The limited specificity, sensitivity and multiplex capacity of detection techniques currently available for important seed-borne pathogens of tomato is a significant risk for the global tomato trade and production industry. These pathogens can be associated with seed at low concentrations but, due to their highly virulent nature, these low levels can be sufficient to infect germinating seedlings and spread to neighbouring plants and fields, potentially causing epidemics and economic losses. In this study, detection techniques currently available for phytodiagnostics were evaluated for the capacity to accurately detect and identify five agronomically important seed-borne pathogens of tomato: Pepino mosaic virus (PepMV), Tomato mosaic virus (ToMV), Clavibacter michiganensis subsp. michiganensis (Cmm), Xanthomonas campestris pv. vesicatoria and Pseudomonas syringae pv. tomato. A prototype diagnostic microarray was also designed in an attempt to develop a tool that could simultaneously detect these five seed-borne pathogens from a single sample. Viral detection based on serological techniques was rapid, accurate and reliable but only detected a single pathogen per assay and required supplementary bioassays to indicate the viability of detected viral pathogens. Selective media plating for bacterial detection demonstrated unreliable recovery of targeted bacteria from infected seed and leaf samples and required supplementary tests to validate the identity of presumptive positives. Assays were lengthy, laborious and sometimes too ambiguous for accurate diagnosis of bacterial pathogens. Nucleic acid-based technologies demonstrated improved sensitivity and specificity for detection of targets from pure culture, leaf and seed extracts, compared to conventional and serological methods, yet also required supplementary bioassays or media assays to validate the viability of detected pathogens. Amplification efficiency however, was affected by the presence of PCR inhibitors and despite positive detection, variable banding intensity in electrophoretic analysis of amplified products necessitated the use of reference cultures to validate diagnosis. The developed microarray incorporated 152 pathogen-specific and control probes to facilitate diagnosis and taxonomic classification of detected pathogens. The array was challenged with pure culture extracts of the five target pathogens, selected related and non-target, unrelated pathogens of tomato. Positive detection of each of the pathogens was demonstrated but the production of hybridisation signals was highly variable and extremely sensitive to minor technical differences. Each of the five pathogens were successfully detected in combination proving that different classes of seed-borne pathogens could be detected from a single sample using the developed microarray. This prototype microarray has good potential for phytodiagnostic screening of the five targeted pathogens, and further validation, optimisation and extension for testing tomato seed samples may facilitate incorporation of this array into standard diagnostic protocols.

Solanum 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.

Simple technologies are required for reducing the post harvest losses of horticultural produce. Edible films are being studied extensively for application on fresh and cut fruits and vegetables. Tomato, being a very nutritious and important food and a highly perishable climacteric fruit, this study was planned to investigate the application of chitosan films. Chitosan is a biodegradable waste product from sea food and is safe for consumption. With a view to broaden its antimicrobial activity it was combined with lysozyme, a lytic enzyme. Since the edible films are sensitive to changes in temperature and humidity, they were studied under ambient and optimal conditions of storage. / This study showed that 1% chitosan was more suitable for tomatoes for storage at both conditions of ambient and low temperature. Respiration study showed that 1% chitosan treatments resulted in more favorable levels of CO 2 production and internal O2. This was reflected in the quality of tomatoes held under these conditions. Two per cent chitosan films were unsuitable due to their high CO2 production and low internal O 2 levels. Spoilage was more apparent in this treatment. Lysozyme addition did not show any additional benefit. / The research in this study has demonstrated that the selection of edible films for horticultural produce needs to be integrated with the requirement of storage conditions of the produce.

Two series of tests were performed in summer 1993 and repeated in summer 1994 to investigate effects of potassium, calcium and water table depth on mechanical properties of tomato fruit. In the first group of tests five mechanical properties stress, strain, ER (ratio of stress to strain at break), energy and toughness were calculated from the force-deformation curve obtained by compression of pericarp disks taken from tomato fruits (cv New Yorker) at the breaker stage. In the second group of tests force, deformation and energy were obtained from puncture tests on whole tomato fruit. The textural parameters were used to compare the effects of the potassium, calcium and water level depths on the mechanical properties of tomatoes. Results showed the effects of calcium and water table depths on the mechanical properties were significant. Tomato fruits exposed to increasing moisture stress levels by increasing water table depth exhibited increased firmness. Increased application of calcium also resulted in increased firmness. Application of different potassium levels had in general no significant effect on breaking stress, strain, ER, energy and toughness of tomato fruit pericarp. / A new method of measuring skin strength of tomatoes is described. The method, refered to as loop method, overcame the problems with the existing method using mechanical grips. Further, the loop method was applied to measure the effect of potassium and calcium on skin strength of tomato. Using the loop method, data were collected on relaxation of tomato skin (epidermis). A computer program was written to model th tensile stress relaxation behaviour of tomato skin. The program was employed to calculate linear and non-linear coefficients of a relaxation model. The fitted values were in a very good agreement with experimental data (R$ sp2>$0.99).

Thesis (M. Ag. Sci.)--University of Adelaide, 1984. / Some ill. mounted. Includes bibliographical references (leaves 106-118).

Thesis(Master)--İzmir Institute of Technology, İzmir, 2005 / Keywords: Tomato, pepper, cucumber mosaic virus, resistance, genetic mapping. Includes bibliographical references (p.49-55)

Thesis (M.S.)--West Virginia University, 2004. / Title from document title page. Document formatted into pages; contains vii, 60 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 56-60).

Thesis (Ph. D.)--Ohio University, March, 2004. / Includes bibliographical references (leaves 202-227).

Thesis (Ph. D.)--Ohio State University, 2005. / Title from first page of PDF file. Document formatted into pages; contains xv, 104 p.; also includes graphics (some col.). Includes bibliographical references (p. 93-104). Available online via OhioLINK's ETD Center

Thesis(M.Sc.(Plant Protection))-- University of Limpopo,2019 / Previously, cucurbitacin-containing phytonematicides that were drench-applied in black plastic containers filled with pasteurised loam soil when placed on the soil surface had no effect on suppression of population densities of root-knot (Meloidogyne species) nematodes. The active ingredients of cucurbitacin-containing phytonematicides, namely, the cucurbitacins, had been shown to be thermophilic, with the failure of the products explained from the view of the variability induced by container-type and aboveground positioning. The view was investigated further using Nemarioc-AL and Nemafric-BL phytonematicides as influenced by container-type and positioning on growth of tomato (Solanum lycopersicum L.) plants and suppression of M. incognita population densities. Tomato cv. ′Floradade′ seedlings were transplanted into 30-cm-diameter brown pot belowground, brown pot aboveground, black pot belowground, black pot aboveground, 5 L polyethylene plastic bag belowground and 5 L polyethylene plastic bag aboveground, each containing 5-dm3 steam-pasteurised sandy loam soil amended with Hygromix at 3:1 (v/v) ratio. Seedlings were inoculated with 2000 eggs and second-stage juveniles (J2) of M. incognita race 2, with Nemarioc-AL and Nemafric-BL phytonematicides applied once 17 days after inoculation in both Experiment 1 and Experiment 2. Also, standard cultural practices were applied throughout the trial. At 56 days after inoculation, container-type and positioning had significant effects on various plant growth and essential nutrient element variables in Experiment 1 and Experiment 2, except that the six treatments did not have significant effects on nutrient elements and nematode population densities in Experiment 2. Relative to brown plastic pot belowground, treatments either increased or decreased plant growth, essential nutrient elements and nematode densities in Experiment 1, with selective similaritiesin Experiment 2. Specifically, nematode variables except for J2 in soil and total nematode population densities were significantly affected by the treatments in Experiment 2. Relative to the standard, plastic bag belowground increased J2 in soil and total population in soil by 18%. In conclusion, both container-type and positioning had effects on the efficacy of phytonematicides on plant growth, accumulation of essential nutrient elements and suppression of nematode population densities. Consequently, in trials where cucurbitacin-containing phytonematicides are conducted in microplots, brown plastic pots with the belowground positioning should be used to enhance the efficacy of the phytonematicides in stimulating plant growth and suppression of nematode population densities.