Evaluation of resistance to tomato curly stunt virus in tomato

[摘要] Solanum lycopersicon (the cultivated tomato) is a commodity of great economic importance in SouthAfrica (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 tomatoproduction in SA. This has brought about the need to develop resistant cultivars to ToCSV. Since allcultivated tomato cultivars are susceptible to ToCSV, resistance genes against the virus found in wildtomato plant species have been introgressed into the cultivated tomato by plant breedingtechniques. Wild relatives of tomato were adapted to many pathogens (including viruses) as well asstresses from the surrounding environment. During breeding for improved fruit quality andincreased yield, the gene networks giving rise to many biotic and abiotic stress resistances have beenlost leaving the domesticated tomato extremely susceptible. Plant breeders have reconstitutedsome of the gene networks into the cultivated tomato that provide tolerance to stresses includingviruses. They have achieved this by the help of marker-assisted selection (MAS), where theassociated marker is used as an indirect selection criterion. This is an important process incommercial breeding programs as it allows for a speedy selection of selected traits in thedevelopment of tomato hybrids. The defence response to abiotic stresses in plants includes theexpression of heat shock proteins (HSPs) that function as stress response proteins, molecularchaperones and proteases which repair or degrade damaged proteins.The objective of this study was to elucidate the type of resistance mechanism of a tomato inbredline (TAM), to ToCSV. Since TYLCV-IL shows 77% nucleotide identity with ToCSV, molecular markersalready 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-ILusing molecular markers already established for the screening of TYCLV-IL resistance genes. TAMwas crossed with susceptible cultivar, Rooikhaki, to produce F1 hybrids. These F1 hybrids wereselfed to produce an F2 population. Infection trials using ToCSV were conducted using TAM inbredline, F1 hybrids and the F2 population. Since TAM did not have any of the known resistance genes toTYLCV-IL, a possible novel resistance source to ToCSV was speculated. A clue to the resistantmechanism against ToCSV resistance in TAM was indicated by the segregation patterns of the F2population after inoculation with ToCSV. The results suggest that the resistance is under the controlof partially dominant resistant genes. The level of resistance of commercial South African tomato cultivars (Tyler and Tovi-star) againstTYLCV-IL was investigated. The heat shock protein (HSP) profiles of these two SA lines includingsusceptible cultivar, Rooikhaki, were treated with abiotic stresses (salt and heat) and results werecompared 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 theresistant cultivars throughout the application when abiotic stresses were applied to the SA resistantand susceptible tomato cultivars as compared to Israel resistant and susceptible breeding lines. Arelation between infection severity and the pattern of HSP expression was found. A higher level ofHSP 70 in resistant tomato plants could contribute to a lower symptom severity phenotype.

[发布机构] University of the Witwatersrand