Abstract
Tomato curly stunt virus (ToCSV) is an economically important begomovirus found in South Africa. This virus causes damage to tomato fruit and foliage and results in a reduction of tomato yields leading to economic losses. The molecular mechanism that ToCSV uses to interact with tomato host plants is complex and not clearly understood. In this study, an infectivity assay of ToCSV infected susceptible (NIL395, S), and resistant (NIL396, R) near-isogenic tomato lines was conducted. This is the first time that these lines have been tested against ToCSV. Quantitative PCR revealed that viral load in the susceptible line increased overtime while ToCSV load was lower in the resistant line at 15 dpi and 35 dpi, S plants accumulated 20-fold and 74-fold more virus respectively than in R plants. In addition, the expression of RDR1 was measured in both lines using RT-qPCR and revealed that the resistant line had elevated levels of RDR1 with 57- fold and 318-fold higher as compared to ToCSV-infected S plants, and showed minimal symptoms. Viral load accumulation was lower when compared to the susceptible line. The results from this study indicate that the NIL396 line behaviour is more in line with a tolerant phenotype instead of a resistant one. While we hypothesis that tolerance is likely linked, in part, to the high expression of the RDR1 gene, it is important to note that it is not exclusively responsible for tolerance and that other factors are most likely involved in combination with RDR1 expression as well.
M.Sc. (Biochemistry)