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Potato spindle tuber viroid on tomato in New Zealand )Tasman)

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: Wed 4 Jan 2023
Source: Stuff [summ. Mod.DHA, edited]
https://www.stuff.co.nz/national/130899146/tomato-crop-destroyed-after-plant-disease-detected

The Ministry of Primary Industries said potato spindle tuber viroid (PSTVd) was detected on tomato plants in commercial glasshouses in Tasman region in late 2022. Biosecurity New Zealand identified a mild form of PSTVd. Plants from 3 glasshouses were removed and buried. The infected glasshouses operated under strict protocols during the process.

The pathogen has not been detected anywhere else, but Biosecurity NZ, together with other stakeholders, will continue to monitor closely for any signs of it. PSTVd had been found in New Zealand on 2 previous occasions and was declared eradicated. Investigations are underway on how PSTVd arrived in the glasshouses this time, including tracing seeds and rootstocks of the infected crop.

[Byline: Katy Jones]

--
Communicated by:
ProMED

[_Potato spindle tuber viroid_ (PSTVd; type member of genus _Pospiviroid_) is an important pathogen of solanaceous crops. Yield losses can be up to 65% in potato and up to 50% in tomato. Symptoms in potato may include spindly shoots; stunting of plants; severely distorted tubers (spindles); and delayed sprouting. In tomatoes, symptoms include leaf chlorosis and distortion; shortening of internodes; stunting of plants; and absence of flowers. Capsicum plants often display only mild symptoms. Solanaceous ornamentals and weeds are often symptomless and may serve as pathogen reservoirs for crop infections. All varieties of tomato and potato appear to be susceptible, but mild strains causing latent infections in some host cultivars exist.

PSTVd is transmitted by true seed in potato and tomato at a rate of up to 100%, depending on the host cultivar. Tomato seed is considered an international quarantine risk (ProMED post 20140122.2222560); the viroid was shown to be present in the embryo and endosperm (see link below). Spread occurs also via infected plants or vegetative plant parts (potato seed tubers, tomato explants, tissue cultures), pollen, mechanical means, and plant-to-plant contact. PSTVd is exceptionally stable and can persist in dried sap or plant residue for considerable time. Only in the presence of _Potato leafroll virus_ (genus _Polerovirus_) can PSTVd also be transmitted by an aphid vector (_Myzus persicae_).

Due to the multiple potential transmission routes and the large number of host species, both epidemiology and control of PSTVd are complicated. Disease management relies mainly on removal of infected plants and other sources of inoculum, phytosanitary procedures, as well as use of certified PSTVd-free seed and other planting material. Pospiviroids are considered an emerging phytosanitary threat worldwide because of their potential effects on a number of very important crops and the high risk of incursions via commercial imports.

The presence of PSTVd (and other pospiviroids) in symptomless weedy hosts has been reported from several areas, including Australia (ProMED post 20161206.4678068). Therefore, the possibility of its continued presence in NZ cannot be excluded after eradication from previously affected crops had been claimed, as mentioned above. "Eradication" of pathogens or diseases has hardly ever been successful anywhere in the past. Proof of absence of a pathogen is principally and practically impossible because it would require that each and every known or potential host, symptomatic or not, as well as all known and potential vectors or pathogen reservoirs are tested with a method that has a 100% rate of reliability.

Maps
New Zealand:
https://www.fotolip.com/wp-content/uploads/2016/05/New-Zealand-Map-1.jpg and
http://ontheworldmap.com/new-zealand/new-zealand-regions-map.jpg (regions)

Pictures
PSTVd symptoms on tomato:
http://www.forestryimages.org/images/768x512/0162082.jpg and
https://www.agric.wa.gov.au/sites/gateway/files/PSTVd%20on%20Rutgers.JPG (compared to healthy)
PSTVd symptoms on potato:
https://www.agric.wa.gov.au/sites/gateway/files/PSTVd%20on%20Atlantic.JPG,
http://www.omafra.gov.on.ca/english/crops/facts/98-02514.jpg (leaf) and
http://www.dpi.nsw.gov.au/__data/assets/image/0003/583842/above-ground-symptoms-of-infected-potato.jpg (whole plant, compared to healthy)
Photo galleries of PSTVd symptoms on tomato and potato:
http://www.forestryimages.org/browse/subimages.cfm?SUB=11936 and
https://gd.eppo.int/taxon/PSTVD0/photos
Symptoms of pospiviroids on different hosts:
https://www.ipmimages.org/search/action.cfm?q=pospiviroid

Links
Information on PSTVd:
https://gd.eppo.int/taxon/PSTVD0,
https://doi.org/10.1079/cabicompendium.43659,
https://www.agric.wa.gov.au/potatoes/potato-spindle-tuber-viroid and via
http://www.apsnet.org/publications/apsnetfeatures/Pages/Viroids.aspx
Seed transmission of PSTVd (and some other viroids):
https://doi.org/10.1007/s10658-016-0868-z
Detection methods and quarantine risk analysis of pospiviroids:
https://doi.org/10.2903/j.efsa.2011.2330 and
https://gd.eppo.int/download/standard/258/pm9-013-1-en.pdf
PSTVd taxonomy via:
https://ictv.global/taxonomy
Biosecurity NZ:
https://www.mpi.govt.nz/biosecurity/
- Mod.DHA]