Les maladies du blé causées par Fusarium, comme la brulure de l’épi (FHB) et la pourriture de la tige (FCR), entrainent une réduction de production, de la qualité du blé et des problèmes de sécurité alimentaire liés à la présence de mycotoxines affectant la santé de l’Homme et des animaux: la plus représentée étant le déoxynivalénol (DON). Le DON est un inhibiteur de la synthèse protéique qui agit durant l’infection comme un facteur de virulence. La glycosylation du DON en D3G (DON-3-O-glicoside) catalysée par des UDP-glycosyltransférases (UGTs) est le principal mécanisme de protection des plantes contre sa toxicité. Dans ce travail, nous avons démontré que la détoxification du DON par l’UGT confère une résistance à large spectre contre les champignons produisant DON F.graminearum et F.culmorum. Nous avons produit des plants de blé dur exprimant de manière constitutive le gène HvUGT13248 (Ubi-UGT) et des plants de blé panifiables exprimant ce gène au niveau du tissu floral (Lem-UGT). Les plants Ubi-UGT ont montré une réduction significative des symptômes de FHB durant les stades précoces et médians de l’infection, et de FCR à tous les stades de l’infection. De plus, les plants Lem-UGT ont montré une corrélation entre les niveaux d’expression de l’UGT et de protection observée. Finalement, nous avons démontré que la pyramidation des gènes associés à des mécanismes de résistance différents peut renforcer la résistance de l’hôte à l’infection. Des plants de blé ont été générés exprimant à la fois l’enzyme HvUGT13248, et des inhibiteurs de glycosidases: AcPMEI ou PvPGIP2, impliqués dans la dégradation de la paroi cellulosique, et qui ont montré une résistance accrue à la FHB. / Fusarium diseases, including Fusarium head blight (FHB) and Fusarium crown rot (FCR) represent major agricultural problems worldwide, causing reduction of grain yield and quality and food safety. In particular, grain contamination by Fusarium mycotoxins, mainly deoxynivalenol (DON), is responsible for health problems in humans and animals. DON is a protein synthesis inhibitor, acting as a virulence factor during pathogenesis. The principal mechanism involved in enhancing plant tolerance to DON is glycosylation, forming DON-3-β-D-glucoside (D3G), performed by specific UDP-glucosyltransferases (UGTs). In this work, we demonstrated that DON-detoxification by UGT confers a broad-spectrum resistance against the DON-producing fungi F. graminearum and F. culmorum, characterized by different time of infection and target organs. We produced transgenic durum wheat plants (Ubi-UGT) constitutively expressing the barley HvUGT13248 and bread wheat plants (Lem-UGT) expressing HvUGT13248 in flower tissues. Ubi-UGT plants revealed significant reduction of FHB symptom, during early-mid stages of infection, and of FCR symptom, throughout the infection timing. The floral-specific expression highlighted a dose-dependent efficacy of the UGT detoxification mechanism. In addition, we demonstrated that pyramiding of genes controlling different resistance mechanisms can further reinforce the host response by stacking transgenes controlling the DON-to-D3G conversion and the inhibition of cell wall degrading enzymes by glycosidase inhibitors in the same wheat genotype. We obtained plants expressing HvUGT13248 and AcPMEI or HvUGT13248 and PvPGIP2, which exhibited increased FHB resistance.

Thesis (MSc (Genetics))--University of Stellenbosch, 2010. / Includes bibliography. / ENGLISH ABSTRACT: Wheat rust is a significant contributor to the total impact of diseases on sustainable wheat production. Genetic resistance, produced by using resistance genes from wheat and other related wild species, is the simplest and most cost-effective way to guard against these diseases. The pyramiding of resistance genes in a single line is a vital practice in bringing about durable resistance. This study aimed to develop a series of doubled haploid (DH) wheat lines containing combination's of wild species genes for rust resistance. Rust resistance genes Lr19 (7BL), Sr31/Lr26/Yr9/Pm8 (1BS) and Lr54/Yr37 (2DL) were combined by means of crossing. Breeders. lines which have complex resistance including Lr24/Sr24 (3DL), Lr34/Yr18 (7D), Sr36 (2BS) and Sr2 (3BS), were used. Marker assisted selection (MAS) was used to type populations for the above mentioned genes. Using the DH method (maize pollination technique), an inbred population was developed from the selected lines, after which the lines were characterised molecularly for the resistance gene translocations which they contain. The study produced 27 lines with diverse genetic profiles. Seven lines contain four translocations (Lr24/Sr24, Lr34/Yr18, Sr2 and Lr19 or Sr31) each, 11 lines contain three genes each, six lines contain two genes each and only three lines contain a single translocation (Lr24/Sr24). The reality that rust pathogens have already overcome three of the resistance genes in the final population . Lr19, Sr31 and Sr24 . is a clear indication of the value of using non-major gene resistance for bringing about durable resistance. The focus should fall ever more greatly upon the application of quantitative trait loci (QTL) for this purpose, which will result in MAS contributing to the development of more durable resistance. The value of the integration of MAS and DH in combination with conventional breeding practices in breeding programmes has already been illustrated internationally for increasing the rate of cultivar development and this is reaffirmed by this study. / AFRIKAANSE OPSOMMING: Koringroes lewer jaarliks .n beduidende bydrae tot die totale impak van siektes wat volhoubare koringverbouing belemmer. Die mees eenvoudige en koste-effektiewe verweer teen hierdie siektes is genetiese weerstand, wat deur weerstandsgene vanaf koring, sowel as wilde verwante spesies, bewerkstellig word. Die stapeling van weerstandsgene in .n enkele lyn word as .n onontbeerlike praktyk om duursame weerstand tot stand te bring, geag. Hierdie studie het ten doel gehad om .n reeks verdubbelde haploiede (VH) koringlyne te ontwikkel wat kombinasies van wilde spesie gene vir roesweerstand bevat. Roesweerstandsgene Lr19 (7BL), Sr31/Lr26/Yr9/Pm8 (1BS) en Lr54/Yr37 (2DL) is deur middel van kruisings gekombineer. Telerslyne wat oor komplekse weerstand beskik wat Lr24/Sr24 (3DL), Lr34/Yr18 (7D), Sr36 (2BS) en Sr2 (3BS) insluit, is gebruik. Merker-bemiddelde seleksie (MBS) is gebruik om populasies vir bogenoemde gene te tipeer. .n Ingeteelde populasie is vanaf die geselekteerde lyne met behulp van die VH metode (mielie-bestuiwing tegniek) ontwikkel, waarna die lyne molekuler vir die weerstandsgeentranslokasies waaroor hul beskik, gekarakteriseer is. Die studie het 27 lyne met diverse genetiese profiele opgelewer. Sewe lyne bevat vier weerstandsgeentranslokasies (Lr24/Sr24, Lr34/Yr18, Sr2 en Lr19 of Sr31) elk, 11 lyne beskik oor kombinasies van drie gene elk, ses bevat twee gene elk en slegs drie lyne beskik oor .n enkele translokasie (Lr24/Sr24). Die realiteit dat die roespatogene reeds drie van die weerstandsgene in die finale populasie . Lr19, Sr31 en Sr24 . oorkom het, benadruk die waarde van die gebruik van nie-hoofgeenweerstand vir die daarstelling van duursame weerstand. Die fokus behoort toenemend meer op die aanwending van kwantitatiewe kenmerk-loci (QTL) vir hierdie doel te val en sal sodoende teweegbring dat MBS bydra tot die ontwikkeling van meer duursame weerstand. Die waarde van die integrasie van MBS en VH in kombinasie met konvensionele telingsmetodiek is reeds internasionaal vir die versnelling van kultivarontwikkeling aangetoon en word ook deur hierdie studie herbevestig.

The latter part of the reproductive growth phase in chickpea (<i>Cicer arietinum</i> L.) often coincides with declining temperature and wet conditions in western Canada, in sharp contrast to many other growing environments. This exacerbates the indeterminate nature of the crop, leading to excessive canopy development, and subsequently resulting in delayed maturity. The objectives of this study were to: i) determine the genetic relationships of short internode, double podding and early flowering traits with earliness of crop maturity; ii) determine the genetic control of major earliness traits in chickpea; iii) assess the patterns of post-flowering dry matter accumulation and partitioning to reproductive parts as related to earliness. <p>The results showed that double podding significantly reduced the number of days taken to maturity, under the conditions where this trait was sufficiently expressed. The best double podding genotypes, i.e. those with 1535% of the podded nodes bearing double pods, were about one week earlier than their single podding counterparts and standard checks. A physiological study revealed that the double podding parental genotype 272-2 partitioned a relatively greater proportion (about 58%) of the total dry matter to pods compared to 4254% in the single podding genotypes. Double podding increased the total number of pods set, and thus the increased demand for assimilates may have precluded further production of stems and leaves, resulting in an earlier transition of reproductive growth to physiological maturity. Days to flowering was positively associated with days to maturity, and partial path analysis revealed that days to flowering contributed to days to maturity indirectly via days to first pod maturity. Days to flowering explained 32% of the variation in days to first pod maturity. However, the short internode trait had an undesirable effect, in that all the short internode segregants were too late to mature. <p>Genetic studies revealed that days to flowering was determined by two major genes plus polygenes in chickpea in the short-season temperate environment of western Canada. The two major genes control over 65% of the phenotypic variation. Also, the additive component of genetic variance was significant for days to first podding, days to first pod maturity, reproductive period, and days to maturity; which is desirable for development of superior inbred cultivars of chickpea. These key phenological traits are interrelated but could be manipulated separately in the breeding process. Additional gain in earliness of crop maturity may be achieved through combined selection for these traits.

The latter part of the reproductive growth phase in chickpea (<i>Cicer arietinum</i> L.) often coincides with declining temperature and wet conditions in western Canada, in sharp contrast to many other growing environments. This exacerbates the indeterminate nature of the crop, leading to excessive canopy development, and subsequently resulting in delayed maturity. The objectives of this study were to: i) determine the genetic relationships of short internode, double podding and early flowering traits with earliness of crop maturity; ii) determine the genetic control of major earliness traits in chickpea; iii) assess the patterns of post-flowering dry matter accumulation and partitioning to reproductive parts as related to earliness. <p>The results showed that double podding significantly reduced the number of days taken to maturity, under the conditions where this trait was sufficiently expressed. The best double podding genotypes, i.e. those with 1535% of the podded nodes bearing double pods, were about one week earlier than their single podding counterparts and standard checks. A physiological study revealed that the double podding parental genotype 272-2 partitioned a relatively greater proportion (about 58%) of the total dry matter to pods compared to 4254% in the single podding genotypes. Double podding increased the total number of pods set, and thus the increased demand for assimilates may have precluded further production of stems and leaves, resulting in an earlier transition of reproductive growth to physiological maturity. Days to flowering was positively associated with days to maturity, and partial path analysis revealed that days to flowering contributed to days to maturity indirectly via days to first pod maturity. Days to flowering explained 32% of the variation in days to first pod maturity. However, the short internode trait had an undesirable effect, in that all the short internode segregants were too late to mature. <p>Genetic studies revealed that days to flowering was determined by two major genes plus polygenes in chickpea in the short-season temperate environment of western Canada. The two major genes control over 65% of the phenotypic variation. Also, the additive component of genetic variance was significant for days to first podding, days to first pod maturity, reproductive period, and days to maturity; which is desirable for development of superior inbred cultivars of chickpea. These key phenological traits are interrelated but could be manipulated separately in the breeding process. Additional gain in earliness of crop maturity may be achieved through combined selection for these traits.

Leaf rust caused by Puccinia hordei is an important disease of barley (Hordeum vulgare) in many regions of the world. Yield losses up to 62% have been reported in susceptible cultivars. The Rph5 gene confers resistance to the most prevalent races (8 and 30) of barley leaf rust in the United States. Therefore, the molecular mapping of Rph5 is of great interest. Genetic studies were performed by analysis of 93 and 91 F2 plants derived from the crosses 'Bowman' (rph5) x 'Magnif 102' (Rph5) and 'Moore' (rph5) x Virginia 92-42-46 (Rph5), respectively. Linkage analysis positioned the Rph5 locus to the extreme telomeric region of the short arm of barley chromosome 3H at 0.2 cM proximal to RFLP marker VT1 and 0.5 cM distal from RFLP marker C970 in the Bowman x Magnif 102 population. Synteny between rice chromosome 1 and barley chromosome 3 was employed to saturate the region within the sub-centimorgan region around Rph5 using sequence-tagged site (STS) markers that were developed based on barley expressed sequence tags (ESTs) syntenic to the phage (P1)-derived artificial chromosome (PAC) clones comprising distal region of the rice chromosome 1S. Five rice PAC clones were used as queries to blastn 370,258 barley ESTs. Ninety four non-redundant EST sequences were identified from the EST database and used as templates to design 174 pairs of primer combinations. As a result, 10 EST-based STS markers were incorporated into the 'Bowman' x 'Magnif 102' high-resolution map of the Rph5 region. More importantly, six markers, including five EST-derived STS sequences, co-segregate with Rph5. Genes, represented by these markers, are putative candidates for Rph5. Results of this study demonstrate the usefulness of rice genomic resources for efficient deployment of barley EST resources for marker saturation of targeted barley genomic region. / Ph. D.