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Source: AgNet West [abridged, edited]
A type of resistance-breaking tomato spotted wilt virus is continuing to spread through production areas of California. The virus has been an issue for growers for a number of decades, but the latest strain is particularly challenging. A single resistance gene that is used in almost all tomato varieties now is no longer adequately protecting from the virus. Since 2016 the issue has become even more of a problem. Tom Turini, Cooperative Extension Vegetable Advisor, [said], "The distribution was ubiquitous. In some areas, it caused a great deal of damage. Other places, it was combination with some other issues that brought yields down."

The strain is creating issues for both fresh market and processing tomatoes. Turini suggests taking an integrated management approach. Work is also being done to evaluate which tomato varieties appear to be the most susceptible to this strain. Researchers are also looking [into] potential alternative sources of resistance. "Before something is released in terms of genetic material that is going to perform at adequate levels and be resistant to this virus, that's going to be a few years off," Turini noted.
[Byline: Brian German]
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[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.

For tomato (_Solanum lycopersicum_), worldwide, the current commercial resistance of cultivars to TSWV is based on a single dominant gene, Sw-5, which is derived from a related wild _Solanum_ species. The TSWV strains referred to above have overcome this Sw-5 based resistance.

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.

Individual states via:

TSWV symptoms on tomato: and
TSWV on a range of hosts: (potato leaf),, (potato tuber), (potato tuber), (capsicum leaf) and (capsicum fruit)
TSWV photo galleries: and
TSWV particles, electron microscopy:
Western flower thrips:

Story also via:
Information on TSWV and tospoviruses:,,, and
Tomato spotted wilt: (affected field), and
Review on tospoviruses, impact and global crop risks:
Virus taxonomy via:
Thrips information:, and
- Mod.DHA


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