First report of Beet soil-borne virus on sugar beet in China

Beet soil-borne virus (BSBV) and Beet virus Q (BVQ) are two members of the genus Pomovirus that are transmitted by Polymyxa betae. BVQ and BSBV are commonly found in fields where Beet necrotic yellow vein virus (BNYVV), the causal agent of rhizomania disease, is present (Henry et al.1986; Koenig et al. 1998; Meunier et al. 2003). During the growing season of 2006, twenty six roots of sugar beet exhibiting moderate to severe symptoms of rhizomania were collected from three fields located in Inner Mongolia and Xinjiang Provinces for a survey to determine whether BSBV and BVQ were present in China. Viral RNA was extracted from partially purified viruses of beet roots as described by Han et al (2000) and tested by RT-PCR using three specific primer sets (BSBV: 5`- ATG GTT GAT CCG CGG TAT GAA G -3` and 5`- CTA TTC AAC CCA GCG CAA ACC AAC-3`; BVQ: 5`- ATG GTT GAT CCA AGA TAT GAG C -3` and 5`-CTA TGA GCC GGT CCA CTT CAA TCC-3`; and BNYVV: 5`- GCG GAT CCA TGT CGA GTG AA G GTA GA -3` and 5`-CGA AGC TTG CTA TTG TCC GGG TGG-3`, based on Acc. Nos. NC003518, NC003511 and S71490 respectively) and designed to amplify coat protein genes for BSBV, BVQ and BNYVV respectively.

Fifteen of the 26 beet samples gave positive reactions for BSBV, 21 for BNYVV and 14 for both BSBV and BNYVV (Fig. 1). BVQ was not detected in any sugar beet sample tested. Subsequently, three RT-PCR products amplified in sugar beet samples collected from different locations with the primers specific to BSBV were cloned and sequenced (GenBank Accession No. EF113300, EF210553 and EF210552). Sequence analysis revealed that these submitted sequences shared nucleotide identity of 98-99 % with the German BSBV isolate (Acc. No. NC003518). The partially purified viruses from infected sugar beet root were used for mechanical inoculation of Chenopodium quinoa and C. amaranticolor, and local lesions were observed on inoculated leaves (Fig. 2). Furthermore, BSBV was also confirmed by RT-PCR (as described above) in the local lesions that appeared approximately 5 days after mechanical inoculation.

Combined, the RT-PCR detection, nucleotide sequences and symptoms on inoculated host plants confirm the presence of BSBV in Inner Mongolia and Xinjiang. To our knowledge, this is the first report of the occurrence of BSBV in China.