The fungus Ophiostoma fimbriatum (E & H) Nann, though exceptionally rare in northern climates, is fairly widespread in tropical and sub-tropical areas of the world causing diseases on many species of plants. The disease producing capabilities of the fungus have become a major economic problem in the growth and storage of sweet potatoes (Ipomoea batatas (L.) Lam) in the southern parts of the United States. The organism is interesting from the point of view that it produces, very readily on sweet potato dextrose agar, two types of asexual or vegetative spores and the perfect stage with the perithecia containing ascospores. Several strains of the fungi have been isolated from natural habitats. This work deals, in general, with a study of the gross morphology of this ascomycete and some observations on the nuclear apparatus of the resting and germinating conidia. More specifically, this study treats with certain factors in nutrition which affect the physiology in such a way that the growth and sporulation characteristics of the organism are altered. Since several strains of 0. fimbriatum have been isolated naturally it is thought that these must have been derived from mutant changes occurring in an original "wild" form which was propagated to more susceptible varietal hosts. As a result, studies are undertaken in an attempt to induce changes in an original culture by adopting artificial mutagenic methods. A pathogenicity experiment is done on sweet potato blocks in the laboratory to ascertain the relative degree of virulence between the new-formed strains. This work shows that the cultural characteristics and reproductive behaviour of this fungus could be modified by specific variations in the culture medium. It is shown among other things, that copper, in the role of a micro-nutrient, plays a definite part in the manifestation of sexuality and in the development of pigmentation in the organism. "Mutations" are produced by using X-irridiation and ultra-violet rays as inductive agents. Many of the new-formed "mutants" are unstable and back mutation to the original "wild" type is common. / Science, Faculty of / Botany, Department of / Graduate

Rust fungi belonging to the order Uredinales have usually been considered the classical examples of obligate parasites amongst plant pathogenic fungi. The development of our knowledge of the metabolism, nutrition and physiology of the rust fungi has been restricted because of our inability to grow these fungi in axenic culture. In the past the physiological and biochemical investigations on rust fungi perse have been limited to studies of the germination and development of germ tubes. The cultivation invitro of Puccinia graminis tritici (Erikss . and .Henri.), Australian race ANZ 126-6,7, by Williams et al. (1966, 1967), together with the report of Turel (1969) on the axenic culture of Melampsora lini (Ehrenb) Lev, race 3 promoted research on culturing rust fungi on artificial medium. An artificial medium containing 3% glucose, Czapek's Mineral salts, 0.1% Evan's peptone, plus defatted BSA supported growth and sporulation of Puccinia graminis tritici race ANZ 126-6,7. Typical pigmented uredospores and teliospores were formed after 6-3 weeks growth. The uredospores were capable of infecting the mesophyll of wheat leaves exposed by stripping back the lower epidermis. Scanning electron microscopy revealed the presence of a coating of unknown chemical composition around the uredospores developed in vitro and not observed on uredospores grown on wheat leaves. Two different strains of Melampsoralini (Ehrenb) Lev were grown on solid media containing 4% sucrose, modified Knop's tissue culture macro nutrients, Berthelot's micro nutrients, yeast extract and peptone. The mycelium was generally binucleate. Spore-like structures were recorded in the stroma which resembled uredospores and teliospores . Addition of 1% defatted BSA to the medium described above greatly increased the frequency of establishment off lax rust colonies. A defined liquid medium, containing Czapek's minerals y Ca++, glucose, as particacid, glutathione and cysteine, and inoculated with uncontaminated uredospores, supported good vegetative growth and sporulation of wheat stem rust (Puccini agraminis f. sp. tritici race ANZ 1 2 6 - 6 , 7). Of six North American races of wheat stem rust fungus tested, only three grew vegetatively on artificial medium. Finally a chemically defined liquid medium containing sucrose , Knop's mineral salts, micro nutrients, aspartic (or glutamic) acid and cysteine supported the growth of vegetative colonies of Melampsora lini race 3 from uncontaminated uredospores in a highly reproducible manner. The formation of uredospores and telio spores of these colonies in the liquid medium was controlled by the level of Ca++ (as Ca(NO₃)₂) and the number of colonies per flask. With 60-70 colonies per flask, uredospore formation occurred on 60 to 70% of the colonies at a Ca++ level 8. 5 mM. A decrease in the Ca++ level to 4.5 mM or colony frequency to 10 per flask resulted in only in frequent sporulation vitro infected in tactcotyledons result with flax rust represents ability to control the growth of parasite in axenic culture. The uredospores produced in a normal manner. This a substantial advance in our this important obligate parasite in axenic culture. / Land and Food Systems, Faculty of / Graduate

Arbuscular mycorrhizal fungi (AMF) are ancient organisms that form symbioses with more than 80% of land plants. Fossil evidence of this partnership dates back 460Ma, when land was first colonized by plants. The mutualistic relationship between host roots and the fungus consists of an exchange of essential nutrients for the proliferation of both organisms, highlighting the importance of the mycorrhizal symbiosis. Despite their extreme longevity, a lack of evidence supporting sexual reproduction has labelled AMF as asexual organisms. However, recent evidence seems to point towards the potential of a cryptic sexuality. Specifically, AMF genomes encode for homologues of proteins that have a role in sexual processes in other fungi, including several typically involved in partner recognition, such as mating-type high mobility group (MATA-HMG) proteins found in mating-type loci. In my thesis, I expanded our analyses to five isolates of the AMF model organism Rhizophagus irregularis, through the acquisition of novel genome data. Some key findings consist of an expansion of MATA-HMG proteins, their unique organizations throughout the genome and the presence of a conserved fungal pheromone pathway. In retrospect, this research uncovers an unprecedented number of AMF genes that are homologues to sex-related genes of other fungi and reveals for the first time their atypical genomic architecture, providing valuable information towards the identification of a cryptic sexuality in these ecologically and economically important organisms.

No description available.

No description available.

No description available.

Phytophthora parasitica, P. citrophthora, and other plant pathogenic fungi were isolated from re-cycled water used to irrigate citrus and other crops. The several propogules of P. parasitica were then studied to determine their survival capabilities in soil and irrigation water. Chlamydospores of P. parasitica were present in field soils from foot-rot infested citrus groves and persisted for at least 60 days in air-dried or moist soils. They germinated in irrigation water or moist soil and formed sporangia within 16 hr. Sporangia were also present in these field soils and survived for at least 60 days in moist soil. They germinated, releasing zoospores into irrigation water 5 min after being inundated. Zoospores were not present in water flooded on air-dried field soil until after 20 hr incubation. Citrus leaves became infected by zoospores within 15 min when placed in zoospore infested water. Although they remained motile in irrigation water for up to 20 hr at 20 C, zoospores encysted when agitated or upon the addition of nutrients, orange peel, or citrus leaves. At low nutrient levels (< 5 mg glucose/liter of sterile distilled water) zoospores germinated and upon cessation of growth the protoplasm contracted within the hyphae and pseudo-septa were formed. Empty cysts or hyphae often lysed; remaining hyphal fragments containing protoplasm survived for at least 40 days at 25 C in untreated waste water and resumed growth upon addition of nutrients. At higher nutrient levels (10-1,000 mg glucose/liter of sterile distilled water) the hyphal tips often produced appressorium-like structures when in contact with the container surface. Exudates from orange peel or citrus leaves stimulated similar activity. The appressorium-like structures usually germinated to produce microsporangia when the nutrients were replaced with untreated irrigation waste water. Some microsporangia persisted in untreated waste water at 25 C for 60 days but most germinated sooner, producing only a single zoospore. Mycelial inoculum from these zoospores was pathogenic to roots of citrus seedlings. Results indicate that P. parasitica is spread by re-cycled irrigation water and that zoospores, or structures produced by them, can play a significant role as survival or dispersal units in re-cycled water.

M. Tech.

Thesis (Ph. D.)--University of Queensland, 2002. / Includes bibliographical references.

Ganoderma lucidum and G. tsugae are two members of the G. lucidum complex. The authenticity of the two wood-rotting species was demonstrated by comparative studies. Ganoderma lucidum is restricted to hardwoods. Its "smooth" walled basidiospores were characterized by narrow, numerous inter-wall pillars. Isolates of G. lucidum produced chlamydospores in culture and had an average growth of 7.8 mm/da at their optimum temperature range of 30-34 C. Ganoderma tsugae is restricted to conifers. Its basidiospores were "rough" walled and had broad inter-wall pillars. Isolates of G. tsugae did not produce chlamydospores in culture and had an average growth of 2.1 mm/da at the optimum temperature range of 20-25 C. Mating systems were determined for both species as heterothallic and tetrapolar. Interspecific matings of homokaryons were incompatible. Homokaryons of a European G. resinaceum isolate were interfertile with homokaryons from North American collections of G. lucidum. The ability of G. lucidum and G. tsugae to decay wood in vitro was studied using the following woods in agar block decay chambers: grape, oak, mesquite, white fir, and Douglas-fir. Grape wood lost the most weight while mesquite the least. G. lucidum isolates generally caused greater weight loss of all woods than did G. tsugae isolates. Both Ganoderma species caused simultaneous decay in all woods. However, chemical analyses of the decayed blocks indicated that selective delignification by both species also occurred in grape and white fir blocks but not in oak or Douglas-fir blocks. Scanning electron microscopy demonstrated various stages of selective delignification and simultaneous decay of all woods tested. Isolates of Ganoderma lucidum infected Dog Ridge variety grape plants, grown in the greenhouse, from below-ground wood block inoculations. Twenty-four plants were inoculated: one plant died and 4 other plants declined. After 24 months reisolations yielded only G. lucidum from the five declining plants, demonstrating pathogenicity. The fungus developed in the heartwood and, in later stages, invaded the sapwood. Infected plants developed water stress symptoms with leaves wilting, yellowing, and dying. Field grape plants inoculated with the fungus developed decay columns as large as 42 cm in 17 mons. Decay was limited to the heartwood; no foliar symptoms occurred.