Thesis (Ph.D.) -- University of Adelaide, Dept. of Agronomy and Farming Systems, 1999. / Bibliography: p. 161-185.

Thesis (M.S.)--Naval Postgraduate School, 1974. / Includes bibliographical references (leaves 78-80).

No description available.

No description available.

No description available.

Graduation date: 1966

Salinity is one of the most serious environmental stresses influencing agriculture drastically decreasing the production of crop plants throughout the world. Due to salinity thousands of hectares of agricultural land are going out of production annually. To cope with the salinity problem, there is keen interest in the development of crop plants displaying resistance to the effects of salinity. A series of experiments was carried out under controlled environmental conditions to determine salt resistance in Rapid Cycling Brassica species (RCB's) at germination early seedling and late growth stage. The effect of increasing salinity concentration was determined in vivo using a compost based growing system and also in-vitro using adapted tissue culture techniques. At germination and during the early seedling stage, low salt concentrations (50-100 mM) stimulated germination and had no significant effect on growth in B. rapa and B. rapa appeared to have greater salt resistance than B. napus. There was no association between salt resistance at the early seedling stage and that at the adult stage. At later growth stages, salinity affected both the relative fresh and dry weights and tissue ion concentration with K: Na balance affected in favour of Na. The relative salt resistance in the six Brassica species was associated with the reduction in the total fresh weight of shoots of salt-treatment plants expressed as the percentage of control but was not associated with K., Na concentration or K/Na ratio in shoots. B. napus and B. carinata showed the greatest salt resistance, B. juncea, B. rapa and B. nigra were intermediate whilst B. oleracea was salt sensitive. Conventional selection for salt resistance was not successful in this study because B. oleracea, B. napus and B. carina/a were not able to complete either their vegetative or reproductive phases and died before completion of the first selection cycle. Whilst, ten percent of plants of B. rapa, B. nigra and B. juncea managed to complete the first selection cycle they failed to complete the second selection cycle. Although, callus induction and maintenance were successful for all 6 RCB's, regeneration of shoots from callus was poor. Also, callus-based selection for salt resistance was unsatisfactory and had variable results and it was concluded that this was not a promising avenue for improving salt resistance in RCB's A cauliflower curd meristem technique was adapted for in-vitro mutagenesis and selection. Mutagenesis was carried out using two mutagens N-nitroso-N-ethylurea or nitroso-methylurea at 1 mM and 2.5 mM. 300 green shoots were recovered from more than 1 ,000,000 explants mutagenised in liquid medium supplemented with 3 mM hydroxyproline as a selection agent. Of eighty in-vitro shoots which where measured for proline content, twelve showed higher proline level than controls. Leaf strip assays of the twelve selected in-vitro shoots and in-vivo weaned plants exposed to a 3 mM and 10 mM hydroxyproline assay showed greater resistance than controls. A few selections also had cross-resistance to salt at 550 mM NaCl and to frost at -7 °C. These results successfully indicated the existence of great opportunities for the production of stress resistance cauliflower plants via mutagenesis and hydroxyproline selection.

Thesis (M.Sc. (Ichthyology & Fisheries Science)) - Rhodes University, 2009.

Thesis (S. M.)--Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2009. / Cataloged from student submitted PDF version of thesis. Includes bibliographical references (p. 41-43).

Geophysical studies have shown that the lower continental crust, especially in Phanerozoic areas, is commonly more conductive and reflective and has a lower seismic velocity than what is expected from the composition of xenoliths and exposed lower crustal terrains. These anomalous in situ properties can be explained by the presence of small amounts of free aqueous fluids in the intergranular space. A compilation of lower crustal geophysical data shows a correlation between electrical resistivity and seismic velocity, in agreement with physical properties models of porous rocks, as well as a general decrease of inferred porosity with geological age. Correlations with geothermal data also show that the reflective and conductive layers usually have their tops near the 400-450°C isotherms suggesting an association with the brittle-ductile transition. The rheology at depth might have an effect on the trapping of the fluids that are in textural equilibrium pores in the ductile crust. Alternatively metamorphic reactions may constrain free fluids to below this depth. Model for the effects of porosity in textural equilibrium pores on seismic and electrical properties of rocks have been developed, and are also in good agreement with the data compilation. Re-processed LITHOPROBE South Cordillera magnetotelluric and seismic reflection data in the Intermontane Belt support a coincidence between the top of low resistivity and high reflectivity of the crust at depths of about 20 km in the west, and about 15 km in the east of the Belt, corresponding to temperatures around 450°C. Two models for reconciling the low vertical permeability required for maintaining the porosity at depth with the interconnection required to reduce the electrical resistivity are presented: one involves the deformation of equilibrium pores by small deviatoric stresses that pinch off the vertical interconnection, the other the flattening and alignment of pores by lower crustal shear processes. A difficulty is recognized in reconciling free aqueous fluids in the lower crust with the expected retrograde metamorphism that should take up any free water. This processes can be avoided if the fluids are of high salinity. High-salinity fluids are in liquid phase in the lower crust, not in supercritical phase as often thought. / Graduate