Includes bibliographical references.

Includes bibliographical references (leaves 265-296). Pathogens associated with root damage were investigated in the Murray Mallee region of South Australia over the 1987-1989 growing seasons. Occurence of fungal species and the root lesion nematode (Pratylenchus neglectus) was assessed, and related to the appearance and severity of symptoms on the roots. Field experiments were supplemented with innoculation tests in the glasshouse and laboratory.

Mycosphaerella graminicola (anamorph Septoria tritici) causes Septoria tritici blotch, a globally important disease of winter wheat. Resistance and pathogenicity generally vary quantitatively. The pathogen reproduces both sexually and asexually, and the pathogen population is highly genetically variable. Several unresolved questions about the epidemiology of this pathosystem are addressed by this research. Among them are whether cultivar-isolate specificity exists, how partial host resistance affects pathogen aggressiveness and sexual reproduction, and how host genotype mixtures influence epidemic progression and pathogenicity. At its release in 1992, the cultivar Gene was highly resistant to M. graminicola, but that resistance had substantially dissolved by 1995. Six of seven isolates collected in 1997 from field plots of Gene were virulent to Gene seedlings in the greenhouse, while 14 of 15 isolates collected from two other cultivars were avirulent to Gene. Gene apparently selected for strains of M. graminicola with specific virulence to it. In a two-year experiment, isolates were collected early and late in the growing season from field plots of three moderately resistant and three susceptible cultivars, and tested on seedlings of the same cultivars in the greenhouse. Isolates were also collected from plots of two susceptible cultivars sprayed with a fungicide to suppress epidemic development. Isolate populations were more aggressive when derived from moderately resistant than from susceptible cultivars, and more aggressive from fungicide-sprayed plots than from unsprayed plots of the same cultivars. Over 5,000 fruiting bodies were collected in three years from replicated field plots of eight cultivars with different levels of resistance. The fruiting bodies were identified as M. graminicola ascocarps or pycnidia, or other. In all three years, the frequency of ascocarps was positively correlated with cultivar susceptibility, as measured by area under the disease progress curve, and was also positively associated with epidemic intensity. For three years, four 1:1 mixtures of a moderately resistant and a susceptible wheat cultivar were planted in replicated field plots. Isolates from the plots were inoculated as bulked populations on greenhouse-grown seedlings of the same four cultivars. Mixture effects on disease progression varied among the years, and were moderately correlated with mixture effects on pathogenicity. / Graduation date: 2002

Bibliography: leaves 318-347. / ix, 347 [24] leaves : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / A major problem in the production of agricultural crops including wheat, is the damage caused by destructive plant parasitic nematodes, among these the root lesion nematode (Pratylenchus spp.) The association of P. neglectus with fungi in ceraeal root disease has been reported. Infection is associated with leaf yellowing, which reduces plant photosynthesis and grain yield. In nematode infested soil, well fertilized crops are usually less affected. / Thesis (Ph.D.)--University of Adelaide, Dept. of Plant Science, 1996?

Errata slip inserted. / Bibliogaphy: leaves [93-109]. / x, 92, [17] leaves, [20] leaves of plates : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Identifes and maps markers associated with the quality traits of grain protein content, milling yield and flour colour, and with genes resistant to stem- and leaf-rust diseases in wheat. / Thesis (Ph.D.)--University of Adelaide, Dept. of Plant Science, Waite Agricultural Research Institute, 1998

Includes bibliographical references (leaves 265-296). / vi, 296 leaves, [14] leaves of plates : ill. (some col.), maps ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Pathogens associated with root damage were investigated in the Murray Mallee region of South Australia over the 1987-1989 growing seasons. Occurence of fungal species and the root lesion nematode (Pratylenchus neglectus) was assessed, and related to the appearance and severity of symptoms on the roots. Field experiments were supplemented with innoculation tests in the glasshouse and laboratory. / Thesis (Ph.D.)--University of Adelaide, Depts. of Plant Science and Crop Protection, 1991

Doctor of Philosophy / The responses of 92 barley genotypes to selected P. hordei pathotypes was assessed in greenhouse tests at seedling growth stages and in the field at adult plant growth stages to determine known or unknown resistances. On the basis of multipathotype tests, 35 genotypes were postulated to carry Rph2, Rph4, Rph5, Rph12, RphCantala alone or combinations of Rph2 + Rph4 and Rph1 + Rph2, whereas 52 genotypes lacked detectable seedling resistance to P. hordei. Five genotypes carried seedling resistance that was effective to all pathotypes tested, of which four were believed to carry uncharacterised resistance based on pedigree information. Field tests at adult plant growth stages indicated that while 28 genotypes were susceptible, 57 carried uncharacterised APR to P. hordei. Pedigree analysis indicated that APR in the test genotypes could have been derived from three different sources. The resistant responses of seven cultivars at adult plant growth stages were believed to be due to the presence of seedling resistance effective against the field pathotypes. Genetic studies conducted on 10 barley genotypes suggested that ‘Vada’, ‘Nagrad’, ‘Gilbert’, ‘Ulandra (NT)’ and ‘WI3407’ each carry one gene providing adult plant resistance to P. hordei. Genotypes ‘Patty’, ‘Pompadour’ ‘Athos’, ‘Dash’ and ‘RAH1995’ showed digenic inheritance of APR at one field site and monogenic inheritance at a second. One of the genes identified in each of these cultivars provided high levels of APR and was effective at both field sites. The second APR gene was effective only at one field site, and it conferred low levels of APR. Tests of allelism between resistant genotypes confirmed a common APR gene in all genotypes with the exception of ‘WI3407’, which based on pedigree information was genetically distinct from the gene common in ‘Vada’, ‘Nagrad’, ‘Patty’, ‘RAH1995’ and ‘Pompadour’. An incompletely dominant gene, Rph14, identified previously in an accession of Hordeum vulgare confers resistance to all known pathotypes of P. hordei in Australia. The inheritance of Rph14 was confirmed using 146 and 106 F3 lines derived from the crosses ‘Baudin’/ ‘PI 584760’ (Rph14) and ‘Ricardo’/‘PI 584760’ (Rph14), respectively. Bulk segregant analysis on DNA from the parental genotypes and resistant and susceptible DNA bulks from F3 lines using diversity array technology (DArT) markers located Rph14 to the short arm of chromosome 2H. Polymerase chain reaction (PCR) based marker analysis identified a single simple sequence repeat (SSR) marker, Bmag692, linked closely to Rph14 at a map distance of 2.1 and 3.8 cM in the populations ‘Baudin’/ ‘PI 584760’and ‘Ricardo’/‘PI 584760’, respectively. Seedlings of 62 Australian and two exotic barley cultivars were assessed for resistance to a variant of Puccinia striiformis, referred to as BGYR, which causes stripe rust on several wild Hordeum species and some genotypes of cultivated barley. With the exception of six Australian barley cultivars and an exotic cultivar, all displayed resistance to the pathogen. Genetic analyses of six Australian barley cultivars and the Algerian barley ‘Sahara 3771’, suggested that they carried either one or two major seedling resistance genes to the pathogen. A single recessive seedling resistance gene, Bgyr1, identified in ‘Sahara 3771’ was located on the long arm of chromosome 7H and flanked by restriction fragment length polymorphism (RFLP) markers wg420 and cdo347 at genetic distances of 12.8 and 21.9 cM, respectively. Mapping resistance to BGYR at adult plant growth stages using a doubled haploid population derived from the cross ‘Clipper’/‘Sahara 3771’ identified two major QTLs on the long arms of chromosomes 3H and 7H that explained 26 and 18% of total phenotypic variation, respectively. The QTL located on chromosome 7HL corresponded to the seedling resistance gene Bgyr1. The second QTL was concluded to correspond to a single adult plant resistance gene designated Bgyr2, originating from cultivar ‘Clipper’.

Thesis (MSc)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Wheat rust, caused by the Puccinia spp., is a global biotic cause of wheat yield losses. This disease can effectively be combatted by implementing rust resistant wheat cultivars. The release of new resistant wheat cultivars is however prolonged due to the time needed to fix resistance genes in a good quality background and develop pure breeding wheat lines. The aim of this study was the pyramiding of novel species derived leaf and stripe rust resistance genes in bread wheat lines through the utilization of high throughput marker assisted selection and microspore derived doubled haploid technology. / AFRIKAANSE OPSOMMING: Koringroes het wêreldwyd verliese in koringopbrengste tot gevolg. Dit word veroorsaak deur die Puccinia fungi. Hierdie siekte kan effektief beveg word deur die verbouing van roesbestande kultivars. Die vrystel van nuwe weerstandbiedende kultivars is egter ‘n langdurige proses weens die tyd verbonde daaraan om weerstandsgene te fikseer in ‘n genetiese agtergrond met ‘n goeie kwaliteit en om dan suiwertelende lyne te ontwikkel. Die doelwit van hierdie studie was om nuwe spesie-verhaalde blaar- en streeproes weestandsgene in koringlyne te stapel met behulp van merker bemiddelde seleksie en mikrospoor geassosieerde verdubbelde haploïede tegnologie.

Thesis (MSc)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Wheat production is globally affected by several different wheat rust diseases. The rust diseases can effectively be controlled by the deployment of multiple resistance genes that confer durable resistance. One of the most effective strategies to incorporate resistance genes is by the implementation of recurrent mass selection as it maximizes opportunities for gene pyramiding. The implementation of a recurrent mass selection program in wheat can effectively be enhanced with the use of genetic male sterility and the incorporation of maker assisted-selection (MAS). The aim of the study was to pyramid wheat rust resistance genes in wheat lines by utilizing a male sterile mediated marker-assisted recurrent selection breeding (MS-MARS) scheme. An existing segregating MS-MARS base population and resistance donor lines carrying genes of interest (Sr26, Sr35 and Sr45) were used as female and male crossing parents. Potential markers for the genes of interest were first identified and validated on the male population. PCR based markers tested for Sr26 and Sr45 easily distinguished between resistant and non-resistant plants in the study, while markers tested for the detection of Sr35 and Sr45 in most instances failed to do so. The identified Sr26 marker (Sr26#43) was successfully added to the SU-PBL’s standardized marker set in a multiplex reaction. The standardized marker set and the co-dominant PCR marker for Sr45 were used to screen male and female populations before and after cross-pollination. Several wheat rust resistance genes were present in various frequencies in both male and female populations prior to the first crossing cycle, except Sr26 and Sr45. Increases in gene frequencies and combinations were obtained after the first crossing cycle, highlighting the effectiveness of the MS-MARS breeding strategy to improve gene frequencies of desirable genes. Two MS-MARS crossing cycles were successfully completed and large numbers of hybrid seeds were produced in a short period of time by selecting male sterile plants based on distinct characteristics induced by the dominant male sterility gene. Future studies will include the wide deployment of Sr26 and Sr45 in the MS-MARS breeding program as markers are now available and can be included in the SU-PBL’s standardized marker set for the effective detection of these genes, the development of gene-specific markers for Sr35 to ascertain the presence of the gene in the MS-MARS population and the specific selection of male sterile plants with wide open glumes to maximize outcrossing rates. / AFRIKAANSE OPSOMMING: Koring produksie word wêreldwyd aansienlik deur koringroes siektes geaffekteer. Die siektes kan doeltreffend beheer word deur die ontplooing van veelvuldige weerstandsgene, wat langdurige weerstand tot gevolg het. Een van die mees doeltreffendste strategieë om weerstandsgene in n koring plant te inkorporeer is deur die implementering van herhalende massa seleksie (HMS), siende dat dit geleenthede vir geen stapeling maksimaliseer. Die implementering van 'n HMS program in koring kan effektief aangewend word met behulp van genetiese manlike steriliteit en merker bemiddelde seleksie (MBS). Die doelwit van hierdie studie was om veelvuldige koringroes weerstandsgene in koring lyne te stapel met behulp van die manlik steriliteits merker bemiddelde herhalende seleksie (MS-MBHS)-telingsskema. ‘n Gevestigde segregerende MS-MARS basis populasie en donor lyne, wat die gene (Sr26, Sr35 en Sr45) van belang dra, was onderskeidelik as vroulike en manlike kruisingsouers gebruik. Potensiële molekulêre merkers vir die gene van belang was eers geidentifiseer in literatuur en op die donor lyne getoets, voordat dit vir die opsporing van die gene in die nageslag gebruik was. Polimerase ketting reaksie (PKR)-gebaseerde merkers wat getoets was vir Sr26 en Sr45, kon maklik tussen weerstand en nie-weerstandbiedende plante in die studie onderskei, terwyl ander merkers vir die opsporing van Sr35 en Sr45 nie so doeltreffend was nie. Die geidentifiseerde Sr26 merker was suksesvol bygevoeg tot die SU-PBL se gestandardiseerde merkerpaneel, in ‘n multipleks reaksie. Die gestandardiseerde merkerpaneel en die ko-dominante PKR merker vir Sr45 was gebruik om die manlike en vroulike populasie te analiseer vir die teenwoordigheid van verskeie weerstandsgene voor en na kruisbestuiwing. Merker analise het die teenwoordigheid van verskeie koringroes weerstandsgene in verskillende frekwensies in beide die manlike en vroulike populasie voor die eerste kruising siklus aangedui. Sr26 en Sr45 was egter afwesig in beide populasies. ‘n Toename in geen frekwensies en kombinasies was waargeneem na die eerste kruising siklus. Dit het gevolglik die doeltreffendheid van die MS-MARS teling strategie beklemtoon. Twee herhalende kruising siklusse was suksesvol voltooi en groot hoeveelhede bastersaad was verkry vanaf steriele plante wat geselekteer was op grond van unieke eienskappe wat hulle vertoon as gevolg van die manlike steriliteits geen. Toekomstige studies sluit in, die groot skaalse gebruik van Sr26 en Sr45 in die MS-MARS teelprogram aangesien merkers nou beskikbaar is en gebruik kan word in die MS-MARS teelprogram vir die doeltreffende opsporing van hierdie gene, die ontwikkeling van ‘n geen-spesifieke merker vir Sr35 om die teenwoordigheid van die geen in die MS-MARS populasie vas te stel, en die selektering van manlike steriele plante met wyd oop kaffies om kruisbestuiwing te verhoog.

M.Sc. / Wheat is one of the most extensively grown small grain crops in Southern Africa. It is a staple food source used by humans, animals and other living organisms around the globe (Feldman, 2001). One of the major threats of wheat production in South Africa is the Russian wheat aphid (RWA), (Kurdjumov), (Diuraphis noxia, Homoptera: Aphididae) (Brooks et al., 1994; Du Toit & Walters, 1984). The RWA was first described as a pest in South Africa in 1978 and in the US in 1986. Thereafter it was rapidly reported as becoming a major pest of cereals in these countries (Brooks et al., 1994; Du Toit & Walters 1984). A short life span, asexual reproduction, the development of resistance towards insecticides and rapid colonisation of the host plant are all factors that have made the management of the RWA a difficult task (Dogimont et al., 2010; Hein et al., 1998). As a result of complications such as these, host plant resistance is the most viable option to counter the RWA (Dogimont et al., 2010). The method of feeding of the RWA is detrimental to the plant as they insert their stylets into, and feed primarily from, the phloem sieve elements. This damages the plants through nutrient drainage (Dixon, 1985; Klingler et al., 2009) and results in a variety of symptoms, the most common being chlorosis, necrosis, wilting, stunting, curling of the leaves (which provides the pest with a sheltered environment protected from predators and pesticides), misshapen or nonappearance of new growth, and localised cell death at the site of aphid feeding. The RWA elicits an increase in essential amino acids in the phloem sap, by triggering the breakdown of proteins in infested wheat leaves (Burd & Burton, 1992; Du Toit, 1986; Haley et al., 2004; Ma et al., 1998; Miller et al., 2001; Walters et al., 1980). It also reduces transport of labelled tracers (amino acids) from the feeding site to the roots and other sinks in the plant. This increases the nutrient concentration at the site of aphid feeding by increasing the import of resources from other sites in the plant, mobilising local resources and blocking their export to other organs. The damage of the foliar tissue that occurs as a result of the RWA feeding is thought to play a role in the pest’s ability to increase the nutritional quality of the host plant (Botha et al., 2006; Goggin, 2007; Shea et al., 2000).