Young shoots and leaves of chayote (Sechium edule (Jacq.) Sw.) are commonly consumed as a vegetable in Taiwan. In Hualien County, the major chayote-production area of Taiwan, as much as 15% of chayote plants were not marketable between September and October 2010 because of mosaic symptoms on the leaves. Three symptomatic leaves were collected from each of three fields in Hualien. All nine samples tested positive for a begomovirus by PCR using general primer pair PAL1v1978B/PAR1c715H (3) and negative for Zucchini yellow mosaic virus, Cucumber mosaic virus, Cucumber green mottle mosaic virus, Melon yellow spot virus, Papaya ringspot virus - type W, Watermelon mosaic virus, and Watermelon silver mottle virus by ELISA (2). On the basis of the high nucleotide sequence identity (97.7 to 99.6%) of the 1.5-kb begomoviral DNA-A fragments, all nine samples were considered infected by the same begomovirus species. The 1.5-kb sequences had greatest nucleotide sequence identity (96.6 to 97.8%) with Squash leaf curl Philippines virus (SLCPHV) pumpkin isolate from Taiwan (1) (GenBank Accession No. DQ866135; SLCPHV-TW[TW:Pum:05]). One sample was selected to complete viral genomic DNA analysis. Abutting primer pairs PKA-V/C (PKA-V: 5′-AACGGATCCACTTATGCACGATTTCCCT-3′; PKA-C: 5′-TAAGGATCCCACATGTTGTGGAGCA-3′) and PKB-V/C (PKB-V: 5′-TGTCCATGGATTGATGCGTTATCGGA-3′; PKB-C: 5′-TGACCATGGCATTTCCGAGATCTCCCA-3′') were used to amplify the complete DNA-A and DNA-B, respectively. The sequences of DNA-A (GenBank Accession No. JF146795) and DNA-B (GenBank Accession No. JF146796) contain 2,734 and 2,715 nucleotides, respectively. The geminivirus conserved sequence TAATATTAC was found in both DNA-A and -B. The DNA-A has two open reading frames (ORFs) in the virus sense (V1 and V2) and four in the complementary sense (C1 to C4). The DNA-B also had one ORF each in the virus sense (BV1) and the complementary sense (BC1). When compared by BLASTn in GenBank and analyzed by MEGALIGN software (DNASTAR, Madison, WI), they were found to have greatest nucleotide identity (98.0 to 99.0% of DNA-A and 96.7% of DNA-B) with SLCPHV isolates from Taiwan. In addition, SLCPHV caused similar symptoms on leaves when transmitted to healthy chayote by viruliferous whitefly. In Taiwan, SLCPHV has been detected and sequenced from naturally infected melon (GenBank Accession No. EU479710), pumpkin (GenBank Accession No. DQ866135), and wax gourd (GenBank Accession No. EU310406). To our knowledge, this is the first report of SLCPHV infecting chayote plants in Taiwan. The prevalence of SLCPHV infection on different cucurbit crops should be taken into consideration for managing viral diseases in Taiwan.
References: (1) W. S. Tsai et al. Plant Dis. 91:907, 2007. (2) W. S. Tsai et al. Plant Dis. 94:923, 2010. (3) W. S. Tsai et al. Online publication. doi: 10.1111/j.1365-3059.2011.02424.x. Plant Pathol., 2011.
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