No description available.

We report here the use of RAPD-PCR (Random Amplified Polymorphic DNA - Polymerase Chain Reaction) to identify segregating loci in the haploid progeny of an Armillaria ostoyae basidiocarp and the construction of the first genetic linkage map of this fungus, one of the causal species of Armillaria Root Disease. Upon screening 75 RAPD primers, 18 were found to identify a total of 43 loci segregating with a 1 : 1 Mendelian ratio. These loci were analysed for linkage among 58 monospore progeny. The map constructed with Mapmaker (LOD = 3.0, r = 0.38) was confirmed by GMendel (LOD = 1.5, r = 0.38). This map arranged 30 loci into 6 linkage groups and 4 linkage pairs. Thirteen markers remained unlinked. Using the Kosambi mapping function the linked loci accounted for approximately 450 cM and the genome was estimated to be 1600 cM. This preliminary map covers approximately 28% of the A. ostoyae genome.

No description available.

Quantitative trait loci (QTL) analysis for Sclerotinia stem rot resistance was carried out in five doubled haploid (DH) populations of Brassica napus. Sclerotinia stem rot is caused by the necrotrophic fungus Sclerotinia sclerotiorum (Lib.) de Bary. Sclerotinia stem rot has worldwide occurrence and causes significant yield losses in many crop species. Several screening methods have been recommended in the literature to evaluate plant resistance to Sclerotinia stem rot. Four controlled environment based screening methods: 1) excised leaf assay, 2) cotyledon assay, 3) mycelial stem inoculation technique and 4) petiole inoculation technique compared for their ability to differentiate between plant susceptibility/resistance, their reliability and suitability for large scale screening using eight B. napus cultivars/lines of varying reaction to S. sclerotiorum. The petiole inoculation technique and the mycelium stem inoculation technique were identified as reliable methods in this study. Previously developed, five B. napus DH populations (H1, H2, H3, DH179 and DH180) segregating for resistance to Sclerotinia stem rot were used in this study. The petiole inoculation technique was used to evaluate resistance to Sclerotinia stem rot. Data on days to wilting was recorded for a two week period. Twelve plants per line were screened in each evaluation and each population was evaluated three times. Two to three day-old mycelial cultures of S. sclerotiorum isolate Canada 77 was used. QTL analyses were carried out using a LOD threshold value of 2.5 on each individual replicate and on the average of all the replicates. In the H1 population, the number of QTL detected ranged from four to six in each analysis. In the H2 population, there were three to six QTL in each analysis. There were two to six QTL in each analysis of the H3 population. In the DH179 population, the number of QTL detected ranged from three to five in each analysis. In DH180 population, the number of QTL identified varied from three to six in each analysis. A number of common QTL were found between the replicates of each population. Five common QTL were identified between these populations. The markers linked to these QTL are now available for marker assisted selection.

Quantitative trait loci (QTL) analysis for Sclerotinia stem rot resistance was carried out in five doubled haploid (DH) populations of Brassica napus. Sclerotinia stem rot is caused by the necrotrophic fungus Sclerotinia sclerotiorum (Lib.) de Bary. Sclerotinia stem rot has worldwide occurrence and causes significant yield losses in many crop species. Several screening methods have been recommended in the literature to evaluate plant resistance to Sclerotinia stem rot. Four controlled environment based screening methods: 1) excised leaf assay, 2) cotyledon assay, 3) mycelial stem inoculation technique and 4) petiole inoculation technique compared for their ability to differentiate between plant susceptibility/resistance, their reliability and suitability for large scale screening using eight B. napus cultivars/lines of varying reaction to S. sclerotiorum. The petiole inoculation technique and the mycelium stem inoculation technique were identified as reliable methods in this study. Previously developed, five B. napus DH populations (H1, H2, H3, DH179 and DH180) segregating for resistance to Sclerotinia stem rot were used in this study. The petiole inoculation technique was used to evaluate resistance to Sclerotinia stem rot. Data on days to wilting was recorded for a two week period. Twelve plants per line were screened in each evaluation and each population was evaluated three times. Two to three day-old mycelial cultures of S. sclerotiorum isolate Canada 77 was used. QTL analyses were carried out using a LOD threshold value of 2.5 on each individual replicate and on the average of all the replicates. In the H1 population, the number of QTL detected ranged from four to six in each analysis. In the H2 population, there were three to six QTL in each analysis. There were two to six QTL in each analysis of the H3 population. In the DH179 population, the number of QTL detected ranged from three to five in each analysis. In DH180 population, the number of QTL identified varied from three to six in each analysis. A number of common QTL were found between the replicates of each population. Five common QTL were identified between these populations. The markers linked to these QTL are now available for marker assisted selection.

This thesis considers the nature of information management on the World Wide Web. The web has evolved into a global information system that is completely unregulated, permitting anyone to publish whatever information they wish. However, this information is almost entirely unmanaged, which, together with the enormous number of users who access it, places enormous strain on the web's architecture. This has led to the exposure of inherent flaws, which reduce its effectiveness as an information system. The thesis presents a thorough analysis of the state of this architecture, and identifies three flaws that could render the web unusable: link rot; a shrinking namespace; and the inevitable increase of noise in the system. A critical examination of existing solutions to these flaws is provided, together with a discussion on why the solutions have not been deployed or adopted. The thesis determines that they have failed to take into account the nature of the information flow between information provider and consumer, or the open philosophy of the web. The overall aim of the research has therefore been to design a new solution to these flaws in the web, based on a greater understanding of the nature of the information that flows upon it. The realization of this objective has included the development of a new model for managing information flow on the web, which is used to develop a solution to the flaws. The solution comprises three new additions to the web's architecture: a temporal referencing scheme; an Oracle Server Network for more effective web browsing; and a Resource Locator Service, which provides automatic transparent resource migration. The thesis describes their design and operation, and presents the concept of the Request Router, which provides a new way of integrating such distributed systems into the web's existing architecture without breaking it. The design of the Resource Locator Service, including the development of new protocols for resource migration, is covered in great detail, and a prototype system that has been developed to prove the effectiveness of the design is presented. The design is further validated by comprehensive performance measurements of the prototype, which show that it will scale to manage a web whose size is orders of magnitude greater than it is today.

No description available.

The fungal pathogen Sclerotinia sclerotiorum (Lib.) de Bary is capable of infecting over 400 plant species including canola (Brassica napus L.). The fungus secretes oxalic acid (OA), which plays an important role in infection and disease progression. An analysis of proteome-level changes associated with infection of susceptible canola leaves by S. sclerotiorum revealed significant changes in the abundance of 32 proteins, including proteins involved in photosynthesis and metabolism, hormone signaling, and antioxidant defense. A similar subset of 37 proteins was affected when leaves were treated with OA alone; this compound also caused a reduction in the activities of a number of antioxidant enzymes, suggesting an OA-mediated suppression of the oxidative burst. To further understand the mechanisms of pathogenesis, the role of Sssp, a predicted secreted protein from S. sclerotiorum, was targeted for analysis. Mutant strains of S. sclerotiorum were generated by disruption of the Sssp gene and characterized for virulence on canola. Based on the extent of symptom development, the virulence of the Sssp-disrupted mutants was significantly reduced relative to the wild-type, indicating that Sssp may play a role in the infection process. Finally, the development of sclerotia, long-term survival structures that serve as a primary source of inoculum for the fungus, was examined. A total of 88 proteins were found to exhibit temporal changes in abundance during sclerotium formation and maturation, including proteins involved in the regulation of melanogenesis. A total of 56 proteins were also identified in the sclerotial exudates, providing a basis for future studies. Collectively, the studies described in this dissertation represent the most comprehensive proteome-level analysis of the canola/S. sclerotiorum interaction and sclerotial development, and could contribute to the development of novel strategies for the management of S. sclerotiorum. / Plant Science

[Abstract]Crown rot, caused by Fusarium pseudograminearum (Fpg), is an important soilborne disease of wheat and barley. The degree of crop damage depends on seasonal conditions. Typically, high moisture conditions early in the season encourage seedling infection from stubble residues. Moisture stress later in the season leads to the production of unfilled “whiteheads”. Current control relies on cultural practices and sowing of partially resistant varieties. In order to understand the nature of partial resistance, I have examined the patterns of disease symptom development and pathogen spread in susceptible and partially resistant tissues of both pot-grown wheat, barley and oat seedlings and field-grown inoculated wheat trials. Further research was conducted to determine whether differences in pathogenicity occur amongst a small subset of Australian Fpg isolates. Seedling experiments confirmed that differences in disease ratings between susceptible and partially resistant genotypes are detected in younger leaf sheaths of older seedlings. At later harvest times differences between these genotypes are not significant in older leaf sheaths. Re-isolation of Fpg from inoculated seedlings has shown that each tissue was infected later in partially resistant genotypes compared to susceptible ones with a significantly lower number of isolations recorded at each harvest time in 42 day old seedlings. Barley cultivars were rapidly infected by the pathogen and exhibited high levels of disease symptoms. By comparison levels of infection in oats were low compared to all other genotypes. No significant differences between genotypes were observed in coleoptile tissues, either in fungal colonisation or development of disease symptoms. Disease development in the subcrown internode varied between lines/cultivars but was not representative of the relative susceptibility of each genotype. The pathogen did not appear to invade plant tissue via the vascular system but rather spread directly across the stem from leaf sheath to leaf sheath. Field trials were designed to study disease symptom development and localisation of Fpg hyphae in all expanded tissues (excluding head and roots) in wheat genotypes of known susceptibility to crown rot. Plants were harvested at approximately fortnightly intervals throughout the growing season. The main effects and interactions of harvest, genotype and tiller on each plant part were examined with a detailed statistical analysis of differences seen in these factors between susceptible and partially resistant wheat genotypes, in two inoculated field trials. While differences between genotypes were mostly not significant at each harvest when disease rating or isolations from leaf sheath tissues were examined, important differences between susceptible and resistant genotypes were seen in disease developments and Fpg infections of stem tissue in field trials. Restriction of pathogen growth and symptom development was more pronounced in the tissues of 2-49 (possesses seedling resistance) than in the field resistant Sunco. At present, the mechanisms that lead to these resistance responses are unknown. The pathogenicity study aimed to determine whether 7 Fpg isolates and a mixed inoculum differed in ability to cause crown rot in 9 wheat genotypes ranging in susceptibility to this disease. Although a genotype*inoculum interaction was significant, there is no evidence of stable pathogenic races in the isolates examined in these experiments. The growth of all isolates was partially inhibited in a consistent manner on resistant genotypes when compared to very susceptible genotypes. These results confirm significant differences in the aggressiveness of Fpg isolates on wheat, evidenced by variation in mean disease severity between isolates growing on a range of host genotypes.

1. Fusarium roseum �Graminearum� was the predominant fungus associated with stalk rot of maize in eastern Australia in the 1972, 1973 and 1974 growing seasons. All isolates of this pathogen were of the Group 2 type. Thus Group 2 contrasts with Group I which is normally isolated :Erora crown rot of wheat and grasses. Other fungi isolated in order of frequency were Diplodia maydis, F. rnoniliforme �Subglutinans�, Bipolaris sorokiniana, Nigrospora oryzac, F. roseum �Semitectum�, F. moniliforme, F. roseum �Equiseti�, F. roseum �Concolor�, Macrophomina phaseolina, Rhizoctonia sp., F. roseum �Acuminatum�, F. oxysporum, F. solani, F. tricinctum and F. roseum �Heterosporum�. The relative isolation frequencies of the fungi varied according to the seasonal conditions. Stalk rots were not of major importance in 1973, a relatively dry growing season. However, in 1974, a wet growing season, stalk rot diseases were common in all areas investigated. 2. Isolates of F. roseum �Graminearum�,derived mainly from wheat and maize but also from other sources and from various regions of eastern Australia, were examined for perithecia formation, colony characteristics, fertility, colony growth, conidia production and conidia size. The distribution of the fungus in field colonized maize and wheat plants was also studied. The Group 1 isolates did not produce perithecia, were heterothallic and very infertile, had a mean colony growth of 4.4 cm per 3 days (range, 3.9- 5.1) and produced relatively large numbers of conidia. In contrast, Group 2 isolates were homothallic and produced perithecia readily, had a mean colony growth of 5.4 cm per 3 days (range, 4.7�6.1) and produced relatively low numbers of conidia. Group 1 isolates were found to be commonly associated with crowns and roots of plants and Group 2 isolates were commonly associated with aerial plant parts. 3. The ability of a number of Group 1 and Group 2 isolates to produce the fungal hormone, zearalenone was assessed. Group I isolates produced three to four times more zearalenone than Group 2 isolates. In addition, a. culture which had previously produced perithecia but had lost that ability following numerous transfers, produced no detectable zearalenone. The results provided good evidence that the observed difference in perithecia formation was directly related to the ability to produce zearalenone. 4. The pathogenicity to wheat, maize and carnations of Group 1 isolates from crown rot affected wheat plants and Group 2 isolates from stalk rot affected maize plants was tested. Pathogenicity of 11 other isolates from teosinte, carnations, pearl millet, wheat and barley scab, banana, ginger and common wheat grass was also assessed. The results indicated that pathogenic specialization exists within F. roseum �Graminearum�. Wheat isolates were the most pathogenic to wheat, carnation isolates were the most pathogenic to carnations and all maize isolates were pathogenic to maize while those from wheat and common wheat grass were not as pathogenic to maize. Moreover, Group 2 isolates were more pathogenic when inoculated in aerial plant parts, and the Group I isolates were more pathogenic when inoculated in plant parts in soil. Inoculations on wheat seedlings in sterile field soil demonstrated that the inherent pathogenicity to wheat seedlings of isolates from wheat and maize were similar. 5. Some factors which could contribute to the observed pathogenic differences between isolates from wheat and maize to wheat seedlings in field soil were examined. Conidia volume, germination rate and inherent germinability in the soil were studied. The Group I isolates had the largest volume, the most rapid germination and the highest inherent germinability. Pathogenicity was positively correlated with conidium volume and inherent germinability. In addition, the inherent germinability and conidium volume were positively correlated. Thus, it was established that pathogenic behaviour of conidia of Group 1 and Group 2 reflected differences in conidia morphology.