First identification of Beet western yellows virus on sugarbeet and lettuce in China

In China, yellowing disease of sugar beet has been reported previously, with Beet yellows virus (BYV; genus Closterovirus) regarded as the viral agent (Liu et al., 1981). During a survey in September 2006, the incidence of diseased sugar beet showing yellowing symptoms ranged from 5 to 30%. The symptoms observed were mainly yellowing, developing mostly in the interveinal tissue of old- and middle-aged leaves (Fig. 1). These symptoms were similar to those reported previously for yellowing disease caused by poleroviruses (Beet western yellows virus, BWYV; Beet mild yellowing virus, BMYV; Beet chlorosis virus, BChV) in other countries(Hauser et al., 2000; Stevens et al., 2005).

To identify the viruses involved, 64 samples of sugar beet were collected from fields in different Provinces (Inner Mongolia, Gansu, Beijing, Hebei, Jilin and Heilongjiang). Total RNA was extracted from leaf tissue and tested by RT-PCR using a universal polerovirus primer pair (5’- GAY TGY TCY GGT TTT GAC TGG -3’ and 5’- TTR TAY TCA TGG TAG GCT TGA G -3’), designed on the basis of an alignment of available sequences (Acc. Nos NC004756, NC003491 and AF352024 ) and BYV-specific primers designed using a published BYV sequence (Acc. No. NC001598). Amplification products of the expected size for a polerovirus (ca.1100 bp) were obtained in 41 samples, whereas BYV was not detected in any sample tested. Five of these RT-PCR products were selected (2 from Inner Mongolia, and 2 from Gansu, 1 from Beijing), cloned and sequenced. The sequences obtained were submitted to GenBank (Acc. Nos EF051249-53). Comparisons showed that these sequences shared between 88-91% nucleotide identity with BWYV (USA isolate; Acc. No. NC004756), while sharing only 73-75% identity with a French BMYV isolate (Acc. No. NC003491), and approximately 70 % identity with BChV (isolate 2a; Acc. No. AF352024). In addition, spherical particles measuring 26 nm in diameter were also observed in some samples by electron microscopy.

In addition to the sugar beet samples, four samples of diseased lettuce were also collected from Beijing. These showed yellowing symptoms and were tested positive by RT-PCR with the polerovirus primers. One sample was sequenced (Acc. No. DQ886589). Sequence analysis revealed that it shared between 88-98% sequence identity with BWYV, including the Chinese isolates from sugar beet described above.

Based on these data, BWYV was confirmed as a causal agent of yellowing disease of sugar beet and lettuce in Northern China. To our knowledge, this is the first definitive identification of BWYV in China.