National Research Centre for Banana, Tiruchirapalli-620102, Tamil Nadu.
Banana streak virus (BSV) is the causal agent of streak disease of banana and plantain and the virus is reported in most of the banana growing countries in the world. Integration of BSV genome in the host banana genome and episomal infection arising from integrated sequences has been reported.
‘B genome’ containing banana cultivars and accessions have been known to have integration of viral genome. Most of the cultivated banana are man made selections derived from inter specific natural hybridization containing accuminata (A) genome and balbisiana (B) genome. In India, BSV disease has become a major threat to an important commercial banana belongs to sub group Mysore (AAB). The virus is a member of plant pararetrovirus, genus badnavirus with non enveloped bacilliform particles contain ∼7.4 -8.0Kbp circular ds DNA genome. BSV infection causes heavy yield loss, which is a major problem in international exchange of banana germplasm. In this investigation, we have cloned and sequenced the complete genomes of two BSV species from banana cv. Mysore. Nine sets of primers were designed from published sequences of BSVOL (Accn No: NC 003381) and BSMysV (NC 006955). Total DNA was isolated from BSV infected, symptomatic leaves and amplified using designed primers with different PCR reactions. The amplified fragments were cloned in pGEM-T easy vector and pUC18. Cloned fragments were sequenced, aligned and edited using Bio-edit software and CLUSTAL-X. One of the viral genome had 99 percent similarity with BSVOL virus and was also more similar to BSVGD sequences. However, in our isolate, a deletion of 450bp in the ORF III of published BSVOL sequence has been observed. It is suspected that the amplification might be from integrated sequences. In case of BSMysV derived primers, the complete genome of the virus has been amplified. The complete 7650 bp genome had 99 per cent sequence homology with published BSMysV sequence. Both the sequences have been deposited in the NCBI genbank (Accession no: DQ 859899; EU 140339). Dual infection of BSV species in Poovan (Mysore) and its implication in germplasm exchange, breeding and tissue culture have been discussed in detail.
