Over the last century, flowering rush (Butomus umbellatus L.: Butomaceae) has escaped its native Eurasian range and has become a problematic species in North America. As an aquatic invasive species, flowering rush has degraded native wetlands and has interfered with human water usage. Although experimental work has been done regarding the reproductive biology of the species, few empirical studies regarding the ecology of the species have been conducted. The research reported here demonstrates that flowering rush is capable of aggressive clonal growth and propagation, and can perform well along a depth gradient from zero to 132cm. Proper management and control of invasive species relies on sound ecological knowledge of the target species, and this work aims to help gather that information.

Made available in DSpace on 2014-06-11T19:30:24Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-03-28Bitstream added on 2014-06-13T19:00:26Z : No. of bitstreams: 1 aguiar_eb_dr_botfca.pdf: 799841 bytes, checksum: 76febcd3057aea23b05ef3cdca2c3afa (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / A poda da parte aérea da mandioca é prática comum nos cultivos comerciais destinados à industrialização. Vem sendo praticada principalmente por possibilitar o controle das plantas infestantes com herbicidas no segundo ciclo vegetativo. Seus efeitos no desenvolvimento das plantas e na produtividade de raízes de mandioca ainda não são claros e resultados controversos são encontrados na literatura. Com o objetivo de estudar os efeitos da poda foram realizados seis experimentos, em dois ambientes: Botucatu, experimentos 1, 3 e 5 e em São Manuel, experimentos 2, 4 e 6. Os experimentos 1 e 2 tiveram como causas de variação cinco variedades de mandioca cultivadas com e sem poda. Os experimentos 3 e 4 avaliaram nove épocas de poda frente a uma testemunha conduzida sem poda. Os experimentos 5 e 6 tiveram como causas de variação quatro densidades de plantio avaliadas com e sem poda. Concluiu-se que: a poda altera a produtividade de matéria seca de raízes de maneira distinta considerando a variedade e o ambiente; a poda anterior ao período de repouso fisiológico ou após o início do segundo ciclo vegetativo reduz a produtividade de matéria seca de raízes; em altas densidades de plantio, a poda reduz de maneira significativa a produtividade de matéria seca de raízes. Desse modo, a poda da parte aérea da mandioca não deve ser recomendada de maneira genérica, devendo considerar entre outros, os fatores avaliados no presente estudo / Cassava pruning is common in commercial crops destined for industrialization, a practice mainly aimed at enabling weed control with herbicides in the second growth cycle. Its effects on plant development and cassava yields remain unclear and controversial results are reported in the literature. With the objective of studying the effects of pruning, six experiments were conducted in two environments: in Botucatu, experiments 1, 3 and 5, and in São Manuel, experiments 2, 4 and 6. In experiments 1 and 2, the established variables were five varieties of cassava cultivated with and without pruning. Experiments 3 and 4 evaluated nine pruning dates compared with control cultivated without pruning. The established variables in experiments 5 and 6 were four planting densities, evaluated with and without pruning. It can be concluded that: cassava pruning causes distinct alterations in the productivity of dry root matter, depending on the variety and culture environment; pruning before or after the period of physiological rest or after the onset of the second growth cycle reduces the productivity of dry root matter; and pruning in high planting densities significantly reduces the productivity of dry root matter. Thus, cassava pruning cannot be recommended as a general practice, as currently occurs, and the factors evaluated in this study should be taken into consideration

Die vorliegende Arbeit liefert neue Kenntnisse über das Konkurrenzverhalten der Sprossscheitelschichten bei der Blattmesophyllbildung und trägt dadurch zum Verständnis der Entwicklungsgeschichte höherer Pflanzen bei. Weißbunte Pflanzen von Peperomia serpens SW. LOUD, Sedum rubrotinctum R. T. CLAUSEN, Pedilanthus tithymaloides (L.) POIT. und Plectranthus coleoides BENTH wurden verwendet, um den Bau des Sprossscheitels und die chimärische Natur des Laubblattes zu analysieren. Durch die Untersuchungen zum Bau des Sprossscheitels und zur Blattanatomie wurden die Anzahl initialer Sprossscheitelschichten und die periklinalchimärische Natur der untersuchten Pflanzen bestätigt. Mit Hilfe von Mittelwertvergleichen der Mächtigkeit L2- und L3-bürtiger Mesophyllgewebe wurde die Beteiligung genetisch verschiedener internaler Sprossscheitelschichten an der Bildung des Blattmesophylls bei Sedum rubrotinctum, Pedilanthus tithymaloides und Peperomia serpens erfasst. Die Existenz histogenetisch grüner L2- oder L3-bürtiger Gewebe verursacht eine Zunahme der Blattquerschnittfläche (Sedum rubrotinctum) und eine Vergrößerung der Blattmesophyllhöhe (Peperomia serpens und Pedilanthus tithymaloides). Es wurden Regenerationsversuche an Blattstecklingen der Periklinalchimäre von Peperomia serpens und Sedum rubrotinctum durchgeführt. Durch In-vivo-Provozierung von Adventivsprossen an Blattstücken und achselknospenfreien Sprossen gelang es, die zwei untersuchten heterohistischen Musterpflanzen von Peperomia serpens ('GGW' und 'GWG') in grüne und weiße Nachkommen zu zerlegen. An Blattstecklingen bildeten sich in der Mehrzahl L3-bürtige Regenerate (ca. 75 %). Eine Beteiligung der L2-bürtigen Gewebe bei der Regeneration war an den Blattrandexplantaten zu beobachten. Das L1-bürtige Hypoderm konnte nur in der In-vitro-Blattregeneration deutlich seine Fähigkeit zur Adventivsprossbildung zeigen. Die Blattregenerationsergebnisse bei Peperomia serpens demonstrieren deutlich, dass sich alle drei Sprossscheitelschichten (L1, L2, L3) an der Blattmesophyllbildung beteiligen können. An Blattstecklingen von Periklinalchimären bei Sedum rubrotinctum bildeten sich grüne, weiße und neue chimärische Adventivsprosse. Aus den Regenerationsergebnissen lässt sich die entscheidende Rolle der L2-bürtigen Gewebe bei der Adventivsprossbildung ablesen. Die Regenerationsergebnisse sprechen dafür, dass die Bildung der Adventivsprosse durch die Beteiligung der L2- und L3-bürtigen Gewebe hervorgerufen wurde und die L1-bürtigen Gewebe an der Adventivsprossbildung nicht beteiligt sein konnten. Demzufolge sind tiefer liegende Gewebe (L2- und L3-bürtige) des Laubblattes beider Arten bei der Bildung der Adventivsprosse entscheidender als die L1-bürtige Epidermis. Das Ausmaß der Beteiligung an der Adventivsprossbildung bei Peperomia serpens und Sedum rubrotinctum wird nicht von der genetischen Herkunft (weiß oder grün) des L2- bzw. L3-bürtigen Gewebes gesteuert, sondern durch die Lage und damit durch die Abstammung der Gewebe aus der entsprechenden Sprossscheitelschicht bestimmt. Die abschließenden Untersuchungen an Plectranthus coleoides, dessen Chlorophyll- und Ploidiechimären quantitativ analysiert wurden, verdeutlichen die Erkenntnisse über die Beteiligung der Sprossscheitelschichten an der Bildung des Blattmesophylls. Es wurde deutlich, dass die Gewebekonkurrenz im Beisein einer doppelten Markierung nicht lagebedingt sein kann, sondern aufgrund verschiedener Ploidiestufen stattfindet. / The studies presented in this thesis provide new insights into the competitive reaction of the shoot apical layers during the foliar mesophyll formation and thus contribute to understanding of plant development. The variegated plants of Peperomia serpens SW. LOUD, Sedum rubrotinctum R. T. CLAUSEN, Pedilanthus tithymaloides (L.) POIT. and Plectranhus coleoides BENTH were used to analyse the cellular organisation of shoot apex and the histogenetic constitution of the leaf. Shoot apex and leaves structural analyses confirm the number of initial shoot apical layers and the periclinal chimeric nature of investigated plants. Quantitative analysis of foliar mesophyll of Sedum rubrotinctum, Peperomia serpens and Pedilanthus tithymaloides have been used to deduce patterns of meristem layers intercellular interaction during mesophyll formation. The expression of the histogenetic green meristem layer (L2 or L3) causes a increase of "mesophyll area" (Sedum rubrotinctum) and a enlargement of "mesophyll height" (Peperomia serpens and Pedilanthus tithymaloides) in leaves. Four periclinal chimeric forms of Peperomia serpens ('GGW' and 'GWG') and of Sedum rubrotinctum ('GGW' and 'GWG'), each of which possesses normal green cell layers but a genetically different chlorophyll-deficient cell layer, were utilized to study the effect of genotype on the ability of the cell layers of in vivo and in vitro leaf cutting to regenerate adventitious shoots and to analyse the competition between apical layers and their derivatives in the plant ontogeny. Among the in vivo adventitious shoots of the leaf cuttings and leaf of Peperomia serpens, shoots were green, white and variegated. The L3-derived cell layer is alone responsible for the formation of ca. 75 % of adventitious shoots. The relative significant contribution of L2-derived cell layers to mesophyll formation increases in margin of leaf. The L1-derived hypoderm in foliar mesophyll of Peperomia serpens were apparently incapable of shoot regeneration of in vivo leaf cutting, yet in both periclinal forms clearly produced green shoots in vitro. Results demonstrate that all initial apical meristem layers in Peperomia serpens can contribute with different ability to foliar mesophyll formation. Adventitious shoots were in vivo induced on leaf of periclinal chimeric plants of Sedum rubrotinctum. Plants derived from leaf culture were three types: green, white and variegated. Among the adventitious shoots of green- and white-margined leaf of Sedum rubrotinctum, most adventitious shoots (ca. 90 %) were L2-derived, a few were L3-derived. Results demonstrate that the L1 derivatives can not contribute to foliar mesophyll formation. According to these results the internal tissues (L2- and L3-derived cell layers) of leaf are more competitive than the epidermis. The lineage of adventitious shoot is not controlled by the genetic origin of L2- and L3-derived tissues, but by the position of these derived tissues according to the shoot apical meristem layer. The last experiments on Plectranthus coleoides which have combined quantitative analysis of variegated- leaf chimeras with quantitative analysis of cytochimeras have begun to shed more light on the contribution of apical meristem layers to foliar mesophyll formation. It has revealed how the ploidy degree of apical layers derivatives in a cytochimera control leaf cell fate more than their position in the meristem.

Orientador: Sílvio José Bicudo / Banca: Teresa Losada Valle / Banca: José Carlos Feltran / Banca: Marina Aparecida de Moraes Dallaqua / Banca: Ricardo Augusto Dias Kanthack / Resumo: A poda da parte aérea da mandioca é prática comum nos cultivos comerciais destinados à industrialização. Vem sendo praticada principalmente por possibilitar o controle das plantas infestantes com herbicidas no segundo ciclo vegetativo. Seus efeitos no desenvolvimento das plantas e na produtividade de raízes de mandioca ainda não são claros e resultados controversos são encontrados na literatura. Com o objetivo de estudar os efeitos da poda foram realizados seis experimentos, em dois ambientes: Botucatu, experimentos 1, 3 e 5 e em São Manuel, experimentos 2, 4 e 6. Os experimentos 1 e 2 tiveram como causas de variação cinco variedades de mandioca cultivadas com e sem poda. Os experimentos 3 e 4 avaliaram nove épocas de poda frente a uma testemunha conduzida sem poda. Os experimentos 5 e 6 tiveram como causas de variação quatro densidades de plantio avaliadas com e sem poda. Concluiu-se que: a poda altera a produtividade de matéria seca de raízes de maneira distinta considerando a variedade e o ambiente; a poda anterior ao período de repouso fisiológico ou após o início do segundo ciclo vegetativo reduz a produtividade de matéria seca de raízes; em altas densidades de plantio, a poda reduz de maneira significativa a produtividade de matéria seca de raízes. Desse modo, a poda da parte aérea da mandioca não deve ser recomendada de maneira genérica, devendo considerar entre outros, os fatores avaliados no presente estudo / Abstract: Cassava pruning is common in commercial crops destined for industrialization, a practice mainly aimed at enabling weed control with herbicides in the second growth cycle. Its effects on plant development and cassava yields remain unclear and controversial results are reported in the literature. With the objective of studying the effects of pruning, six experiments were conducted in two environments: in Botucatu, experiments 1, 3 and 5, and in São Manuel, experiments 2, 4 and 6. In experiments 1 and 2, the established variables were five varieties of cassava cultivated with and without pruning. Experiments 3 and 4 evaluated nine pruning dates compared with control cultivated without pruning. The established variables in experiments 5 and 6 were four planting densities, evaluated with and without pruning. It can be concluded that: cassava pruning causes distinct alterations in the productivity of dry root matter, depending on the variety and culture environment; pruning before or after the period of physiological rest or after the onset of the second growth cycle reduces the productivity of dry root matter; and pruning in high planting densities significantly reduces the productivity of dry root matter. Thus, cassava pruning cannot be recommended as a general practice, as currently occurs, and the factors evaluated in this study should be taken into consideration / Doutor

Le Cacao swollen shoot virus (CSSV) est un virus infectant le cacaoyer transmis par des cochenilles farineuses de la famille des Pseudococcidae. La maladie qui en découle existe aujourd'hui dans les principales zones de production de cacao d'Afrique de l'Ouest qui représentent 72% de la production mondiale de cacao. Le CSSV a été découvert en 1922 au Ghana et identifié avec certitude dans le Kloto au Togo en 1955 ; le premier isolat étudié moléculairement est l'isolat très virulent Agou1 du Togo. Cet isolat provoque des gonflements de tiges et de rameaux ainsi que des colorations rouge intense au niveau des nervures des jeunes feuilles engendrant ensuite une défoliation complète de l'arbre et sa mort au bout de 5 ans. La progression actuelle du CSSV dans les nouvelles zones de production, notamment au Togo (Litimé) en 1996 et en Côte d'Ivoire (Issia, Bouaflé, Sinfra) en 2000, indique une nouvelle émergence de la maladie. La découverte de ces nouveaux foyers soulève des questionnements sur l'origine des isolats et sur les mécanismes épidémiologiques impliqués dans la propagation de la maladie à l'échelle parcellaire et à l'échelle des territoires.Ces questionnements scientifiques sont pris en compte dans cette étude à trois niveaux : i) l'analyse statistique de la répartition spatiale et temporelle de la maladie à l'échelle des parcelles (fonctions de Ripley et analyse du nombre de liens entre arbres malades) et la cartographie des dynamiques d'évolution au moyen de systèmes d'information géographique (SIG), ii) la diversité moléculaire des isolats de CSSV en lien avec leur répartition géographique afin d'établir une carte de répartition dans les deux régions de production (Kloto et Litimé) et d'essayer de retracer l'historique de la propagation du virus, iii) la cartographie des zones cacaoyères, des cacaoyères saines en comparaison aux cacaoyères malades, à l'échelle des territoires par la combinaison des données satellites Spot5 à 2.5 m de résolution spatiale et des motifs de paysage relevés sur le terrain.L'analyse spatiale avec les fonctions de Ripley et l'analyse du nombre de liens ont montré que les différents états sanitaires (sain, malade, mort) des cacaoyers sont agrégés indiquant ainsi une propagation à partir de foyers d'infection au niveau parcellaire. L'analyse du nombre de liens indique un processus de contamination de plante à plante dans les parcelles. Les études des dynamiques d'évolution au moyen de SIG ont montré à travers des cartes de densités que les cacaoyers malades et les cacaoyers morts sont regroupés en agrégats dans les parcelles et que la taille de ces agrégats augmente entre les deux années d'observation (2008 et 2009). Les dynamiques de changement ont permis de détecter une progression de la maladie plus rapide dans certaines parcelles, qui peut s'expliquer par leur moins bon entretien. La caractérisation des isolats de virus dans les cacaoyères togolaises a montré l'existence de trois groupes dont les groupes A et B uniquement dans le Litimé, et le groupe C uniquement dans le Kloto, indiquant une forte différenciation géographique. Les coefficients de corrélation de Pearson et de Spearman indiquent qu'il existe un lien entre distance génétique et distance géographique des isolats du groupe A, ce qui implique une contamination de proche en proche pour ce groupe à l'échelle du territoire. Compte tenu de la différenciation marquée entre les groupes du Kloto et du Litimé, nous pouvons conclure que les cacaoyères du Litimé n'ont pas été contaminées par du matériel venant du Kloto mais plus probablement à partir de parcelles cacaoyères situées au Ghana et contaminées précédemment pour se répandre ensuite dans le Litimé. L'étude des images satellites a montré qu'il n'existait pas de relation simple entre l'état sanitaire des motifs de cacaoyers et leur radiométrie en raison de la forte hétérogénéité du système agroforestier du Litimé / Cacao swollen shoot virus 'CSSV ' is a virus transmitted by mealybugs, insects of the Pseudococcidae family. The disease occurs in all the main cocoa-growing areas of Western Africa. It induces swellings on shoots and roots and mosaic and chlorosis on the leaves and has caused very serious crop losses in Ghana, Nigeria and more recently, Togo and Côte d'Ivoire. The cocoa production in Western Africa, representing about 72 % of the worldwide production is particularly important for the economic equilibrium of these countries. The actual progress of the CSSV epidemic in the large production areas in Togo like ‘Litimé' and ‘Kloto' and in Côte d'Ivoire (Issia, Bouaflé, Sinfra) requires to understand and forecast its spread in time. The discovery of these new focuses of the disease raises questions about the origin of the isolates and the mechanisms involved in the epidemiological spread of the disease at field scale and across territories.These scientific questions are addressed in this study at three levels: i) the spatial and temporal distribution of disease across the plots with statistical methods (Ripley and analysis of the number of links) and geographical information systems (GIS) to map the dynamics of evolution, ii) the molecular diversity of CSSV isolates related to their geographical distribution in order to establish a distribution map in the two regions of production (Kloto and Litimé) and try to understand the history of the virus spread, iii) the mapping of cocoa area in Litimé, the mapping of disead cocoa in comparison with healthy cocoa at the territories scale by combining satellite data with SPOT5 2.5 m spatial resolution and landscape motifs field surveys.The spatial analysis with Ripley's method and analysis of the number of links have shown that the different states of health (healthy, disead, dead) of cocoa trees are aggregated indicating a spread by patch at plot level. The analysis of the number of links indicates a process of contamination from plant to plant in the plots. Studies of the dynamics of evolution from Sig showed through density maps that disead cocoa trees and dead cocoa tree are grouped into clusters in the plots and the size of these aggregates increases significantly between the two years observation (2008 and 2009). The dynamics of change have detected a similar progression of the disease in plots 2 and 3 speedy than Parcel 1. This difference of the disease progress on the three plots can be explained by better maintenance of Parcel 1. The characterization of virus isolates on cocoa plots in Togo has shown the existence of three groups with groups A and B only in the Litimé, and group C only in the Kloto, indicating strong geographical differentiation. The correlation coefficients of Pearson and Spearman indicate a link between genetic distance and geographical distance of the isolates of group A, which implies a contamination step by step for this group at territories scale. Given the marked differentiation between the groups of Kloto and Litimé, we can conclude that the cocoa tree of Litimé were not contaminated with material from the Kloto but more likely from plots located in Ghana and previously infected then spread in the Litimé. The study with the satellite images showed that there was no simple relationship between the health patterns of cocoa trees and their radiometry because of the high heterogeneity of the agroforestry system of Litimé. The combination of landscape motifs and radiometry, however, possible to distinguish areas with dominant "cocoa", areas dominated by "crops", areas dominated by "forest". Among the areas to be dominant "cocoa", we have distinguished the cocoa denuded areas that correspond to potential disease areas and cocoa shade. These various studies indicate that disease progression is slow and works gradually. Emergences observed in new areas probably come from human movements

Submitted in fulfilment of the requirements for the degree of Master of Applied Sciences in Biotechnology, Durban University of Technology, Durban, South Africa, 2015. / In contrast to orthodox seeds, recalcitrant seeds are short-lived, shed at relatively high water contents (WCs), and are desiccation sensitive. Presently, the only option for long-term conservation of genetic resources of such plant species is by cryostorage in liquid nitrogen (LN; -196°C) or in the vapour phase over LN (at -150⁰C to -160⁰C). A number of cryopreservation protocols applied for recalcitrant zygotic embryos or embryonic axes of tropical/sub-tropical species have reported survival as either root or shoot development or callus formation, with no shoot or root production after cryopreservation. This is a consequence of the challenges encountered when optimising the WC for successful cryopreservation across species. Other shortcomings may also be the formation of ice or the sensitivity to desiccation resulting in lethal damage or poor re-growth. However, for successful cryopreservation, a normal plantlet with a shoot and a root needs to be obtained post-cryo. Specimens required for successful cryopreservation must be small; therefore embryonic axes excised from seeds have been often used as the explants of choice. However, in some cases, excised embryonic axes of mature recalcitrant seeds are too large to be cryopreserved, or, even if small, may be adversely affected by excision, dehydration and/or immersion in LN, thus failing to produce plantlets after cryopreservation. As a result, in such cases, there is a need to develop explants alternative to zygotic axes such as buds derived from in vitro shoots, shoot meristems, or shoot apices and somatic embryos. These alternative explants must have a high capacity for plantlet formation before and after cryopreservation. The present study aimed to successfully cryopreserve shoot apices of Trichilia emetica and T. dregeana, tropical recalcitrant-seeded tree species, and monitor the responses or effects of some of the procedural steps involved in cryopreservation on the survival and shoot production from these shoot apices. The main foci of the investigation were to produce vigorous plantlets after cryopreservation and ultimately develop a protocol for the successful cryopreservation of germplasm of these species. Furthermore, this study reports on a number of factors that may affect survival after cryopreservation, viz. WC of the explants, PVS2 treatment, production of reactive oxygen species (ROS) and levels of endogenous total aqueous antioxidants (TAA) during the various steps of cryopreservation. The effects of the various steps of cryopreservation on the ultra-structure of the shoot apices were also observed. Cathodic protection (by using highly reducing cathodic water; CW) of the explants was attempted to improve vigour and shoot production from the surviving shoot apices after cryopreservation as cathodic water has been reported to ameliorate the excessive burst of ROS, which often accompanies the stresses imposed by the procedural steps of cryopreservation. Experiments were also performed to optimise the medium for vigorous shoot formation from the shoot apices. Shoot apices of T. emetica in this study had an initial WC of ca. 2.2 g g -1 dry weight (DW) upon excision. Although the WC of the shoot apices decreased slightly after cryoprotection with PVS2, it did not result in sufficient dehydration before cooling. Upon retrieval from LN, 68% of the shoot apices survived and 40% of those produced shoots. Treatment of shoot apices with CW did not improve the survival or shoot production from the apices following cryo-retrieval. This could be a direct consequence of increase in WC of the shoot apices following CW treatment. Water content is not the only factor affecting successful cryopreservation; the production of ROS and the level of antioxidants may also have an impact on regrowth after cryogen exposure. Rapid changes in temperature when the samples are cryo-stored and then rewarmed result in an increase in ROS production, which could have affected the shoot production. More importantly the antioxidant activity showed a rapid decrease during recovery, especially in the CW treated shoot apices, which might have also led to the poor survival and shoot production from the shoot apices. Ultrastructural observations showed the injurious effects of PVS2 treatment typified by derangement of plastids, development of numerous small vesicles along the cell membrane and abnormalities in the structure of the nuclear envelope in the shoot apical cells both before and after cryogen exposure. Following cryo-retrieval, the meristem cells were extensively deteriorated – indicating non-survival, however, some shoot apices had areas of surviving cells which might have led to 40% shoot production after cryopreservation. Based on the studies on optimising medium composition for shoot formation from the apices, woody plant medium (WPM) with 1 mg L-1 BAP + 0.1 mg L-1 IBA was found to be the best medium which gave a higher shoot production of 67 – 70% before cryopreservation compared with only 18 – 20% shoot formation on media used previously. Therefore, this medium was used as the recovery medium. Encapsulation-dehydration of the shoot apices and the use of PVS3 instead of PVS2 for cryoprotection were also employed in an attempt to improve the survival and shoot production after post-cryo, but both methods did not result in any shoot production although 92% and 90% of the shoot apices survived cryogen immersion, respectively. While the shoot apices of T. emetica resulted in 40% shoot production following retrieval from LN and recovery on WPM with 1 mg L-1 BAP + 0.1 mg L-1 IBA, attempts to further improve the shoot production were not successful. The results of this study suggest that the shoot apices used were possibly not sufficiently developed, and with the commensurately high WC, proved to be unsuitable explants for germplasm conservation of T. emetica. The injurious effects of PVS2 treatment both before and after cryogen exposure as observed from the ultra-structural studies provide a clue to the repeated failure to cryopreserve embryonic axes of many tropical recalcitrant-seeded species after treatment with PVS2. Maintaining mother material in culture for longer durations before explant excision in order to allow better development of the axillary buds and render the cytosol more concentrated, and optimising the exposure duration to loading solution and concentration of sucrose in the loading solution might however, provide sufficient dehydration tolerance to PVS2 leading to successful vitrification up on cooling.

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Fitoplasmas são agentes causais de diversas doenças em numerosas espécies botânicas cultivadas, daninhas e silvestres. São procariotos que não apresentam parede celular, parasitas intracelulares obrigatórios, habitantes do floema e da hemolinfa, sendo transmitidos naturalmente por insetos vetores do tipo cigarrinhas. Plantas de oliveira apresentando sintomas tipicamente induzidos por fitoplasmas, caracterizados por desenvolvimento lento e superbrotamento de ramos com folhas de tamanho reduzido, foram observadas na cidade de Extrema (MG). A anomalia provoca danos significativos, pois retarda o início de produção e reduz o rendimento da cultura. Sintomas semelhantes foram relatados em olivais implantados em outros países, onde a doença foi associada aos fitoplasmas. O objetivo deste trabalho foi demonstrar a associação de fitoplasma com as plantas afetadas e identificar o fitoplasma presente nas árvores doentes. Para isto foram utilizadas as técnicas moleculares de PCR e RFLP, além de análise filogenética. Os resultados revelaram a presença de fitoplasmas em 73% das árvores sintomáticas analisadas, evidenciando que os sintomas observados no campo eram induzidos por fitoplasma. A doença foi denominada de vassoura-de-bruxa da oliveira. A identificação molecular permitiu classificar o fitoplasma como um representante do grupo 16SrVII-B. Este é o primeiro relato da ocorrência de fitoplasma em plantas de oliveira no Brasil. Em termos mais amplos, é o primeiro relato da associação de um fitoplasma do grupo 16SrVII com a doença vassoura-de-bruxa da oliveira, a qual, em outros países, está associada a fitoplasmas distintos do fitoplasma identificado no presente trabalho. / Phytoplasmas are causal agents of diverse diseases occurring in numerous botanical species, among them cultivated, weeds and wild plants. They are wall-less prokaryotes, obligate intracellular parasites, inhabitants of phoem vessels and hemolymph, and naturally transmitted by insect vectors belonging to the group of the leafhoppers. Olive trees exhibiting symptoms typically induced by phytoplasmas, characterized by slow growth and shoot proliferation with small leaves, were observed in the municipality of Extrema (MG). The anomaly provokes significant damage due to the delay in the beginning of the production and yield reduction of the crop. Similar symptoms have been reported in olive orchards cultivated in other countries, where the disease was associated with phytoplasmas. The objective of the present investigation was to demonstrate the association of phytoplasma with affected plants and identify the phytoplasma present in diseased trees. PCR assays, RFLP analysis and phylogenetic analysis were used to molecular characterization of the phytoplasma. The results revealed the presence of phytoplasma in 73% of the symptomatic trees, evidencing that the symptoms observed in field were induced by phytoplasma. The disease was designated by olive witches\" broom. The molecular identification allowed classify the phytoplasma as a representative of the 16SrVII-B group. This is the first report of the occurrence of phytoplasma in olive plants in Brazil. Moreover, this is also the first report of the association of a group 16SrVII phytoplasma with olive whitches\" broom disease, which has been described in other countries in association with phytoplasmas different from the phytoplasma identified in the present study.

This thesis examines the growth response and inter-relationships between shoots and roots of plants grown in compact soil. In the field, two topsoil and two subsoil conditions were created with five vegetable crops sequentially grown. Between 6 and 12% of the root system grew in the compact subsoil, which had a soil strength of 3.1 c.f. 1.9 MPa in the loosened subsoil. Both the root length density (Lv) and the specific root length were lower in the compact subsoil (80% and 30%, respectively). This had no effect on shoot growth when water and nutrients were well supplied. Compensatory root growth in the lose soil above the compact subsoil occurred in broccoli plants. As a result plants grown in soil with or without a compact subsoil had a similar total root length but with altered root distribution. When the water and nitrogen supplied to the soil was reduced, the lower subsoil Lv in the compact subsoil did not restrict water or N acquisition. This was possibly due to a large increase in the specific uptake per unit length of root, by the fewer roots in the compact subsoil. Compared to the subsoil treatments, only small changes in topsoil physical properties occurred when tillage was ceased. From the field trials the proportion and time of root growth into compact soil appeared important in determining the plant response. In a series of split-root experiments (horizontal and vertical arrangements of compact and loose soil) compensatory root growth in the loose soil only occurred when the root system was exposed to horizontally compact soil When compensatory root growth did not occur shoot growth was reduced. This resulted in there being a close relationship between total root length and leaf area. Further test results support a direct effect of mechanical impedance on shoot growth with a rapid (within 10 minutes) and large (50%) reduction in leaf elongation occurring when roots were mechanically impeded. In the field only plants whose roots were totally exposed to compact soil had reduced shoot growth with very compact subsoil having no effect. / Doctor of Philosophy (PhD)

The shoot apical meristem (SAM) is the structure that shapes the aerial architecture of the plant, by producing lateral organs throughout development. In the model plant Arabidopsis thaliana, the SAM is always identifiable as a characteristic dome, whether it is found in the centre of a rosette of leaves or at the tip of an inflorescence. When senescence occurs and organogenesis ceases, the now inactive SAM still retains its characteristic appearance and it is never consumed into a terminal structure, such as a flower. Mutant plants that undergo termination represent a valuable tool to understand how the SAM structure and function are maintained during plant life. The aim of this work was to investigate the dynamics of meristem development through morphological and genetic studies of three Arabidopsis mutants that exhibit distinct modes of SAM termination: distorted architecture 1 (dar1), adenosine kinase 1 (adk1) and terminal flower 2 (tfl2). The dar1 mutation is characterised by a severely distorted cellular architecture within the SAM. We propose that dar1 affects the pattern of cell differentiation and/or cell proliferation within the SAM apical dome, resulting in termination by meristem consumption. Instead, the adk1 mutation affects the organogenic potential of the SAM, without altering its structure. The adk1 mutant has increased levels of cytokinins and, as a consequence of this, cell division is enhanced and cell differentiation is prevented in the apex, causing termination by meristem arrest. Finally, tfl2 is mutated in the conserved chromatin remodelling factor HP1, a transcriptional repressor with multiple roles during plant development. The tfl2 SAM terminates by conversion into a floral structure, due to de-repression of floral identity genes. Interestingly, tfl2 mutants also show an altered response to light, an indication that TFL2 might act as a repressor also in the context of light signalling.