| Summary: | Student Number : 0314429G -
MSc research report -
School of Molecular and Cell Biology -
Faculty of Science === Tomato (Lycopersicon esculentum) is a horticultural commodity of great
economic importance in many parts of the world, including South Africa. A
previous study identified a new begomovirus, Tomato curly stunt virus (ToCSV),
as the causative virus of a new and potentially devastating disease of tomatoes in
South Africa. In this study, symptomatic plants, suspected of infection with an
uncharacterized ToCSV isolate (01/2521) were collected for screening from
Pietermaritzburg, South Africa. A host range study was conducted with the
original ToCSV isolate (99/0631). Two small DNA molecules (1449 nts and 755
nts) were found associated with ToCSV [01/2521] using near-full length primers
AL1c2745 and PAR1v32 specific for ToCSV. A single small DNA molecule (842
nts) was also found in association with the original ToCSV isolate. Nucleotide
sequence analysis revealed that the two small DNA molecules (1449bp and
755bp) have no significant nucleotide sequence identity (less than 20%) with any
known begomovirus. The 842bp molecule has the most significant nucleotide
sequence identity (48%) to that of ToCSV (AF261885), while less than 20%
nucleotide sequence identities were found when compared with other
begomoviruses. Nucleotide sequence alignment of the 842bp DNA molecule to
the ToCSV sequence, showed that this small DNA molecule is a chimeric
molecule that could have arisen through recombination, partly from the coding
regions of the ToCSV genome, but the rest of the molecule is of unknown origin.
All three small DNA molecules identified in this study were compared to some
known begomovirus associated subgenomic molecules and satellite molecules,
and sequence identities of less than 20% were found. To our knowledge, this is the
first report of a small DNA molecule found associated with the ToCSV genome.
The complete genome sequence of ToCSV [01/2521] was not determined. Based
on the results we obtained from the host range study, all the chosen test plants are
not susceptible to ToCSV infection. The infectivity of all the small molecules
identified in this study, is currently being investigated.
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