First Report of Bean common mosaic virus Infecting Azuki Bean (Vigna angularis) in China

Azuki bean (Vigna angularis Ohwi & Ohashi) is one of the traditional grain legumes in China. From 2010 to 2013, mosaic and crumpling symptoms on leaves and stunting, all typical symptoms of a viral disease, were observed on cultivars CWA030, CWA221, and JCA002 of azuki bean with incidence rates of 30 to 100% and yield losses of 50 to 95% in the three fields of Changping district, Beijing. To identify the possible viral pathogen(s), 21 symptomatic leaf samples from different cultivars were collected and total RNA was extracted from the samples and subjected to RT-PCR testing with degenerate primers targeting portions of the coding regions of Cucumovirus capsid protein (CP) (1) and Potyvirus NIb (2); these viruses had been reported in azuki bean. Fragments of 940 bp and 350 bp corresponding to Cucumovirus CP and Potyvirus NIb, respectively, were amplified from all the samples collected. Sequencing of the PCR products from nine samples, followed by BLAST analysis, confirmed the presence of Cucumber mosaic virus (CMV) and Bean common mosaic virus (BCMV). All the samples tested were also positive with direct antigen coating (DAC)-ELISA using specific antiserum to CMV or BCMV (Agdia, Elkhart, IN). The CMV CP gene (GenBank Accession No. KJ467817) shared 99% sequence identity with a China CMV isolate (DQ873558). To further characterize the BCMV strain found, fragments of 3,388 bp spanning BCMV NIa, NIb, CP and 3'UTR regions were amplified with another primer set, BCMV-F (5'-AGCAAGTCAATTTACAAGGGACTTC-3') and BCMV-R (5'-GGAACAACAAACATTGCCGTAGCTAC-3') from three samples, and three independent clones from each sample were sequenced. Sequence analysis revealed that this segment (KJ467816) shared 98% identity with the BCMV azuki bean strain (U60100). To the best of our knowledge, this is the first report of BCMV, together with CMV, naturally infecting azuki bean in China. Further attention should be paid to this emerging viral disease and measures should be taken to control the spread of BCMV. References: (1) S. K. Choi et al. J. Virol. Methods 83:1345, 1999. (2) L. Zheng et al. Plant Pathol. 59:1345, 2010.