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First Report of Watermelon mosaic virus Naturally Infecting Cucumis anguria

Watermelon mosaic virus (WMV, Potyvirus) is an important virus of cucurbit crops worldwide, although it is rarely found in tropical regions. Cucumis anguria L. is a native species from tropical regions of Africa and can be found as a volunteer or cultivated plant in the Neotropic (1). In Venezuela, C. anguria is a ubiquitous volunteer cucurbit that grows in crop fields year round and may serve as reservoir for viruses. In 2009 and 2010, during surveys for viruses in cultivated and wild cucurbits, WMV was found at a low frequency (3 out of 284 samples) and two out of three positive samples were C. anguria. One of these samples was used to mechanically inoculate WMV to melon (Cucumis melo L.) and zucchini squash (Cucurbita pepo L.) plants. Typical symptoms of WMV were observed 2 weeks after inoculation and viral identification was confirmed by double antibody sandwich (DAS)-ELISA. Based on whole genome sequences, three phylogenetic groups of WMV, namely groups G1 to G3, are defined (2). Since molecular characterization of this virus is scarce in South America, the complete sequence of a WMV isolate recovered from C. anguria (hereafter, VE10-99) was obtained. RNA extractions, amplification procedures, and sequencing analyses were performed according to Desbiez and Lecoq (2). The total sequence length of VE10-99 isolate was 10,039 nucleotides, excluding the polyadenylated tail (GenBank Accession No. KC292915). This isolate had the typical potyviral genome organization, exhibiting a unique large ORF with 9 putative cleavage sites. In a BLAST analysis, the isolate most closely related to VE10-99 was the Chilean isolate CHI87-620 (EU660580), sharing 96% nucleotide identity. Phylogenetic analyses showed that VE10-99 belongs to group G2 of WMV. No evidence for recombination was found in the genome of VE10-99. Although recombination events have been noticed between members of G1 and G3, recombinant isolates between members of G2 and G1 are more frequent (2). In fact, the isolate CHI87-620 had been the only bona fide member of G2 until the sequencing of VE10-99. G2/G1 recombinants seem to have almost completely replaced the parental isolates throughout the world, probably due to a better fitness (2). To our knowledge, WMV natural infections in C. anguria had not been described before. The finding of a bona fide G2 member in Venezuela raises the question about the origin of G2 group. Currently, the prevalence of WMV appears reduced compared to the previous survey performed in Venezuela in 1966 (16 WMV-positive plants out of 95 samples) (3).

References: (1) F. Chitty and R. Lopez. Acta Bot. Venez. 30:19, 2007. (2) C. Desbiez and H. Lecoq. Arch. Virol. 153:1749, 2008. (3) R. Lastra. Plant Dis. Rep. 52:171, 1968.

ERRATUM: A correction was made to this Disease Note on June 9, 2014. The author R. Gustavo was changed to G. Romay.