Tulip (Tulipa spp.) is an ornamental plant of major economic importance in Japan. Regions in Toyama Prefecture are some of the most productive for producing tulip bulbs, shipping approximately 50 million bulbs annually. However, mosaic diseases caused by viruses such as Tulip breaking virus (TBV) currently limit bulb production in these areas. Only the potyviruses TBV and Lily mottle virus (LMoV) have been reported infecting tulip in Japan. A virus isolate from tulip with flower-breaking symptom in Toyama Prefecture was tentatively named OE4 and was presumed to be LMoV after detection by LMoV-specific reverse transcription-polymerase chain reaction (RT-PCR) (4). When OE4 was mechanically inoculated on test plants (13 species from six families), RT-PCR confirmed that it infected plants in the Liliaceae (Tulipa spp., Lilium formosanum, and L. concolor) with mosaic symptoms but did not induce any symptoms in Chenopodium quinoa, Tetragonia tetragonoides, and Nicotiana benthamiana. According to Dekker et al. (2) LMoV and Tulip band breaking virus (TBBV) infected Tulipa spp. and TBBV did not infect C. quinoa, T. tetragonoides, N. clevelandii, and N. benthamiana, species that were local or systemic hosts for LMoV. To analyze the genomic sequence of OE4, a primer set was designed for amplifying the coat protein (CP) gene of LMoV, with 5′ -GCAAATGAGACACTCAATG-3′ as a forward primer and 5′-TTACATAGAAATTCCAAGTAAG-3′ as a reverse primer. The fragment obtained was cloned and sequenced (DDBJ/EMBL/GenBank Accession No. AB078007). The CP gene of OE4 consisted of 825 nucleotides and had 86.5% identity (90.6% identity in deduced amino acid sequence) with the CP gene of LMoV-Netherlands (S44147) (3). When it was compared with partial sequences (277 nucleotides) of LMoV (S60810) and TBBV (S60805) (2), the nucleotide sequence identities were 89.9 and 96.4%, respectively. Multiple alignment and a phylogenetic tree based on the 277 nt of the tulip potyviruses, including OE4, showed the close relationship between OE4 and TBBV. These results indicated that OE4 was an isolate of TBBV. However, the CP amino acid sequence identity between TBBV and LMoV was more than 80%, and it seemed logical that TBBV be assigned to a strain of LMoV, according to potyvirus species demarcating criteria (1). Another screening using RT-PCR based detection, and an inoculation test for 55 flower-breaking tulips collected from fields in Toyama Prefecture revealed that four tulip plants were infected with TBBV and 54 with TBV. This suggests that TBV is more prevalent than TBBV, and we need to produce an attenuated virus of TBV, which will be effective for managing tulip breaking disease in the prefecture.
References: (1) P. H. Berger et al. Family Potyviridae. Pages 703--724 in: Virus Taxonomy. Academic Press, San Diego, CA, 2000. (2) E. L. Dekker et al. J. Gen. Virol. 74:881, 1993. (3) S. A. Langeveld et al. J. Gen. Virol. 72:1531, 1991. (4) T. Se and S. Kanematsu. Ann. Phytopathol. Soc. Jpn. 64:420, 1998.
