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Date: January 2008
Source: British Society for Plant Pathology, New Disease Reports vol.
16 [edited]
<http://www.bspp.org.uk/ndr/jan2008/2007-89.asp>

Yellow leaf curl disease of pumpkin in Thailand is associated with Squash leaf curl China virus

Yellow leaf curl disease causes heavy losses to cucurbit crops in Thailand. Previously, we have detected _Tomato leaf curl New Delhi virus_ from infected cucumber (_Cucumis sativus_), wax gourd (_Benincasa hispida_), cantaloupe (_Cucumis melo_) and muskmelon (_Cucumis melo_) plants in Thailand. Pumpkin (_Cucurbita pepo_) is also severely affected by this disease. Three pumpkin plants exhibiting leaf curling and yellowing symptoms (Fig.1) were collected from Kamphaensaen, Nakom Pathom in Thailand during 2001.

PCR [Polymerase Chain Reaction] was conducted specific for begomovirus DNA-A. A product of the full DNA A was sequenced (2736 nucleotides). Efforts to detect DNA-B component associated with the virus by PCR were unsuccessful. The DNA-A contained the 5 open reading frames [ORF] typical of begomoviruses, 2 in the virion sense and 3 in the complementary sense. Comparison of the complete nucleotide sequence of this begomovirus with those of full-length begomoviral DNA-A's available showed the highest nucleotide sequence identity (95 and 89 percent) with _Squash leaf curl China virus_ (SLCCNV) and _Squash leaf curl Philippines virus_ (SLCPHV), respectively. For ORF V1 (coat protein), this begomovirus had the highest amino acid sequence identity with its counterparts in SLCCNV (97 percent) and SLCPHV (97 percent).

Therefore, the present virus is an isolate of SLCCNV, which we designate SLCCNV-Thailand. This is a 1st report of SLCCNV infecting pumpkin in Thailand.

Figure 1: Leaf curling and yellowing symptoms of infected pumpkin originating from Thailand infected with _Squash leaf curl China virus_ <http://www.bspp.org.uk/ndr/jan2008/2007-89-1.jpg>.

[Byline: T. Ito et al.]

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[The _Cucurbitaceae_ contain many crops of importance to human nutrition worldwide. Plant viruses that infect edible cucurbits pose major constraints to cucurbit production. Among the most important are the circular single-stranded DNA whitefly-transmitted viruses in the family _Geminiviridae_. This family includes the genus _Begomovirus_ to which _Squash leaf curl China virus_ (SLCCNV) and other members of the squash leaf curl viral clade belong. SLCCNV has so far been reported from China and Viet Nam, whereas other members of the clade have been found in different regions. Other clades of begomoviruses are, for example, the tomato leaf curl complex, which includes _Tomato leaf curl New Delhi virus_ mentioned above, and the tomato yellow leaf curl complex. All these viruses generally cause symptoms of leaf yellowing and distortion leading to reduced plant vigor and yield losses, but they may vary in host range and geographical distribution.

All cucurbit-infecting begomoviruses reported at present have a bipartite genome (called DNA-A and DNA-B in the report above).
Begomoviruses are transmitted by whitefly vectors and can often also be transmitted by mechanical means and grafting.

Whiteflies are widely distributed and have a very wide host range of more than 600 plant species. Weed species can serve as insect reservoirs making control difficult. Whiteflies have been reported to transmit over 100 virus species, including many begomoviruses, but also cause serious crop damage by direct feeding.

Disease management of begomoviruses relies on control of the vector and possible pathogen and/or vector reservoir plants. This has occasionally caused problems with chemical residues on fruits. In some cases, crop cultivars with increased virus resistance are available.

Maps
Thailand:
<http://www.lib.utexas.edu/maps/middle_east_and_asia/thailand_pol_2002.jpg>  and <http://healthmap.org/promed?v=15.1,101,5>
Thailand provinces:
<http://www.lib.utexas.edu/maps/middle_east_and_asia/thailand_admin_2005.jpg>

Pictures
_Squash leaf curl virus_ symptoms:
<http://www.apsnet.org/online/feature/btabaci/image/whitefly3.jpg>  (on squash), <http://www.forestryimages.org/images/192x128/2511041.jpg>  (on watermelon) Elecron micrograph of _Begomovirus_ particles:
<http://www.ncbi.nlm.nih.gov/ICTVdb/WIntkey/Images/em_gemin_2.jpg>
Whitefly:
<http://www.extension.umn.edu/yardandgarden/YGLNews/images2/whitefly.jpg>

Links
Begomoviruses of cucurbits, including SLCCNV:
<http://jvi.asm.org/cgi/content/full/82/4/1959>
Genus _Begomovirus_ taxonomy and species list:
<http://www.ncbi.nlm.nih.gov/ICTVdb/ICTVdB/00.029.0.03.htm>
List of viruses in the squash leaf curl complex:
<http://www.ncbi.nlm.nih.gov/ICTVdb/Ictv/vn_indxS.htm>
List of viruses in tomato yellow leaf curl and leaf curl complexes:
<http://www.ncbi.nlm.nih.gov/ICTVdb/Ictv/vn_indxT.htm>
Whitefly information via:
<http://whiteflies.ifas.ufl.edu/>
- Mod.DHA]