First Report on the Occurrence of Cucumber mosaic virus on Fragaria ananassa in China

More than 20 viruses are known to infect strawberry (Fragaria ananassa), and a substantial number of these include new viruses identified since 2000 that can contribute to disease complexes (2). The most serious virus related losses in commercial strawberries are caused by aphid transmitted viruses (3,4,5). A survey was undertaken from 2012 to 2013 to investigate virus prevalence in commercial strawberries in rural areas of Hebei Province around Beijing, China, that were exhibiting virus symptoms. Visual observations revealed that the incidence of virus-like symptoms ranged from 30 to 50% of the plants and these symptoms included yellowing, leaf malformation, sometimes combined with severe stunting and deformed flowers or fruits. Leaf samples were tested for Strawberry vein banding virus (SVBV), Strawberry mottle virus (SMoV), Strawberry mild yellow edge virus (SMYEV), and Strawberry crinkle virus (SCV), which are the four most prevalent aphid-transmitted viruses in single or mixed infections (2). Testing was conducted by RT-PCR using total RNA extracted from fresh symptomatic strawberry leaves (3). SVBV was detected in 58 of 190 samples, but all of the samples tested negative for SMoV, SMYEV, and SCV. Aphids were present on many of the plants, so the samples were tested for Cucumber mosaic virus (CMV) because CMV is prevalent in Beijing gardens and farms, and recently had been shown to infect maize in China (5). This RT-PCR was carried out with the CMV primer pair CM420-F (5'-TGATTCTACCGTGTGGGTGA-3') and CM420-R (5'-CCGTAAGCTGGATGGACAAC-3') to amplify a portion of the capsid protein coding region and the conserved 3'non-translated regions of the genomic RNAs. This test revealed the presence of 43 CMV-positives out of 190 samples, and only 16 of these samples were co-infected with both SVBV and CMV. Samples infected with CMV only had leaf malformations and yellowing, while no CMV was found in symptomless samples. One of the amplified, CMV-specific DNA fragments was sequenced directly from the PCR product and showed 93.8% nucleotide sequence identity and 100% amino acid sequence identity to the CMV subgroup I (GenBank Accession No. D10538) (1). Subsequent ELISA tests for the CMV presence verified the RT-PCR results (Agdia, Elkhart, IN), and transmission electron microscopy observations revealed 28 nm spherical particles characteristic of CMV in strawberry samples tested positive for CMV. However, we were unable to detect either CMV or SVBV in 89 of the 169 samples from symptomatic plants, which suggested possible presence of the other pathogen(s). To the best of our knowledge, this is the first report of natural infections of CMV in strawberry plants. These data suggests that CMV is a potential threat to strawberry production. References: (1) M. Q. K. Andrew et al. Virus taxonomy: IXth Report of the ICTV, 970, Elsevier, 2012. (2) R. R. Martin and I. E. Tzanetakis. Plant Dis. 97:1358, 2013. (3) J. R. Thompson et al. J. Virol. Methods 111:85, 2003. (4) I. E. Tzanetakis et al. Plant Dis. 90:1343, 2006. (5) R. Wang et al. J. Phytopathol. 161: 880, 2013.