First Report of Squash vein yellowing virus Affecting Watermelon and Bitter Gourd in Puerto Rico

In 2005, symptoms of watermelon vine decline (WVD) were observed on a 200-acre watermelon farm in Santa Isabel, on the south central coast of Puerto Rico. WVD symptoms included leaf curling, mosaics, and internode necrosis. In early growth stages of WVD, reduced vigor and plant stunting occurred. At flowering, symptoms progressed to necrosis and wilting of vines. A 2006 to 2007 survey demonstrated that fungal pathogens were not associated with the presence of WVD symptoms (3,4). By 2006, other watermelon fields were also affected. Field trials in 2007 and 2008 with insect-proof cages and insecticides suggested a role of whiteflies (Bemisia tabaci) in the transmission of a virus (3,4). Here, we report that watermelon and pumpkin plants were successfully infected in Puerto Rico by mechanical inoculation and through B. tabaci transmission assays, similarly to transmissions previously conducted in Florida with Squash vein yellowing virus (SqVYV) (1). In addition, plants of Cucurbita moschata exhibited vein clearing symptoms typical of SqVYV after mechanical inoculation with extracts from watermelon plants with WVD symptoms. In 2011, eight watermelon samples from plants exhibiting WVD syndrome were collected in Guánica, Santa Isabel, Juana Díaz, and Mayagüez, and two Momordica charantia samples were collected from Mayagüez. RNA was extracted from all 10 original samples, as well as from plants that were used in mechanical and vector transmission assays, using RNeasy Plant Mini Kit (Qiagen, Valencia, California), and all samples were found positive for SqVYV by reverse transcription-PCR, using previously described primers and methods (1,2). In all cases, a single ~1-kb PCR fragment was revealed, and PCR fragments from four samples were selected for direct sequencing. All sequences showed high levels (>99%) of nucleotide identity with SqVYV sequences from Florida (JF897989, JF897985, and JF897984). Sequences of the SqVYV CP gene from Puerto Rico were deposited in GenBank under accession numbers KC713961 to KC713964. To our knowledge, this is the first report of SqVYV in Puerto Rico associated with WVD syndrome in cucurbits, and thus has implications for management of viral diseases of watermelon in the Caribbean. This is also the first detection of SqVYV outside of the continental United States in both watermelon and a wild species, M. charantia (bitter gourd). References: (1) S. Adkins et al. Phytopathology 97:145, 2007. (2) S. Adkins et al. Plant Dis. 92:1119, 2008. (3) C. Estévez de Jensen et al. Phytopathology 98:S52, 2008. (4) L. Polanco-Florián. El marchitamiento súbito de la sandía [Citrullus lanatus (Thumb.) Matsum & Nakai]. M.S. thesis, University of Puerto Rico, Mayagüez, PR, 2009.