Thesis (M.S.)--University of Wisconsin--Madison, 1969. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis--University of Wisconsin--Madison. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 120-126).

The principal aim of the study was to further the knowledge of the interaction between Alternaria linicola and the host plant linseed (Linum usitatissimum). A novel detached cotyledon in vitro bioassay was developed to allow the quantification of disease resistance of Linum material to A. linicola. Differences were apparent between the disease response scores of four linseed varieties when tested with seven isolates of the pathogen which differed in aggressiveness. However, there was no significant difference between the disease response scores of the varieties and no change in the ranking of varieties over three experiments. This indicated that the varieties behaved in a predictable manner to each isolate during each test. Accordingly, in a subsequent study, 102 Linum accessions were challenged with an aggressive and a non-aggressive isolate. About 75 % of the accessions gave a moderate response, although there was a continuous distribution of resistance from high susceptibility to resistant. Accessions at both extremes of the disease response consisted of breeding material, currently grown varieties and near relatives of the host species. For example, one of the more resistant accessions tested was Linum angustifolium. A sub-set of nine Linum accessions was chosen (a range of susceptible, moderately-resistant and resistant material) and the resistance response of the material to an aggressive and a non-aggressive A. linicola isolate was investigated using a whole seedling inoculation technique. A comparison of the response of the material during the seedling test with that of the detached in vitro assay indicated that the latter test systematically, but marginally, overestimated the disease response. The in vitro bioassay scores and the seedling test scores were positively correlated following inoculation with the more aggressive of the two isolates. It was suggested that the resistance response of material could be accurately predicted by the in vitro bioassay but that a certain level of isolate aggressiveness was necessary to differentiate between responses of the accessions. Since large isolate-line interactions with respect to resistance scores were not observed, the results implied that resistance was polygenically determined. These results indicate that the bioassay for disease resistance produces an accurate measure of resistance and provides plant breeders with a useful tool which can be utilised during breeding programs.

No description available.

Cryphonectria canker of Eucalyptus, caused by Cryphonectria cubensis, is considered to be one of the most important fungal diseases affecting Forestry in South Africa. This disease also occurs in other tropical and sub-tropical regions of the world, including South America, Australia and South East Asia. Due to the commercial importance of C. cubensis, several recent studies in South Africa have focused on the elucidation of population diversity and phylogenetic relationships of the fungus from diverse geographic origins. These studies have resulted in more effective tree breeding programmes, and the identification of the possible origin for C. cubensis in South Africa. In this thesis, various aspects of the biology of C. cubensis in South Africa and Colombia are addressed. These studies have focused on the elucidation of the diversity of populations of the fungus occurring in Colombia and South Africa, as well as determination of the phylogenetic relationships of C. cubensis from Colombia. The sexual reproductive system of the fungus from Colombia has also been investigated . . In an investigation into the phylogenetic relationships of C. cubensis isolates from Colombia (Chapter IT), it was found that these isolates are most closely related to other South American isolates. This finding suggests that properties displayed by populations in other South American countries can be extrapolated to the Colombian population, and vice versa. The Colombian isolates were distinct from C. cubensis found in South East Asia, implying a more distant relatedness between these isolates. A study of homothallism and the possibility of sexual outcrossing in Colombian C. cubensis isolates (Chapter III), revealed that the fungus is homothallic. This was shown by allowing single ascospore isolates to reproduce sexually on Eucalyptus twigs, followed by genetic analysis of progeny using DNA fingerprinting. The DNA fuigerprinting profiles of these progeny were identical, indicating that no outcrossing had occurred. The sexual event was, therefore, due to self-fertilisation. In contrast, when progeny from naturally occurring perithecia were analysed genetically using vegetative compatibility groups (VCGs) and DNA fingerprinting, results suggested that oucrossing had occurred, but only to a limited extent. C. cubensis in Colombia is therefore homothallic, but can outcross. Presumably, the same is true for other populations of the fungus in South America. The genotypic diversity of the Colombian population of C. cubensis was investigated using VCGs and RAPDs. Results of this study indicated that the genotypic diversity of this population was similar to diversities previously found for other South American populations of C. cubensis. However, the phenotypic (VCG) and genetic (RAPD) data for the Colombian population were significantly different. The estimation of genotypic diversity based on RAPDs was significantly higher than the same figure for VCG data The reason for the difference in obtained values is attributed to the low level of sensitivity ofVCGs to detect genetic differences between isolates. In Chapter V, a novel technique for obtaining polymorphic, micro satellite-like DNA markers from fungi is described. The technique is based on the identification and characterisation of polymorphic DNA fragments originating from a random amplification of micro satellite sequences using the polymerase chain reaction (PCR). Sequence data from these fragments were used to construct specific primers to amplify polymorphic loci from genomic DNA. The technique has a high success rate in comparison to traditional techniques for the isolation of polymorphic markers. It was also shown that markers obtained with the new technique can be used to differentiate C. cubensis isolates originating in South Africa from those originating in other countries. The last chapter (VI) of this thesis represents the first intensive molecular population diversity study of C. cubensis in South Africa Using polymorphic markers from an earlier study (Chapter V), it was possible to assess the molecular variation of the South African population, and to compare this with phenotypic data obtained previously. It was found that molecular and phenotypic data yield different estimations of population diversity. An estimation of the gametic disequilibrium of the South African C. cubensis population revealed that the tested alleles were randomly associated. Such a situation is expected for populations that preferentially reproduce sexually, and consequently outcross. These figures are, however, only an indirect indication that outcrossing occurs in the South African population. Future studies on the South African C. cubensis population would need to be based on a larger number of markers, and should also include a greater number of isolates of the fungus. Knowledge gained through the studies presented in this thesis will hopefully aid to develop more effective control strategies against Cryphonectria canker of eucalypts. However, new questions about the biology of C. cubensis have emerged that need urgent attention. Data from this thesis might, therefore, prove important to future studies of the fungus. / Dissertation (MSc (Agric))--University of Pretoria, 2000. / Genetics / unrestricted

Differences associated with the mating type alleles of Didymium iridis and Physarum polycephalum were examined with fluorescent antibody and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Heteroabsorption of each anti-myxamoebal serum followed by testing serum activity using immunofluorescence showed there is no strain-specific activity in any of the anti-myxamoebal sera, but the sera was shown, to be genera specific. Intergeneric differences and similarities were shown in the electrophoretic patterns of the myxamoebal protein extracts from P. polycephalum, D. iridis, and Dictyostelium discoideum when compared. Intraspecific differences were noted in D. iridis.

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Heterobasidion annosum (Fr.) Bref., is a pathogenic hymenomycete which causes white-rot of coniferous trees throughout temperate regions of the Northern Hemisphere. The fungus can be divided into three intersterility groups (IS-groups) in Europe and two IS-groups in North America based on in vitro sexual compatibility and, loosely, on host tree preference. European P, S and F IS-groups prefer pine, spruce and fir respectively, and North American P and S groups prefer pine and fir respectively. This work describes the identification of discriminating characters which reflect underlying genetic differences accumulated between the IS-groups. Two genetic loci in the ribosomal DNA repeat and RFLPs in total genomic DNA were examined. Intraspecific divergence was found in the DNA sequence of PCR amplified internal transcribed spacer region (ITS) in ribosomal RNA repeat unit. It was found that various mutation detection techniques such as RFLP, single strand DNA conformation polymorphism (SSCP), heteroduplex DNA polymorphism and amplification refractory mutation system (ARMS) were applicable for the detection of base variations in the ITS region and therefore for the identification of IS-groups. However, since European S and F strains are genetically closely related to each other, these two were not unequivocally distinguishable. Intergenic spacer region (IGS) in the rRNA repeat unit in H. annosum was also amplified by PCR. The five IS-groups were distinguished by RFLP analysis of the IGS region, though there remained some European S and F group isolates which were also identical at this locus. RFLP in total genomic DNA was seen on ethidium bromide stained agarose gel after electrophoresis and found to be able to differentiate the European IS-groups unambiguously. RFLPs in total genomic DNA revealed with minisatellite probes were also found to be useful for IS-group identification.