A ProMED-mail post
ProMED-mail is a program of the International Society for Infectious Diseases

November 4, 2003
From: J Phytopathol 2003 (Oct); 151(10): 535 [edited]

Molecular characterization of a strain of squash leaf curl China virus from the Philippines
T Kon, S Hase, H Takahashi, M Ikegami (Department of Life Science, Graduate School of Agricultural Science, Tohoku University, Sendai 981-8555, Japan), LM Dolores, NB Bajet (University of the Philippines, Los Banos, Philippines)

The complete nucleotide sequence of infectious cloned DNA components (A and B) of the causal agent of squash leaf curl disease in the Philippines was determined. DNA-A and DNA-B comprise 2739 and 2705 nucleotides, respectively; the common region is 174 bases in length.

5 ORFs were found in DNA-A and 2 in DNA-B. Partial dimeric clones containing DNA-A and DNA-B, constructed in a binary vector and transformed into _Agrobacterium tumefaciens_, induced systemic infection in agro-inoculated pumpkin plants (_Cucurbita moschata_).

The total DNA-A sequence was most closely related to that of squash leaf curl China virus (SLCCNV) (88 per cent identity), although the existence of B component of SLCCNV has not been reported. The deduced coat protein was like that of SLCCNV (98 per cent amino acid sequence identity) and the Philippines virus has low sequence identity to squash leaf curl virus (SLCV) and squash mild leaf curl virus (SMLCV) (63 and 64 per cent total nucleotide sequence identities, respectively).

From these results, we propose that the Philippines virus be designated squash leaf curl China virus-[Philippines] (SLCCNV-[PH]).

[The evolution of the Philippines strain is not unexpected, as new strains are constantly emerging. In addition to Squash leaf curl Philippines virus, there are 2 other strains -- SLCV (type strain) and Squash leaf curl China virus (Yunnan). Squash leaf curl begomovirus (SLCV) is transmitted by 2 whitefly species -- the sweet potato whitefly _Bemisia tabaci_ and the silverleaf whitefly, _B. argentifolii_ -- although some taxonomists suggest that these species are really biotypes. Squash and watermelon are preferred hosts. Disease management utilizes cultural control (eradication of infected plants, use of UV-absorbing greenhouse plastic films, and aluminum plastic mulches) and biological control (use of parasitoids such as _Encarsia_ and _Eretmocerus_ spp). Use of insecticides is not very efficacious because whiteflies tend to congregate on the undersides of leaves.
References: <http://plantpathology.tamu.edu/Texlab/Vegetables/wmelon/slcv.htm>
<http://ag.arizona.edu/PLP/plpext/diseases/vegetables/watermelon/watermelonslcv.htm> - Mod.DH]