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First report of lettuce necrotic leaf curl virus in France

A ProMED-mail post <https://url.emailprotection.link/?bczGkw5NaxKViInVN3o8WI7SkfPjCplYcnrvkSnR7vDdzBseB4Z4JgOzMtf4NyhKwZ-87t_ekCqY4X1TR9IACFg~~>

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Date: December 2020
Source: Plant Disease [edited]
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Ref: Svanella-Dumas L, et al.: First report of lettuce necrotic leaf curl virus infecting cultivated lettuce in France. Plant Dis, First Look. 2020; DOI: 10.1094/PDIS-11-20-2348-PDN.

Abstract [abridged, edited]

-----------------------------

_Lettuce necrotic leaf curl virus_ (LNLCV, genus _Torradovirus_, family Secoviridae) has so far only been reported in the Netherlands in open field lettuce. It was the 1st torradovirus described from non-tomato host and, contrary to whitefly-transmitted tomato[-infecting] torradoviruses, aphids are its natural vectors.

In October 2019, a symptomatic lettuce (JG3, cv. "Tregoney") was collected in an open field in southwestern France. Symptoms included stunted and deformed leaves with light necrosis and yellow spotting along minor veins of older leaves. Double-stranded RNAs were purified, and analysis of sequence data identified 2 RNAs sharing, respectively, 85.5% and 83.3% nucleotide (nt) identity with the RNAs 1 and 2 of the LNLCV reference isolate.

To confirm the presence of LNLCV in the original JG3 plant, it was used to mechanically inoculate indicator _Nicotiana benthamiana_, _Chenopodium quinoa_, and _C. amaranticolor_ plants. Only _N.

benthamiana_ developed symptoms, in the form of smaller and yellowed leaves. All inoculated plants were tested one month post-inoculation for the presence of LNLCV. LNLCV was detected in 3 out of 4 inoculated _N. benthamiana_ plants. The lettuce JG3 isolate RNA1 shows 86.5% nt identity with the reference isolate, while the taxonomically informative protease-polymerase regions share 96.8% aa [amino acid] identity. JG3 RNA2 shares 84.8% nt identity, while the movement protein and capsid subunits share, respectively, 92.5% and 98.3% aa identity. The smaller upstream ORF [open reading frame] is also conserved and shows 94.8% aa identity with the reference isolate.

To our knowledge, this represents the 1st report of a natural infection of LNLCV in cultivated lettuce in France and anywhere outside the Netherlands. Since no other viruses were detected in the sequence dataset, LNLCV is most likely responsible for the mild necrosis and leaf deformation symptoms observed on the JG3 plant that appear to be similar to those initially described for LNLCV. While the pathogenicity of LNLCV in lettuce appears to be firmly established, further studies are needed to establish its distribution and prevalence, to understand why this pathogenic and aphid-transmitted virus is not more widely reported and whether it has the potential to increase in impact as a potential emerging agent on field lettuce crops.

Communicated by: PestLens <PestLens@usda.gov>

[_Lettuce necrotic leaf curl virus_ (LNLCV) was first identified in symptomatic lettuce plants from a single field in the Netherlands in 2011. Subsequently, transmission by the currant-lettuce aphid _Nasonovia ribisnigri_ in a semi-persistent manner was shown. After a preliminary risk analysis by Netherlands authorities, it is considered to have the potential of major impact on lettuce production if the vector is present.

The currently known tomato-infecting torradoviruses referred to above are _Tomato torrado virus_ (ToTV), _Tomato marchitez virus_ (ToMarV), as well as a new species tentatively named Tomato chocolate virus (ToChV).

Maps

France:

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Europe, overview:

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Pictures

LNLCV symptoms & particles:

<https://url.emailprotection.link/?bSU81mq2I3ntBhY3sSnRFdKo_8MPYofFi1QGX_F6wxXBXYequKjlX6yWFJuwv8-8EROR7WdVKMaSj5oCHL9Cdwp-h01vkt21ygG-Pto5-5OibCQmKn-eLr6q6trGJZHrwngOlOHPu7JMStycsgW_04Brj6CUJnLVqltVJSJeIWMV7Cok0qZZ0srxYGBrMpPsoo7mvrsdUPsMu_shP0-Neng~~>

_N. ribisnigri_:

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