Bibliography: leaves 207-220. / 220 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Pseudomonas corrigata strain 2140 (Pc2140), isolated from wheat field soil in Australia, antagonises the take-all fungus, Gaeumannomyces graminis var. tritici (Ggt) in vitro and significantly reduces take-all symptoms on wheat in pot trials. This study investigates the mechanisms by which the biocontrol agent reduces the disease symptoms. Biochemical analysis of metabolites of P. corrugata 2140 reveal a number of compounds potentially antagonistic to Ggt and which may play a role in disease control. These include water-soluble antibiotics, siderophores, proteases, peptides and volatiles including hydrogen cyanide. / Thesis (Ph.D.)--University of Adelaide, Dept. of Crop Protection, 1996

Thesis (MSc (Genetics))--University of Stellenbosch, 2009. / Worldwide, the rust diseases cause significant annual wheat yield losses (Wallwork 1992; Chrispeels & Sadava 1994). The utilization of host plant resistance to reduce such losses is of great importance particularly because biological control avoids the negative environmental impact of agricultural chemicals (Dedryver et al. 1996). The wild relatives of wheat are a ready source of genes for resistance to disease and insect pests. A large degree of gene synteny still exists among wheat and its wild relatives (Newbury & Paterson 2003). It is therefore possible to transfer a chromosome segment containing useful genes to a homologous region in the recipient genome without serious disruption of genetic information. Special cytogenetic techniques are employed to transfer genes from the wild relatives to the wheat genomes (Knott 1989). Unfortunately the transfer of useful genes may be accompanied by the simultaneous transfer of undesirable genes or redundant species chromatin which has to be mapped and removed (Feuillet et al. 2007). DNA markers are extremely useful for the characterisation and shortening of introgressed regions containing genes of interest (Ranade et al. 2001), and may also be used for marker aided selection of the resistance when the genes are employed commercially. Eight wheat lines containing translocations/introgressions of wild species-derived resistance genes were developed by the Department of Genetics (SU). These lines are presently being characterized and mapped and attempts are also being made to shorten the respective translocations. This study aimed to find DNA markers for the various translocations and to convert these into more reliable SCAR markers that can be used in continued attempts to characterize and improve the respective resistance sources. A total of 260 RAPD and 21 RGAP primers were used to screen the eight translocations and, with the exception of Lr19, it was possible to identify polymorpic bands associated with each translocation. However, it was not possible to convert all of these into more reliable SCAR markers. The primary reason for this was the low repeatability of most of the bands. Certain marker fragments turned out to be repeatable but could not be converted successfully. Some of the latter can, however, be used directly (in RAPD or RGAP reactions) as markers. The Lr19 translocation used in the study (Lr19-149-299) is a significantly reduced version of the original translocation and failure to identify polymorphisms associated with it can probably be ascribed to its small size. The following numbers of markers (direct and converted into SCARs) were Worldwide, the rust diseases cause significant annual wheat yield losses (Wallwork 1992; Chrispeels & Sadava 1994). The utilization of host plant resistance to reduce such losses is of great importance particularly because biological control avoids the negative environmental impact of agricultural chemicals (Dedryver et al. 1996). The wild relatives of wheat are a ready source of genes for resistance to disease and insect pests. A large degree of gene synteny still exists among wheat and its wild relatives (Newbury & Paterson 2003). It is therefore possible to transfer a chromosome segment containing useful genes to a homologous region in the recipient genome without serious disruption of genetic information. Special cytogenetic techniques are employed to transfer genes from the wild relatives to the wheat genomes (Knott 1989). Unfortunately the transfer of useful genes may be accompanied by the simultaneous transfer of undesirable genes or redundant species chromatin which has to be mapped and removed (Feuillet et al. 2007). DNA markers are extremely useful for the characterisation and shortening of introgressed regions containing genes of interest (Ranade et al. 2001), and may also be used for marker aided selection of the resistance when the genes are employed commercially. Eight wheat lines containing translocations/introgressions of wild species-derived resistance genes were developed by the Department of Genetics (SU). These lines are presently being characterized and mapped and attempts are also being made to shorten the respective translocations. This study aimed to find DNA markers for the various translocations and to convert these into more reliable SCAR markers that can be used in continued attempts to characterize and improve the respective resistance sources. A total of 260 RAPD and 21 RGAP primers were used to screen the eight translocations and, with the exception of Lr19, it was possible to identify polymorpic bands associated with each translocation. However, it was not possible to convert all of these into more reliable SCAR markers. The primary reason for this was the low repeatability of most of the bands. Certain marker fragments turned out to be repeatable but could not be converted successfully. Some of the latter can, however, be used directly (in RAPD or RGAP reactions) as markers. The Lr19 translocation used in the study (Lr19-149-299) is a significantly reduced version of the original translocation and failure to identify polymorphisms associated with it can probably be ascribed to its small size. The following numbers of markers (direct and converted into SCARs) were v identified: S8-introgression (Triticum dicoccoides) = one RAPD and two SCARs; S13-translocation (Aegilops speltoides) = four RAPDs, three RGAPs and five SCARs; S15-translocation (Ae. peregrina) = one RAPD and two SCARs; S20-translocation (Ae. neglecta) = two RAPDs, two RGAPs and one SCAR. The markers are already being employed in current projects aiming to map and shorten these translocations. Some of the markers can be combined in multiplex reactions for more effective mass screening. No repeatable markers could be identified for the four remaining translocations (S12 from Ae. sharonensis; S14 from Ae. kotschyi; Smac from Ae. biuncialis and Lr19-149-299 from Thinopyrum ponticum).

T. aestivum ssp. spelta Iranian type has long been thought to potentially be the direct non-free threshing hexaploid progenitor. I evaluated a RIL population derived from a cross between CS and Iranian spelta accession P503 to identify loci suppressing free-threshabilty in P503. Identification of QTL associated with threshability in region known to harbor the Tg2A gene, and an inactive tg2D allele supported the hypothesis of Iranian spelta being derived from a more recent hybridization between free-threshing hexaploid and emmer wheat. Parastagonospora nodorum is an important fungal pathogen and secretes necrotrophic effectors that evoke cell death. In this research, a DH population segregating for Snn5 was used to saturate Snn5 region of chromosome 4B with molecular markers. The physical distance between Snn5 flanking markers was narrowed to 1.38 Mb with genetic distance of 2.8 cM. The markers developed in this study will provide a strong foundation for map-based cloning of Snn5.

Please read the abstract in the section 07chapter7. / Dissertation (MSc (Genetics))--University of Pretoria, 2002. / Genetics / unrestricted

Pyrenophora tritici-repentis (Ptr) is the necrotrophic fungus responsible for tan spot of wheat (Triticum aestivum). Ptr causes disease on susceptible wheat cultivars through the production and secretion of host-selective toxins (HSTs). HSTs are compounds that are only known to be produced by fungi and considered to be primary determinants of pathogenicity. Infiltration of these toxins into sensitive wheat elicits the same symptoms as the pathogen, which simplifies investigations of host- pathogen interactions due to exclusion of the pathogen. These characteristics make HSTs ideal molecules to dissect molecular plant-microbe interactions. Known HSTs of Ptr include Ptr ToxA (ToxA), Ptr ToxB (ToxB) and Ptr ToxC (ToxC). ToxA is the most characterized toxin of Ptr, as well as the first proteinaceous HST identified. The proposed mode-of-action for ToxA includes internalization into sensitive wheat mesophyll cells, localization to the chloroplast, photosystem perturbations and elicitation of high amounts of reactive oxygen species (ROS), all of which lead to necrosis. However, it is still unknown how ToxA is transported to the chloroplast. To identify additional interacting components involved in ToxA symptom development, genes were silenced in tobacco plants (Nicotiana benthamiana) using the tobacco rattle virus (TRV) virus-induced gene-silencing (VIGS) system. Four genes were identified that potentially could play a role in ToxA-induced cell death: a 40S ribosomal subunit, peroxisomal glycolate oxidase (GOX), a thiamine biosynthetic enzyme (Thi1), and the R-gene mediator, Sgt1. Ptr exhibits a complex race structure determined by the HST(s) produced and the symptom(s) elicited on sensitive wheat cultivars. Currently, there are eight characterized races and other HSTs and races have been proposed. Isolate SO3 was discovered in southern Oregon and elicits ToxA-like symptoms on a wheat differential set, yet lacks the ToxA gene. The transcriptome of SO3 was sequenced, assembled, and aligned to a ToxA-producing isolate, Pt-1C-BFP, which will aid in the identification of the protein(s) that may be responsible for these ToxA-like symptoms. SO3 contains a set of 497 sequences that were not found in the ToxA-producing isolate Pt-1C-BFP (BFP). These sequences should be further investigated to identify those that encode small secreted proteins (SSPs) and could potentially serve as HSTs and pathogenicity factors of SO3. / Graduation date: 2013

Made available in DSpace on 2015-03-26T13:36:45Z (GMT). No. of bitstreams: 1 texto completo.pdf: 381629 bytes, checksum: ba2d77de1fafa6029bbd57e8ee35252d (MD5) Previous issue date: 2013-03-25 / Blast, caused by the fungus Pyricularia oryzae, has become an economically important disease in wheat. The objective of this study was to determine the effect of silicon (Si) on the photosynthetic gas exchange parameters (net CO 2 assimilation rate (A), stomatal conductance to water vapor (g s ), internal CO 2 concentration (C i ), and transpiration rate (E)) and chlorophyll fluorescence parameters (maximum quantum quenching (F v /F m and F v '/F m '), photochemical (q P ) and nonphotochemical (NPQ) quenching coefficients and electron transport rate (ETR)) in wheat plants grown in a nutrient solution containing 0 (-Si) or 2 mM Si (+Si) and inoculated with P. oryzae. The leaf Si concentration significantly increased for the +Si plants compared to the - Si plants and contributed to a decrease in the severity of blast symptoms. For the inoculated +Si plants, A was significantly higher at 72 (14%), 96 (12%) and 120 (58%) hours after inoculation (hai) when compared with their inoculated -Si counterparts. The g s and E were significantly higher by 60 and 42% at 120 hai for the inoculated +Si plants compared with the inoculated -Si plants, respectively. Significant differences between non-inoculated and inoculated plants were observed from 48 to 120 hai for A, g s and E and from 48 to 96 hai for C i . For the inoculated +Si plants, significant differences of F v /F m between the -Si and +Si treatments occurred at 48, 96 and 120 hai and at 72, 96 and 120 hai of F v '/F m '. The values of F v /F m significantly decreased by 1, 3 and 5% at 48, 96 and 120 hai, respectively, in the -Si plants compared with the +Si plants. Significant decreases of 10, 11 and 22% at 72, 96 and 120 hai, respectively, were observed for F v '/F m ' in the -Si plants when compared with the +Si plants. Significant differences between the non-inoculated and inoculated plants occurred from 48 to 120 hai for F v /F m and F v '/F m ', respectively. For the inoculated plants, significant differences between the -Si and +Si treatments occurred at 96 hai for both q P and NPQ and 72 and 120 hai for ETR. Significant differences between the non-inoculated and inoculated plants occurred at 120 hai for q P and at 96 and 120 hai for ETR. The total chlorophyll content (a + b) and the chlorophyll a/b ratio significantly decreased for the -Si plants compared with the +Si plants. The results of this study clearly demonstrate that the severity of blast symptoms decreased in wheat plants supplied with Si. These plants also exhibited improved gas exchange performance and less dysfunctions at the photochemical level. / A brusone, causada pelo fungo Pyricularia oryzae, tornou-se uma doença economicamente importante no trigo. Este estudo teve como objetivo determinar o efeito do silício (Si) sobre os parâmetros das trocas gasosas (taxa de assimilação líquida de CO 2 (A), condutância estomática ao vapor de água (g s ), a concentração interna de CO 2 (C i ) e taxa de transpiração (E)) e parâmetros de fluorescência da clorofila (eficiencia quântica máxima do fotosistema II (F v /F m e F v '/F m '), fotoquímica (q P ) e coeficiente de extinção não-fotoquimico (NPQ) e a taxa de transporte de eletrons (TTE)) em plantas de trigo crescendas em recipiente com solução nutritiva contendo 0 ou 2 mM de silício (Si) e inoculadas com P. oryzae. A concentração foliar de Si incrementou-se significativamente para plantas, contribuindo à dismunição da severidade da brusone. Para plantas inoculadas com +Si, A foi significativamente maior a 72 (14%), 96 (12%) e 120 (58%) hai do que em suas contrapartes inoculadas. A g s e E foram significativamente maiores em 60 e 42%, respectivamente, às 120 hai para as plantas inoculadas +Si em comparação com as plantas inoculadas -Si. Diferenças significativas entre as plantas inoculadas e não inoculadas ocorreu entre as 48 a 120 hai para A, g s e E e entre as 48 a 96 hai para C i . Para as plantas inoculadas +Si, diferenças significativas para F v /F m entre os tratamentos Si e +Si foram encontradas às 48, 96 e 120 dai e às 72, 96 e 120 hai para F v '/ F m '. Os valores de F v /F m diminuiram significativamente em 1, 3 e 5%, respectivamente, aos 48, 96 e 120 hai para plantas -Si, em comparação com as plantas de +Si. Reduções significativas de 10, 11 e 22%, respectivamente, às 72, 96 e 120 hai para F v '/F m ' ocorreu para as plantas -Si, em comparação com as plantas +Si. Diferenças significativas entre as plantas inoculadas e não inoculadas ocorreu às 48 a 120 hai para F v /F m e F v '/F m '. Para as plantas inoculadas, diferenças significativas entre os tratamentos -Si e +Si ocorreu apenas às 96 hai para ambos q P e NPQ e às 72 e 120 hai para TTE. Diferenças significativas entre as plantas inoculadas e não inoculadas só ocorreu em 120 hai para q P e às 96 e 120 hai para TTE. A concentração de clorofila total (a + b), e a razão de clorofil a/b diminuiu significativamente para as plantas -Si, em comparação com as plantas de +Si. Os resultados deste estudo demonstraram claramente que a severidade da brusone diminuiu em plantas de trigo supridas com Si em paralelo a um melhor desempenho das trocas gasosas e menores perdas disfuncionais ao nível fotoquímico.

The Russian wheat aphid (RWA) (Diuraphis noxia Kurdjumov) is one of the important insect pests of wheat (Triticum aestivum L.), barley (Hordeum vulgare L.) and other grasses. To date, there are four RWA biotypes identified in South Africa. The virulent biotypes emerged, partly due to climate change and new genetic variations within populations of RWA; hence there is a need to improve host-plant resistance, as an effective control measure. Bread wheat (Triticum aestivum L.) accession Cereal Introduction (CItr) 2401 is known to be resistant to all RWA biotypes worldwide. The goal of this study was to use a backcrossed near-isogenic line (NIL) BC5F5 mapping population, developed from a cross between CItr 2401 and susceptible Kavkaz, to identify and validate single nucleotide polymorphism (SNP) markers linked to the resistance phenotype in CItr 2401. This was achieved by (i) conducting a preliminary study that evaluated the suitability of simple sequence repeat (SSR) markers previously reported in literature for discriminating stacked RWA resistance genes and, (ii) employing SNP markers for the first time in a RWA resistance study as a future alternative to the widely used SSR markers. None of the tested SSR markers showed potential use in marker-assisted selection (MAS). The mapping population was phenotypically evaluated for RWA resistance using the four South African biotypes, viz. RWASA1, RWASA2, RWASA3 and RWASA4. Analysis of variance (ANOVA) showed significant (P<0.001) differences of genotypes after confirming the normality of residuals and homogeneity of variance. The Illumina iSelect 9,000 wheat SNP platform was used to genotype the two crossing parents and a selection of 24 NIL genotypes from the mapping population. Eight SNP markers found to be linked to the phenotype were converted to breeder-friendly and high-throughput Kompetitive allele-specific polymerase chain reaction (KASP) markers. The designed KASP markers were validated on the two crossing parents, the 24 NIL sent for SNP genotyping, on the mapping population and on the preliminary study genotypes for their effectiveness. The KASP assays developed in this study will be useful for stacking the RWA resistance from CItr 2401 with other Dn genes effective against the RWA. / Life and Consumer Sciences / M. Sc. (Life Sciences)