Family: Nanoviridae

Genus: Babuvirus


Distinguishing features

Babuviruses have been reported exclusively from monocotyledonous plants, specifically those in the order Zingiberales and Arecales (Thomas 2019). They are transmitted in a circulative, non-propagative manner by their aphid vectors including Micromyzus kalimpongensis for cardamom bushy dwarf virus (CBDV) (Ghosh et al., 2016), Pentalonia nigronervosa for abaca bunchy top virus  (ABTV) (Su et al., 2003) and banana bunchy top virus  (BBTV) (Magee 1940) and P. caladii for BBTV (Watanabe et al., 2013). 


See discussion under family description

Genome organization and replication

Babuviruses share six common, DNA genome components named DNA-R, DNA-S, DNA-C, DNA-M, DNA-N, and DNA-U3 (Figure 2. Nanoviridae). All but DNA-U3 are also shared with members of the genus Nanovirus

The function of DNA-U3 is unknown. Although a transcript has been described for an Australian isolate of BBTV (BBTV-[AU]; L41576) (Herrera-Valencia et al., 2007), many other BBTV isolates, as well as CBDV and ABTV, lack an identifiable ORF. In DNA-R, a small nested ORF encoding a protein of ca. 5 kDa has been described for BBTV and CBDV although these proteins are unrelated, and the ORF is not present in ABTV. This ORF has been shown to be transcribed for BBTV. 

Nucleotide differences ranging from 7 to 20% have been observed for the individual genes, and 22–46% for their respective CR-M, of two ABTV isolates, one from the Philippines and the other from Sarawak, Malaysia (Sharman et al., 2008). Similarly, two groups of BBTV isolates, designated the Asian and South Pacific groups (Karan et al., 1994), or South-East Asian and Pacific-Indian Ocean groups, respectively (Yu et al., 2012), are distinguished based on obvious sequence differences across all components (Karan et al., 1994, Banerjee et al., 2014). The nucleotide sequences of the major gene of DNA-R, for example, differ by 7.5%, with a mean difference of 5.6% in amino acid sequence between the two geographic groups. More strikingly, the CR-M of DNA-R has a mean difference of 32% between groups, whereas the intra-group CR-M variation does not exceed 6% (Karan et al., 1994). 

Replication strategy is typical of the family Nanoviridae


All characterized babuviruses have monocotyledonous hosts. Both ABTV and BBTV infect Musa spp. in the family Musaceae. Additionally, BBTV has been shown to naturally infect Ensete superbum (Musaceae) (Selvarajan and Balasubramanian 2013), Alpinia purpurata (Thomas 2019){Thomas, 2019 #10792} and Heliconia aurantiaca (Hamim et al., 2017), and experimentally also Alpinia zerumbet, Canna indica (all from the order Zingiberales) and Colocasia esculenta (Araceae) (Pinili et al., 2013). CBDV has been reported from Amomum subulatum (Zingiberaceae). Economically important diseases are caused in banana and alpinia by BBTV, in abaca by ABTV and BBTV, and in cardamom by CBDV. 


BBTV is serologically unrelated to members of the genus Nanovirus. However, BBTV antibodies have been used for the detection of the babuviruses ABTV and CBDV. Out of 10 monoclonal antibodies raised against BBTV, only two reacted with ABTV. This is consistent with a capsid protein (CP) amino acid sequence difference of about 20% between ABTV and BBTV (Sharman et al., 2008). 

Species demarcation criteria

Members of different species generally have an overall nt sequence identity of <80% across all six combined genome components. As babuviruses can have overlapping host ranges and be transmitted by a similar range of aphid species, biological criteria appear to be of limited use for species discrimination within the genus. Although species-specific monoclonal antibodies (where available) can be used for discrimination of viruses belonging to a certain species, preference should nowadays be given to molecular criteria.