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First Report of Cucurbit chlorotic yellows virus Infecting Cucurbits in Taiwan

In April 2009, chlorosis, yellows, and bleaching accompanied with green veins and brittleness on the lower leaves of cantaloupe (Cucumis melo L.) were observed in Lunbei Township, Yunlin County, Taiwan. The same symptoms were also found on cucumber (Cucumis sativus L.), pumpkin (Cucurbita moschata Duchesne), watermelon (Citrullus lanatus (Thunb.) Matsum. & Nakai), bottle gourd (Lagenaria siceraria (Molina) Standl.), and oriental pickling melon planted in other areas of Yunlin and Changhua counties in central Taiwan. Large populations of whiteflies were observed in association with the diseased cucurbit crops, and they were further identified as silverleaf whitefly (Bemisia argentifolii Bellows & Perring) by PCR with specific primers BaBF (5′-CCACTATAATTATTGCTGTTCCCACA-3′) and l2-N-3014R (5′-TCCAATGCACTAATCTGCCATATTA-3′) (3). In June 2009, samples from symptomatic cantaloupe were collected for virus diagnosis. Flexuous filamentous virions of 700 to 900 nm were observed in crude sap of the symptomatic cantaloupe tissues with transmission electron microscopy. On the basis of the suspected insect vector, symptomology, and virus morphology, a Crinivirus species was suspected as the causal agent. A nested reverse transcription (RT)-PCR assay with degenerate deoxyinosine-containing primers developed for detection of Closterovirus and Crinivirus (1) was conducted. Total RNAs extracted from 16 symptomatic cantaloupe samples with a Plant Total RNA Miniprep Purification Kit (Hopegen, Taichung, Taiwan) were analyzed, and a 0.5-kb DNA fragment was amplified from eight of them. The PCR products were sequenced and the sequences were identical among samples. A comparison of the submitted sequence (Accession No. HM120250) with those in GenBank showed that the sequence was identical to the Hsp70h sequences of Cucurbit chlorotic yellows virus (CCYV) isolates from Japan (Accession No. AB523789) (4) and China (Accession Nos. GU721105, GU721108, and GU721110). To identify CCYV infection in the field, the specific primers, Crini-hsp70-f (5′-GCCATAACCATTACGGGAGA-3′) and Crini-hsp70-r (5′-CGCAGTGAAAAACCCAAACT-3′), that amplify a 389-bp DNA fragment corresponding to the nucleotide 1,324 to 1,712 of RNA2 of the original CCYV Japan isolate (Accession No. AB523789) were designed for detection of CCYV. In RT-PCR analyses, CCYV was identified in cantaloupe (305 of 599 samples), watermelon (27 of 93 samples), cucumber (all 15 samples), melon (82 of 92 samples), pumpkin (8 of 10 samples), and bottle gourd (10 of 17 samples) showing chlorosis and yellowing. The 389-bp DNA fragment was also amplified by RT-PCR with the primer pair Crini-hsp70-f/Crini-hsp70-r from total RNA extracts of 29 of 116 silverleaf whitefly individuals collected from the diseased cantaloupe fields in Lunbei Township from August to October, 2009. CCYV is a newly characterized Crinivirus species, first discovered in Japan in 2004 (2) and also found in China in 2009. To our knowledge, this is the first report that CCYV is emerging as a threat to cucurbit productions in Taiwan.

References: (1) C. I. Dovas and N. I. Katis. J. Virol. Methods 109:217, 2003. (2) Y. Gyoutoku et al. Jpn. J. Phytopathol. 75:109, 2009. (3) C. C. Ko et al. J. Appl. Entomol. 131:542, 2007. (4) M. Okuda et al. Phytopathology 100:560, 2010.