A 2014 nationwide survey of the distribution of Soybean Mosaic Virus (SMV), Soybean Yellow Mottle Mosaic Virus (SYMMV) and Soybean Yellow Common Mosaic Virus (SYCMV) major viruses in South Korean soybean fields, and changes from 2012 isolate prevalence

In 2014 symptomatic soybean samples were collected throughout Korea, and were tested for the most important soybean viruses found in Korea, namely Soybean mosaic virus (SMV), Soybean yellow common mosaic virus (SYCMV), and Soybean yellow mottle mosaic virus (SYMMV). SYMMV was most commonly detected, followed by SMV. Only a few samples were found to be infected by SYCMV; of these, three samples were positive for double infection of SYMMV and SYCMV. Phylogenetic analysis of HC-Pro of the SMV isolates collected in 2014 from the eight provinces of Korea showed that most isolates were distinct from the most common Korean isolate detected in 2012, but related to other Korean, Chinese and North American isolates. No isolates varying in HC-Pro amino acid residues implicated in efficiency of RNA silencing suppression activity were detected in 2014. Phylogenetic analysis of ORF1 of both 2012 and 2014 SYCMV isolates showed differentiation into three subgroups. However, the geographical distribution of all three viruses in 2014 was essentially the same as observed in 2012. Quantitative real time PCR data also indicated a similar pattern of dual infected viruses occurrence as existed in 2012. Results showed SMV/SYMMV double infection RNA accumulation was not changed as much as SYMMV/SYCMV double infection. However, between double infection SMV/SYMMV, SYMMV RNA accumulation level rises more than SMV, and SYCMV RNA accumulation level decline a little compare with SYMMV. In summary, the 2014 survey showed that SMV and SYMMV are still the most prevalent soybean viruses in Korea, and all three viruses were still dispersed in the same areas where they were detected in 2012, although with an apparent shift towards SMV Group I isolates compared to 2012. The reason for the shift in SMV isolates across all Korean provinces is not clear, as seed transmission through farmer-saved seed is presumed to be the main source of infection within the crop.