Unité de Phytopathologie, UCL, Croix du Sud, 2 bte 3, B-1348 Louvain-la-Neuve, Belgium
Beet necrotic yellow vein virus (BNYVV), the causal agent of rhizomania disease on sugar beet, has been reported in Belgium for more than 16 years. Other soilborne viruses belonging to the genus Pomovirus, such as Beet soilborne virus (BSBV) (3) and Beet virus Q (BVQ) (1), are suspected pathogens of sugar beets grown in Belgium. During the 2000 growing season, more than 20 fields showing rhizomania-like and yellowing symptoms on sugar beet leaves were investigated for the presence of BVQ, BNYVV, and BSBV. All samples were checked by enzyme-linked immunosorbent assay (ELISA) using commercial BNYVV (Sanofi Diagnostics Pasteur, Marnes-La-Coquette, France) and BSBV/BVQ (DSMZ, Braunschweig, Germany - AS-0576 polyclonal, AS-0576/2 MAb) antisera. RNA was extracted from sugar beet rootlets using an RNeasy extraction kit (Qiagen, Hilden, Germany), before performing a reverse transcription-polymerase chain reaction (RT-PCR) using primers (5′-GCTGGAGTATATCACCGATGAC-3′ and 5′-AAAATC TCGGATAGCATCCAAC-3′) designed to specifically amplify a 510-bp region of BVQ RNA-1. The presence of BSBV and BNYVV was also checked by RT-PCR using previously described primers (1,2). The BVQ-derived PCR product was sequenced and proved to be more than 99% identical to the Wierthe BVQ isolate nucleotide sequence. Soil transmission of BVQ was demonstrated through a bioassay using soil dilutions with quartz and sugar beet cv. Cadyx as bait. After 6 weeks, BVQ was detected by RT-PCR in bait plants. The putative vector, Polymyxa betae, was identified by lactophenol-cotton blue staining of the roots followed by microscopic examination. BVQ produces irregularly shaped local lesions that appear ≈5 days after mechanical inoculation and tend to spread along veins. BVQ was detected in six fields located in the Polders Region and Brabant Province of Belgium. BVQ was always found in sugar beet samples coinfected with BNYVV and BSBV. The economic significance of BVQ and its interaction with other viruses is not known.
References: (1) R. Koenig et al. J. Gen. Virol. 79:2027, 1998. (2) M. Saito et al. Arch. Virol. 141:2163, 1996. (3) M. Verhoyen and M. Van den Bossche. Parasitica. 44:71, 1987.