Ustilsgo syntherismae (Schwein.) Peck, which causes loose smut of crabgrass, infects its host systemically and destroys seed production. Greenhouse experiments were carried out to investigate the mode of infection, the disease incidence that can be obtained by artificial inoculation and the conditions necessary for optimum infection, cross-infection on southern and smooth crabgrass, and the reasons for the late observance of the disease. U. syntherismse infected southern crabgrass, Digitaria ciliaris (Retz.) Koeler, by both seed-borne and soil-borne teliospore inoculum. Disease incidence was high (84-91%) in some treatments. Higher rates of teliospore application resulted in larger percentages of smutted plants. When infesting the potting mixture, the highest percentages of smutted plants were obtained when infestation and planting were done at the same time. Earlier or later planting resulted in fewer smutted plants. When planting at various depths, greater numbers of smutted plants were obtained when inoculated seed were planted 0.5 to 1.0 cm below the surface versus planting on the surface or at greater depths. The appearance of 50% of infected plants' first panicles (in greenhouse experiments) was delayed by 4.5 weeks compared to the emergence (50%) of first panicles from healthy plants. In cross inoculation experiments, southern and smooth crabgrass plants developed smut only when inoculated with spores collected from large and smooth crabgrass~ respectively. / Master of Science

Call number: LD2668 .T4 1948 S34 / Master of Science

No description available.

No description available.

A comparative light and electron microscope technique has been used to study the cytological changes accompanying teliospore (i.e. probasidium) germination in Ustilago hordei (Pers.) Lagerh. Special emphasis has been placed on determining the ultrastructural events involved in karyokinesls, especially meiosis, and cytokinesis. The thesis is divided into five parts, of which the first is concerned with pre-germinal differentiation. The great increase in microanatomical complexity which occurs during the pre-germinal stages is due largely to an increase in the amount of endoplasmic reticulum (ER) and to the formation of "primary hydration vacuoles." Evidently the nuclear envelope gives rise to the new ER which in turn dilates to form the vacuoles. This is accompanied by an increase in mitochondrial size and the development of patches of patches of "flocculent cytoplasm." Part II concerns the initiation and subsequent extension of the metabasidium (i.e. promycelium). Initiation involves the localized degradation of the inner spore wall, and deposition of new wall material. The ER and spherosome-like bodies seem to be associated with these activities. Once spore wall rupture has occurred the structural basis of promycelial extension is unknown but changes in the number, size, and distribution of the spherosome-like organelles appear to have profound effects on the differentiation of the organism. Septation, knee-joint formation, and budding are discussed in part III. Elaborate membrane complexes are associated with cross wall initiation. A membranous plate is completed across the cell before septal wall thickening begins. The initiation of sporidia (i.e. basidiospores) involves a localized plasti-cization of the promyoelial wall followed by degradation of the old wall and subsequent synthesis of new wall material. Bridge-formation results when two adjacent cells give rise to bud-like processes which grow together and subsequently fuse to produce a protoplasmic bridge. The structure and activities of the metabasidial nuclei and their associated structures are discussed in part IV, Both meiosis and mitosis are unusual in that the two chromatin bodies apparently remain attached to the centriolar-kinetochore-equivalent and at least one of the chromatin bodies in attached to the nucleolus throughout the division cycle. The results are compatible with Brown and Stack's (1971) model for somatic nuclear division in some fungi. Membrane complexes, resembling those which Initiate septa, form in association with prophase nuclei and maintain a specific relation with the nucleus throughout division. In part V the suggestion is made that these complexes form part of a mechanism controlling the positional relationships of nuclear and cell divisions in the promycelium. / Science, Faculty of / Botany, Department of / Graduate

Call number: LD2668 .T4 1963 H32 / Master of Science

<p>Fungi display diverse growth forms. Some grow as unicellular yeasts, some grow as multicellular hyphae, while others switch between these two growth forms, i.e., the dimorphic fungi. Dimorphism is found in many pathogenic fungi, and it is thought to be a strategy to maximize their fitness during different stages of life cycles. The corn smut fungus <i>Ustilago maydis</i> serves as a renowned model organism for studying fungal dimorphism and its role in pathogenesis. However, knowledge only from the model species may not be expanded to other species unless multispecies studies have been demonstrated. In this dissertation, I performed comparative analyses to examine if knowledge from <i>U. maydis</i> is translational to other dimorphic fungi. First, a physiological study was conducted to find what can serve as a common signal for dimorphic transition of several Ustilaginomycotina species. I found that the lipid serves as a potential common cue for yeast-to-hyphal transition in most dimorphic species, while alternate types of energy-source carbohydrate do not affect fungal dimorphism. In addition, pectin and high temperature can also trigger filamentous growth in some Ustilaginomycotina species. Second, I performed comparative transcriptomics to determine if a mechanism for yeast-to-hyphal dimorphic transition is conserved across multiple dimorphic species. Three species of Ustilaginomycotina (<i>U. maydis</i>, <i>Tilletiopsis washingtonensis </i>and <i>Meira miltonrushii</i>) plus one species from Ascomycota (<i>Ophiostoma novo-ulmi</i>) were included in the analyses. I found that the similarity of transcriptomic alteration is not dependent on phylogenetic relatedness. Genes in amino acid transport and metabolism, energy production and conversion and cytoskeleton are commonly altered during the dimorphic transition of all studied species. Moreover, I discovered several core genes which can play a conserved role in transducing signals for the dimorphic transition. Finally, I performed comparative analyses of 190 fungal genomes to determine genomic properties that are associated with types of fungal growth form. I found that small genome size is a characteristic for yeast-like fungi. Few indicator genes, such as genes encoding proteins in the NADPH oxidase complex and cytoskeletons, which are predominantly lost in yeast-like fungi in both Ascomycota and Basidiomycota. However, many other genes are associated with types of growth form in a lineage-specific manner. Findings from this dissertation will serve as fundamentals for future research in fungal cell biology, especially in fungal dimorphism. Additionally, results from this study suggest cautions when extrapolating results from model species onto non-model species.</p>

Thesis (MSc)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Only a limited number of systems involving anther-smut fungi have been studied, usually due to the economic significance of their crop plant hosts. A smut fungus of the genus Thecaphora has been discovered infecting Oxalis hosts in South Africa. This pathogenic fungus, Thecaphora capensis, produces dark-coloured spores in the anthers of host flowers, rendering it an anther-smut fungus. The host genus is the seventh largest plant genus in the Cape Floristic Region (CFR) and the largest geophytic genus of this region. Nine Oxalis species that host T. capensis have been identified across a wide distribution in the CFR of South Africa. A preliminary assessment of T. capensis infections of Oxalis was conducted in 2009, which provided a foundation for further research into the ecological and evolutionary consequences of hosting this fungus. In this study, a comprehensive host diversity assessment was conducted to determine the extent of infected Oxalis individuals within the CFR. Three new Oxalis host species for Thecaphora capensis were discovered. This brings the total number of known hosts to twelve. The morphological and reproductive effects of the fungus were assessed on two host species (O. incarnata and O. lanata) by comparing healthy and infected individuals of these species. Infection by Thecaphora capensis had a significantly negative effect on both of these factors. Host resources appear to be co-opted for fungal spore production, since floral morphological characters of infected individuals were reduced in size. Furthermore, infection by T. capensis ensured near-universal sterility in both hosts. Differences in floral characters and pollinator preferences for healthy Oxalis incarnata and O. lanata individuals from disease-free and diseased populations were compared to determine the evolutionary influence of Thecaphora capensis infections. It was shown that this pathogen can have a significant evolutionary influence on its hosts, showing its ability to shape flower size and pollinator activity in O. lanata, but not in O. incarnata. A need has therefore been identified to assess these evolutionary forces independently for each host and its pathogen before making erroneous assumptions for conservation practices. Plant pollinators play an integral role in plant fitness. Pollinator movements within a population are important when between-flower spore transfer by pollinators increases the likelihood of new infections. Pollinator movements may be influenced by host density and the frequency of diseased individuals, amongst other factors. Pollinators were found to mediate Thecaphora capensis spore transfers within diseased Oxalis populations. Host density and disease frequency affected the number of spores transferred under field and standardized conditions. More research is required to investigate confounding factors in these complex systems. This study highlighted the complexities of a fungal-plant-insect relationship, the evolutionary consequences of such fungal infections and the various factors influencing the likelihood of new infections. This research adds to the limited body of knowledge on multi-organismal interactions in the CFR and provides a base for more detailed future studies on this intriguing system. / AFRIKAANSE OPSOMMING: 'n Brandswam, wat deel is van die Thecaphora genus,is ontdek in 'n Oxalis blom waar dit die gasheer plant se blom gebruik om spore in te produseer. Die swam, Thecaphora capensis, produseer donker gekleurde spore in die helmknoppe van die blomme van gasheer plante, daarom word dit geklasifiseer as 'n brandswam van die helmknop. Die gasheer plante van die swam is deel van die genus Oxalis, die sewende grootste plant genus in die Kaapse Floristiese Streek (KFS) en die grootste geofitiese genus in die streek. Nege Oxalis species is al klaar identifiseer as gasheer plante van T. capensis. Hulle is versprei oor 'n groot area van die KFS van Suid Afrika. 'n Primêre ondersoek van T. capensis infeksies op Oxalis is in 2009 onderneem. Hierdie ondersoek het gelei tot meer vrae oor die sisteem en het 'n goeie fondasie geskep vir verdere navorsing rakende die ekologiese koste verbonde daaraan om as gasheer plant vir 'n swam op te tree. 'n Deeglike ondersoek is in die KFS aangepak om die Oxalis gasheer plante van die brand swam te identifiseer en om voort te bou op die basiskennis wat in die primêre ondersoek daargestel is. Drie nuwe Oxalis gasheer plante van Thecaphora capensis is ontdek. Die totale aantal gasheer plante staan nou op twaalf. Gesonde en geinfekteerde individuele gasheer plante is gebruik om die morfologiese en reproduktiewe effekte van die swam te toets in twee Oxalis spesies (O. incarnata en O. lanata). Die negatiewe gevolge om 'n gasheer plant van die brand swam te wees was duidelik toe gesonde en geinfekteerde individuele met mekaar vergelyk is. Dit kom voor asof gasheer plante se hulpbronne vir spoor produksie gebruik word, want hulle is morfologies kleiner en meestal steriel. Die evolusionêre effek van Thecaphora capensis op 'n populasie is getoets met gesonde individuele in populasies van twee Oxalis spesies. Blomkenmerke en insek bestuiwers van gesonde individue in gesonde en geinfekteerde populasies is ondersoek om die effekte van T. capensis op populasies te toets. Daar is suksesvol gedemonstreer dat swamme sterk evolusionêre kragte uitoefen, en die vermoë het om plantpopulasies te vorm en te verander, ofskoon nie in alle gevalle ewe sterk nie. Daarom is dit belangrik om die evolusionêre kragte vir elke gasheer plant en sy patogeen onafhanklik te assesseer, sonder om algemene aannames te maak in bewaringspraktyke. Plantbestuiwers speel 'n belangrike rol in die fiksheid van plante. Hulle kan hul fiksheid verbeter deur bestuiwers te lok met blomme en deur aspekte geassosieer met blomme. Die bewegingspatrone van plantbestuiwers is baie belangrik indien hulle helmknop-geproduseerde spore van brandswamme vervoer instede van stuifmeel, want dit vergroot die kanse vir nuwe infeksies. Die bewegingspatrone van plantbestuiwers word, onder andere, beinvloed deur die digtheid en frekwensie van geinfekteerde individue. Plantbestuiwers speel 'n belangrike rol in die vervoer van Thecaphora capensis spore in geinfekteerde Oxalis populasies. Die digtheid en frekwensie van geinfekteerde blomme het die vervoer van spore geaffekteer onder veld en gestandardiseerde kondisies, alhoewel baie veranderlikes so 'n komplekse natuurlike sisteem beinvloed. Hierdie studie beklemtoon die kompleksiteit van 'n fungus-plant-insek verhouding, die gevolge van so 'n interaksie en die verskeie faktore wat die waarskynlikheid van nuwe infeksies beinvloed. Tot dusver is daar 'n beperkte aantal sisteme soos hierdie bestudeer waarin 'n brandswam van die helmknop betrokke is, en die enkele beskikbare studies is onderneem meestal as gevolg van hulle ekonomiese effekte op landboukundig belangrike gasheer plante. Hierdie studie verteenwoordig 'n belangrike byvoeging tot die inter-organismiese studies in die KFS. 'n Holistiese ekologiese oorsig soos hierdie verskaf 'n belangrike basis vir toekomstige studies en bewarings- en bestuurspraktyke.