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 SouthudAfrica (SA) as well as worldwide. A destructive viral disease known as Tomato curly stunt virus,udToCSV-[ZA:Ond:98], belonging to the genus Begomovirus has negatively impacted on tomatoudproduction in SA. This has brought about the need to develop resistant cultivars to ToCSV. Since alludcultivated tomato cultivars are susceptible to ToCSV, resistance genes against the virus found in wildudtomato plant species have been introgressed into the cultivated tomato by plant breedingudtechniques. Wild relatives of tomato were adapted to many pathogens (including viruses) as well asudstresses from the surrounding environment. During breeding for improved fruit quality andudincreased yield, the gene networks giving rise to many biotic and abiotic stress resistances have beenudlost leaving the domesticated tomato extremely susceptible. Plant breeders have reconstitutedudsome of the gene networks into the cultivated tomato that provide tolerance to stresses includingudviruses. They have achieved this by the help of marker-assisted selection (MAS), where theudassociated marker is used as an indirect selection criterion. This is an important process inudcommercial breeding programs as it allows for a speedy selection of selected traits in theuddevelopment of tomato hybrids. The defence response to abiotic stresses in plants includes theudexpression of heat shock proteins (HSPs) that function as stress response proteins, molecularudchaperones and proteases which repair or degrade damaged proteins.udThe objective of this study was to elucidate the type of resistance mechanism of a tomato inbredudline (TAM), to ToCSV. Since TYLCV-IL shows 77% nucleotide identity with ToCSV, molecular markersudalready established for the detection of resistance genes for TYLCV-IL were used to screen TAM.udThe inbred line, TAM, was screened for the absence of any of the known resistant genes to TYLCV-ILudusing molecular markers already established for the screening of TYCLV-IL resistance genes. TAMudwas crossed with susceptible cultivar, Rooikhaki, to produce F1 hybrids. These F1 hybrids wereudselfed to produce an F2 population. Infection trials using ToCSV were conducted using TAM inbredudline, F1 hybrids and the F2 population. Since TAM did not have any of the known resistance genes toudTYLCV-IL, a possible novel resistance source to ToCSV was speculated. A clue to the resistantudmechanism against ToCSV resistance in TAM was indicated by the segregation patterns of the F2udpopulation after inoculation with ToCSV. The results suggest that the resistance is under the controludof partially dominant resistant genes. The level of resistance of commercial South African tomato cultivars (Tyler and Tovi-star) againstudTYLCV-IL was investigated. The heat shock protein (HSP) profiles of these two SA lines includingudsusceptible cultivar, Rooikhaki, were treated with abiotic stresses (salt and heat) and results wereudcompared with a similar study conducted with TYCLV-IL resistant and susceptible tomato cultivars.udHeat shock protein 70 accumulation patterns were similar in that HSP70 was more stable in theudresistant cultivars throughout the application when abiotic stresses were applied to the SA resistantudand susceptible tomato cultivars as compared to Israel resistant and susceptible breeding lines. Audrelation between infection severity and the pattern of HSP expression was found. A higher level ofudHSP 70 in resistant tomato plants could contribute to a lower symptom severity phenotype.