Bibliography: leaves 245-271 / xiv, 271 leaves, [47] leaves of plates : ill ; 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 Physiology, 1985

The aim of this study was to analyse testcross-material that was generated during a homoeologous pairing-induction experiment. Absence of the homoeologous pairing suppressor gene, Ph1, was employed to induce meiotic pairing between the Lr59 translocation (Aegilops peregrina) and 1AL of normal wheat. The study aimed to characterize the test-cross plants derived from this experiment and to identify recombinants which retained the least amount of species chromatin but which still contained the Lr59 gene. The test-cross F1 population, 07M5 (total 635 plants), was screened for Lr59 resistance by inoculating seedlings with the leaf rust pathotype, UVPrt8. The 168 resistant plants were characterized with molecular markers in order to identify recombinants. The data were used to construct a physical map which showed the relative sizes of the recombinants and which could be used to identify those recombinants which contained the least amount of residual species chromatin. Microsatellite (Xcfa2219, Xbarc83 and Xgwm164) and SCAR (S15T3) analysis was used for the initial identification of recombinants. The results showed that 152 of the 168 resistant plants were recombinants for the four loci; that eight of the remaining 16 plants represented non-recombinant, wild species-types and that the last eight plants represented the wheat parental-types which were resistant (and thus, also recombinants). This extremely high recombination frequency can largely be attributed to strong segregation distortion that was evident in the cross. It is also possible that the translocation segment could derive from the S genome rather than the U genome of Ae. peregrina. The S genome is closer related to the wheat genomes than the U genome and may be more prone to recombination. With the use of the microsatellite and SCAR data, a physical map was constructed which showed the relative location of the Lr59 gene on the translocation. It appeared that the eight shortest recombinants retained terminal species chromatin. In an attempt to characterize the eight recombinants, additional marker loci had to be identified within that region. RAPD, iv AFLP and DArT markers were investigated for this purpose. RAPD analyses did not produce any useful markers. AFLP and DArT analyses did identify useful markers with which the eight recombinants could be screened. The data showed which recombinants probably retained the least amount of species chromatin. Seeing that AFLP and DArT markers are anonymous and that the distances between marker loci are unknown, it is not possible to say which recombinant is the shortest and consequently it will be nessecary to also evaluate the group of eight recombinants agronomically in order to identify the most useful ones. The results showed that multiple cross-overs apparently occured on both sides of Lr59. Multiple cross-overs are higly unlikely in material of this nature, therefore it was speculated that the observation resulted from incomplete synteny between the telomeric areas of the translocation and 1AL. A structural difference between the two chromosome regions might have given rise to abnormal meiotic pairing structures and thus unexpected gamete genotypes. Each of the eight recombinants did express one or more of the Ae. peregrina derived AFLP loci which can in future be verified for use as a marker for marker assisted selection. The study succeeded in identifying a number of potentially useful recombinants which contain the Lr59 resistance. It would, however, be risky to select only one of the shortest recombinants for further development on the basis of the present knowledge as some recombinants may contain genetic abnormalities which resulted from reduced synteny in the Lr59 region. It would therefore be wise to further evaluate all eight recombinants before the best one is selected for agronomic use.

M.Sc. (Botany) / Wheat is the second most important grain crop produced in South Africa. It is mostly used for human consumption (e.g. biscuits, rusks, breakfast cereals, and bread) with the remainder being used as seed and animal feed. Wheat is also used for production of alcohol for ethanol, absorbing agents for adhesives, disposable diapers and industrial uses as starch on coatings (Department of Agriculture, Forestry and Fisheries, 2011). The leading wheat producing areas in South Africa since 1994 are the Western Cape (38 %), Free State (26 %) and Northern Cape (17 %) (Department of Agriculture, Forestry and Fisheries, 2011). There are two main classes of cultivated wheat, these are durum wheat (Triticum durum) that contributes 5 % and common or bread wheat (Triticum aestivum L.), which contribute 95 % of the world wheat production (Kiplagat, 2005). One of the major threats to wheat production in South Africa and other countries is the Russian wheat aphid (RWA), (Kurdjumov), (Diuraphis noxia, Hemiptera: Aphididae) (Brooks et al., 1994). In South Africa, the Russian wheat aphid was reported as a pest of wheat in 1978 in the Eastern Free State (Walters, 1980). In the beginning of the 1979 season, it was detected only in the Eastern Free State, but quickly spread to the Western Free State and parts of Lesotho. Infestations were also isolated in some areas of KwaZulu-Natal, North West and Gauteng Province (Walters et al., 1980). Aphids are soft bodied insects and are the most economically important phloem feeders impacting on plants (Dixon, 1985; Klingler et al., 2009). Aphids damage plants in four ways. Firstly, they ingest vital plant metabolites including large volumes of translocated sugars from the phloem sap, diverting energy from the plant and reducing yield. Secondly, they secrete saliva into the plant tissues while probing the layers of leaf to find the phloem, in some instances the secreted saliva is thought to be phytotoxic (Dedryver et al., 2010). The physical damage done to the leaf along with the toxic attributes of the saliva leads to localized necrosis in some aphid plant interactions (Klingler et al., 2009). Thirdly, aphids act as virus vectors and they can be transmitted in a non-circulative or circulative manner (Chen et al., 2012).

Please read the abstract in the section 00front of this document / Dissertation (MSc (Agric) Plant Pathology)--University of Pretoria, 2003. / Microbiology and Plant Pathology / unrestricted

Thesis (MScAgric)--Stellenbosch University, 1998. / ENGLISH ABSTRACT: Eyespot is an important disease of spring wheat (Triticum aestivum L.). Four species of Ramulispora are associated with this disease, of which Tapesia yallundae and T. acuformis. are common. This thesis investigates the broader subjects of genetic variability, reproductive dynamics and fungicide resistance in Tapesia yallundae. Each of the chapters treats specific but related topics. T. yallundae, which is the only species thus far reported from South Africa, has been associated with yield losses of up to 50%. To enable the implementation of more accurate and effective control measures, understanding the dynamics of reproduction and the genetics of the pathogen is of utmost importance. Of the many plant disease control measures such as cultural practices, sanitation, biological control, etc., fungicide application is the most commonly resorted to measure in eyespot control. This thesis investigates the broader subjects of genetic variability, reproductive dynamics and fungicide resistance of Tapesia yallzll7dae. Fungicide application, however, is not without problems. The pathogen can build up resistance to fungicides. The most commonly used fungicides in eyespot control include the benzimidazole carbendazim, triazoles such as flusilazole, tebuconazole, propiconazole, bromuconazole, flutriafol, fenbuconazole, triademinol, and the imidazole, prochloraz. Cases of resistance to the groups listed above have been reported. Frequent monitoring for resistance is thus crucial to prevent wastage of fungicide and unnecessary impregnantation of the environment with potentially ineffective chemicals. In chapter 2 of this thesis 300 isolates of T. yallundae from 15 fields were evaluated for resistance against carbendazim, flusilazole, tebuconazole, propiconazole, bromuconazole, flutriafol and fenbuconazole. These results indicated that to some triazoles, such as fenbuconazole, a high level of resistance was already present in field populations. In a sexually reproducing fungus such as T. yallundae, knowledge pertaining to its ability to pass resistance factors to offspring is equally important. Mating studies were, therefore, also conducted with parental strains that showed signs of triazole resistance. Three generations were subsequently tested for resistance to five triazoles, namely flusilazole, tebuconazole, propiconazole, bromuconazole and flutriafol. Results of this study showed variable sensitivity in progeny, which indicated quantitative inheritance of resistance to triazoles. Although the sexual stage has not yet been observed in the field in South Africa, this knowledge lays the foundation for the long-term understanding of the population dynamics of the fungus. The ability of a heterothallic ascomycete population to reproduce sexually is dependent on the availability of its two mating types, MATI-I and MATI-2, their distribution, and female fertility amongst other factors. In the UK. the teleomorph is commonly observed in the field, which is in contrast to the situation in South Africa, where it has only been induced in the laboratory. A comparative study between the South African and the UK. populations was therefore undertaken. Isolates representative of the two populations were mated with tester strains as both sperm recipients and as sperm donors. This allowed the percentage of hermaphrodites to be determined. No difference in terms of female fertility was observed between the South African and the UK. populations, with both populations showing low effective population numbers. These data suggested, therefore, that the teleomorph would also occur more frequently in South Africa if the climate was more indusive to its development. The overall results of this study indicated that eyes pot could still be controlled by means of fungicide application in South Africa. Although a shift in sensitivity was observed towards fenbuconazole and flusilazole, no resistance was detected towards carbendazim. The latter might be due to the absen<.:eof the sexual stage in the field, coupled by the monocyclic nature of the pathogen and sensible fungicide regimes. The absence of T. acujormis makes the disease situation less complicated in terms of fungicide application and management. Continuous surveys will have to be conducted, however, to monitor this situation in future. / AFRIKAANSE OPSOMMING: Hierdie studie ondersoek die genetiese variasie, reproduksie dinamika en fungisied weerstand in Tapesia yallundae. Elke hoofstuk handel oor spesifieke maar verwante onderwerpe. Oogvlek is 'n belangrike siekte van lentekoring (Triticum aestivum L.). Vier spesies van Ramulispora word geassosieer met die siekte, waarvan Tapesia yallundae en T. acuformis mees algemeen voorkom. T. yallundae, wat tans die enigste spesie is wat in Suid-Afrika aangeteken is, het al verliese van tot 50% veroorsaak. Om meer akkurate en effektiewe beheermaatreels te implementeer, is dit noodsaaklik om die oorlewingsdinamika van die patogeen te verstaan. Van al die siektebeheermaatreels soos kulturele praktyke, sanitasie, biologiese beheer ens., bly fungisiedbehandeling die mees algemene maatreel vir die beheer van oogvlek. Fungisiedtoediening het egter ook verskeie probleme. Die patogeen kan weerstand opbou teen die fungisied. Die mees algemene fungisiedes wat vir oogvlekbeheer aangewend word sluit onder meer die benzimidasool karbendazim in, triasole soos flusilasool, tebukonasool, propikonasool, bromukonasool, flutriafol, fenbukonasool, triadimenol, en die imidasool, prochloraz. Weerstand is egter reeds teen hierdie middels bekend. Gedurige monitering vir weerstand is dus krities om die vermorsing van fungisied en besoedeling van die omgewing met oneffektiewe middels te beperk. In hoofstuk 2 van hierdie manuskrip word 300 isolate van T. yallundae van 15 lande geevalueer vir weerstand teenoor karbendazim, flusilasool, tebukonasool, propikonasool, bromukonasool, flutriafol en fenbukonasool. Resultate dui daarop dat teen sommige van hierdie triasole, soos bv. fenbukonasool, daar reeds 'n hoe vlak van weerstand teenwoordig was in veldpopulasies. In 'n seksueel reproduserende fungus soos T. yalluJ1dae, is dit noodsaaklik om te bepaal wat sy vermoe is om weerstandbiedenheid aan die nageslag oor te dra. Om die rede is paringstudies ook op ouers wat tekens van weerstand teenoor triasole getoon het uitgevoer. Drie generasies was gevolglik getoets vir weerstand teenoor vyf triasole, naamlik flusilasool, tebuconasool, propikonasool, brumukonasool en flutriafol. Resultate van die studie het 'n variasie in sensitiwiteit van die nageslag getoon, wat op 'n kwantitatiewe oorerwing van weerstand teen £riasole dui. Alhoewel die teleomorf nog nie in lande in Suid-Afrika opgemerk is nie, Ie hierdie kennis die fondament vir die langtermyn vertolking van die populasie dinamika van hierdie fungus. Die vermoe van 'n heterotalliese askomiseet populasie om seksueel voort te plant is afhanklik van die beskikbaarheid van sy twee paringstipes, MATI-I en MATl-2, hul verpreiding, vroulike vrugbaarheid en ander faktore. Alhoewel die teleomorf algemeen in lande in die Verenigde Koninkryk opgemerk word, is dit in kontras met die situasie in Suid-Afrika, waar hierdie stadium nog slegs in die laboratorium gelnduseer kon word. 'n Studie is dus onderneem om die Suid-Afrikaanse en V.K. populasies met mekaar te vergelyk. Isolate van die twee populasies is dus gepaar met paringsisolate as beide sperm ontvangers en sperm donors. Hierdie prosedure het dit moontlik gemaak om die persentasie hermafrodiete te bepaal. Geen verskille in vroulike fertiliteit is tussen die Suid-Afrikaanse en V.K. populasies bespeur nie, en beide populasies het ook 'n lae effektiewe populasie getal getoon. Hierdie data het dus voorgestel dat die teleomorf ook meer algemeen in Suid-Afrika sou voorkom as die klimaat meer geskik was vir teleomorf vormmg. Die resultate van hierdie studie het tot die slotsom gelei dat oogvlek steeds deur fungisiedbehandeling in Suid-Afrika beheer kan word. Alhoewel daar 'n merkbare verskuiwing in sensitiwiteit teenoor fenbukonasool en flusilasool was, was geen weerstand teenoor karbendazim waargeneem nie. Laasgenoemde kan dalk toegeskryf word aan die afwesigheid van die teleomorf in die veld, gekombineer met die monosikliese natuur van die patogeen en gebruik van alternerende fungisiedes. Die afwesigheid van T. acuformis maak die plaaslike siektetoestand minder gekompliseerd in terme van fungisied aanwending en bestuur. Voortdurende opnames sal egter uitgevoer moet word om hierdie situasie ook in die toekoms te monitor.

Bibliography: leaves 307-329. This study concludes that in soils in South Australia where root-rotting fungi and P. neglectus exist together, root disease of wheat is caused by their combined effect. Evidence suggests that P. neglectus not only contributes to this interaction through mechanical wounding of roots, but also causes biochemical and physiological changes in plants, making them more prone to fungal infection.

Bibliography: leaves 207-220. 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.

Bibliography: leaves 307-329. / xvi, 329 leaves, [21] leaves of plates : ill. (chiefly col.), map ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / This study concludes that in soils in South Australia where root-rotting fungi and P. neglectus exist together, root disease of wheat is caused by their combined effect. Evidence suggests that P. neglectus not only contributes to this interaction through mechanical wounding of roots, but also causes biochemical and physiological changes in plants, making them more prone to fungal infection. / Thesis (Ph.D.)--University of Adelaide, Dept. of Plant Science, 1996

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).