Taro (Colocasia esculenta L. Schott) is an important crop worldwide. In China, the growing area and productivity of taro increased greatly in recent years. During the 2010 to 2013 growing seasons (from May to July), the incidence of Cucumber mosaic virus (CMV) in taro was determined. Leaf samples from 91 taro plants, including 26 plants of cv. Hongyayu grown in Jiangxi Province in eastern China, 33 plants of cv. Eyu no.1 grown in Hubei Province in central China, and 32 plants of cv. Baiyu grown in Guangxi Province in southwest China were collected randomly and tested for the presence of CMV by reverse transcription (RT)-PCR. Some sampled plants of cv. Hongyayu and Eyu no.1 showed leaf chlorosis or chlorotic spots, and most of the plants of these three cultivars showed feather-like mosaic symptom on their leaves, which was confirmed to be associated with the infection of Dasheen mosaic virus (DsMV) in our previous studies (3). Total RNA was extracted from leaves using CTAB protocol reported by Li et al. (1). Primer set forward 5′-ATGGACAAATCTGAATCAACC-3′/reverse 5′-TAAGCTGGATGGACAACCCGT-3′ (4) was used for the amplification of a 777-bp fragment, which contains the complete capsid protein (CP) gene of 657 bp. PCR products of the expected size were identified from 11 taro samples, including two samples of Hongyayu, three Eyu no.1, and six Baiyu plants. The result did not show any specific association between the symptoms observed and CMV infection. The obtained PCR products were cloned individually into the vector pMD18-T (TaKaRa, Dalian, China). Three independent clones derived from each product were sequenced by Genscript Corp., Nanjing, China. Pairwise comparison of CP gene sequences (Accession No. of one representation CP sequence: KF564789) showed 99.7 to 99.8% nucleotide (nt) and 99.1 to 99.5% deduced amino acid (aa) sequence identity among themselves, and 92.0 to 94.3% and 76.5 to 77.7% nt identities with corresponding sequences of CMV isolates in subgroup I and subgroup II (2), respectively. The maximum likelihood phylogenetic trees of nt and aa sequences generated by Clustal X v1.8 revealed that all these CMV isolates from taro in China fell into subgroup I. To further confirm the CMV infection, leaf saps of CMV infected taro plants of cv. Eyu no.1 were mechanically inoculated onto Pinellia ternate and Cucumis sativus. Plants of P. ternate showed local chlorotic lesions on the inoculated leaves and downward curl of newly grown leaves, and C. sativus showed local chlorotic lesions on the inoculated leaves and crinkle of newly grown leaves at 10 to 15 days post inoculation. The RT-PCR detection confirmed the CMV infection in those inoculated plants, and that the plants of P. ternate were also positive to DsMV, further complementing the results obtained above. To our knowledge, this is the first report of CMV occurrence in taro plants grown in China. Our results indicated that taro plants were widely infected by CMV isolates in subgroup I. This study provides important information for further evaluating the viral sanitary status of taro germplasm and improving the certification program of taro propagation materials in China.
References: (1) R. Li et al. J. Virol. Methods 154:48, 2008. (2) P. Palukaitis et al. Adv. Virus. Res. 62:241, 2003. (3) S. M. Shi et al. Acta Hortic. Sin. 39:509, 2012. (4) P. D. Xu et al. Chinese J. Virol. 15:164, 1999.