Thesis (M.Sc.(Agric))(Plant Production)--University of Pretoria, 2004. / Title from opening screen (viewed March 11th, 2005). Includes summary. Includes bibliographical references.

Thesis (Ph.D.) -- Australian National University, 2007.

Thesis (Ph.D.) - University of Queensland, 2005. / Includes bibliography.

Thesis (Ph. D.)--Oregon State University, 2008. / Printout. Includes bibliographical references. Also available on the World Wide Web.

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Thesis (MSc)--University of Stellenbosch, 2002. / ENGLISH ABSTRACT: Soil salinity is a major limiting factor of plant and crop growth, because the absorption of water and nutrients is such a complex process while low and moderate salinity are omnipresent. Plant growth is affected negatively if a specific ion concentration exceeds its threshold and becomes toxic. The detrimental effect of soil affected by salt on crop production is increasing worldwide (Tanji, 1990). The level to which plants can tolerate high salinity levels is genetically controlled with several physiological and genetic mechanisms contributing to salt tolerance (Epstein & Rains, 1987). The most effective way of addressing the limitations of crop productivity in saline areas, is the development of salt tolerant varieties. Understanding the genetics of salt tolerance is, therefore, necessary for the development of an effective breeding strategy for salt tolerance. The department of Genetics (US) conducts a wide crosses research programme aiming to transfer genes for salt tolerance to wheat and triticale. The donor species, Thinopyrum disticum, an indigenous coastal wheat grass, adapted to high concentrations of salt, was crossed with cultivated rye (Secale cereale) in an attempt to study the genetics of salt tolerance (Marais et al., 1998). The primary goal of this study was to find molecular markers (RAPD and AFLP) which associate with chromosomes promoting salt tolerance for later attempts to transfer the genes to triticale. Seventy clones of secondary hybrids (Th disticum /4x-rye 1/2x-rye) were tested for salt tolerance and showed different levels of salt tolerance. RAPD-marker analyses were used to identify polymorphisms between salt tolerant and salt sensitive plants. Twelve RAPD primers produced clear, analyzable and repetitive polymorphic . fragments that can be used as useful markers. Different AFLP-primer combinations were tested against the genotypes of 15 clones (Marais & Marais 2001, unpublished data) and produced approximately 2000 clearly distinguishable AFLP fragments, of which 54 (3%) were polymorphic fragments. Two RAPD fragments and 4 AFLP fragments that can be used as possible markers for the presence of chromosomes that contribute to salt tolerance were identified. The interpretation of the markers was complicated by heterogeneity among plants with regard to the origin of their chromosomes and the genetic diversity of the rye genome. It is also possible that chromosome re-arrangement took place during backcrossing, which could have complicated the data. / AFRIKAANSE OPSOMMING: Versouting is een van die groot beperkende faktore op plant- en gewasgroei, omdat die opname van water en voedingstowwe so In ingewikkelde proses is en die effek van lae of matige versouting so alomteenwoordig is. Plantgroei word nadelig geaffekteer as 'n spesifieke ioonkonsentrasie sy drempelwaarde oorskry en toksies word. Die nadelige effek van soutgeaffekteerde grond op gewasproduksie, is wêreldwyd aan die toeneem (Tanji, 1990). Die vlak waartoe plante hoë konsentrasies sout kan hanteer is onder genetiese beheer met verskeie fisiologiese en genetiese meganismes wat 'n bydrae maak tot soutverdraagsaamheid (Epstein & Rains, 1987). Die mees effektiewe manier om die beperkinge op gewas produktiwiteit in versoute gebiede te oorkom, is die ontwikkeling van soutverdraagsame variëteite. Begrip van die genetika van soutverdraagsaamheid is dus noodsaaklik vir die ontwikkeling van In effektiewe telingsstrategie. Die departement Genetika (US) bedryf tans 'n wye-kruisings navorsingsprogram waarmee gepoog word om gene vir soutverdraagsaamheid na korog en koring oor te dra. Die skenkerspesie, Thinopyrum disticum, In inheemse strandkoringgras wat aangepas is by hoë konsentrasies sout, is gekruis met verboude rog (Secale cereale) in 'n poging om die oorerwing van soutverdraagsaamheid te bestudeer (Marais et al., 1998). Die hoofdoel van hierdie studie was om molekulêre merkers (RAPD en AFLP) te vind, wat assosieer met chromosome wat soutverdraagsaamheid bevorder en om nuttige merkers daar te stel vir latere pogings om die gene na korog en koring oor te dra. Ongeveer 70 klone van sekondêre hibriede (Th distichum I 4x-rog /I 2x-rog) is onderwerp aan souttoetse en het verskillende grade van soutverdraagsaamheid getoon. RAPDmerker analise is gebruik om polimorfismes te identifiseer tussen soutverdraagsame en soutsensitiewe plante. Twaalf RAPD inleiers het duidelike, ontleedbare en herhalende polimorfiese fragmente opgelewer en moontlike nuttige merkers uitgewys. Verskillende AFLP-inleier kombinasies, wat getoets is teen die genotipes van 15 klone (Marais & Marais, 2001 ongepubliseerde data) het ongeveer 2000 duidelik onderskeibare AFLP fragmente geproduseer, waarvan 54 (3%) polimorfiese fragmente was. Twee RAPD fragmente en 4 AFLP fragmente is geïdentifiseer wat as moontlike kandidaat merkers gebruik kan word vir die identifisering van chromosome wat bydra tot soutverdraagsaamheid . Die interpretasie van die merkers is bemoeilik deur heterogeniteit tussen die plante wat betref die agtergrond van chromosome wat hulle besit en die genetiese diversiteit van die rog genoom. Dit is ook moontlik dat chromosoom herrangskikking plaasgevind het tydens terugkruising, wat die data verder kon kompliseer.

Nitrogen (N) loss in the form of volatilized ammonia (NH₃) is a considerable problem when ammonium (NH₄⁺) forming fertilizers are applied to calcareous or alkaline soils. Large areas of agricultural land, contain alkalinity and salinity problems, are potentially suitable for crop production with little alteration. This study was conducted to determine and compare the effectiveness of urea phosphate (UP) in reducing soil alkalinity and NH₃ loss. The volatilization of NH₃ from UP and urea (U) was studied on 3 selected soils (Hayhook SL, Laveen L and Latene L) using an aeration system. Urea phosphate and U were each applied at rates of 0, 50, 100 and 200 ppm-N either to the surface dry or in solution or mixed with the soil. The volatilized NH₃ was trapped in sulfuric acid, sampled periodically and analyzed for N using the semi microkjeldahl distillation apparatus. The effect of UP, Sulfur-Foam (SF), Phosphuric Solution (PHP) and a mixture of SF and UP (Mix) on leaching soil sodium (Na) and salinity was also studies on two soils (Pima L and Crot CL) in columns. Each of these amendments was applied at a rate of one and two equivalent amounts of the exchangeable Naₑₓ. The highest N loss in the form of NH₃ occurred when U was applied to Hayhook soil. However, UP applied to Hayhook soil (neutral to acidic, coarse textured and low CaCO₃ content) resulted in the lowest NH₃-N loss. Less NH₃-N loss was found from U application to Laveen and Latene soils (fine textured with higher CaCO₃ content) than with Hayhook soil. The general trend was higher N loss, in the form of volatilized NH₃, with surface application dry or in solution than when mixed with the soil. This trend showed an increase in the amount of volatilized NH₃ with increasing rate of N application. Urea phosphate was as effective as PHP or Mix (acid containing fertilizers) treatments in reducing soil salinity and alkalinity in Pima and Crot soils. No difference was found between rates of application (1 and 2 equivalent amount of Naₑₓ) except for soil pH. A similar trend in the decrease in soil salinity was found to that of the pH which was in the order PHP, UP, Mix, SF and control treatments. No significant difference was found between SF and control treatments in all parameters. No significant difference was found between treatments for exchangeable Ca. This was affected by the Ca compounds present in the soil. Generally, UP is a potential fertilizer for supplying N and phosphorus (P) as plant nutrients, reducing NH₃ volatilization, and can be used as a soil amendment to control soil salinity and alkalinity.