Herbicides have become a key component in modern agricultural production. Meanwhile, there is a concern that some herbicides persist past the growing season of the treated crop, and negatively influence the production of the subsequently planted crops. Amongst various herbicides used in western Canada, acetohydroxyacid synthase (AHAS)-inhibiting herbicides warrant special attention given their residual properties and acute plant toxicity at low concentrations in soil. Soil residual AHAS inhibitors have the potential to influence both leguminous host plants and their bacterial symbiotic partners; consequently, the use of an AHAS inhibitor in a given year can negatively influence the inoculation success and grain yield of legumes cropped in the following year. <p>The present thesis project focused on one of the AHAS inhibiting herbicides (flucarbazone) and studied its potential for carryover injury and negative influence on the success of inoculation in field pea. A series of growth chamber and field experiments were conducted to test the following null hypothesis: the presence of residual flucarbazone in soil does not affect nodulation of field pea by inoculum rhizobia. <p>A growth chamber experiment clearly demonstrated the susceptibility of field pea to the presence of flucarbazone in soil where the lowest concentration of flucarbazone amendment (5 ìg kg1) significantly reduced the crop growth. In contrast, a field study failed to reveal any negative effects of flucarbazone use on crop growth and N2 fixation. <p>It was concluded that if the weather and soil conditions favour decomposition of flucarbazone as described in the present study, flucarbazone applied at the recommended field rate will not persist into the following season at high enough concentrations to negatively influence field pea growth, grain yields, and inoculation success. To ensure safety of rotational crops, it is important to strictly adhere to the herbicide application guidelines. Additionally, producers are cautioned to be particularly aware of the environmental and soil conditions that may reduce the rate of herbicide degradation.

L'architecture du couvert constitue un levier susceptible de limiter le développement épidémique des mycoses aériennes des plantes. La grande variabilité des caractéristiques architecturales du pois fait du pathosystème Mycosphaerella pinodes/pois un candidat idéal pour une telle étude. Deux hypothèses sont testées pour expliquer la montée de la maladie de la base vers le haut du couvert en cours de culture : i) la présence d'un gradient de réceptivité des organes du pois liée à leur niveau de sénescence, et ii) la présence d'un gradient d'humectation avec une durée d'humectation plus longue à la base des couverts. Au champ, trois cultivars ont été semés à plusieurs densités afin d'obtenir divers scénarios architecturaux. Les couverts les plus denses présentent des niveaux de sénescence plus élevés générés par les indices de surface foliaire des étages supérieurs ainsi qu'un niveau de maladie plus sévère. Une étude analytique complémentaire, réalisée en conditions contrôlées, a montré la plus grande réceptivité à l'ascochytose des organes sénescents. Les mesures microclimatiques montrent une augmentation générale de la durée d'humectation au sein des couverts par rapport à l'extérieur durant les périodes pluvieuses, seules périodes favorables à l'infection d'après notre modélisation adaptée du modèle de Magarey et al. Nos résultats montrent ainsi que l'architecture impacte directement et indirectement le développement épidémique, mais ne peut fournir seule un échappement total à la maladie ; elle doit donc être combinée à d'autres méthodes de lutte.

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.

Peas dominate New Zealand grain legume production and they are a major export crop. However, weeds are a major problem particularly under organic production, where the use of synthetic chemicals is prohibited. To address this limitation, a research program to study weed control in peas was done to provide both conventional and organic farmers a sustainable weed management package. This was done through three field experiments over two growing seasons, 2006/07 and 2007/08. Experiment 1, (2006/07) evaluated the effect of 50, 100 and 400 plants m² on crop yield, and weed growth of Aragon, Midichi or Pro 7035 with and without cyanazine. Experiment two explored the physiology of two pea genotypes, the leafed (Pro 7035) and the semi leafless (Midichi) sown at three dates. A herbicide treatment was included as a control. In the third experiment Midichi, was used to investigate the effect of different pea and weed population combinations and their interaction on crop yield and weed growth. All crops were grown at Lincoln University on a Templeton silt loam soil. In Experiment one, herbicide had no effect on total dry matter (TDM) and seed yield (overall mean seed yield 673 g m²). There was also no significant difference in mean seed yield among the pea genotypes, Aragorn, Pro 7035 and Midichi, (overall mean, 674 g m²). The lowest average seed yield, 606 g m² was from 400 plants m² and the highest, 733 g m², from 50 plants m², a 21% yield increase. A significant herbicide by population interaction showed that herbicide had no effect on seed yields at 100 and 400 plants m². However, cyanazine treated plots at 50 plants m² gave 829 g m² of seed. This was 30% more than the 637 g m², from plots without herbicide. In Experiment 1 pea cultivar and herbicide had no significant effect on weed counts. In Experiment 2 the August sowing gave the highest seed yield at 572 g m². This was 62% more than the lowest yield, in October. Cyanazine treatment gave a mean seed yield of 508 g m², 19% more than from unsprayed plots. There was a significant (p < 0.05) sowing date x genotype interaction which showed that in the August sowing genotype had no effect on seed yield. However, in September the Pro 7035 seed yield at 559 g m² was 40% more that of Midichi and in October it gave 87% more. Weed spectrum varied over time. Prevalent weeds in spring were Stachys spp, Achillea millefolium L., and Spergular arvensis L. In summer they were Chenopodium album L., Rumex spp, Trifolium spp and Solanum nigrum L. Coronopus didymus L., Stellaria media and Lolium spp were present in relatively large numbers throughout the season. In Experiment 3 seed yield increased significantly (p < 0.001) with pea population. Two hundred plants m² gave the highest mean seed yield at 409 g m² and 50 plants m² gave the lowest (197 g m²). The no-sown-weed treatment gave the highest mean seed yield of 390 g m². This was due to less competition for solar radiation. There was no difference in seed yield between the normal rate sown weed and the 2 x normal sown weed treatments (mean 255 g m²). It can be concluded that fully leafed and semi-leafless peas can be sown at similar populations to achieve similar yields under weed free conditions. Increased pea sowing rate can increase yield particularly in weedy environments. Early sowing can also increase yield and possibly control problem weeds of peas (particularly Solanum spp), which are usually late season weeds. Herbicide can enhance pea yield but can be replaced by effective cultural methods such as early sowing, appropriate pea genotype and high sowing rates. Additional key words: Pisum sativum L., semi-leafless, fully leafed, cyanazine, pea population, weed population, sustainable, TDM, seed yield, weed, weed counts, sowing date, weed spectrum, seed rates.

Isoflavone synthase (IFS; CYP93C) plays a key role in the biosynthesis of the plant secondary metabolites, isoflavonoids. These phenolic compounds, which are well-known for their multiple biological effects, are produced mostly in leguminous plants (family Fabaceae). However, at least 225 of them have also been described in 59 other families, without any knowledge of orthologues to hitherto known IFS genes from legumes (with the single exception of sugar beet - Beta vulgaris, from the family Chenopodiaceae). In view of these facts, this masters thesis has focused on two main objectives: (1) to identify isoflavone synthase genes in selected leguminous and non-leguminous plants exploiting the PCR strategy with degenerate and non-degenerate primers, and (2) to find a system for the verification of the correct function of these genes. Our methodology for the identification of IFS orthologues was successfully demonstrated in the case of two examined legumes - Phaseolus vulgaris L. and Pachyrhizus tuberosus (Lam.) Spreng, in the genomic DNA of which the complete IFS sequences have been newly identified. To design a procedure for ascertaining the correct function of these genes and others once they have been completely described, a pilot study with IFS from Pisum sativum L. (CYP93C18; GenBank number...

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The contamination of process pea (Pisum sativum L.) crops by the immature fruit of black nightshade (Solanum nigrum L.) and hairy nightshade (S. physalifolium Rusby var. nitidibaccatum (Bitter.) Edmonds) causes income losses to pea farmers in Canterbury, New Zealand. This thesis investigates the questions of whether seed dormancy, germination requirements, plant growth, reproductive phenology, or fruit growth of either nightshade species reveal specific management practices that could reduce the contamination of process peas by the fruit of these two weeds. The seed dormancy status of these weeds indicated that both species are capable of germinating to high levels (> 90%) throughout the pea sowing season when tested at an optimum germination temperature of 20/30 °C (16/8 h). However, light was required at this temperature regime to obtain maximum germination of S. nigrum. The levels of germination in the dark at 20/30 °C and at 5/20 °C, and in light at 5/20 °C, and day to 50 % germination analyses indicated that this species cycled from nondormancy to conditional dormancy throughout the period of investigation (July to December 2002). For S. physalifolium, light was not a germination requirement, and dormancy inhibited germination at 5/20 °C early in the pea sowing season (July and August). However, by October, 100% of the population was non-dormant at this test temperature. Two field trials showed that dark cultivation did not reduce the germination of either species. Growth trials with S. nigrum and S. physalifolium indicated that S. physalifolium, in a non-competitive environment, accumulated dry matter at a faster rate than S. nigrum. However, when the two species were grown with peas there was no difference in dry matter accumulation. Investigation of the flowering phenology and fruit growth of both species showed that S. physalifolium flowered (509 °Cd, base temperature (Tb) 6 °C) approximately 120 °Cd prior to S. nigrum (633 °Cd). The fruit growth rate of S. nigrum (0.62 mm/d) was significantly faster than the growth rate of S. physalifolium (0.36 mm/d). Because of the earlier flowering of S. physalifolium it was estimated that for seedlings of both species emerging on the same date that S. physalifolium could produce a fruit with a maximum diameter of 3 mm ~ 60 °Cd before S. nigrum. Overlaps in flowering between peas and nightshade were examined in four pea cultivars, of varying time to maturity, sown on six dates. Solanum physalifolium had the potential to contaminate more pea crops than S. nigrum. In particular, late sown peas were more prone to nightshade contamination, especially late sowings using mid to long duration pea cultivars (777-839 °Cd, Tb 4.5 °C). This comparison was supported by factory data, which indicated that contamination of crops sown in October and November was more common than in crops sown in August and September. Also, cultivars sown in the later two months had an ~ 100 °Cd greater maturity value than cultivars sown in August and September. Nightshade flowering and pea maturity comparisons indicated that the use of the thermal time values for the flowering of S. nigrum and S. physalifolium can be used to calculate the necessary weed free period required from pea sowing in order to prevent the flowering of these species. The earlier flowering of S. physalifolium indicates that this species is more likely to contaminate pea crops than is S. nigrum. Therefore, extra attention may be required where this species is present in process pea crops. The prevention of the flowering of both species, by the maintenance of the appropriate weed free period following pea sowing or crop emergence, was identified as potentially, the most useful means of reducing nightshade contamination in peas.

The association between individual plant performance and seed yield variability within and between field pea crops was investigated. In 1988/89 six F8 genotypes with morphologically distinct characteristics were selected from a yield evaluation trial. Analysis of the individual plant performance within these crops indicated an association between low seed yields and the location and dispersion of plant harvest index (PHI) and plant weight (PWT) distributions. The analyses also showed there was a strong linear relationship between the seed weight (SWT) and PWT of the individual plants within each crop, and that the smallest plants tended to have the lowest PHI values. A series of 20 simulations was used to formalize the relationships between SWT, PWT and PHI values within a crop into a principal axis model (PAM). The PAM was based on a principal axis which represented the linear relationship between SWT and PWT, and an ellipse which represented the scatter of data points around this line. When the principal axis passed through the origin, the PHI of a plant was independent of its PWT and the mean PHI was equal to the gradient of the axis. However, when the principal axis had a negative intercept then the PHI was dependent on PWT and a MPW was calculated. In 1989/90 four genotypes were sown at five plant populations, ranging from 9 to 400 plants m⁻². Significant seed and biological yield differences were detected among genotypes at 225 and 400 plants m⁻². The plasticity of yield components was highlighted, with significant genotype by environment interactions detected for each yield component. No relationship was found between results for yield components from spaced plants and those found at higher plant populations. The two highest yielding genotypes (CLU and SLU) showed either greater stability or higher genotypic means for PHI than genotypes CVN and SVU. Despite significant skewness and kurtosis in the SWT, PWT, and PHI distributions from the crops in this experiment, the assumptions of the PAM held. The lower seed yield and increased variability in PHI values for genotype CVN were explained by its higher MPW and the positioning of the ellipse closer to the PWT axis intercept than in other genotypes. For genotype SVU, the lower seed yield and mean PHI values were explained by a lower slope for the principal axis. Both low yielding genotypes were originally classified as having vigorous seedling growth and this characteristic may be detrimental to crop yields. A method for selection of field pea genotypes based on the PAM is proposed. This method enables the identification of weak competitors as single plants, which may have an advantage over vigorous plants when grown in a crop situation.