http://hdl.handle.net/2440/14759 2013-04-30T04:23:55Z http://hdl.handle.net/2440/77182 Title: Epidemiology and management of ascochyta blight of field pea (Pisum sativum) in South Australia. Author: Davidson, Jennifer Anne Abstract: Ascochyta blight disease (synonym: blackspot) of field pea has worldwide distribution and regularly causes AUD$25 million loss per annum in Australian field pea (Pisum sativum) crops. This study provides new information on the causal pathogens and management strategies to reduce loss from this disease. Research involving sowing dates, genotypes and fungicide treatments was conducted to identify optimal management strategies. Earlier sowing generally resulted in higher yield except when ascochyta blight was severe. Yield response to fungicide application varied with disease severity, sowing date and genotype. The optimum sowing period was within a week of the first autumn rains in low rainfall regions and 3 weeks after the first autumn rains in medium and medium - high rainfall regions. Earlier flowering genotypes were the highest yielding particularly when sown early and subjected to strategic fungicide applications. The pathogen, Phoma koolunga, was recognised for the first time as a component of the ascochyta blight disease complex in southern Australia. The species was described morphologically. Sequences of the internal transcribed spacer region were distinct from those of the accepted causal pathogens of ascochyta blight of field pea viz. Didymella pinodes, Phoma medicaginis var. pinodella and Ascochyta pisi. Symptoms on field pea seedlings caused by P. koolunga were indistinguishable from those caused by D. pinodes, other than a 24 h delay in manifestation of symptoms. P. koolunga was detected across field pea cropping soils in South Australia but rarely from other Australian states while D. pinodes plus P. medicaginis var. pinodella were widespread. The quantity of DNA of these pathogens detected in soils was positively correlated with ascochyta blight lesions in a pot bioassay. Soil-borne inoculum gradually decreased in the 3 years following a field pea crop. DNA tests and pathogen isolation from naturally infected field pea plants showed P. koolunga to be an important component of the disease complex in South Australia. P. koolunga and D. pinodes were equally responsible for disease symptoms, while P. medicaginis var. pinodella had a minor role in the disease complex. Interaction between D. pinodes, P. medicaginis var. pinodella and P. koolunga was investigated in controlled conditions. Colony diameter of the former was reduced on potato dextrose agar (PDA) amended with filtrate from broth cultures of P. koolunga, as was colony diameter of D. pinodes on PDA amended with filtrate from P. medicaginis var. pinodella or D. pinodes. This effect was shown to be fungistatic rather than fungicidal. When coinoculated onto leaves on field pea plants, or onto excised leaf discs, either the quantity of DNA of D. pinodes and of P. medicaginis var. pinodella, or the mean lesion diameter of these pathogens, was significantly reduced when co-inoculated with P. koolunga. P. koolunga was not influenced by co-inoculation. D. pinodes demonstrated self-antagonism. D. pinodes is considered the principal pathogen of concern in this complex. This study further investigated the relationship between ascospore numbers of D. pinodes at sowing and disease at the end of the season. Ascospores released from stubble infested with ascochyta blight were counted periodically in a wind tunnel. A model was developed to predict disease severity in relation to ascospore numbers, distance from infested field pea stubble, and rainfall. The model was validated with an independent dataset. A threshold level of ascospores of D. pinodes was identified above which disease did not increase. The findings from this study have been incorporated into management recommendations for field pea in southern Australia. Growers are encouraged to manipulate sowing dates according to the temporal release of ascospores, and select a cultivar that has the best agronomic yield potential for the sowing date, and to use fungicide strategically. The recommendation also emphasises field selection based on commercial testing for the presence of soil-borne inoculum of D. pinodes, P. medicaginis var. pinodella and P. koolunga. 2011-12-31T13:30:00Z http://hdl.handle.net/2440/77097 Title: Cellular and molecular mechanisms involved in the repair of the injured growth plate in young rats. Author: Macsai, Carmen Elizabeth Abstract: The growth plate cartilage, which is located at the ends of children’s long bones, is responsible for longitudinal growth of the skeleton. However, due to its cartilaginous composition and its location, the growth plate is commonly injured, mostly through fractures. An undesirable outcome to growth plate fracture is the bony repair of the injured cartilage at the fractured area. Consequently, children often incur skeletal angular deformities and growth arrest. Current corrective surgical treatments for these outcomes are highly invasive, and therapeutic interventions are not possible as little is known about the mechanisms and pathways that lead to bone bridge formation. Using a rat model, previous studies have shown sequential inflammatory, fibrogenic, osteogenic and bone maturation responses involved in the bony repair of the injured growth plate. However, structural changes in the growth plate, at both the injury site and at the non-injured area, have not been closely examined previously, and little is known about the molecular mechanisms underlying the bony repair. Therefore, this PhD study, using a rat tibial growth plate injury model, aimed to examine the effects of growth plate injury on the structure and composition of the injured growth plate in a longitudinal study using micro-CT and histology. Microarray analysis of the injury site only, collected using laser capture microdissection was used to identify potential cellular and molecular mechanisms involved in bone bridge formation. In addition, Real Time RT-PCR on adjacent uninjured growth plate was used to examine potential cellular/molecular changes at the uninjured area and on whole growth plate scrapes to examine the potential involvement of Wnt signalling in bone bridge formation. Micro-CT analysis revealed a significant increase in bone material within the injury site (when compared to normal) at 14 and 60 days post-injury, where 12% and 40% of the injury site was replaced by bone, respectively. Interestingly, although there were no changes in growth plate thickness between injured and normal rats at either day 14 or 60, at day 60, many small bone tethers formed at the adjacent growth plate outside the injury site but none were found in normal aged-matched control rats. Histological studies revealed dereased proliferation but increased apoptosis of chondrocytes at the adjacent growth plate cartilage, and RT-PCR analysis revealed differential expression of apoptosis-regulatory genes Bcl-2 and FasL (compared to normal), confirming the increase in apoptosis in the adjacent uninjured growth plate. Down-regulation of Sox-9 and IGF-1 on days 7 and 14 suggests that growth plate injury may slow down the rate of longitudinal growth by decreasing chondrocyte proliferation and/or differentiaiton soon after injury. Lastly, bone matrix protein osteocalcin was increased on day 60, suggesting degeneration and bone formation at the adjacent uninjured area. Microarray analysis identified changes in several key BMP and Wnt signalling components across the time-course of bone bridge formation, including BMP-2, BMP-6, BMP-7, chordin, chordin-like 2, and Id-1, and β-catenin, Csnk2a1, SFRP-1 and SFRP-4, respectively, in early stages of bone bridge formation (day 4 and day 8). Osteocalcin expression was also prominent at day 8, supportive of osteoblast development and bone formation. During later stages (day 14), active bone formation and remodelling was prominent and was largely regulated by the BMP signalling pathway (increased BMP-1 and BMP-6 but decreased inhibitor chordin), as well as by Traf6, Fgfr1, osteopontin, Mmp9 and Wnt signalling, where several genes were up and down-regulated. Expression levels of Wnt signalling inhibitors (SFRP-1, SFRP-4 and Wisp1) were increased at days 8 and 14 and may be negatively regulating bone formation during the osteogenic phases of the repair of the growth plate injury site. Findings were also suggestive of an overall increase in the canonical Wnt signalling pathway at days 4 and14, supported by increased expression of β-catenin and drecreased expression of Wnt inhibitors, and decreased expression of Fzd1 and Fzd2 and increased Lef1 expression, respectively. Overall, this study found a complex balance between the canonical and non-canonical Wnt pathways as well as an association with BMP signalling over the time-course of bone bridge formation. Lastly, Real-Time PCR on Wnt signalling components revealed significant changes in gene expression of Wnt genes, receptors and inhibitors, but were inconclusive as the method of tissue isolation was not specific enough to represent true changes in gene expression. 2011-12-31T13:30:00Z http://hdl.handle.net/2440/77096 Title: Buyer and seller relationships in Malaysia’s dairy industry. Author: Boniface, Bonaventure Abstract: This thesis examines buyer and seller relationships between dairy producers and milk buyers in Malaysia. The study investigates the determinants of long-term relationships. While relationship marketing has received considerable attention in many other industry sectors, few studies have addressed the food industry. The existing agri-food studies emphasize long-term relationships, investigating variables such as trust, relationship quality and guanxi networks. This thesis addresses how buyers and sellers interact and what influences them to engage in longer-term relationships to improve their business performance. The specific research objectives are to investigate: (i) the determinants of relationship quality and its influence towards long-term relationships; (ii) the determinants of trust and its influence towards supplier loyalty; (iii) the influence of price satisfaction dimensions towards loyalty and business performance; (iv) segmentation of producer perceptions of the relationships; and (v) consumers’ preferences and consumption of dairy products. The study develops and tests a long-term relationship measure of loyalty and relationship commitment. The thesis identifies commitment and loyalty as the essential measures of long-term relationships. Data was collected from 133 dairy producers through face-to-face interviews in Malaysia in June and July 2009. The random sample of producers came from the Department of Veterinary Services database. The data are representative of dairy farm operations throughout Malaysia, providing representative examples of the marketing channels, contracting methods and memorandum of understanding used between producers and buyers. The various scales of operation in Malaysia are also represented. 2011-12-31T13:30:00Z http://hdl.handle.net/2440/77095 Title: Transcription factors important in the regulation of salinity tolerance. Author: Dow, Michael James Sandland Abstract: Salt tolerant plants are able to survive in saline soils by the virtue of an array of channels and pumps that minimise sodium entry into roots and loading into the xylem, as well as the sequestration of sodium in the vacuole of the cells of both root and shoot. Regulation of genes involved in conferring salt tolerance is thought to occur via a network of transcription factors. In this project, the aim is to identify transcription factors that are important in regulating genes involved in salinity tolerance. Affymetrix Rice 57K GeneChip data from a previous project were used to analyse gene expression with and without salt stress in the shoots and roots of the salt sensitive Oryza sativa cultivar IR29 and the salt tolerant cultivars FL478, IR63731 and Pokkali. Transcription factors showing differential expression between the salt sensitive and salt tolerant cultivars were identified and confirmed by qRT-PCR. Six transcription factors with confirmed expression patterns were selected and transgenic rice plants were generated either constitutively or salt inducibly over-expressing each of the transcription factor coding sequences. Plants were also made expressing artificial microRNAs designed to reduce levels of transcripts of each transcription factor. The altered expression of five transcription factors, OsOrphan19, OsEREB67, OsbHLH17, OsLUX and OsMYB54 affected plant salinity tolerance, as evidenced by changes in Na⁺ and K⁺ accumulation and plant fresh weight. These five transcription factors show significant homology to other previously known stress responsive genes thus suggesting their involvement in plant stress responses. Further experiments such as chromatin immunoprecipitation sequencing and RNA-sequencing of transgenic plants need to be performed to identify the target promoters and downstream genes, respectively, to determine the precise role of these transcription factors in plant responses to salt stress. 2011-12-31T13:30:00Z