Disputats. Universität Hohenheim, 2005.

Les associations de cultures céréales-légumineuses participent au développement d'agrosystèmes performants et durables. La proportion de chaque espèce dans le couvert ainsi que leur productivité sont cependant fortement dépendantes de l'équilibre entre compétition et complémentarité interspécifique. Le partage de la lumière entre la céréale et la légumineuse est donc déterminant dans le fonctionnement des associations. La structuration physique de la canopée, qui conditionne l'interception du rayonnement lumineux, résulte de la mise en place de l'architecture aérienne des individus composant le peuplement. Afin d'appréhender les relations entre architecture et partage du rayonnement dans les associations blé-pois (Triticum aestivum L.-Pisum sativum L.), un modèle 3D de la morphogénèse aérienne du pois, baptisé L-Pea, a été développé sur la base de l'approche plante virtuelle. Des expérimentations ont été conduites afin i) de caractériser la morphogénèse de génotypes de pois contrastés cultivés sous différentes conditions (serre/champ, pur/associé), et ii) de modéliser l'architecture aérienne du pois. Un simulateur tripartite, intégrant les modèles L-Pea, ADEL-Blé (modèle architecturé de blé) ainsi que CARIBU (modèle de transferts radiatifs), a ensuite été construit afin de créer une association virtuelle. Cette approche de type plante virtuelle s'est révélée pertinente dans l'optique d'étudier le déterminisme architectural du partage de la lumière dans les associations blé-pois. Ce simulateur a par ailleurs montré que des paramètres architecturaux (e.g. ramifications, entrenoeuds) peuvent affecter de manière significative et dynamique le partage de la lumière et donc le développement de l'association. Cette thèse se propose i) de démontrer la pertinence de l'approche plante virtuelle pour appréhender le partage du rayonnement dans les associations et ii) de contribuer à la sélection/construction de variétés/idéotypes adaptés aux couverts plurispécifiques.

Leaf rust and stripe rust of wheat (Triticum aestivum L.) are caused by the fungal pathogens Puccinia triticina, and Puccinia striiformis f.sp. tritici, respectively. In North America, the incorporation of adult-plant resistance (APR) genes into breeding lines has been an important strategy to achieve durable resistance to both diseases. Previously, the spring wheat cultivar AC Domain was reported to express an effective level of adult-plant resistance (APR) to leaf rust under field conditions. Early gene postulation work had suggested AC Domain might carry the APR gene Lr34 due to its phenotypic similarity to other Lr34 carrying lines. However, new gene specific markers have shown that AC Domain is not a carrier of Lr34. The objective of this research was to genetically localize the resistance in AC Domain, which is important because the cultivar has frequently been used as a parent in Canadian breeding programs, primarily for its value as a source of pre-harvest sprouting resistance. A mapping population of 185 doubled haploid (DH) lines derived from the cross ‘RL4452’ by ‘AC Domain’ was used for this study. RL4452 is a known carrier of Lr34. During 2011-2012, the DH population was evaluated in field leaf rust nurseries at Saskatoon, SK and Portage, MB and at a stripe rust nursery at Lethbridge, AB. Field results indicated that rust resistance in the mapping population was variable, with lines ranging from highly resistant, to highly susceptible. DH lines carrying Lr34 showed a high level of resistance to both diseases. Thus, the non-Lr34 carriers were genotyped using select SSR markers, and by an Illumina 9k Infinium iSelect SNP assay for subsequent quantitative trait loci (QTL) analysis. QTL analysis revealed that AC Domain donated a major resistance QTL located on chromosome 2BS, that mapped 46 cM proximal to markers linked to Lr16, and explained a significant portion of the leaf and stripe rust phenotypic variance in all test environments. In addition, this QTL was significantly associated with the expression leaf tip necrosis (LTN), reduction in area under the disease progress curve (AUDPC), and coefficient of infection (CI). In certain environments the interaction between the 2B QTL and Lr34 was additive resulting in a superior level of rust resistance. Indoor rust testing showed AC Domain was susceptible to both diseases at the seedling stage. Taken together these results suggest that the identified resistance in AC Domain is likely due to the presence of an APR gene, on chromosome 2BS.

[Truncated abstract] The hydraulic properties of the roots of three crop species important to Western Australia were examined: wheat (Triticum aestivum), narrow-leafed lupin (Lupinus angustifolius) and yellow lupin (L. luteus). Generally, the hydraulic conductivity (Lpr) of root systems differs between species and can change in response to adverse conditions. To determine the significance of root anatomy and aquaporin activity on the pathway of water flow through roots, water flow was measured across cell membranes, individual roots and whole root systems. The combination of measurements identified that wheat and lupin roots have contrasting hydraulic properties. Wheat roots absorb water preferentially in the apical region, whereas lupin roots appear to absorb water more evenly along the entire root length. Lupin roots have a greater axial hydraulic conductance than wheat, due to more abundant xylem vessels and axial conductance increases with root length, in conjunction with xylem vessel development. However, water flow through the radial pathway is the limiting factor in whole root hydraulic conductance, in all species. Modelling and the inhibition of aquaporin activity with mercuric chloride demonstrated that radial water flow in wheat roots occurs by a combination of the cell-to-cell and apoplastic pathways, but in lupins, water flow appears to be predominantly apoplastic. Despite the presence of aquaporins in root cell membranes of all species, their role in regulating bulk water flow across roots is not clear in lupins, because of the significance of the apoplastic pathway ... After draining the chambers, the root systems of yellow lupin resumed growth, but there was no subsequent recovery in narrow-leafed lupin root systems. The growth and survival strategies of wheat and lupin root systems are disparate. Wheat root systems are comprised of numerous fine, highly branched, individual roots that extract water near the root tips and have the ability to regulate flow. These attributes may be advantageous in non-uniform or variable environments. Moreover, the ability of wheat roots to regulate flow may not only support survival during waterlogging, but also enhance recovery. In comparison, lupin root systems are designed like conduits, for the rapid uptake and transport of water when conditions are favourable. However, their thick taproots and lack of regulation of water transport or anatomical changes make them unsuitable for very wet soils.

Triticum aestivum (bread wheat), one of the most globally important cereal crops, is vulnerable to fusarium head blight (FHB). The disease is mainly associated with the pathogen Fusarium graminearum and generates yield losses and mycotoxin contaminated grains with low quality. One possible solution to overcome this problem is the production of FHB resistant wheat varieties by crossing with strongly resistant germplasm from either wheat or closely related species. Thinopyrum elongatum is a wild grass that carries genetic resistance to FHB on the long arm of its chromosome 7E (7EL). In the first part of this research project, five Th. elongatum accessions were characterized for their response to F. graminearum infection. In the second part, BC1F4 progeny derived from the cross CS-ph1b × CS-7E(7D) were characterized to better define the 7E fragments introgressed into the 7D chromosome. Progeny were screened with a series of known 7E-specific genetic markers and for their FHB resistance. Among the 43 wheat plants tested, twelve FHB resistant progeny were shown to carry a similar, smaller 7EL introgressed fragment based on genetic marker screening. To characterize further the introgressed 7EL fragments, additional 7EL-specific markers as well as 7DL-specific markers for homoeologous wheat sequences were designed. As neither wheat nor Th. elongatum genomes were fully sequenced at the time, this made the designing procedure challenging; a cross-walking strategy between wheat and Th. elongatum draft genomic sequences was used. Twelve pairs of markers for homoeologous sequence regions of 7EL and 7DL chromosomes plus six individual 7EL- and four 7DL-specific markers were successfully designed. Nine novel 7EL-specific markers were associated with the smallest 7EL fragment carrying FHB resistance. That smallest introgressed 7EL fragment replaced approximately half of the 7DL chromosome, based on the absence of 7DL markers in some progeny. The novel 7EL- and 7DL-specific markers as well as the proposed genetic order for novel and previously designed markers contributed greatly to the characterization of the introgressed 7EL fragments in the 7DL chromosome. Further analysis of progeny from the next generations of these plants and from other families will be required to confirm the results and possibly obtain much smaller 7EL fragments.

L’étude des interactions entre les plantes au sein de couverts hétérogènes pourrait permettre une meilleure utilisation des associations variétales de blé, car nous manquons de connaissances sur la manière dont les complémentarités, synergies et compétitions entre variétés affectent leurs performances dans ces conditions. Notre étude s'est focalisée sur la compréhension de l'impact de la compétition pour la lumière sur l'architecture aérienne du blé, en couplant une analyse expérimentale et une approche par modélisation. Nous avons dans un premier temps, caractérisé la plasticité de l’architecture aérienne en réponse à la modification de la densité de semis, pour 20 génotypes contrastés de blé tendre. Ainsi, nous avons déterminé que le nombre d’axes par plante était le trait le plus plastique pour tous les génotypes. Nous avons ensuite développé un modèle individu-centré représentant le développement du blé du semis à la floraison. Ce modèle est composé de deux parties : une partie descriptive du développement foliaire basée sur un modèle existant (ADEL-blé) et une partie plus mécaniste où nous avons intégré une régulation du tallage par la ressource lumineuse. Cette régulation du tallage se fait selon deux hypothèses simples : (1) la plante arrête d'émettre des talles dès que le Green Area Index (GAI) de son voisinage atteint une valeur seuil et (2) une talle meurt si la quantité de lumière qu'elle intercepte est inférieure à un seuil critique. La dynamique de tallage simulée par le modèle sur une large gamme de densité de semis est proche de la dynamique de tallage observée expérimentalement. Nous avons également caractérisé expérimentalement la plasticité de l’architecture aérienne de huit génotypes de blé en réponse à la compétition dans différentes associations variétales binaires. Ces analyses ont révélé des réponses assez différentes de celles mesurées en culture pure, soulignant la spécificité de certaines interactions entre plantes de génotypes différents. Ces essais ont confirmé que les associations contribuaient généralement à une augmentation de la production, en particulier dans des itinéraires techniques économes en intrants. Nous avons montré que des associations variétales comprenant des génotypes avec des hauteurs différentes permettaient d’avantager fortement le génotype haut sans trop pénaliser le génotype court. Ce travail a permis de développer un formalisme simplifié des processus régulant le tallage, qui va permettre d'explorer et optimiser les complémentarités/compétitions entre variétés dans des peuplements multi-variétaux. A terme le modèle pourra être couplé à des modèles génétiques pour mieux décrire l'impact de l'interaction plate-plante dans la valeur sélective des individus dans des populations hétérogènes. / The understanding of the interactions between plants within heterogeneous crops could allow for a more efficient use of wheat varietal mixtures, as there is a gap of knowledge on the complementarity, synergy and competition that develop among varieties within these systems. Our study is focused on competition for light, and its impact on the above ground architecture of wheat, coupling experimental analysis and model development. We first characterized the plasticity of the aerial architecture in response to different sowing densities, for 20 contrasting genotypes of winter wheat. The number of axes per plant was shown to be the most plastic trait for all genotypes. We developed an individual-based model representing wheat growth, from the sowing to flowering. The model is composed of two parts: a descriptive part of the foliar development based on the ADEL-wheat model and a mechanistic part which accounts for the regulation of tillering by light. Tillering is regulated by two simple hypotheses: (1) tillering stops when a critical value of local Green Area Index (GAI) is reached, (2) a tiller dies if the amount of intercepted light falls below a critical threshold. A realistic tillering dynamics was simulated by our model over a wide range of sowing densities, with a good fit with experimental data. We also experimentally characterized the plasticity of plant architecture for eight wheat genotypes observed in various two-components varietal mixtures. Contrasted plastic responses were observed when compared to those expressed in pure stands, underlining the specificity of certain plant-plant interactions. These experiments confirmed that the cultivar mixtures generally contribute to an overyielding, particularly in low-input agriculture . Finally, our results revealed that variety mixtures including genotypes with different heights may provide an advantage to the taller genotype with limited tradeoff on the short genotype. This work contributed to the development of a simplified formalism for tillering process, allowing to explore and optimize complementarities / competitions between plants within variety mixtures. Ultimately, the model could be coupled with a genetic model, in order to better describe the impact of plant-to-plant interactions in the selective value of individuals in heterogeneous populations.

Das Wurzelwachstum von Winterweizen wurde erfasst und modelliert, um teilflächenspezifisches Boden- und Düngemanagement zu verbessern. Die Variation von Wurzellängendichten im Feld wurde über zwei Vegetationsperioden hinweg an zwei unterschiedlichen Standorten in Ostdeutschland untersucht. Zur Auswertungserleichterung der hohen Anzahl an Wurzelproben, wurde eine halbautomatische Methode zur Bildanalyse von Wurzeln entwickelt. Der Einfluss von Änderungen bezüglich Bodenwasserstatus und Bodendichte bzw. Durchdringungswiderstand auf das Wurzelwachstum wurde untersucht. Die erhobenen Felddaten dienten gleichzeitig dazu, die Bodenwasser- und Wurzelwachstumsberechnung des Modells CERES-Wheat zu validieren. Das Modell simulierte die unterschiedlichen Bodeneigenschaften sowie die Wurzellängendichten und Bodenwassergehalte nur unzureichend. Der Effekt von Änderungen der Niederschlagsmengen auf die Simulationen von Wurzellängendichten und Bodenwassergehalten wurde anhand einer Unsicherheitsanalyse getestet und war extrem gering. Des Weiteren wurde eine Methode für praktische Zwecke entwickelt, mit der die Generierung von räumlich hoch aufgelösten Bodeninformationen unter Verwendung limitierter Eingangsdaten möglich ist. Die Modellkalkulationen basieren auf der Dempster-Shafer-Theorie. Anhand von multitemporal und multimodal erfassten Bodenleitfähigkeitsdaten, die Eingangsdaten für den Modellansatz sind, wurden Bodentypen und Texturklassen bestimmt. Das Modell generiert eine digitale Bodenkarte, die flächenhafte Informationen über Bodentypen und Bodeneigenschaften enthält. Die Validation der Bodenkarte mit zusätzlich erhobenen Bodeninformationen ergab gute bis sehr gute Ergebnisse. / Winter wheat root growth was measured and modelled to improve site-specific soil and fertilizer management in commercial wheat fields. Field variations in root length densities were analysed at two contrasting sites in East-Germany during two vegetation seasons. A semi-automated root analysing method was developed to facilitate analyses of large numbers of samples. Influences of variations in soil water states, bulk densities and penetration resistances on spatial distributions of roots were quantified. Differences in soil characteristics were large between the two sites and affected root growth considerably. The same field data was used for validating the soil moisture and root growth calculations of the widely applied growth model CERES-Wheat. Simulations of root length densities, soil physical properties and soil water contents were inadequate. The effects of changes of rainfall variabilities on simulated root length densities and soil water contents were tested by uncertainty analysis but were negligible low. A methodology for generating soil information for practical management purposes at a high degree of spatial resolution using limited input information was developed. The corresponding model calculations were carried out based on the Dempster and Shafer theorem. Soil types and texture classes were determined with multimodally and multitemporally captured data of soil electrical conductivities which are required input data of the new model approach. The model generates a digital map with extensive information of spatial variations in soil properties. The validation of the generated soil map with soil data from independent measurements yielded close correlation between measured and calculated values.

It is widely accepted that bioavailability, rather than total soil concentration, is preferred when assessing the risk associated with metal contamination. Despite this, debate continues on what constitutes a bioavailable pool and how to best predict bioavailability, especially in relation to crop plants. The overall aim of this thesis was to assess and validate measures of cadmium (Cd), copper (Cu), nickel (Ni) and zinc (Zn) bioavailability in a range of soils amended with metal salts and biosolids. Six potential measures of bioavailability were investigated and compared: total metal; 0.04 M EDTA extraction; 0.05 M Ca(NO₃)₂ extraction; soil solution extracted using rhizon probes; effective solution concentration (CE) determined using diffusive gradients in thin films (DGT); and modelled free ion activities (WHAM 6.0). These were compared to shoot metal concentrations obtained from plants grown in three soils with contrasting properties treated with biosolids and metal salts. The first study involved a wheat seedling (Triticum aestivum) assay carried out under controlled environmental conditions on incubated soils treated with metal salts and biosolids. Results showed that the presence of biosolids resulted in increases of DOC, salinity, Ca and Mg in soil solution as well as total concentrations of Cu and Zn, dry matter was also adversely affected by increased levels of salinity. The addition of biosolids did not significantly alter the extractability or solubility of Cd, Cu, Ni and Zn although concentrations of Cd in shoots were significantly lower in plants grown in biosolids amended soils compared with unamended soils. The second study involved a field experiment that used 20 cm diameter by 30 cm deep soil monoliths of the same three soils treated with metals and biosolids, and perennial ryegrass (Lolium perenne) was grown for 24 months. Results revealed the addition of biosolids significantly increased the amount of DOC, salinity, Ca and Mg in solution. The presence of biosolids also significantly altered the bioavailability of Cd, Cu, Ni and Zn, as measured by soil solution, CE and free ion activity. However, this change had little effect on plant metal uptake. The length of time following treatment application had the greatest effect on soil chemistry and metal availability, resulting in pH decreases and increases in DOC, soil solution salinity, Ca and Mg. The free ion activities of each metal increased with time, as did soil solution Cd and Zn and CE-Cu, with results for Zn indicative of migration through the soil profile with time. Plant uptake of Ni and Zn also changed with time. Nickel concentrations in shoots decreased, while concentrations of Zn in shoots increased. The findings from the two studies demonstrated that biosolids increased the amount of DOC, salinity, Ca and Mg present in soil solution. In the lysimeter study measures of metal availability were affected in soils amended with biosolids, but this did not effect shoot concentrations. The overall predictive strengths of the six potential measures of bioavailability was investigated using results from the previously described experiments and related studies carried out by ESR and Lincoln University using nine different soils amended with combinations of biosolids and metal salts. Of the four metals Ni provided the strongest correlations between metal bioavailability and shoot concentrations, with 0.05 M Ca(NO₃)₂ extraction giving the strongest relationship for Ni concentrations in shoots (r² = 0.73). This suggests that the solubility of Ni is highly indicative of shoot concentrations and that Ca(NO₃)₂ is a robust measure of Ni bioavailability. In addition Ca(NO₃)₂ provided the best estimate of Zn bioavailability (r² = 0.65), and CE-Cd provided the best measure of Cd bioavailability, although it could only describe 47 % of shoot Cd concentration. Results for Cu were typical of previously described studies as assays of Cu availability are almost always poorly correlated with shoot concentrations, with total Cu having the strongest relationship (r² = 0.34). Methods based on the extractability and solubility of Cu in soils were poor indicators of Cu concentration in shoots. Overall, the addition of biosolids did not alter the outcome of these bioavailability assays, and results indicated that total metal concentrations present in the soils and biosolids matrix, plus length of time since soil treatment, had a greater affect on metal bioavailability.

Fusarium head blight (FHB), caused mainly by Fusarium graminearum (teleomorph: Gibberella zeae), is one of the most damaging diseases of wheat. A ‘Brio’/‘TC 67’ spring wheat population was used to map quantitative trait loci (QTLs) for resistance to FHB, and to study the association of morphological and developmental characteristics with FHB resistance. Interval mapping (IM) detected a major QTL on chromosome 5AL for resistance to disease severity (type II resistance) and Fusarium-damaged kernels (FDK) under greenhouse and field conditions, respectively. Inconsistent QTL(s) was also detected on chromosome 5BS for disease severity and index using field data. The associations of plant height and number of days to anthesis were negative with disease incidence, severity, index, and deoxynivalenol (DON) accumulation data under field conditions. However, number of days to anthesis was positively correlated with disease severity (greenhouse) and FDK (field). Awnedness had a negative effect on FHB, namely the presence of awns resulted in less disease in the population. Spike threshability also affected FHB so that the hard threshable genotypes represented lower disease. Phylogenetic relationships of putative F. graminearum isolates from different sources were characterized using Tri101 gene sequencing data. Canadian and Iranian isolates clustered in F. graminearum lineage 7 (=F. graminearum sensu stricto) within the F. graminearum clade while the isolates received from CIMMYT, Mexico were placed in F. graminearum lineage 3 (=Fusarium boothii) within the Fg clade or Fusarium cerealis. The PCR assay based on the Tri12 gene revealed the presence of the NIV, 3-ADON, and 15-ADON chemotypes with 15-ADON being the predominant chemotype. While we did not find the NIV chemotype among the Canadian isolates, it was the predominant chemotype among the Iranian isolates. High variation in aggressiveness was observed among and within Fusarium species tested, with the isolates of F. graminearum sensu stricto being the most aggressive and the NIV chemotype being the least aggressive. The interactions between Fusarium isolates and wheat genotypes from different sources were investigated by inoculating isolates of F. graminearum sensu stricto and F. boothii on wheat genotypes. Significant differences were observed among the genotypes inoculated by single isolates. Results also showed significant interactions between Fusarium isolates and wheat genotypes. The F. boothii isolates from CIMMYT produced low disease symptom and infection on wheat genotypes regardless of the origin of the genotypes while F. graminearum sensu stricto isolates from Canada and Iran resulted in higher FHB scores.

Fusarium head blight (FHB), caused mainly by Fusarium graminearum (teleomorph: Gibberella zeae), is one of the most damaging diseases of wheat. A ‘Brio’/‘TC 67’ spring wheat population was used to map quantitative trait loci (QTLs) for resistance to FHB, and to study the association of morphological and developmental characteristics with FHB resistance. Interval mapping (IM) detected a major QTL on chromosome 5AL for resistance to disease severity (type II resistance) and Fusarium-damaged kernels (FDK) under greenhouse and field conditions, respectively. Inconsistent QTL(s) was also detected on chromosome 5BS for disease severity and index using field data. The associations of plant height and number of days to anthesis were negative with disease incidence, severity, index, and deoxynivalenol (DON) accumulation data under field conditions. However, number of days to anthesis was positively correlated with disease severity (greenhouse) and FDK (field). Awnedness had a negative effect on FHB, namely the presence of awns resulted in less disease in the population. Spike threshability also affected FHB so that the hard threshable genotypes represented lower disease. Phylogenetic relationships of putative F. graminearum isolates from different sources were characterized using Tri101 gene sequencing data. Canadian and Iranian isolates clustered in F. graminearum lineage 7 (=F. graminearum sensu stricto) within the F. graminearum clade while the isolates received from CIMMYT, Mexico were placed in F. graminearum lineage 3 (=Fusarium boothii) within the Fg clade or Fusarium cerealis. The PCR assay based on the Tri12 gene revealed the presence of the NIV, 3-ADON, and 15-ADON chemotypes with 15-ADON being the predominant chemotype. While we did not find the NIV chemotype among the Canadian isolates, it was the predominant chemotype among the Iranian isolates. High variation in aggressiveness was observed among and within Fusarium species tested, with the isolates of F. graminearum sensu stricto being the most aggressive and the NIV chemotype being the least aggressive. The interactions between Fusarium isolates and wheat genotypes from different sources were investigated by inoculating isolates of F. graminearum sensu stricto and F. boothii on wheat genotypes. Significant differences were observed among the genotypes inoculated by single isolates. Results also showed significant interactions between Fusarium isolates and wheat genotypes. The F. boothii isolates from CIMMYT produced low disease symptom and infection on wheat genotypes regardless of the origin of the genotypes while F. graminearum sensu stricto isolates from Canada and Iran resulted in higher FHB scores.