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International Society for Infectious Diseases

Date: Wed 13 Jun 2018
Source: HortiDaily[edited]

Symptoms of lettuce fusarium wilt have been identified at the existing
outbreak sites [ProMED-mail post] in Lancashire [England]
in May and June this year [2018]. No outbreaks apart from these sites
have been reported so far in the UK.
As the season progresses, it is important to monitor for suspected
symptoms. Growers should first check for possible infection by cutting
a few plants with suspect symptoms from top to bottom and looking for
vascular browning. If this symptom is confirmed, then it is
recommended that a sample is sent promptly for diagnosis of fusarium
wilt at the University of Warwick [England]. Researchers will provide
individual growers with _Fusarium_ species and race found. Anonymised
results, if positive, will also be used to alert industry via AHDB
[Agriculture and Horticulture Development Board] to new disease
outbreaks by county.
Communicated by:

[Fusarium wilt of lettuce caused by the fungus _Fusarium oxysporum_
f.sp. _lactucae_ (synonym _lactucum_) 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. 3 races are known to cause disease in lettuce, with up to 70
per cent 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 temperatures. Once
introduced to an area, the 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.
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.
In the UK, fusarium wilt of lettuce was reported for the 1st time only
recently, in late 2017 (ProMED-mail post It was identified as
race 4 which is particularly aggressive; no chemical treatments or
resistant varieties are known for it so far.
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.
UK: <> and
<> (with
Europe, overview:
Fusarium wilt on lettuce plants:
<> (affected field)
Symptoms on taproots:
Additional information on lettuce wilt outbreak in UK:
Information on fusarium wilt of lettuce:
_F. oxysporum_ f.sp. _lactucae_ taxonomy:
- Mod.DHA]
[See Also:
Fusarium wilt, lettuce - UK: 1st rep
Fusarium wilt, lettuce - Netherlands
Fusarium wilt, lettuce - USA: (AZ)
Fusarium wilt, lettuce - USA (AZ): first report
Fusarium wilt, lettuce - Europe
and additional items on fusarium diseases in the archives]
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