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First Report of Cucumber mosaic virus on Vigna marina in Taiwan

Vigna marina (Burm.) Merr., the dune bean or notched cowpea, is a tropical creeping vine that grows on sand dunes along the coastal regions of Taiwan. Although V. marina is a weed, some varieties are also grown for fodder and food. This legume is a natural host of Bean common mosaic virus in the Solomon Islands (1) and Alfalfa mosaic virus or Beet western yellows virus in Australia (2). In April 2009, plants of V. marina showing severe mosaic and chlorotic ringspots on the foliage were found in the coastal region of Hualien County in eastern Taiwan. Indirect ELISA on a single diseased plant showed positive results with antibodies against the cucumber isolate of Cucumber mosaic virus (CMV) but negative to Broad bean wilt virus-1, Broad bean wilt virus-2, and some potyviruses (Agdia Inc., Elkhart, IN). A pure isolate of CMV was obtained from V. marina through three successive passages of single lesion isolation in sap-inoculated Chenopodium quinoa. Results of mechanical inoculations showed that the CMV-V. marina isolate was successfully transmitted to C. amaranticolor, C. murale, C. quinoa, Chrysanthemum coronarium, Gomphrena globosa, Nicotiana benthamiana, N. tabacum cv. Vam-Hicks, Phaseolus limensis, P. lunatus, P. vulgaris, Tetragonia tetragonioides, V. marina, V. radiata, and V. unguiculata subsp. sesquipedalis. These results of artificial inoculations were confirmed by ELISA. Homologous reactions of the CMV-V. marina isolate with a stock polyclonal antiserum against the CMV-cucumber isolate (4) were observed in sodium dodecyl sulfate-immunodiffusion. To determine the specific CMV subgroup, total RNA was extracted from inoculated leaves of C. quinoa using the Total Plant RNA Extraction Miniprep System (Viogene, Sunnyvale, CA). A DNA fragment of 940 bp covering the 3′ end of the coat protein gene and C-terminal noncoding region of RNA-3 was amplified using the Cucumovirus-specific primers (3) after reverse transcription (RT)-PCR with AccuPower RT/PCR PreMix Kit (Bioneer, Daejeon, Korea). The product was gel purified by Micro-Elute DNA/Clean Extraction Kit (GeneMark Technology Co., Tainan, Taiwan) and cloned in yT&A Cloning Vector System (Yeastern Biotech Co., Taipei, Taiwan) for sequencing (Mission Biotech Co., Taipei, Taiwan) and the sequence was submitted to GenBank (No. HM015286). Pairwise comparisons of the sequence of CMV-V. marina isolate with corresponding sequences of other CMV isolates revealed the maximum (95 to 96%) nucleotide identities with CMV subgroup IB isolates (strains Nt9 and Tfn) compared with 94 to 95% identities with subgroup IA isolates (strains Y and Fny) or 77 to 78% identities with subgroup II (strains LS and Q). These results suggest that CMV is the causal agent for the mosaic disease of V. marina in Taiwan and the isolate belongs to subgroup I. To our knowledge, this is the first report of V. marina as a natural host of CMV. This strain of CMV with specific pathogenicity could threaten crop production in the coastal zones. In addition, V. marina associated with native coastal vegetation was injured by CMV infection, which might lead to ecological impacts on shoreline fading.

References: (1) A. A. Brunt. Surveys for Plant Viruses and Virus Diseases in Solomon Islands. FAO, Rome, 1987. (2) C. Büchen-Osmond, ed. Viruses of Plants in Australia. Retrieved from http://www.ictvdb.rothamsted.ac.uk/Aussi/aussi.htm. September, 2002. (3) S. K. Choi et al. J. Virol. Methods 83:67, 1999. (4) S. H. Hseu et al. Plant Prot. Bull. (Taiwan) 29:233, 1987.