Un modèle de morphogenèse aérienne de graminées fourragères, nommé L grass, a été développé lors de travaux précédents. Le but de la thèse est de proposer une méthode d'insertion de la morphogenèse racinaire dans ce modèle afin de tenir compte de l'impact des ressources telluriques sur la structure et le fonctionnement de la plante.</br>Un simulateur de plante entière de ray-grass anglais (Lolium perenne L.) incorporant (i) des règles d'autorégulation de l'architecture aérienne, (ii) le développement architecturé du système racinaire, (iii) des processus de coordination entre les parties aérienne et racinaire et (iv) un système d'allocation du carbone a été développé. La nature autorégulée du modèle lui permet de reproduire les réponses à l'intensité d'une défoliation et à la compétition pour la lumière sans nécessiter de contrôle central. Le couplage du modèle avec un modèle de sol permet de simuler le développement de la plante subissant différents scénarios d'apport en eau sans nécessiter de consignes morphogénétiques données a priori.</br>La représentation architecturée du système racinaire présente quelques limites, principalement en termes de ressources informatiques, pour les simulations de peuplements. Afin de pallier ces limites, un modèle continu de dynamique de densités racinaires a aussi été incorporé pour simuler l'enracinement. Les comparaisons entre les deux modèles de système racinaire ont montré l'intérêt indéniable des modèles de densités racinaires notamment pour les études à l'échelle d'un couvert végétal. / A model of the shoot morphogenesis of forage grasses, called L-grass, was developed in previous studies. The aim of this thesis is to propose a method for introducing root morphogenesis in the current model so the effect of telluric resources availability can be taken into account for shaping plant form and functioning.</br>A simulator of perennial ryegrass (Lolium perenne L.) whole plant, which includes (i) the rules of shoot architecture self-regulation,(ii) the architectural development of the root system, (iii) the coordination processes between shoot and root parts and (iv) a system of allocation of carbon, was developed. The self-adaptable character of the model allows the reproduction of the responses to the intensity of defoliation and the competition for sunlight without the need of any central control. The coupling of the model with a soil model enables to recreate the development of the plant undergoing different scenarios of water supply with no requirement of previously established morphogenetic guidelines.</br>The architectural representation of the root system presents some shortcomings, mainly regarding the need in computing power when simulating plant populations. In order to overcome these limitations, a continuous model of the dynamics of root densities has been also incorporated to simulate plant rooting. The comparison between both models of root systems has shown the undeniable interest of modeling root density, especially for the studies at the vegetation cover level.

The aim of this research was to identify the mechanisms that underpin changes in respiratory capacity during acclimation to temperature. Dark respiration, enzyme activities and leaf ultrastructure were measured from ryegrass (Lolium perenne) in controlled environmental chambers and two species of native grass (Chionochloa rubra & C. pallens) growing at different altitudinal ranges on Mount Hutt, Canterbury, New Zealand. The overall hypothesis was that the changes in both mitochondrial numbers and enzyme activity underpin the greater respiratory capacity observed in response to decreasing temperatures. Gas exchange measurements were carried out to measure rates of dark respiration (Rd) in leaves of both ryegrass and tussocks. Respiratory homeostasis (full acclimation) was achieved in ryegrass leaves but only partial acclimation in both species of tussock plants. Dark respiration rates for warm-grown ryegrass were greatly reduced compared to cool-grown grasses. Rd was lower for C. rubra growing at the base of the mountain (450m) compared to plants at a higher altitude (1060m). The dark respiration rates were also lower for C. pallens growing at 1070m than at 1600m. When comparing Rd between high and low altitude plants, it was significantly lower in low altitude plants at 450m than at 1600m. Oxygen consumption was measured in intact leaves and roots, crude mitochondria and isolated mitochondria from ryegrass to investigate whether a change in respiratory capacity was involved with changes in Rd. Mitochondrial respiratory capacity was slightly reduced in warm leaves and roots (not significantly). The respiratory capacity results from isolated mitochondria for C. rubra (at 450m and 1060m) and C. pallens (at 1070m and 1600m) were consistent with the hypothesis that plants from warm sites have lower respiratory capacity in comparison to plants from cool sites. Based on these results and those of previous studies, it was concluded that respiratory flux for any given temperature is not simply determined by maximal capacities of the respiratory apparatus but rather a combination of the availability of substrate supply, the demand for respiratory products (i.e. ATP) and/or the maximal capacity of respiratory enzymes. Utilizing transmission electron micrographs, it was found that mitochondria were significantly less abundant in warm-grown than cool-grown ryegrass mesophyll cells. Mitochondria dimensions increased slightly between the cool and warm treatment. At lower altitudes (C. rubra), there was a significant decrease in mitochondria numbers with decreasing elevation. At higher altitudes (C. pallens), there was no noticeable change in mitochondria numbers between 1070m and 1600m. It was concluded that mitochondrial abundance for the controlled and field experiments, and mitochondrial sizes in the field, were associated with changes in Rd. The maximal activities of fumarase and succinate dehydrogenase (SDH) in isolated mitochondria from leaves of ryegrass and tussock were measured spectrophotometrically. The results in the controlled experiment indicate that enzymes other than fumarase and SDH could be responsible for the increased respiratory capacity observed in cold acclimated leaves of ryegrass. However, fumarase maximal activity was significantly reduced in C. rubra at low altitude compared with C. pallens growing at high altitude - this suggests that it may be involved in the differences in respiratory capacity and Rd between the two sites. Succinate dehydrogenase did not differ significantly in response to altitude. The large difference between the two field sites for fumarase activity is comparable to the large difference in Rd and reduction in mitochondrial abundance and dimensions seen between the two sites. This supports the overall hypothesis that cool-grown plants keep up with energy demands at low temperatures by increasing enzyme concentrations/capacity. The results of this study are supportive of the hypothesis that growth in low altitudes and warm conditions will result in the reduction of Rd as a consequence of: (1) temperature sensitivity of the respiratory apparatus, resulting in the reduction of the respiratory capacities of mitochondria; (2) a reduction in mitochondria size and numbers; and as a consequence of this (3) a reduction in the activities of mitochondrial enzymes. However, these responses are species specific and vary according to the range of temperatures experienced by plants in the field and controlled environments.

Endophytic fungi (A. coenophialum and A. lolii) which infect grasses produce ergot alkaloids that serve as the grasses' chemical defenses and enhance the vigor of the grass. Turf-type tall fescue with high endophyte levels has been deliberately developed to produce a greener, more vigorous, pest-resistant turf. Consumption of endophyte-infected grass causes various toxicity symptoms in livestock. Cattle in the southeastern and midwestern United States, where tall fescue is grown on 14 million hectares, often develop signs of toxicosis during summer months from grazing plants in fected by A. coenophialum. A more severe form of the disease, fescue foot, has been associated with cold environment and reported in late fall and winter months not only in the southeastern United States but also in the northwest United States. In New Zealand, where perennial ryegrass is grown on 7 million hectares of pasture, sheep often develop a condition called ryegrass staggers from grazing plants infected by A. lolii. New Zealand reports economic losses grazing plants infected by A. lolii. New Zealand reports economic losses associated with the sheep industry of $205 million per year. In the United States, economic losses associated with the beef cattle industry alone is estimated at $600 million per year. Range finding experiments and case studies of fescue foot and perennial ryegrass staggers (PRGS) were conducted on cattle and sheep under grazing and barn conditions. The main objective was to determine threshold levels of the endophyte toxins, ergovaline (EV) (appendix 1) and lolitrem B (appendix 2), associated with the diseases of fescue foot and PRGS respectively. Fescue foot was experimentally induced in cattle under barn studies in the spring with 825 ppb ergovaline. The ergovaline contaminated feed was given for a period of 42 days. Similar barn studies in sheep in spring to early summer did not produce clinical fescue foot with up to 1215 ppb. Field studies of natural fescue foot in a herd of sheep were conducted, (ie 540 ppb) values of ergovaline in the feed, but clinical disease was not produced in late fall through winter. A case study from a herd of sheep revealed 813 ppb dietary ergovaline had produced fescue foot in the months of fall (November). Fields of perennial ryegrass (PRG) where sheep received 2,135 ppb lolitrem B toxin were associated with clinical cases of PRGS in 42 sheep of 237 sheep (18 percent incidence rate) in the Willamette Valley of Oregon. Three months later, sheep on this same field which then had 1,465 ppb lolitrem B, did not have PRGS. These were the first range finding experiments undertaken in this locale to document threshold levels of endophyte toxins associated with fescue foot and PRGS. / Graduation date: 1994

Plant species were assessed for recolonization of a brownfield in Muncie, IN. In a greenhouse study, soil was seeded to perennial ryegrass (Lolium perenne), red clover (Trifolium pratense) and sunflower (Helianthus annuus). Selected pots were amended with leaf compost and mycorrhizal fungi. Soil and plant tissue were analyzed after 30 and 90 days. Ryegrass and compost were studied at the brownfield site. In the greenhouse, red clover was capable of concentrating the greatest quantity of Cd, Cu, Cr, Ni, and Pb in above-ground biomass (all soil treatments combined). Compost + mycorrhizal fungi treatment resulted in highest Cd, Cu, and Zn plant concentrations (all plant treatments combined). Compost resulted in the highest tissue Cr and Ni concentrations. The reported study demonstrates that this brownfield is capable of being revegetated by turf and legume species. Each infertile and/or toxic site must be assessed for revegetation species on a case-by-case basis. / Department of Natural Resources and Environmental Management

Lolium perenne L. (perennial ryegrass) generally fails to persist under the sub-tropical cpnditions of South Africa. Furthermore, little research data are available on how to manage this species locally. This study was designed to identify the management options, particularly with r espect to grazing defoliation, which would help enhance the longevity of perennial ryegrass pastures. This was addressed by: 1) reviewing on-farm management practices of perennial ryegrass in KwaZulu-Natal; 2) conducting a detailed two-year field study of the effects of grazing frequency (HF, MF and LF = high, medium and low frequency, respectively) and intensity (HI, MI and LI = high, medium and low intensity, respectively), rotationally applied with the addition of a continuous grazing treatment (CG), on parameters linked to persistency. tiller population dynamics, dry matter These included: (DM) yield and quality, perennial ryegrass vigour, weed invasion and root development; and 3) examining effects of different levels of applied nitrogen (N) during the establishment year on various parameters linked to persistency. These included: tiller population densities, DM yield and quality, perennial ryegrass vigour, weed invasion and root development. The review of on-farm management practices of perennial ryegrass growers in KwaZulu-Natal revealed that reasonably high rates of N application (e.g. 350 and 250 kg N ha¯¹ a¯¹ to perennial ryegrass as pure and clover-based stands, respectively) are important for pasture survival. However, a consistent distribution of the applied N is even more important (i. e. at least seven split applications of N onto pure stands of perennial ryegrass and five onto perennial ryegrass-clover). In terms of grazing management, the period of absence of animals from the pasture during summer was identified as the most important grazing variable affecting pasture survival (i.e. ≥ 21 days). Also, the length of the period of occupation by animals should be as short as possible, particularly during summer (i. e. ≤ 3 days). Paying careful attention to summer irrigation is also an important variable contributing to pasture survival. Grazing intensity was not highlighted as an important contributor to pasture survival. In terms of tillering potential, DM yield and quality (cellulose dry matter disappearance and herbage N) and perennial ryegrass vigour, perennial ryegrass followed definite seasonal trends. These were highest during autumn and spring and were lowest during the mid to late summer period. Perennial ryegrass was most susceptible to general sward degradation through poor management during the mid to late summer period when the danger from weed invasion is greatest and its growth potential, vigour and tillering abilities are lowest within these seasonal periods, grazing defoliation produced marked effects. In terms of tiller survival, DM yield, plant vigour, reduced weed invasion and root production, treatments incorporating low frequency grazing (e.g. LFLI and LFHI) generally out-performed (P≤0.05) those incorporating high frequency grazing, irrespective of the intensity (e.g. HFHI, HFLI, and continuous grazing (CG)). The defoliation treatment incorporating medium frequency and intensity (MFMI) (currently the recommended defoliation strategy for perennial ryegrass) was also out-performed in many instances (P~0.05) by the low frequency treatments (e.g. LFHI and LFLI) . During the establishment year, increasing levels of applied N increased (P≤O. 05) perennial ryegrass DM yields and herbage quality. Models predicting the response of DM yield and quality to applied N suggest linear responses up to 720 kg N ha¯¹ a¯¹. Further refinement of such models and the inclusion of animal production parameters is recommended. Maximum (P≤0.05) tiller population densities occurred at applied N levels of 480 kg ha¯¹ a¯¹. Perennial ryegrass vigour increased (P≤O. 05) with increasing levels of applied N up to 480 kg h¯¹ a¯¹, but individual tiller vigour decreased. Increasing levels of applied N up to 360 kg ha¯¹ a¯¹ suppressed (P≤O. 05) weed tiller densities. Increasing levels of applied N (up to 600 kg h¯¹) increased (P≤O. 05) the root organic matter (OM) per unit volume of soil in the top 5 cm of the soil and decreased root OM per unit volume in the 10 - 20 cm soil depth category. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1994.

Hydrolytic enzymes degrade macromolecules into smaller components. These enzymes are important in fungal nutrition and have been implicated in the pathogenicity and virulence of pathogenic fungi towards their hosts. However, it is unknown if hydrolytic enzymes play important roles in mutualistic symbioses. In this study, the function of two different classes of hydrolytic enzymes was examined in the mutualistic symbiosis between the fungal endophyte Epichloë festucae and perennial ryegrass (Lolium perenne cv. Nui). Nine members of a gene family encoding subtilisin-like proteases were identified in E. festucae. The prt2, prt3 and prt5 genes encode putative extracellular proteins belonging to the proteinase K subfamily 1, and prt1 and prt6 encode putative extracellular proteins belonging proteinase K subfamily 2. The prt7 and prt8 genes encoded pyrolysin-like enzymes from subfamilies 1 and 2. The prt4 gene encodes a putative vacuolar protease, while the kex2 gene encodes a putative proprotein convertase. Expression analysis showed that the prt1, prt3, prt5, prt4 and kex2 genes, but not the prt2 gene, were expressed in culture. The prt1 and prt3 genes appeared to be up-regulated in planta compared to culture. The function of prt1 and prt2 in the symbiotum between E. festucae and perennial ryegrass was characterised by expressing these genes under the control of the Aspergillus nidulans gpdA or the E. festucae F11 ltmM promoters. No major differences in hyphal or plant morphology were observed between symbioses containing wild type E. festucae or endophyte strains containing the prt1 or prt2 transgenes. The gcnl gene, which encodes a β-1,6-glucanase, was identified immediately downstream of the prt2 gene. The function of the gcnl gene was characterised by gene replacement and testing the phenotype during growth in culture and in planta. E. festucae ∆gcnl strains grew normally on glucose-containing media. On media containing the β-1,6-glucan pustulan, ∆gcnl strains did not form aerial hyphae or hydrolyse pustulan, which the wild type strain did. This phenotype was partially complemented by growth of the ∆gcnl mutant in close proximity to wild type strains, and fully complemented by insertion of the gcnl gene. This suggests that the gcnl gene encodes the major β-1,6-glucanase activity of E. festucae.

The aim of this research was to identify the mechanisms that underpin changes in respiratory capacity during acclimation to temperature. Dark respiration, enzyme activities and leaf ultrastructure were measured from ryegrass (Lolium perenne) in controlled environmental chambers and two species of native grass (Chionochloa rubra & C. pallens) growing at different altitudinal ranges on Mount Hutt, Canterbury, New Zealand. The overall hypothesis was that the changes in both mitochondrial numbers and enzyme activity underpin the greater respiratory capacity observed in response to decreasing temperatures. Gas exchange measurements were carried out to measure rates of dark respiration (Rd) in leaves of both ryegrass and tussocks. Respiratory homeostasis (full acclimation) was achieved in ryegrass leaves but only partial acclimation in both species of tussock plants. Dark respiration rates for warm-grown ryegrass were greatly reduced compared to cool-grown grasses. Rd was lower for C. rubra growing at the base of the mountain (450m) compared to plants at a higher altitude (1060m). The dark respiration rates were also lower for C. pallens growing at 1070m than at 1600m. When comparing Rd between high and low altitude plants, it was significantly lower in low altitude plants at 450m than at 1600m. Oxygen consumption was measured in intact leaves and roots, crude mitochondria and isolated mitochondria from ryegrass to investigate whether a change in respiratory capacity was involved with changes in Rd. Mitochondrial respiratory capacity was slightly reduced in warm leaves and roots (not significantly). The respiratory capacity results from isolated mitochondria for C. rubra (at 450m and 1060m) and C. pallens (at 1070m and 1600m) were consistent with the hypothesis that plants from warm sites have lower respiratory capacity in comparison to plants from cool sites. Based on these results and those of previous studies, it was concluded that respiratory flux for any given temperature is not simply determined by maximal capacities of the respiratory apparatus but rather a combination of the availability of substrate supply, the demand for respiratory products (i.e. ATP) and/or the maximal capacity of respiratory enzymes. Utilizing transmission electron micrographs, it was found that mitochondria were significantly less abundant in warm-grown than cool-grown ryegrass mesophyll cells. Mitochondria dimensions increased slightly between the cool and warm treatment. At lower altitudes (C. rubra), there was a significant decrease in mitochondria numbers with decreasing elevation. At higher altitudes (C. pallens), there was no noticeable change in mitochondria numbers between 1070m and 1600m. It was concluded that mitochondrial abundance for the controlled and field experiments, and mitochondrial sizes in the field, were associated with changes in Rd. The maximal activities of fumarase and succinate dehydrogenase (SDH) in isolated mitochondria from leaves of ryegrass and tussock were measured spectrophotometrically. The results in the controlled experiment indicate that enzymes other than fumarase and SDH could be responsible for the increased respiratory capacity observed in cold acclimated leaves of ryegrass. However, fumarase maximal activity was significantly reduced in C. rubra at low altitude compared with C. pallens growing at high altitude - this suggests that it may be involved in the differences in respiratory capacity and Rd between the two sites. Succinate dehydrogenase did not differ significantly in response to altitude. The large difference between the two field sites for fumarase activity is comparable to the large difference in Rd and reduction in mitochondrial abundance and dimensions seen between the two sites. This supports the overall hypothesis that cool-grown plants keep up with energy demands at low temperatures by increasing enzyme concentrations/capacity. The results of this study are supportive of the hypothesis that growth in low altitudes and warm conditions will result in the reduction of Rd as a consequence of: (1) temperature sensitivity of the respiratory apparatus, resulting in the reduction of the respiratory capacities of mitochondria; (2) a reduction in mitochondria size and numbers; and as a consequence of this (3) a reduction in the activities of mitochondrial enzymes. However, these responses are species specific and vary according to the range of temperatures experienced by plants in the field and controlled environments.

Thesis (Ph. D.) -- Lincoln University, 2007. / Also available via the World Wide Web.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniversitet, 2005. / Härtill 5 uppsatser.

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