A study of the molecular variability of some South African isolates of tobacco necrosis virus
The relationship of various tobacco necrosis viruses, isolated from various crops and other sources in South Africa was determined. An isolate from avocado was chosen for partial characterisation to confirm that it was a member of the Necrovirus group of plant viruses. TNV was detected in potatoes that exhibited abnormal necrotic foliar symptoms and a D-type TNV was isolated and identified from the Up-to-Date potato variety. Immunoelectroblotting assay grouped the TNV isolates studied into two serotypes (A and D). This result was confirmed by NA hybridization with probes derived to the coat protein of an A- (TNVWheat) and a D-type (TNV-Papaya green lesion) isolate. RT-PCR with A and D specific primers did not amplify the coat protein of three A- and D-type TNV isolates which appears to indicate that the detection by PCR with specific primers is too selective to be used for a general test, unless degenerate primers to a more conserved region of the coat protein gene are used. Sequence analysis of the coat protein gene was used to determine the phylogenetic relationship amongst nine TNV isolates examined and also by comparison to three isolates for which the coat protein gene had already been sequenced. Sequence analysis showed high degree of homology amongst the A-type isolates and the D-type isolates, with approximately 45 % homology between the two TNV types.
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Department of Molecular and Cell Biology