First Report of Bean common mosaic virus Infecting Mungbean (Vigna radiata) in China

Bean common mosaic virus (BCMV) is a member of the genus Potyvirus and one of the numerous viruses that can infect Phaseolus vulgaris. In May of 2013, we planted more than 100 varieties of mungbean in fields and a greenhouse of Nanjing. Mungbean (Vigna radiata (Linn.) Wilczek.) with leaves displaying mosaic and shrinkage typical of viral infection was observed in a greenhouse and a field in Nanjing. About 60% of the varieties can be infected. The symptoms in some sources from Southeast Asian countries and wild germplasm are heavier, while the symptoms are lighter on the local varieties. It can be transmitted to mungbean via aphid or mechanical inoculation, or by seeds. The infected leaves were collected for electron micrograph analysis. Pinwheel inclusion and filamentous virus particles were observed, indicating a Potyvirus infection. To confirm the presence of Potyvirus infection, total RNA was extracted from plants from the greenhouse and field, and RT-PCR was performed using universal Potyvirus primers (Sprimer (+) 5'-GGXAAYAAYAGYGGXCAZCC-3'; X=A, G, C or T, Y=T or C, Z=A or G); M4T (5'-GTTTTCCCAGTCACGAC(T)-3'), which amplify a region of the 3' fragment of the RNA-dependent RNA polymerase of potyviruses (1). The 596-bp sequence was found to be 95% identical to the BCMV isolate HB (GenBank Accession No. KC478389.1). To confirm the presence of BCMV, three leaf samples were randomly collected and all were determined to be positive when subjected to ELISA using BCMV-specific antibodies. The virus infecting mungbean was identified as BCMV and the strain was named BCMV-JAAS (KJ866945). Using gene-specific primers (BCMV-cp-F: 5'-CAAAAGGACAAGGATTGAGGA, BCMV-cp-R: 3'-ACAACAAACATTGCCGTAGC) for the reported coat protein gene in BCMV, a 1,080-bp gene fragment was amplified from the total RNA of the isolate, and subsequent sequence analysis indicated that an 862-bp region contained the complete cp gene that encodes a 228 amino acid protein. The nucleotide sequences of the cp gene from the isolate shared 96% homology with the reported BCMV-HB. The phylogenetic trees based on the CP gene show that BCMV-JAAS (KJ866945) was most closely related to other Chinese BCMV isolates (KF439722.1 and AJ132145.1) followed by Azuki mosaic virus (AB012663.1) and Peanut stripe virus (U34972.1). These results indicate that the virus associated with the mosaic disease in mungbean is an isolate of BCMV. To our knowledge, this is the first report of BCMV infecting mungbean in China. BCMV affects a wide range of legume crops and can spread rapidly, causing serious harm. The discovery could effectively control BCMV and characterize the prevalent BCMV strains. Research utilizing whole-genome sequencing of the mungbean isolate is continuing and is currently being expanded to characterize the genetic diversity of the virus, assisting in the study of the evolution of the virus. Reference: (1) J. Chen and J. P. Chen. Chin. J. Virol. 18:372, 2002.