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).

M.Sc. (Botany and Plant Biotechnology) / Wheat (Triticum aestivum L.) is the one of the three most extensively cultivated cereal crops worldwide (Shewry, 2009). In South Africa, wheat is cultivated in both summer and winter rainfall regions as monocultures typical to modern industrialised agriculture. Monocultures provide uniform crop quality and allow processes such as planting and harvesting to be mechanised (Altieri et al., 2009). However, the genetically homogeneous nature of monocultures increases the vulnerability of the crop to both biotic and abiotic stresses (Faraji, 2011). Future food production is challenged by predicaments such as an increasing human population while the ratio of arable land to population is decreasing. Yield losses of wheat due to biotic factors alone were estimated as 29 % (2001-2003) (Oerke, 2006). The need to reduce the gap between attainable yield and actual yield is therefore crucial in order to maximise crop production for future food security (Duveiller et al., 2007). One of the most damaging pests to worldwide wheat production is the Russian wheat aphid (RWA), Diuraphis noxia (Kurdjumov) (Arzani et al., 2004). A native pest of central Asia, the RWA has spread to all cereal producing areas of the world with the exception of Australia (Burd et al., 2006). While feeding on susceptible hosts, the aphid injects an eliciting agent into the host, which causes the breakdown of the chloroplast and cellular membranes, leading to the appearance of symptoms typical of RWA feeding, including leaf rolling (Botha et al., 2005). Leaf rolling creates a sheltered environment for the aphid from insecticides and predators, and this together with their parthenogenic and viviparous reproductive nature makes their rapid increase in numbers extremely difficult to control (Goggin, 2007). Resistant wheat genotypes currently represent the most effective long term solution to control RWA infestations; however resistance breaking aphid biotypes are rapidly overcoming the incorporated resistance genes under field conditions (Burd et al., 2006; Jankielsohn, 2011). Understanding the molecular basis of plant resistance to the RWA is crucial in creating cultivars with durable resistance (Botha et al., 2005).

Most breeding programs aim at developing superior germplasm and better cultivars that combine high yield, disease and pest resistance, and end-use quality to satisfy the requirements of the growers as well as industry. A population, consisting of 138 F2-8 recombinant inbred lines (RILs) derived from a cross between ‘Steele-ND’ and ND 735, was evaluated to study the inheritance pattern of the septoria tritici blotch (STB)-resistant genes, agronomic and quality traits. The framework map made of 392 markers, including 28 simple sequence repeat (SSR) markers and 364 DArT markers, spanned a total distance of 1789.3 cM and consisted of 17 linkage groups. The map position of quantitative trait loci (QTL) found in this study coincided with the map position of durable STB resistance genes, Stb1. Thirteen QTL were detected for agronomic and quality traits. More saturation of the current map is needed to explore more QTL for this population.

Thesis (PhD (Agric)) -- Stellenbosch University, 2003. / ENGLISH ABSTRACT: Stripe (yellow) rust of wheat, caused by Puccinia striiformis f.sp. tritici, was first detected as a single introduction into South Africa in 1996. Two additional pathotypes have since been identified. Control of the disease may be achieved by use of genetic adult plant resistance (APR) as is present in the local cultivar 'Kariega'. The aim of this project was to understand the genetic basis of the APR in 'Kariega' to facilitate breeding of new varieties with genetic resistance to stripe rust. A partial linkage map of a 'Kariega X Avocet S' doubled haploid population covering all 21 wheat chromosomes was generated using 208 DNA markers, viz, 62 SSR, 133 AFLP, 3 RGA and 10 SRAP markers, and 4 alternative loci. The different marker techniques detected varying polymorphism, viz, overall SSR: 46%, AFLP: 7%, SRAP: 6% and RGA: 9%, and the markers produced low levels of missing data (4%) and segregation distortion (5%). A significant feature of the linkage map was the low polymorphism found in the D genome, viz, 19% of all mapped DNA markers, 11% of all AFLP markers and 30% of the total genome map distance. A region exhibiting significant segregation distortion was mapped to chromosome 4A and a seedling resistance gene for stem rust (Puccinia graminis f.sp . tritici), Sr26, mapped to chromosome 6A close to three SSR markers. The leaf tip necrosis gene, Ltn, which was also segregating in the population, mapped to chromosome 7D. Protocols for SRAP and RGA were optimised, and SRAP marker use in wheat genetic linkage studies is reported for the first time. The linkage map was used together with growth chamber and replicated field disease scores for QTL mapping. Chromosomes showing statistically significant QTL effects were then targeted with supplementary SSR markers for higher resolution mapping. The quality of disease resistance phenotypic data was confirmed by correlation analysis between the different scorers for reaction type (0.799±0.023) and for transformed percentage leaf area infected (0.942±0.007). Major QTL were consistently identified on chromosome 7D (explaining some 25-48% of the variation) and on chromosome 2B (21-46%) using transformed percentage leaf area infected and transformed reaction type scores (early and final) with interval mapping and modified interval mapping techniques. Both chromosomal regions have previously been identified in other studies and the 7D QTL is thought likely to be the previously mapped APR gene Yr 18. Minor QTL were identified on chromosomes lA and 4A with the QTL on 4A being more prominent at the early field scoring for both score types. A QTL evidently originating from 'Avocet S' was detected under growth chamber conditions but was not detected in the field, suggesting genotype-environment interaction and highlighting the need for modifications of growth chamber conditions to better simulate conditions in the field. The genetic basis of the APR to stripe rust exhibited by 'Kariega' was established by mapping of QTL controlling this trait. The linkage map constructed will be a valuable resource for future genetic studies and provides a facility for mapping other polymorphic traits in the parents of this population with a considerable saving in costs. / AFRIKAANSE OPSOMMING: Streep of geelroes van koring word veroorsaak deur Puccinia striiformis f. sp tritici, en is die eerste keer in 1996 in Suid-Afrika na introduksie van 'n enkele patotipe waargeneem. Twee verdere patotipes is sedertdien in Suid-Afrika gei"dentifiseer. Beheer van die siekte word veral moontlik gemaak deur die gebruik van genetiese volwasseplantweerstand soos gei"dentifiseer in die plaaslike kultivar 'Kariega'. Die doel van hierdie studie was om die genetiese grondslag van die streeproesweerstand te ontrafel ten einde die teling van nuwe bestande kultivars moontlik te maak. 'n Verdubbelde haplo1ede populasie uit die kruising 'Kariega X Avocet S' is aangewend om 'n gedeeltelike koppelingskaart vir die volle stel van 21 koring chromosome saam te stel. Die kaart het uit 208 DNA merkers, nl., 62 SSR, 133 AFLP, 3 RGA, 10 SRAP merkers en 4 ander lokusse bestaan. Totale polimorfisme wat deur die verskillende merkersisteme opgespoor is, was as volg: SSR: 46%, RGA: 9%, AFLP: 7% en SRAP: 6%. Die mate van ontbrekende data was gering (4%) asook die mate van segregasie distorsie (5%) van 'n enkele geval wat op chromosoom 4A gekarteer is. 'n Prominente kenmerk van die koppelingskaart is die relatiewe gebrek aan polimorfiese merkers op die D-genoom, nl., slegs 19% van alle DNA merkers en 11% van alle AFLP merkers wat slegs 30% van die totale genoom kaartafstand bestaan het. Die stamroes (Puccinia graminis f. sp. tritici) saailingweerstandsgeen, Sr26, karteer op chromosoom 6A naby drie SSR merkers. Die geen vir blaartipnekrose, Ltn, karteer op chromosoom 7D. Protokolle vir SRAP en RGA merkers is ge-optimiseer en gebruik van SRAP merkers in koppelings-analise word vir die eerste keer in koring gerapporteer. Die koppelingskaart is in kombinasie met groeikamerdata en gerepliseerde veldproefdata gebruik om die gene (QTL) vir volwasseplant streeproesweerstand te karteer. Chromosome met statisties betekenisvolle QTL is met aanvullende SSR merkers geteiken om die resolusie van kartering verder te verhoog. Die kwaliteit van fenotipiese data, soos in die proewe aangeteken, is bevestig deur korrelasies te bereken tussen lesings geneem deur onafhanklike plantpataloe (0.799 ± 0.023 vir reaksietipe en 0.942 ± 0.007 vir getransformeerde persentasie blaaroppervlakte besmet). Hoofeffek QTL vir die twee maatstawwe van weerstand is deur middel van die metodes van interval QTL kartering en gemodifiseerde interval QTL kartering konsekwent op chromosome 7D (25-48% van variasie verklaar) en 2B (21-46% van variasie verklaar) ge"identifiseer. In vorige studies is aangetoon dat beide chromosome 7D en 2B QTL vir volwasseplant streeproesweerstand dra. Die 7D QTL is waarskynlik die weerstandsgeen, Yr 18. QTL met klein effekte op weerstand is op chromosome lA en 4A ge"identifiseer. Die effek van laasgenoemde geen was meer prominent in die velddata in die vroee datum van weerstandsbeoordeling. Een QTL, afkomstig van 'Avocet S', is slegs onder groeikamertoestande identifiseerbaar. Dit dui op moontlike genotipe-omgewing wisselwerking en beklemtoon die noodsaaklikheid om aanpassings te maak in groeikamertoestande vir beter simulasie van veldproeftoestande. Die genetiese grondslag van volwasseplantweerstand teen streeproes in die kultivar 'Kariega' is deur QTL kartering bepaal. Die 'Kariega X Avocet S' koppelingskaart kan as 'n waardevolle basis dien vir toekomstige genetiese ontledings van ander polimorfiese kenmerke in die populasie.

Thesis (PhD)--Stellenbosch University, 2015 / ENGLISH ABSTRACT : Diuraphis noxia Kurdjumov (Russian Wheat Aphid; RWA) is a pest of wheat and barley that has spread from its home range in the fertile crescent to most wheat producing countries except Australia. Since its first introduction to South Africa and the USA in the late 20th century, breeding programs for wheat phenotypes resistant to the aphid were put in place. Conventional breeding practices rely on phenotypic screening to verify traits carried by offspring and genetic tools such as marker assisted selection (MAS) have greatly aided this process in speed and accuracy. The size and complexity of the wheat genome, its allopolyploid nature and repetitive elements have, however, posed a challenge to studies on the genetics of this cereal crop. Many studies have focused on chromosome 3B which is the largest of the wheat chromosomes and easily separated from the redundant genomic background by techniques such as flow cytometry. The similarity in size of the remaining chromosomes however, limits the application of flow cytometry to their isolation. Databases such as Grain-Genes (http://wheat.pw.usda.gov/GG2/index.shtml) house marker data from various mapping studies for all wheat chromosomes and in 2014 the International Wheat Genome Sequencing Consortium (IWGSC) completed the draft genome sequence of wheat categorized by chromosome. Sources of resistance (Dn resistance genes) against RWA are located on chromosome 7D. but despite the marker and sequence data available currently, mapping studies specific for the Dn resistance genes are few. Additionally, sequence data available is derived from cultivars susceptible to RWA and is not comprehensively annotated and assembled in many cases. In this study, we demonstrate a novel, combined approach to isolate and characterize the Dn resistance genes through the use of a genetic map constructed from Amplified Fragment Length Polymorphism (AFLP), Expressed Sequence Tag (EST) and microsatellite markers and a physical map constructed from Next Generation Sequencing (NGS) data of ditelosomic chromosomes (7DS and 7DL) isolated by microdissection on the PALM microbeam system. A 122.8 cM genetic map was produced from 38 polymorphic AFLP markers and two ESTs with the microsatellite Xgwm111 as anchor to related genetic maps. Through comparison to maps available on GrainGenes the location of the Dn1 resistance gene was narrowed down to a deletion bin (7DS5-0.36-0.62) on the short arm of chromosome 7D with an AFLP marker (E-ACT/M-CTG_0270.84) mapping closely at 3.5 cM and two ESTs mapping at 15.3 cM and 15.9 cM from Dn1. Isolation of individual chromosome arms 7DS and 7DL using the PALM Microbeam system allowed sequencing of the chromosome without the redundancy of the remainder of the hexaploid genome. Through isolating the chromosome arms in this way, a >80-fold reduction in genome size was achieved as well as a major reduction in repetitive elements. Analysis of the sequencing data confirmed that 7DL is the physically shorter arm of the chromosome though it contains the majority of protein coding sequences. / AFRIKAANSE OPSOMMING : Diuraphis noxia Kurdjumov (Russiese koring-luis; RWA) is « pes wat op koring en gars voorkom. Die pes het vanaf sy tuiste in die midde Ooste na meeste koringproduserende lande behalwe Australië versprei. Sedert die eerste bekendstelling van RWA in Suid Afrika en die VSA in die vroeë 20ste eeu is teelprogramme ten gunste van koring lyne met weerstand teen RWA begin. Tradisionele teelprogramme maak op fisieise observasie van die fenotipe staat om te verifieer of plante in die nageslag die gewenste eienskap dra. Genetiese metodes soos merkerondersteunde seleksie (MAS) versnel hierdie selekteringsproses grootliks. Die grootte en kompleksiteit van die koring genoom asook die polyploïde en herhalende natuur daarvan is « groot hindernis vir genetiese studies van hierdie graangewas. Baie studies het op chromosoom 3B gefokus wat die grootste van die koring chromosome is en dus maklik vanaf die res van die oorbodige genomiese agtergond deur tegnieke soos vloeisitometrie geskei word. Die ooreenkoms in grootte tussen die res van die chromosome bemoeilik die toepassing van vloeisitometrie om hulle te isoleer. Databasisse soos GrainGenes (http://wheat.pw.usda.gov/GG2/index.shtml) bevat merker data vanaf verskeie karterings-studies vir al die chromosome en in 2014 het die "International Wheat Genome Sequencing Consortium"(IWGSC) die voorlopige basispaarvolgorde van die koring genoom bekendgestel, gekategoriseer volgens chromosoom. Weerstandsbronne (Dn weerstandsgene) teen RWA kom meestal op chromosoom 7D voor. Ten spyte van merker en basispaarvolgorde data tans beskikbaar is karterings-studies spesifiek tot die Dn gene skaars en basispaarvolgorde data is vanaf kultivars afkomstig wat nie weerstandbiedend teen RWA is nie en waarvan die annotasie en samestelling baie keer nie goed is nie. In hierdie studie demonstreer ons « nuwe, gekombineerde aanslag om die Dn weerstandsgene te isoleer en karakteriseer deur van « genetiese kaart opgestel met "Amplified Fragment Length Polymorphism"(AFLP), "Expressed Sequence Tag"(EST) en mikrosatelliet merkers asook « fisiese kaart saamgestel deur die volgende-generasiebasispaarvolgordebepaling van ditelosomiese chromosome (7DS en 7DL) geïsoleer deur mikrodisseksie met die "PALM Microbeam"sisteem gebruik te maak. « Genetiese kaart van 122.8 cM was met 38 polimorfiese AFLP merkers en twee EST merkers geskep. Die mikrosatelliet, Xgwm111, is ook ingesluit en het as anker vir verwante genetiese-kaarte gedien. Deur vergelyking met genetiese-kaarte op GrainGenes is die posisie van die Dn1 weerstandsgeen vernou na « delesie bin (7DS5-0.36-0.62) op die kort arm van chromosoom 7D met « AFLP merker (EACT/ M-CTG_0270.84) wat ongeveer 3.5 cM vanaf die geen karteer. Die twee EST merkers is 15.3 cM en 15.9 cM vanaf die geen gekarteer. Isolering van die individuele chromosoom arms, 7DS en 7DL, deur van die "PALM Microbeam"sisteem gebruik te maak het basispaarvolgordebepaling van die chromosoom toegelaat sonder die oortolligheid van die res van die hexaploïde genoom. Deur die chromosoom so te isoleer is « >80-maal verkleining in genoom grootte bereik insluitend « groot reduksie in herhalende elemente. Analise van die data vanaf basispaarvolgordebepaling het bevestig dat chromosoom 7D die fisiese kleiner chromosoom is maar dat dit die meerderheid van proteïn koderende basispaarvolgordes bevat.

Bibliography: leaves 133-152 / iv, 152 leaves, [47] leaves of plates : ill. (1 col.) ; 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, 1987

Thesis (MSc (Genetics))--University of Stellenbosch, 2005. / The Russian wheat aphid, Diuraphis noxia (Mordvilko), is a serious insect pest of wheat and barley. It affects the quality and yield of grain by sucking plant sap from the newest growth whilst toxic substances are injected that destroy plant tissue. The Russian wheat aphid also acts as a vector of plant viruses. The cultivation of aphid resistant cultivars is the preferred control strategy and nine resistance genes, designated Dn1 to Dn9, have been identified. Another undesignated gene, Dnx, was found in the wheat accession PI220127. Mapping of the resistance genes relative to known markers will improve their use in breeding programs. The dominant RWA resistance gene, Dn5, was identified in the accession PI294994 and mapped to chromosome arm 7DL. However, recent reports have placed Dn5 on ...