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http://www.isid.org

Date: Mon 10 May 2021
Source: FreshPlaza [summ., edited]
https://www.freshplaza.com/article/9319554/fol-race-1-is-a-critical-issue-for-lettuce-production-in-norway/

Lettuce is produced in Norway both in field and greenhouses. Greenhouse lettuce is one of the most important vegetables grown year-round. In winter 2018, wilting symptoms were observed on soil-grown lettuce in southeast Norway. Affected plants showed stunted growth, wilting of outer leaves, and brownish discoloration of vascular tissues of taproots and crowns. According to the growers, the disease caused an estimated 10% of yield losses.

Fungal isolates were obtained from crowns and roots of diseased plants collected from the greenhouse in 2018 and 2019. Morphological and DNA sequences analyses indicated that the pathogen was _Fusarium oxysporum_ f.sp. _lactucae_ (FOL) race 1. The results were [confirmed] by Koch'postulate. Using differential lettuce cultivars, colony patterns of recovered isolates confirmed the isolate [as] race 1.

Greenhouse lettuce in Norway is mainly produced in hydroponics. FOL is here reported to cause damages in soil-grown lettuce. Nevertheless, FOL in hydroponic systems has been reported in Japan and Thailand. Thus, the possibility of infections in hydroponics remains a big concern for lettuce production in Norway.

[Source publication:
https://apsjournals.apsnet.org/doi/10.1094/PDIS-01-21-0134-PDN]

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

[Fusarium wilt of lettuce caused by the fungus _Fusarium oxysporum_f.sp. _lactucae_ (FOL) can affect plants of any age. Symptoms include leaf yellowing, tip burn, and necrosis, as well as browning of vascular tissues and rotting of the tap root. Plants may be stunted and fail to form heads; infected seedlings wilt and may die. Disease incidence can range from a few plants up to large areas within a field.

The pathogen occurs in soils worldwide and is commonly found on roots of healthy plants. Most strains cause no damage to their hosts, but severe strains can block the water-conducting xylem and lead to wilting. Races 1, 2, and the particularly aggressive race 4 are known to cause disease in lettuce, with up to 70% crop losses reported. Lettuce cultivars have been reported to differ significantly in susceptibility, with some leaf and romaine types highly resistant. Disease severity may also depend on fungal populations in the soil, inoculum levels, and temperature.

Spread occurs mainly on contaminated seed, with soil, infected crop debris, irrigation water, and human activities (for example on farm machinery and tools). Disease management requires an integrated approach including crop rotation and phytosanitary measures (including steam treatment of soil) to avoid spread to new fields. For related fusarium pathogens, flooding of fields has been reported to reduce fungal survival in the soil. Once introduced to an area, FOL fungi may survive indefinitely on the roots of asymptomatic reservoir hosts. Thus, resistant lettuce varieties and rotation crops can contribute to
an increase in soil inoculum.

Different strains of the fungus cause wilting diseases with serious losses in other crops, such as banana (Panama disease), guava, vanilla, date palm, and a range of cucurbits. Each of the pathovars is highly specialised, attacking only a single crop species.

Maps
Norway (with counties):
http://www.lib.utexas.edu/maps/europe/norway.gif
Europe, overview:
https://mapofeurope.com/wp-content/uploads/2018/03/europe-political-map.jpg

Pictures
Fusarium wilt on lettuce plants:
http://people.umass.edu/jmeagy/Lettuce-fusarium%20wilt.jpg,
http://ucanr.edu/blogs/anrnews/blogfiles/5375.jpg,
http://ag.arizona.edu/crop/vegetables/advisories/images/FusariumSymptoms.jpg
and
http://ag.arizona.edu/plp/plant-images/plant11.jpg (affected field)
Symptoms on taproots:
http://ucanr.org/blogs/SalinasValleyAgriculture/blogfiles/6898.jpg

Links
Information on fusarium wilt of lettuce:
https://gd.eppo.int/taxon/FUSALC,
http://www.ipm.ucdavis.edu/PMG/r441100911.html,
http://www.cals.arizona.edu/crop/presentations/2003/matheron120303.pdf,
http://onlinelibrary.wiley.com/doi/10.1111/ppa.12135/abstract and
http://www.calgreens.org/control/uploads/Gordon_-_Fusarium_wilt_of_lettuce.pdf
_F. oxysporum_ f.sp. _lactucae_ taxonomy:
http://www.indexfungorum.org/Names/NamesRecord.asp?RecordID=586936
NIBIO:
https://www.nibio.no/en
- Mod.DHA

HealthMap/ProMED map:
Norway: http://healthmap.org/promed/p/107]

[See Also:
2018
----
Fusarium wilt, lettuce - Ireland: 1st rep, UK spread
http://promedmail.org/post/20180910.6018539
Fusarium wilt, lettuce - UK: (England)
http://promedmail.org/post/20180618.5861084
2017
----
Fusarium wilt, lettuce - UK: 1st rep
http://promedmail.org/post/20171030.5412370
2015
----
Fusarium wilt, lettuce - Netherlands
http://promedmail.org/post/20151022.3734467
Fusarium wilt, lettuce - USA: (AZ)
http://promedmail.org/post/20150721.3525165
2003
----
Fusarium wilt, lettuce - USA (AZ): first report
http://promedmail.org/post/20030922.2393
2002
----
Fusarium wilt, lettuce - Europe
http://promedmail.org/post/20020821.5103
and additional items on fusarium diseases in the archives]

 

Website: http://www.isid.org

Published: May 17, 2021