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First Report of Papaya leaf curl virus Infecting Papaya Plants in Taiwan

Papaya leaf curl disease was first reported in India in 1939 (1). Caused by begomovirus, Papaya leaf curl virus (PaLCV) (2), this disease was discovered in the papaya orchards of southern Taiwan in 2002. Infected papaya developed symptoms such as downward curling of leaves, twisted petioles, vein enation, and stunting. Diseased plants produced small and distorted fruits that tend to fall prematurely. Typical twin virion was observed in the diseased papaya cells by electron microscopy. In addition, our whitefly-transmission test demonstrated that the sweet potato whitefly (Bemisia tabaci) could transmit this virus. For further molecular identification, two opposing primers were selected for the polymerase chain reaction (PCR) detection of PaLCV from the published nucleotide sequences of PaLCV (Genbank Accession No. NC004147) (3). The primer pair, composed of the forward primer 5′ -GCT AGA AAT TAT GTC GAA GCG-3′ and the reverse primer 5′-TCA ACT ACA ACC TGA GGA AAG C-3′, was designed to amplify a PaLCV-specific 1,031-bp fragment containing 774 bp of the coat protein gene open reading frame (CP-ORF) using PCR. Five diseased papaya samples with typical leaf-curl symptoms tested positive in the PCR-based assay with this specific primer pair, whereas five healthy papaya samples tested negative. However, the sequencing results of the PCR product from five PaLCV-infected papayas indicated the CP-ORF of PaLCV in Taiwan (PaLCV-Tw) was somewhat different from PaLCV in India (PaLCV-Id). The DNA sequences (Genbank Accession No. AY183472) of CP-ORF of PaLCV-Tw were 80% identical to those of PaLCV-Id, and their translated amino acid sequences were 77% identical. This indicates that PaLCV-Tw and PaLCV-Id are two different species or strains.

References: (1) K. M. Thomas and C. S. Krishnaswamy. Curr. Sci. 8:316,1939. (2) S. Saxena et al. Plant Dis. 82:126, 1998. (3) S. Saxena et al. Biochem. Mol. Biol. Int. 45:101, 1998.