Proefschrift--Utrecht. / "Stellingen" (1 leaf) laid in. Bibliography: p. 66-72.

Proefschrift--Utrecht. / "Stellingen" (1 leaf) laid in. Bibliography: p. 66-72.

Thesis (M.S.)--University of Wisconsin--Madison, 1963. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 92-96).

Previous taxonomic studies culminated in the current differentiation of the mitosporic fungal genera Drechslera, Curvularia, Bipolaris and Exserohilum. The circumscription of Drechslera and Exserohilum are generally accepted and supported by the association with the teleomorphic ascomycetous genera Pyrenophora and Setosphaeria respectively. The separation of Curvularia and Bipolaris, both anamorphs of Cochliobolus, has been disputed. Many highly similar species have been described that share features of more than one genus. In this study 45 strains representing 14 species of Bipolaris, Curvularia and Exserohilum were characterised with regard to spore morphology, growth characteristics in culture and host preferences. Nucleic acid-based methods were used to evaluate the status of current morphological species. Integration of all this information represents a new approach to the taxonomy of this group. A list of Bipolaris, Curvularia and Exserohilum species known to occur in South Africa is provided and confrrmed their host relations presently known from the literature and includes eight new records. The stability of various spore dimensions and physiological reactions of cultures was analysed by using First Order Inductive Logic (FOIL) and a Decision Tree (DT) algorithms. Both tools proved spore shape to be more consistent than dimensions, and that colony diameter on days three to five, provided measurements with the best diagnostic value. Colony growth rates can be diagnostic within the long-spored species (fusoid to cylindrical spores) but not between the short-spored (clavate to navicular spores) species of the Bipolaris-complex. Differences in colony diameters from five of 25 culture-based tests enabled FOIL to differentiate between species with 79% certainty. Partial sequencing of the 28S rRNA encoding gene differentiated between Exserohilum species and a second group including Bipolaris and Curvularia species. The molecular marker type, Inter-simple sequence repeats (ISSR) using four anchored primers DBD-(AC)7, BDB-(CAC) 5, DHB-(CGA) 5 and VHV -(GT) 7G, were used with the similarity coefficients of Dice and Pearson and the clustering method of Ward to reveal various levels of intra-specific variability. ISSR data indicated greater similarity between Cochliobolus anamorph species with three to four septate conidia than the species with multiseptated conidia. All short-spored species investigated are plurivorous while the long-spored species seem to have a definite graminicolous host preference. Based on these observations it is proposed that the genera Curvularia and Bipolaris be retained as distinct taxa but amended: plurivorous mitosporic Cochliobolus species with short, clavate or navicular spores should be assigned to Curvularia and mitosporic Cochliobolus species with fusoid to cylindrical spores with gramicolous host preferences should be assigned to Bipolaris. The study confrrmed Exserohilum to be a well-defmed genus. Exserohilum inaequale was found to be synonymous with C. cymbopogonis. Two species, separated only on spore length, E. longirostratum and E. rostratum should be retained since they are also distinct in physiology and ISSR patterns. Integration of physiological traits, spore dimensions, host relationships and ISSR fingerprint patterns can therefore enhance the taxonomy of the Bipolaris complex. / Thesis (PhD (Botany))--University of Pretoria, 2005. / Plant Science / unrestricted

In the first of two parts of the investigation, the stimulation of Armiil aria mellea (Fr.) Quél., a common root-rotting fungus, by Aureobastdium pullulans (DeBary) Arnaud was studied. A. pullulans is an ubiquitous imperfect fungus, inhabiting soil and other substrates. It was shown to produce in culture a volatile, heat stable, neutral substance which stimulated the mycelial development, rhizomorph initiation and rhizomorph elongation of A. mellea. A. pullulans is the only microorganism reported so far to stimulate the growth of A. mellea. The effect of ethanol on the growth of A. mellea was similar to the effect of a cell-free filtrate from a liquid culture of A. pullulans. The cell-free filtrate was shown by gas chromatography to contain ethanol. Ethanol supplied daily as 50 ppm in a glucose-asparagine medium resulted in a ten-fold increase in the number of rhizomorphs produced by A. mellea. The effects of 3-indolylacetic acid, ɣ-(indole-3)-n-butyric acid, the sodium salt of 2,4-dichlorophenoxyacetic acid and tryptophane on the growth of A. mellea were tested, but the stimulatory effect of A. pullulans was not reproduced by them. One rhizomorph tip of A. mellea could develop an extensive rhizomorph system in autoclaved soil if the stimulatory substance produced by A. pullulans was available. In the second part of the investigation the effect of soil moisture and the related effect of some soil-inhabiting Fungi imperfecti on the spread through soil of the root-rotting Basidiomycete Coniopnora puteana (Schum. ex Fr.) Karst.were studied. A soil moisture level of 20 - 25% saturation was satisfactory for the growth of C. puteana in non-sterile soil. At this moisture level C. puteana was able to grow out from a small alder disc inoculum in the centre of a petri dish and invade alder discs at the periphery of the dish. In wetter conditions (50% saturation and higher) it was unable to grow out into the soil. In autoclaved soil the cptimum moisture level for the growth of C. puteana was between 75% and 100% saturation. Small amounts of non-sterile soil were added to autoclaved soil at different moisture levels, with an effect on the growth of C. puteanas similar to that of completely non-sterile soil. Trichoderma viride Pers. ex Fr., a known antibiotic producer, was inoculated in autoclaved soil and produced a greater inhibition of C. puteana in the wetter treatments than in drier ones. The inhibitory effect of Acti-dione (cycloheximide), an antifungal antibiotic active in the pH range 3-5, was examined in non-sterile soil end in autoclaved soil. The same concentration of antibiotic resulted in a greater inhibition of the growth of C. puteana at the higher moisture levels than at the lower ones. / Science, Faculty of / Botany, Department of / Graduate

In view of the objects set forth in this thesis, and with analysis of the data obtained, a few points in conclusion may be taken as being reasonably true and evident. On the basis of consistently different and respectively characteristic physiologic traits it appears that Beauveria B is distinct from Beauveria A, even though they are essentially similar in morphology and pathogenicity. Whether they are distinct species, or are strains of the same species is unsettled. Physiologic characteristics popular to different species of closely related fungi may be used to supplement morphology and pathogenicity as criteria of classification and reidentification. In the limited host range studies, the Beauveria species were most cosmopolitan in parasitism. The Entomophthora species were largely uninfective for the insects used and under the conditions obtained, possibly having been in culture so long as to loose virulence. Endosclerotium was highly specific for a single host, the mealy bug. In this study of entomogenous fungi, embracing membrane of several representative groups, it does not appear that they can be characterized as a group apart from other fungi on the basis of physiology. They grow saphrophytically on a wide range of some 50 different proteins, sugars, nutrient solid media, and organic acids. In contrasting the physiological characteristics of the slow growing E. saphaerosperma with the other two species of Entomophthora, it can be stated that consistently different physiologic results were correlated with the distinctly different morphology. Further, the near identical physiological behavior by E. apiculata and E. saphaerosperma, paralleled with essentially similar morphology, may prove that these two are one and the same species. In the case of Endosclerotium, it may be observed that slow growth and cultural inflexibility seem to be correlated with extreme host specificity. The liquefaction of gelatin and the peptinization of proteins indicate that the Entomophthora species produce proteinase enzymes in abundance. / Master of Science