iii, 113 leaves : tables, graphs, photos ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Plant Pathology, 1978

Polyclonal antisera produced against spores, soluble protein and the whole mycelium fractions of Didymella lycopersici reacted with the homologous and heterologous antigens. The most sensitive antiserum was that raised against the whole mycelium, the soluble protein and the spore, in decreasing order of sensitivity. Using the antiserum raised against the whole mycelium it was possible to detect D. lycopersici on diseased plants and infested seeds. Cross reactivity was observed between the antisera produced to D. lycopersici and D. applanata, D. bryoniae and other tomato fungal pathogens including Fusarium spp. and B. cinerea. ELISA was most sensitive and reliable compared to double immunodiffusion, and latex tests. No reactions were obtained using the latex agglutination procedure and no antiserum detected spores in double diffusion tests. Protein profiles on SDS-PAGE revealed that the total number of protein bands decreased with increased age of cultures of D. lycopersici incubated in liquid media. Western blots probed with the antiserum raised against the whole mycelium showed that protein bands from extracts of both D. lycopersici and D. applanata were antigenic. / Land and Food Systems, Faculty of / Graduate

No description available.

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.

Many parasitic diseases display symptoms beyond the areas invaded by the parasite itself. This suggests that toxic metabolic products of the pathogen diffusing in front of its advancing growth brings about derangements in unoccupied tissues at times far remote from the focus of infection. [...]

TA and TB toxins are host-specific phytotoxins produced by the fungus Altemaria altemata f. sp. Iycopersici, the causative agent of stem canker disease in tomato. The two toxins are similar in structure: TB lacks the C(5) hydroxy group present in TA toxin. Both compounds are isolated as an equilibrium mixture of the two esters formed by either the C(13) or C(14) hydroxy groups of the (2S,4R,5R,11R,13S,14R,15R)-1-amino-11,15¬dimethylhepta-decane-2,4,5, 13, 14-pentol backbone with the Re prochiral carboxy group of tricarballylic acid. The synthesis for these toxins is necessary in order to study their structure-activity relationships. The aim of the synthetic study outlined in this dissertation is the development and implementation of methodology for the synthesis of the C(1)-C(9) unit of the C17 aminopentol backbone of TA toxin with the appropriate stereochemistry. Retrosynthetic analysis of the C17 aminopentol backbone of TA toxin identifies (2R,4S,-5R,6R)-2,6-dimethyloctane-1.4,5-triol, synthon B, and (2S,4R,5R)-1-amino¬nonane-2,4,5,9-tetrol, synthon A as key intermediates for the proposed synthesis. Further analysis of synthon A identifies the C9 synthon (2S,4R,5R)-nonane-1,2,4,5,9-pentol, as the target molecule which can be derived from the C7 synthon (2S,3R)-1,2-epoxyheptane-3,7¬diol. The work presented in this dissertation shows that the protected intermediate corresponding to the abovementioned C7 synthon, can be prepared from 1,5-pentanediol by a number of functional group trans-formations using appropriate protecting group strategy (O-TBS, O-TBDPS and O-benzyl groups) and introduction of the two stereogenic centres by using Sharpless epoxidation/kinetic resolution methodology. Nucleophilic opening of the terminal epoxide using cyanide was successful but using chiral sulfoxide methodology for the introduction of the third stereogenic centre and the concomitant one¬-carbon chain extension, failed: in the case of both an acetonide and a dibenzyl protected C8 intermediate a rearrangement occurred. Alternative methods for nucleophilic opening of the terminal epoxide ring and concomitant or subsequent chain extension were investigated and as a result a different synthetic route is proposed. / Dissertation (MSc (Chemistry))--University of Pretoria, 2006. / Chemistry / unrestricted

No description available.

A study was undertaken to investigate the morphological host-parasite interactions of selected resistant and susceptible lines of tomato to Meloidogyne incognita, M. incognita var. acrita, M. javanica, M. hapla and M. arenaria and to determine the mode of inheritance of nematode resistance and the number of genetic factors controlling resistance to the root-knot nematodes. Four resistant varieties of tomato were crossed with one susceptible variety. The F₁ populations showed hybrid vigor for height, yield, and fresh weight of roots, stems, and leaves. Resistance to M. javanica, M. incognita, M. incognita var. acrita was dominant and susceptibility was recessive. The F₂ populations segregated in a 3:1 ratio showing resistance is a monofactorial dominant character and controlled by the same gene. The resistant parents, and the F₁ and F₂ populations did not show resistance to M. hapla and M. arenaria. Anatomical studies showed that there were some slight differences between resistant and susceptible varieties. In resistant varieties a compact layer of cells was formed around the body of the nematode which may have caused the noticeable reduction in nematode development and egg-formation. Giant cells formed in resistant varieties were much smaller and fewer in number than in susceptible varieties. The contrast between these two reactions by the resistant and the susceptible hosts suggests that resistance is related to the cellular response of the host to the parasite. In the root penetration and attraction study it was observed that when 2000 larvae were used as inoculum, they freely penetrated the roots of susceptible seedlings whereas in resistant roots very few larvae entered and most remained half embedded in the roots even at the 96 hour interval after inoculation. When the concentration of the larvae inoculum was increased from 2000 to 8000 per seedling, the larvae entered the roots of resistant seedlings as freely and as rapidly as they entered the roots of susceptible ones, demonstrating that the concentration of inoculum is an important factor in penetration. / Ph. D.

Anthracnose of tomato was first described by Chester in 1891. It has been of economic importance to the growers of canning tomatoes nearly ever since. Anthracnose is cause by Colletptrochum phomoides (sacc.) Chester which appears to have different physiologic and morphologic forms. There is evidence that it is a soil organism but this remains to be definitively proved. The organism has a broad pH range and different isolates show different temperatures opimums but about the same temperature range for growth. The organism does not show the “dual phenomenon” but does sector frequently. Sectors are morphologically different from the parent mycelium and offers an explanation as to the origin of different strains of the organism. / Master of Science