A mixture of begomoviruses in leaf curl-affected tobacco in Karnataka,South India

摘要

Tobacco leaf curl is widespread in several states in India including Andhra Pradesh, Gujarat, Karnataka, Bihar and West Bengal. Tobacco leaf curl virus (TbLCV) isolates collected from five different parts of India induced four distinct symptom phenotypes (group I, II, III & IV) on tobacco cultivars Samsun and Anand 119 (Valand & Muniyappa, 1992). PCR was performed on DNA extracted from group I and IV leaf curl-affected tobacco from Karnataka, India using degenerate begomovirus-specific primers. Subsequent cloning and sequencing of PCR products revealed preliminary evidence for the presence of at least three begomoviruses in the affected material following alignment of a 333 bp region of the coat protein gene (CP). The complete CP and common region (CR) of two putative begomoviruses, Tobacco leaf curl virtis-Karnatakal (TbLCV-Kar1) and Tobacco leaf curl virus-Karnataka2 (TbLCV-Kar2), were sequenced using PCR clones obtained with designed sequence-specific primers. Phylogenetic analysis of the CP and CR of TbLCV-Kar1 and TbLCV-Kar2 placed them in the Asian Old World begomovirus cluster. The two viruses differed from each other significantly in both the CP gene and the CR (<90% nucleotide sequence identity). This difference, in conjunction with distinct iterative sequences strongly suggests that these begomoviruses are distinct from one another. Group I and IV tobacco were also found to harbour a possible third begomovirus following the 333 bp CP alignment. Comparison of TbLCV-Kar1 and TbLCV-Kar2 with other geminiviruses, showed that both sequences shared high nucleotide sequence identity (>90%) with other begomoviruses in either the CP or CR, thereby suggesting these viruses to be possible strains of other reported begomoviruses. Combined comparison of the CP and CR sequences however, suggests that the two viruses are not strains of other reported begomoviruses, but may be distinct begomoviruses that could have arisen through recombination events during mixed infections.