/4387048.jpg

Links
Information on INSV:
https://gd.eppo.int/taxon/INSV00,
https://gd.eppo.int/download/doc/141_datasheet_INSV00.pdf,
https://www.researchgate.net/publication/257652670_Impatiens_necrotic_spot_virus,
https://extension.psu.edu/impatiens-necrotic-spot-virus and
https://www.plantmanagementnetwork.org/pub/php/brief/2005/insv/
INSV in lettuce:
https://www.growingproduce.com/vegetables/how-to-manage-impatiens-necrotic-spot-virus-in-lettuce/ and
https://www2.ipm.ucanr.edu/agriculture/lettuce/Tospoviruses/
Virus taxonomy via:
https://talk.ictvonline.org/taxonomy/
Information on thrips:
http://www.cals.ncsu.edu/course/ent425/library/compendium/thysanoptera.html. - Mod.DHA

HealthMap/ProMED map:
California, United States: http://healthmap.org/promed/p/204]

See Also

2020
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Impatiens necrotic spot virus, lettuce - Greece: 1st rep, emerging 20200728.7618822
2019
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Impatiens necrotic spot virus, capsicum - USA: (MA) 20190611.6514103
2008
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Tospoviruses, lettuce - USA: (CA) 20080601.1758
2005
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Impatiens necrotic spot, potato - USA (NY) 20050312.0735
2000
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Impatiens necrotic spot tospovirus, peanuts - USA 20000530.0869
1999
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Impatiens necrotic spot tospovirus - Israel 19991107.1993
and additional items on tospoviruses in the archives

Website: http://www.isid.org

Published: October 8, 2021