Basella rugose mosaic virus, a new potyvirus infecting Basella rubra

Basella rubra and B. alba (Malabar spinach) are plants of the family Basellaceae, native to tropical Asia. They were introduced into Taiwan during the 1660s and are grown as vegetables and herbs. In 2001, mosaic and rugose symptoms were observed on leaves of B. rubra in the Taipei area (Fig. 1).

Extracts from these plants caused chlorotic lesions on inoculated leaves of Chenopodium amaranticolor and C. quinoa; the latter became systemically infected. A virus isolate, BR, was obtained after three successive single lesion isolations from C. amaranticolor. Following mechanical inoculation B. rubra and B. alba seedlings produced symptoms similar to field diseased plants and Nicotiana benthamiana and N. clevelandii displayed mosaic symptoms. Transmission electron microscopy of negatively-stained sap extracts showed the presence of flexuous filaments c.680 nm in length. Using indirect ELISA, plants of B. rubra and C. quinoa with symptoms tested positive for potyvirus using an anti-potyvirus group monoclonal antibody (Agdia Inc., Elkhart, IN, USA). The only potyvirus previously reported to infect a member of the Basellaceae (Ullucus tuberosus) is Ullucus mosaic virus (Brunt et al., 1982). However this virus differs from isolate BR, as it causes local lesions in C. quinoa. The 3'-terminal region of the BR isolate was amplified by RT-PCR from total RNA of diseased plants, using a potyvirus-specific degenerate primer (PNIbF1) and an oligo-dT primer (Huang & Chang, 2005). A 1.8 kb fragment, including partial NIb, the CP and 3' UTR, was obtained and cloned. Two independent clones were sequenced and a BLAST search was performed against the NCBI database. Sequence analysis of the putative capsid protein gene revealed that the highest amino acid and nucleotide sequence identities were 70% and 68% respectively, between the BR isolate (DQ394891) and all other searched potyvirus sequences. According to the species demarcation criteria for the Potyviridae (Adams et al., 2005) the BR isolate is a new potyvirus and is herein designated as Basella rugose mosaic virus (BaRMV).