First Report of Schlumbergera Virus X in Dragon Fruit (Hylocereus spp.) in Spain.

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Dragon fruit (Hylocereus undatus) is a high-value fruit crop, introduced about a decade ago in the mainland of Spain. In 2021, chlorotic spots were observed on young cladodes in a commercial dragon fruit orchard in the province of Seville (southern Spain). Sap extracts from 4 symptomatic cladodes were used to mechanically inoculate indicator plants: no symptoms were produced in Datura stramonium plants, but Chenopodium amaranticolor reacted with chlorotic local lesions and prickly pear plants (Opuntia ficus-indica) showed irregular yellow ringspot symptoms on young cladodes at 30 days post inoculation. Total RNA was extracted from all 4 symptomatic cladodes as previously described (Pallas et al. 1987). Reverse transcription (RT)-PCR, which was carried out with M-MLV-RT and Go Taq Pol (Promega Biotech Ibérica, SL, Madrid, Spain) and tobamovirus primers (Dovas et al. 2004), failed to produce any amplicons. Electrophoretic analysis of dsRNA, extracted from symptomatic cladodes, yielded a banding pattern similar to the one reported for potexviruses (Valverde et al. 1986). Primers specific for Cactus virus X (Kim et al., 2016) failed to produce amplicons, whereas potexvirus group primers (Potex F5/Potex R2) (van der Vlugt and Berendsen 2002), amplified an expected 584-bp amplicon from RNA extracts of all 4 field-collected samples. The RT-PCR products from the four samples were Sanger-sequenced. All showed identical sequence results (GenBank Accession MZ614940) with a predicted amino acid identity of 99% with the corresponding RNA-dependent RNA polymerase amino acid sequence of Schlumbergera virus X (SchVX) (GenBank Accession No. ACD99908). SchVX-specific primers (431s, 5'-TTTGAGGAGTTCGTCAGCAAGA-3' and 431As, 5'-TCAAGAGCCCATTGAGAGAGTG-3') that were designed based on the new sequence, amplified the expected amplicon of around 430 nucleotides from the total RNA extracts of the four samples. The amplicons were Sanger-sequenced and the expected nucleotide sequence was obtained. This pair of primers were used in RT-PCR tests on subsequent surveys in 2 commercial dragon fruit greenhouses from the province of Seville, and in 1 experimental greenhouse in the province of Almeria. All samples from 25 symptomatic plants of H. undatus, H. hybridum, H. costaricensis, and H. purpusii in Seville and from 1 symptomatic H. undatus plant from Almeria tested positive for SchVX, while 15 asymptomatic plants tested negative. The results obtained in this investigation support that SchVX is present in the cladodes of dragon fruit plants expressing the symptoms. SchVX has been reported previously from H. undatus from Brasil (Duarte et al. 2008) and from prickly pear in Mexico (De La Torre-Almaráz et al. 2016), and to our knowledge, this is the first report of the virus in Spain. These findings suggest that SchVX has been introduced in dragon fruit farms from Spain and propagation of this emerging crop through planting of cuttings should include testing for this virus in order to prevent further spread.