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: January 2020
Source: Crop Protection [edited]
<https://www.sciencedirect.com/science/article/pii/S0261219419302947>
[ref: S Charoenvilaisiri et al (2020): Occurrence and distribution of begomoviruses infecting tomatoes, peppers and cucurbits in Thailand.
Crop Protection 127, article no. 104948; doi:10.1016/j.cropro.2019.104948]
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Incidence of begomoviruses infecting tomatoes, peppers, and cucurbits was investigated in major production fields in the north, northeastern, central, and southern regions of Thailand between January 2015 and June 2017.
Of 585 samples subjected to polymerase chain reaction (PCR), 57% were positive for begomovirus infection. Nucleotide sequence analysis of coat protein (CP) and replication initiation protein (Rep) genes identified 15 previously known begomovirus species, 7 of which were reported infecting these crops in Thailand for the 1st time.
The predominant species were different depending on the host plant and location: _Tomato yellow leaf curl Thailand virus_ (TYLCTHV) for tomato; _Pepper yellow leaf curl Thailand virus_ (PepYLCTHV) for pepper; _Tomato leaf curl New Delhi virus_ (ToLCNDV) for loofah, bitter gourd, cucumber, and melon; _Squash leaf curl China virus_(SLCCNV) for pumpkin and wax gourd.
A candidate novel bipartite begomovirus designated Melon yellow mosaic virus was also identified from a northeastern province of Thailand.
[The] isolate from a melon with yellow mosaic symptoms formed a separate group in both CP and Rep phylogenetic trees. CP and Rep of [the isolate] shared the highest nucleotide sequence identity at 90% and 86%, respectively, with [an isolate] of SLCCNV from Viet Nam.
These relatively low percent identities suggested that it is potentially a new species. Molecular characterization [was carried out].
The results demonstrate that the diversity of begomoviruses infecting tomatoes, peppers, and cucurbits in Thailand is higher than previously realized. The data only represent general trends between 2015 and 2017. Diversity of begomoviruses in each crop and location is expected to be dynamic due to the high rate of mixed infections and recombination of begomoviruses, as well as the increase in movement of plant materials and their whitefly vectors. There is an urgent need to develop assays that facilitate begomovirus identification for species-specific screening of resistance as well as for persistent monitoring of the spread and emergence of begomoviruses in the future.
--
Communicated by: ProMED-mail <promed@promedmail.org>
[Begomoviruses are transmitted by different whitefly vectors (such as _Bemisia tabaci_ biotypes). 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. Many begomoviruses can also be transmitted by mechanical means and grafting, but seed transmission was considered absent for this group. However, recent work has indicated likely seed transmission of _Tomato yellow leaf curl virus_ (TYLCV) in tomato and some other hosts (see links below).
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 and elimination of possible pathogen and/or vector reservoir plants. In some cases, crop cultivars with increased virus resistance are available.
Species in the leaf curl and yellow leaf curl clades cause similar diseases and are considered to be the biggest constraint to solanaceous and cucurbit crops, both in terms of yield losses (up to 100 percent in tomato) and loss of fruit quality. Symptoms may include distortion and yellowing of leaves and stems, stunting of plants, reduced flowering and severe loss of plant vigour. A large number of geographical variants of the viruses are being identified and many of them have now been classified as separate species.
Frequent recombination events, which may occur even more frequently during coinfections, are considered to be the basis for the diversity within the clades. Variations in host range and specificity exist both amongst viral species and between different strains within species.
The new recombinant viruses are often more aggressive and have a widened host range (for example, see ProMED-mail post http://promedmail.org/post/20190906.6658287), compared to each of the partners, and so pose an increased risk to solanaceous and cucurbit crops worldwide.
Maps
Thailand:
<http://legacy.lib.utexas.edu/maps/middle_east_and_asia/thailand_trans-2013.jpg>
and
<http://healthmap.org/promed/p/151>
Asia, overview:
<http://www.worldatlas.com/webimage/countrys/as.htm>
Pictures
ToLCNDV symptoms on cucurbits:
<http://cienciacebas.files.wordpress.com/2013/09/aranda-1.jpg>
(zucchini) and
<http://cienciacebas.files.wordpress.com/2013/09/aranda-2.jpg>
(cucumber & melon)
Leaf curl disease on tomato:
<https://c8.alamy.com/comp/ACGAME/tomato-yellow-leaf-curl-virus-symptoms-on-tomato-leaves-on-plants-ACGAME.jpg>,
<http://www.daff.qld.gov.au/__data/assets/image/0018/55530/Tomato-leaf-curl-virus-35-days-250.jpg>,
<http://www.daff.qld.gov.au/__data/assets/image/0003/65847/Tomato-leaf-curl-virus-56-days-250.jpg>,
<http://microfarmgardens.com/storage/leaf%20curl_3.jpg>, and <http://2.bp.blogspot.com/_bMncWNHcSHM/S_TwfAoj_yI/AAAAAAAAAjE/dvx1eij0RNU/s1600/leaf+curl+contaminated.jpg>
Photo gallery of symptoms of different begomoviruses:
<http://www.forestryimages.org/browse/TaxImages.cfm?fam=651&genus=Begomovirus>
Whiteflies:
<https://www.planetnatural.com/wp-content/uploads/2012/12/whitefly.jpg>
and
<https://www.pinpointpestcontrol.com/images/whitefly-on-plant.jpg>
Links
Information on ToLCNDV:
<https://www.eppo.int/ACTIVITIES/plant_quarantine/alert_list_viruses/tomato_leafcurl_newdelhi>,
<https://onlinelibrary.wiley.com/doi/full/10.1111/ppa.12978>,
<https://www.frontiersin.org/articles/10.3389/fmicb.2019.00140/full>,
and
<https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5691616/> (review) Information on tomato leaf curl viral diseases:
<http://www.oisat.org/pests/diseases/viral/leaf_curl__virus.html>
Novel ToLCNDV recombinant viruses:
<https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5127021/> and <https://link.springer.com/article/10.1007%2Fs10327-019-00849-7> (with
SLCCNV)
Information on SLCCNV:
<https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5473258/> and <https://www.tandfonline.com/doi/full/10.1080/03235400902952301>
Seed transmission of TYLCV:
<https://www.nature.com/articles/srep19013.pdf> and via <https://gd.eppo.int/reporting/article-6367>
Genus _Begomovirus_ description:
<http://www.dpvweb.net/notes/showgenus.php?genus=Begomovirus>
Virus taxonomy via:
<https://talk.ictvonline.org/taxonomy/>
Information on whiteflies:
<http://www.issg.org/database/species/ecology.asp?fr=1&si=106> and via <https://projects.ncsu.edu/cals/course/ent425/text18/plantvectors.html>
- Mod.DHA]
[See Also:
2019
----
Virus diseases, multiple crops: global impact
http://promedmail.org/post/20191119.6787466
Tomato leaf curl New Delhi virus, cucurbits - Portugal: 1st rep
(FA,AC) http://promedmail.org/post/20190906.6658287
2018
----
Undiagnosed leaf curl virus, tomato seed - Egypt
http://promedmail.org/post/20181012.6086559
Leaf curl viruses, tomato & cucurbits - Italy: (SC)
http://promedmail.org/post/20180319.5697141
2017
----
Tomato leaf curl New Delhi virus, zucchini - Morocco: 1st rep (SS)
http://promedmail.org/post/20171206.5487792
Tomato leaf curl New Delhi virus, zucchini - Spain: (AN)
http://promedmail.org/post/20171114.5442041
2016
----
Vegetable viruses - Jamaica
http://promedmail.org/post/20160421.4173419
Tomato leaf curl virus, eggplant - India: (TN)
http://promedmail.org/post/20160415.4160915
Tomato leaf curl New Delhi virus, cucurbits - Italy: 1st rep (SC)
http://promedmail.org/post/20160327.4121164
2014
----
New viruses, capsicum & citrus - multicountry
http://promedmail.org/post/20140801.2647775
Tomato yellow leaf curl virus - Ghana: (TV)
http://promedmail.org/post/20140717.2616753
Tomato leaf curl New Delhi virus - Spain: (AN) alert
http://promedmail.org/post/20140321.2345942
2013
----
Tomato leaf curl New Delhi virus, zucchini - Spain: (MU) 1st report
http://promedmail.org/post/20131223.2131729
Yellow leaf curl & blights, tomato - Pakistan: (SD)
http://promedmail.org/post/20130206.1531086
2008
----
Squash leaf curl China virus, pumpkin - Thailand: 1st rep.
http://promedmail.org/post/20080306.0921
2003
----
Squash leaf curl China virus - Philippines: new strain
http://promedmail.org/post/20031104.2735
and additional items on begomoviruses in the archives]
Topics
Species
