Barley yellow dwarf virus (BYDV), an aphid transmitted luteovirus, is the most widespread and economically damaging virus of cereal crops. The work in this thesis aims to characterise the basis of the naturally occurring resistance to BYDV in cereals in three ways: Firstly, by facilitating the isolation of the Yd2 gene for BYDV resistance from barley by a map-based approach. Secondly, by determining if a BYDV resistance gene in rice is orthologous to Yd2. Thirdly, by establishing if other BYDV resistance genes in non- Ethiopian barleys are allelic to Yd2. It is hoped that the information generated in this study will ultimately assist in the production of BYDV resistant cereal cultivars. A detailed genetic map of the Yd2 region of barley chromosome 3 was constructed, containing 19 RFLP loci, the centromere and the Yd2 gene. Yd2 mapped on the long arm, 0.5 cM from the centromere, and in the mapping population of 106 F2 individuals, perfectly cosegregated with the RFLP loci XYlp, and Xwg889. This map represents the first stage in a project to isolate the Yd2 gene by a map-based approach. The isolation of Yd2 could help to elucidate the molecular mechanism of the Yd2-mediated BYDV resistance, and may allow the production of BYDV resistant cereals by genetic transformation. The RFLP markers mapped closest to Yd2 could also be useful in barley breeding, by enabling selection for both the presence of Yd2 and the absence of agronomically undesirable traits known to be closely linked to Yd2. Genetically Directed Representational Difference Analysis (GDRDA) is a technique based on subtractive hybridisation, which can be used to identify RFLP markers closely linked to a gene of interest. Two GDRDA experiments were performed with the intention of generating additional RFLP markers close to Yd2. However, the first experiment yielded RFLP probes that were not derived from the barley genome, while the second experiment yielded probes that detected repetitive sequences. It was concluded that GDRDA is of limited use in generating further markers close to Yd2. To isolate the Yd2 gene by a map-based approach, a much larger mapping population will need to be analysed to genetically resolve markers tightly linked to Yd2. If the two morphological markers uzu dwarf and white stripe,,j flank Yd2, then they could assist in this task by enabling the visual identification of F2 seedlings resulting from recombination close to Yd2. However, in this study, both morphological markers were found to be located distal to Yd2. Therefore, these two morphological markers can not be used together to facilitate high resolution genetic mapping of the Yd2 locus. It may be possible to use large-insert genomic DNA clones from the relatively small genome of rice to generate further RFLP markers close to the Yd2 gene in barley, provided that the order of orthologous sequences in barley and rice is conserved close to the Yd2 locus. To assess the feasibility of this approach, RFLP probes used to identify loci close to Yd2 were mapped in rice using a segregating rice F2 population. Five of the RFLP loci mapped together and in the same order as RFLP loci mapped close to Yd2 in barley using the same probes. By comparing the location of RFLPs mapped by other researchers in rice using probes mapped close to Yd2, the region of conserved linkage between rice and the Yd2 region was tentatively identified as the central portion of rice chromosome 1. The collinearity shown by orthologous sequences in barley and rice indicated that it may indeed be possible to use rice to assist in generating RFLP markers close to Yd2. Of all the cereals, rice is the most amenable to map-based gene isolation, due to its small genome, well developed physical and genetic maps, and its ability to be genetically transformed with high efficiency. If a BYDV resistance gene that is orthologous to Yd2 could be identified in rice, this gene could be isolated with relative ease, and then used to identify barley cDNA clones corresponding to Yd2 gene by virtue of the sequence homology expected between these genes. To test if a BYDV resistance gene from an Italian rice line is orthologous to Yd2, recombinant-inbred rice lines previously characterised for this gene were analysed using probes mapped close to Yd2 in barley. No genetic linkage was detected between the RFLP loci and the BYDV resistance gene, indicating that the gene is unlikely to be orthologous to Yd2. BYDV resistance alleles at the Yd2 locus which are of a non-Ethiopian origin may show interesting differences to Ethiopian Yd2 resistance alleles. To identify barleys which may contain resistance alleles of Yd2, ten BYDV resistant barleys not known to contain Yd2 were assessed for their resistance to the PAVadel isolate of BYDV in the glasshouse. CI 1179, Rojo, Perry, Hannchen, Post and CI 4228 were found to be the most resistant under these conditions, and were analysed further. If the resistance from these barleys is controlled by alleles of Yd2, RFLP markers close to Yd2 will be expected to cosegregate with the resistance in F2 families derived from crosses between these resistant barleys and the BYDV susceptible barleys Atlas and Proctor. RFLPs suitable for use in these allelism tests were identified using probes mapped close to Yd2. However, time did not permit the analysis of these F2 populations. / Thesis (Ph.D.) -- University of Adelaide, Dept. of Plant Science, 1996

Errata attached to inside front cover. / Bibliography: leaves [156-188] / vi, 155, [33] leaves, [48] leaves of plates : ill. (some col.) ; 30cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Plant Science, 2001

Includes bibliographical references. The thesis aims to characterise the basis of naturally occuring resistance to BYDV in cereals in three ways: i. A map-based approach to the isolation of the Yd2 gene for BYDV resistance from barley. -- ii. Determining if a BYDV resistance gene in rice is orthologous to Yd2. -- iii. Establishing if other BYDV resistance genes in non-Ethiopian barleys are allelic to Yd2.

Errata sheet pasted on front end-paper. / Includes bibliographical references. / v, 125, [99] leaves, [3] leaves of plates : ill. (chiefly col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Plant Science, (1995?)

No description available.

Call number: LD2668 .T4 1961 V39

No description available.

Endo-β-mannanase is an endohydrolase enzyme responsible for the breakdown of mannan-containing polysaccharides common in the cell walls of many plants. The action of endo-β-mannanase in barley, its optimum temperature and pH for action, temporal and spatial localization, activity in the presence of hormones and sugars and its effect on the seed's mechanical strength were assayed. The development of a spectrophotometric assay for endo-β-mannanase detection was also trialed. The optimum temperature and pH for these experiments were found to be 37℃ and pH 7. Using these parameters, the endo-β-mannanase enzyme was found to be initially localized in the seed coat and moved through to the endosperm over time. The detected level of enzyme activity increased in the presence of gibberellic acid and glucose, or decreased when abscisic acid was added. Similar results were seen when the embryo was removed and the endosperm and seed coat were incubated in hormone- and sugar-containing media. The presence of exogenous endo-β-mannanase did not affect the mechanical strength of the seed but there was a strong correlation between increasing endo-β-mannanase activity and decreasing mechanical strength over time. The spectrophotometric assay for quantifying endo-β-mannanase in extracts showed promise but did not reach fruition due to unexplained sources of variation. The localization and regulation of endo-β-mannanase in barley were similar to those seen in other plants, such as tomato, lettuce and coffee. These findings have biotechnological applications within the brewery industry. By increasing the mobilization of reserves such as mannan, it is thought that the seedling can utilize this secondary carbohydrate source instead of, or at least supplementing, glucose which was mobilized from starch. This will theoretically reduce the starch and glucose lost during the malting period leaving a higher sugar content free for fermentation.

Leaves of young barley (Hordeum vulgare cv Arivat) seedlings were examined anatomically, physiologically and cytologically to infer the pathway of transpirational water movement and to understand the basis for the selective responsiveness of the growing region to osmotic stress. Vessels with open lumens were found to extend from the intercalary meristem to the expanded blade, and all vessels are present in 5 functional vascular bundles (FVB) which are separated by 20 to 30 closely packed mesophyll cells and 2 to 3 immature vascular bundles (IVB). Heat pulse transport data confirmed the anatomical suggestion that water will move throughout the leaf in open vessels and they showed also that osmotic stress will reduce water transport within 1 min, which is before transpiration is lowered. Water representing about 2 per cent of the total tissue water was obtained by centrifuging cut sections of the growing region at 5 X g against an adsorptive surface. This water is probably xylem plus cell wall water because it is easily removed, its volume is 2X that calculated to be in the vessels, and it exchanges more readily with the water in the nutrient solution than the bulk tissue water. This lack of free exchange indicates apoplastic water is somewhat separated from mesophyll cells, and it is hypothesized that osmotic stress causes sudden growth cessation and initation of metabolic changes because (a) reduced water availability together with ongoing transpiration will cause a sudden reduction in the xylem's water potential, (b) there is a lateral transmission of this reduced water potential through walls of all cells in the growing region, and (c) cells can respond in some way to changes in water potential around them. Most cells in the expanded blade are considered unresponsive to osmotic stress because transpirational water will move predominantly from the 5 FVB through the closest stomata, so only cells closest to those bundles will be altered rapidly by stress.

Durum grain quality is affected by many factors, but water and nitrogen are factors that the grower can control. The purpose of this research was to determine 1) the nitrogen application rate required at pollen shed to maintain adequate grain protein levels if irrigation is excessive or deficient during grain fill and 2) if nitrogen applications during grain fill can elevate grain protein. Field research was conducted at the Maricopa Agricultural Center using the durum varieties Duraking, Minos, and Turbo. The field was treated uniformly until pollen shed when nitrogen was applied at rates of 0, 30, and 60 lbs/acre. During grain fill, the plots were irrigated based on 30, 50, or 70% moisture depletion. In a separate experiment, nitrogen fertilizer was applied at a rate of 30 lbs N/acre at pollen shed only, pollen shed and the first irrigation after pollen shed, and pollen shed and the first and second irrigation after pollen shed. Irrigation had no effect on grain protein level, although increasing nitrogen rates at pollen shed from 0 to 30 and 30 to 60 lbs N/acre increased protein by 1 percentage point. Nitrogen fertilizer application at the first irrigation after pollen shed increased grain protein content from 10.4 to 11.4% and application at the first and second irrigation after pollen shed increased grain protein content further to 11.9% averaged over varieties. Irrigation management during grain fill may not play as large a role in controlling grain protein content as was originally thought except perhaps on heavy soils, and nitrogen fertilizer application during grain fill may not be too late to increase grain protein content.