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First report of tomato leaf curl New Delhi virus on zucchini in Morocco

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: December 2017
Source: Plant Disease [edited]
<https://apsjournals.apsnet.org/doi/abs/10.1094/PDIS-10-17-1600-PDN>

[Ref: A Sifres et al (2017): First Report of _Tomato leaf curl New Delhi virus_ infecting Zucchini in Morocco. Plant Disease, accepted for publication; DOI: 10.1094/PDIS-10-17-1600-PDN]

_Tomato leaf curl New Delhi virus_ (ToLCNDV) is a devastating pathogen causing significant yield losses to several crops. During spring 2017, generalized leaf symptoms including yellowing and curling, as well as stunting of plants were observed in several zucchini fields of one of the commonest commercial Moroccan cultivar, 'Suha' F1 [near] Agadir [Souss-Massa Region].

Leaf samples from 9 symptomatic and 3 asymptomatic plants were tested for ToLCNDV with an immune strip test. Only the symptomatic samples were positive [for] begomoviruses. To confirm the identity of the virus, DNA from the symptomatic samples was analyzed by PCR, to amplify 505 bp and 677 bp fragments of viral DNAs A and B, respectively. Amplicons were obtained from all the samples positive for ToLCNDV [by] immune strip. PCR products were sequenced and showed nucleotide identity higher than 99 per cent with ToLCNDV isolates of Spain.

DNA from 2 positive samples was used for rolling-circle amplification to clone DNA-A and DNA-B. [The segments] were 2738 nt long for DNA-A and 2684 nt long for DNA-B and shared [more than] 99 per cent nucleotide identity with the complete sequence from ToLCNDV isolates infecting tomato and zucchini in Spain. Efforts to identify the presence of additional begomoviruses or DNA satellites by PCR, using universal primers, were negative.

This is the first report of the presence of ToLCNDV in Morocco, that could therefore represent a serious threat for valuable cucurbit crops in this and other countries of northern Africa. Thus, it is necessary to implement efficient control measures to prevent further spread of the virus and minimize yield losses.

Communicated by: ProMED-mail <promed@promedmail.org>

[_Tomato leaf curl New Delhi virus_ (ToLCNDV; genus _Begomovirus_) has been reported to cause severe yield losses on tomato and watermelon crops on the Indian subcontinent. It belongs to the tomato leaf curl and yellow leaf curl clades of the genus. Known species in these clades cause similar diseases on solanaceous and other crops and can lead to considerable yield losses. Begomoviruses are transmitted by different whitefly vectors (such as _Bemisia tabaci_ biotypes), and many can also be transmitted by mechanical means and grafting, but they are not seed transmitted.

Whiteflies in themselves are serious pests of many vegetable crops. If virus sources are available locally, high vector numbers are often reflected in high levels of the viral diseases they transmit.

Begomovirus control is particularly difficult in open field crops due to the widespread presence and wide host range of whiteflies. Disease management may include pathogen exclusion, vector control, as well as elimination of possible pathogen and/or vector reservoir plants. In some cases, crop cultivars with increased virus resistance are available.

ToLCNDV was limited to Asia until it was reported from Europe for the 1st time in 2013 on cucurbits in Spain (ProMED-mail post http://promedmail.org/post/20131223.2131729). It has since also been reported from Italy (ProMED-mail post http://promedmail.org/post/20160327.4121164) and Tunisia (see link below) and was included in the alert list of the European Plant Protection Organisation (EPPO). ToLCNDV has a wider host range than the related _Tomato yellow leaf curl virus_, which had previously been present in the region.

The source of the Mediterranean incursion so far remains unknown.

Recent research (see link below) has shown that a novel recombinant strain causes the severe damage to cucurbit crops in the region, but poorly infects tomatoes. In Spain, a genetically uniform virus population was identified which would be compatible with a recent introduction. Major concerns in the region are a continued spread, both geographically and in host range, and the potential of coinfections with other begomoviruses already present which may lead to synergistic enhancement of symptoms as well as emergence of further strains due to additional recombination events.

Maps

Morocco:

<https://www.welt-atlas.de/datenbank/karten/en/karte-2-38-en.gif>

Morocco regions:

<https://www.ezilon.com/maps/images/africa/political-map-of-Morocco.gif>

Africa, overview:

<http://www.worldatlas.com/webimage/countrys/africa/maps/africa.jpg>

Pictures

ToLCNDV symptoms:

<http://cienciacebas.files.wordpress.com/2013/09/aranda-1.jpg>

(zucchini) and

<http://cienciacebas.files.wordpress.com/2013/09/aranda-2.jpg>