Dias, Katia2013-01-312013-01-312013-01-31http://hdl.handle.net/10539/12342Solanum lycopersicon (the cultivated tomato) is a commodity of great economic importance in South Africa (SA) as well as worldwide. A destructive viral disease known as Tomato curly stunt virus, ToCSV-[ZA:Ond:98], belonging to the genus Begomovirus has negatively impacted on tomato production in SA. This has brought about the need to develop resistant cultivars to ToCSV. Since all cultivated tomato cultivars are susceptible to ToCSV, resistance genes against the virus found in wild tomato plant species have been introgressed into the cultivated tomato by plant breeding techniques. Wild relatives of tomato were adapted to many pathogens (including viruses) as well as stresses from the surrounding environment. During breeding for improved fruit quality and increased yield, the gene networks giving rise to many biotic and abiotic stress resistances have been lost leaving the domesticated tomato extremely susceptible. Plant breeders have reconstituted some of the gene networks into the cultivated tomato that provide tolerance to stresses including viruses. They have achieved this by the help of marker-assisted selection (MAS), where the associated marker is used as an indirect selection criterion. This is an important process in commercial breeding programs as it allows for a speedy selection of selected traits in the development of tomato hybrids. The defence response to abiotic stresses in plants includes the expression of heat shock proteins (HSPs) that function as stress response proteins, molecular chaperones and proteases which repair or degrade damaged proteins. The objective of this study was to elucidate the type of resistance mechanism of a tomato inbred line (TAM), to ToCSV. Since TYLCV-IL shows 77% nucleotide identity with ToCSV, molecular markers already established for the detection of resistance genes for TYLCV-IL were used to screen TAM. The inbred line, TAM, was screened for the absence of any of the known resistant genes to TYLCV-IL using molecular markers already established for the screening of TYCLV-IL resistance genes. TAM was crossed with susceptible cultivar, Rooikhaki, to produce F1 hybrids. These F1 hybrids were selfed to produce an F2 population. Infection trials using ToCSV were conducted using TAM inbred line, F1 hybrids and the F2 population. Since TAM did not have any of the known resistance genes to TYLCV-IL, a possible novel resistance source to ToCSV was speculated. A clue to the resistant mechanism against ToCSV resistance in TAM was indicated by the segregation patterns of the F2 population after inoculation with ToCSV. The results suggest that the resistance is under the control of partially dominant resistant genes. The level of resistance of commercial South African tomato cultivars (Tyler and Tovi-star) against TYLCV-IL was investigated. The heat shock protein (HSP) profiles of these two SA lines including susceptible cultivar, Rooikhaki, were treated with abiotic stresses (salt and heat) and results were compared with a similar study conducted with TYCLV-IL resistant and susceptible tomato cultivars. Heat shock protein 70 accumulation patterns were similar in that HSP70 was more stable in the resistant cultivars throughout the application when abiotic stresses were applied to the SA resistant and susceptible tomato cultivars as compared to Israel resistant and susceptible breeding lines. A relation between infection severity and the pattern of HSP expression was found. A higher level of HSP 70 in resistant tomato plants could contribute to a lower symptom severity phenotype.enTomatoes - Diseases and pests.Tomatoes - Disease and pest resistance.Plant viruses.Thesis