Finger millet (Eleusine coracana) productivity in East Africa has remained low in all production agro-ecologies for decades owing to the low yielding potential of existing that are susceptible to the blast disease caused by the fungus Magnaporthe grisea (Hebert) Barr. and the limited research on the crop. The region holds large finger millet germpasm collections whose value is not yet been fully exploited. However, with the ongoing breeding efforts through hybridization, there is a need to comprehensively characterize the germplasm to identify valuable traits to address biotic and abiotic stresses that affect finger millet productivity. Studies on gene action and inheritance of key traits that contribute to yield improvement are also required to help formulate an effective breeding strategy for finger millet improvement. The objectives of this study were to (i) determine the genetic diversity in a set of germplasm from East Africa (ii) determine association between grain yield and its component traits (iii) identify genotypes for target production agro-ecologies (iv) identify blast resistant finger millet genotypes for use in breeding and production and (v) generate information on the inheritance of blast, grain yield and yield components for the development of an effective breeding strategy. A total of 340 finger millet accessions were collected from three countries in East Africa: Kenya, Tanzania and Uganda and 80 global minicore accessions sourced from ICRISAT-India. High phenotypic variability in the germplasm was recorded for 23 quantitative traits, blast reaction and five qualitative traits. Both morphological and molecular characterization (using SSR markers) of the 340 accessions revealed higher diversity within than among the countries Kenya, Tanzania and Uganda. Seven morphological clusters and three major genetic clusters were detected. Morphological diversity delineation was largely influenced by leaf sheath length, plant height, peduncle length, panicle exertion and grain yield. The mean polymorphic information content (PIC) of 19 polymorphic markers was 0.606 with mean alleles of 195 with sizes that ranged from 148-474 base pairs. The Kenyan and Tanzanian accessions had higher diversity than the Ugandan with the Kenyan and Ugandan, and the Kenyan and Tanzanian accessions being closely related than the Tanzanian and Ugandan. The low diversity in the Ugandan accessions could be attributed to higher research intervention in the country leading to the promotion and use of improved cultivars. Efforts have to be directed towards collection and conservation of valuable diversity before it is lost. The diversity in plant height, maturity, yield and blast reaction and the cluster groups detected in the germplasm should provide a basis for finger millet improvement through hybridization and selection. Higher genotypic than phenotypic correlations were recorded for most of the traits studied with grain yield having high positive correlations with finger width, grains per spikelet, threshing percent, peduncle length and panicle exertion. Both grain yield and days to flowering had negative correlations with all three blast types (leaf, neck and finger). Path coefficient analysis revealed that productive tillers per plant, 1000 grain mass, grains per spikelet and threshing percent had positive direct genetic effects on grain yield with strong indirect effects from several of the other traits which necessitates simultaneous selection for those traits with strong direct effects and those with strong indirect effects for grain yield improvement. High broad sense heritability estimates and high genetic advance as percent of mean were recorded in fingers per panicle, flag leaf sheath length, 1000 grain mass, finger length, peduncle length, panicle exertion, number of leaves per plant and leaf sheath length probably indicating the predominance of additive gene effects in controlling these traits hence the potential for improvement through selection. Adaptation and stability analysis using the GGE biplot model identified Lanet 2012 long rains, Serere 2012 long rains and Miwaleni 2012 long rains as the most discriminating environments for the low temperature, sub-humid mid altitude and dry lowland areas, respectively. Alupe 2012 long rains was the ideal environment for genotype discrimination for blast while Lanet 2012 long rains was best for grain yield. Genotypes G3, G5, G17, G25, G28, G36 and G71 were identified as being stable across environments and G1, G18, G19, G37, G54, G61, G74, G75, and G77 were found ideal for specific adaptation. Disease severity scores were highly negatively (P<0.01) correlated with days to flowering and grain yield suggesting that early lines suffered more disease damage leading to reduced yield. Resistant genotypes were slow blasting (probably associated with horizontal resistance) which may enable them to withstand blast pathogen variability for longer periods. Nine genotypes were identified with high resistance to blast and will be useful for breeding as blast resistance sources. Resistant genotypes had low AUDPC values and disease severity rating for the three blast types and vice-versa for susceptible genotypes. Further investigations need to be carried out to determine the possibility of the three blast types being controlled by the same genes. Early maturing blast susceptible genotypes with good yield potential could be utilized in areas with low blast prevalence. To understand the gene action for inheritance of the various traits 16 F2 families plus their four female and four male parents were evaluated at Alupe and Kakamega western Kenya under artificial blast inoculation. Significant additive genetic effects were recorded for all traits (except for finger width and grains per spikelet) meaning that improvement for these traits would be possible through the common selection methods for self pollinating crops. Parent lines KNE 392, and KNE 744 and IE 11 were found to be suitable for blast resistance breeding while Okhale 1 was found to be suitable for high grain yield and blast resistance improvement due to their high desirable GCA effects. Most of the F2 families showed transgressive segregation for the three blast types in either direction which gives hope for the development new pure lines with better blast resistance than the parents. Crosses IE 3104 x KNE 796, KAT FM 1 x Okhale 1, IE 11 x Okhale, IE 11 x P 224 and KNE 744 x KNE 392 have potential to generate lines with blast resistance due to their high desirable SCA effects. The F2 segregation distributions for blast indicated quantitative inheritance. However the one to four minimum number of genes (effective factors) detected for resistance control in all the three blast types was not in sync with the segregation patterns in the F2 families and further investigations are required. There were differences in segregation patterns between crosses which may suggest the presence of different resistance genes in the different parents used. This would call for gene pyramiding for durable resistance. These results confirm the potential of sourcing valuable parental stocks in the local germplasm for the development of genotypes to improve finger millet productivity in East Africa. Already some of the high yielding and blast resistant genotypes identified here have been incorporated in the regional cultivar trials. The diversity information generated will facilitate effective conservation and utilization of this germplasm. Results of gene action for inheritance of the various traits from this study will enable breeders to develop sound breeding strategies for finger millet improvement in the region. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2013.

Thesis (D. Min.)--Western Seminary, 1993. / Abstract. Includes test/surveys in French. Includes bibliographical references (leaves 359-372).

Thesis (Ph.D.)--University of the Witwatersrand, Faculty of Science, 1987

Review of literature shows that rocks of all ages from the Archaean to the early Phanerozoic host pegmatite-based mineralisation in the central and southern region of the African continent. The greatest concentrations occur in the Archaean and late Proterozoic orogenic belts, while early to middle Proterozoic granites do not, in general, host mineralisation. Pan-African mineralisation is present, but is not widespread. Some deposits previously considered to be of Pan-African have been shown to be of Proterozoic age. In common with occurrences of other regions, the deposits are closely associated with small, late- to post-tectonic granites. Therefore, preliminary assessment of the potential of granites as sources of pegmatite mineralisation should utilise satellite data or aerial photographs. The granites also tend to be alkaline and peraluminous. Thus, in the next stage, chemical analysis for selected major and trace elements should be conducted directly on granites if they occur as small plutons. For large granitic batholiths or terranes, preliminary stream-sediment surveys may be necessary to reduce the size of the target area. Subsequently, pegmatite zonation around suitable granites should be assessed as it allows attention to be focussed on areas likely to host the specific type of mineralisation being explored for.

Thesis (Ph. D.)--Earth and Atmospheric Sciences, Georgia Institute of Technology, 2007. / Dr. Curry, Judy, Committee Member ; Dr. Webster, Peter, Committee Member ; Dr. Weber, Rodney, Committee Member ; Dr. Ingall, Ellery, Committee Member ; Dr. Robert Dickinson, Committee Chair.

The role of the South African National Defence Force (SANDF) has changed considerably in the last decade. The emphasis has moved from protecting the country's borders to peacekeeping duties in Central Africa and even further North. Communications between the peacekeeping missions and the military bases back in South Africa is vital to ensure the success of these missions. Currently use is made of satellite as well as High Frequency (HF) communications. There are drawbacks associated with these technologies (high cost and low data rates/interference respectively). Successful long distance ionospheric propagation in the low Very High Frequency (VHF) range will complement the existing infrastructure and enhance the success rate of these missions. This thesis presents a feasibility study to determine under what ionospheric conditions such low VHF communications will be possible. The International Reference Ionosphere (IRI) was used to generate ionospheric data for the reflection point(s) of the signal. The peak height of the ionospheric F2 layer (hmF2) was used to calculate the required antenna elevation angle. Once the elevation angle is known it is possible to calculate the required F2 layer critical frequency (foF2). The required foF2 value was calculated by assuming a Maximum Useable Frequency (MUF) of 20% higher than the planned operational frequency. It was determined that single hop propagation is possible during the daytime if the smoothed sunspot number (SSN) exceeds 15. The most challenging requirement for successful single hop propagation is the need of an antenna height of 23 m. For rapid deployment and semi-mobile operations within a jungle environment it may prove to be a formidable obstacle.

Doctorat en Sciences politiques et sociales / info:eu-repo/semantics/nonPublished

Forest elephant (Loxodonta africana cyclotis) sociality is relatively little-studied due to the difficulties of making direct observations in rainforests. In Central Africa elephants aggregate at large natural forest clearings known as bais, which have been postulated to offer social benefits in addition to nutritional resources. This thesis explores the role of these clearings as social arenas by examining bai use within three main themes; ecology, sociality and risk factors. Seasonal changes in elephant use of the Maya Nord bai (Republic of Congo) are described, along with the demography of the visiting population. Elephant visit rate was highly variable; the number of elephants using Maya Nord in an observation day ranged from 0 to 117 animals. This variability was unrelated to local resource availability and productivity suggesting that bai use occurs year round. Elephants in Odzala-Kokoua do not show high fidelity to a single clearing; 454 elephants were individually identified and re-sighted an average of 1.76 times (range 1-10) during the twelve month study period. Previous bai studies have yet to quantify how elephants associate with one another within the bai area. This study examines socio-spatial organisation and associate choice using two measures of association within the 0.23 km2 bai area; aggregations (all elephants present in the clearing) and parties (elephants spatially co-ordinated in activity and movement) and distinguishes these from parties that range together (i.e. arrive and leave together). Social network analyses (SocProg) were used to describe inter- and intra-sexual multi-level organisation in the bai environment, and to illustrate the non-random nature of elephant aggregations and parties. Bais were shown to function as social arenas; female elephants showed active choice of certain associates and active avoidance of others when creating parties, whereas males were less discriminatory. Parties formed in the clearing (mean size= 3.93, SE= 0.186) were larger than ranging parties (mean size= 2.71, SE= 0.084) and elephants stayed for 50% longer in the clearing when they associated with individuals from outside their ranging party. Inter- and intra-sexual relationships were maintained within the clearing, and these are suggested to offer elephants essential opportunities for social learning. The patterning and nature of the relationships observed at the Maya Nord clearing indicates that forest elephants use a fission-fusion social structure similar to that of savannah elephants (Loxodonta africana africana); relationships are significantly structured by age- and sex- and underpinned by individual identity. Old experienced females hold key roles for forest elephants, and male relationships are superimposed on the network of female associations. Odzala-Kokoua elephants use bais to maintain their social relationships despite being highly sensitive to the anthropogenic risks involved in using these open areas. The results of this study suggest that forest and savannah elephants lie on the same social continuum, balancing social “pulls” to aggregate against the ecological “pushes” that force groups to fission. Previous models of savannah elephant sociality construct levels of association and social complexity upwards from the basic mother-calf unit (e.g. Wittemyer & Getz 2007). My results suggest that it may be more appropriate to consider elephant sociality and associations as in dynamic equilibrium between social and ecological influences acting at all levels of grouping, and to explicitly test how these underlie the opportunity costs that elephants are willing to pay in order to maintain social groupings.

Human pressure on forest resources increased significantly during the past decades through land use and land use change, especially in the tropics where forest clearing is a major source of CO2 release in the atmosphere. Consequently, forests are the focus of international environmental policies and discussions aiming to reduce emissions from deforestation and forest degradation (i.e. REDD+). The capacity of participating countries to regularly provide accurate forests C stocks measurements at a national scale thus represents an important challenge to address. In dense forests, generally only the above ground biomass (AGB) is measured as it accounts for more than 50% of total C stocks. However, important gaps remain at each scale of measurement, i.e. from felled tree to regional mapping, with the resulting errors propagation through these different scales being probably the most concerning issue.<p><p>In the present work, we propose to address these issues by using a multi-scale approach in order to improve our global understanding of AGB variations in dense tropical forests of Central Africa. In particular, we studied (i) forest AGB prediction from remote-sensing textural analysis, (ii) the potential role of largest trees as predictor of the entire forest-stand AGB and (iii) intra- and inter-individual radial variation of wood specific gravity (WSG, i.e. oven-dry mass divided by its green volume) and its potential consequences on the estimation of the AGB of the tree. <p>First, we analyzed the potential use of textural analysis to predict AGB distribution based on very high spatial resolution satellite scenes. In particular, we used the Fast Fourier Transform Ordination (FOTO) method to predict AGB from heterogeneous forest stands of the Democratic Republic of the Congo (DRC). Here, based on 26 ground plots of 1-ha gathered from the field, plus a successful combination of Geoeye and Quickbird contrasted scenes, we were able to predict and to map AGB with a robust model (R² = 0.85; RMSE = 15%) based on textural gradients. <p>Secondly, the research of AGB indicators was focused on the dissection of the role played by largest trees. Here we found largest trees not only hold large share of forest carbon stock but they contain the print of most of forest-stand structure and diversity. Using a large dataset from western Cameroon to eastern DRC, we developed a non-linear model to predict forest carbon stock from the measurement of only a few large trees. We found the AGB of the 5 % largest stems allow to predict the AGB of the entire forest-stand yielding an R² of 0.87 at a regional scale. Focusing on largest trees species composition, we also showed only 5 % of species account for 50 % of total AGB.<p>In the end, we investigated inter- and intra-individual WSG variations. Despite recognized inter- and intra-specific variations along the radial axis, their ecological determinants and their consequences on trees aboveground biomass assessments remain understudied in tropical regions. To our knowledge, it has never been investigated in Africa. Using a 3-D X-Ray scanner, we studied the radial WSG variation of 14 canopy species of DRC tropical forests. Wood specific gravity variance along the radial profile was dominated by differences between species intercepts (~76%), followed by the differences between their slope (~11%) and between individual cores intercept (~10%). Residual variance was minimal (~3%). Interestingly, no differences were found in the comparison of mean WSG observed on the entire core and the mean WSG at 1-cm under the bark (intercept ~0; coefficient = 1.03). In addition, local values of WSG are strongly correlated with mean value in the global data base at species level. <p><p>I deeply believe these results favor the development of promising tools to map and to estimate accurately the AGB of tropical forest-stands. The information provided by largest trees on the entire forest-stand is particularly interesting both for developing new sampling strategies for carbon stocks monitoring and to characterize tropical forest-stand structure. In particular, our results should provide the opportunity to decrease current sampling cost while decreasing its main related uncertainties, and might also favor an increase of the current sampling coverage. <p> / Doctorat en Sciences agronomiques et ingénierie biologique / info:eu-repo/semantics/nonPublished

La diversité végétale exceptionnelle des forêts tropicales a toujours suscité une part d’incompréhension chez les scientifiques qui tentent de comprendre les processus à l’origine de cette diversité, ainsi que les mécanismes expliquant les changements spatiaux de composition spécifique. Une des clés de ce dernier mystère résiderait dans l’influence de la différentiation des niches écologiques, mais aussi de la dispersion limitée des graines et d’événements stochastiques (purement aléatoires et non prévisibles). La niche d’une espèce contraint celle-ci à s’établir dans un habitat présentant des gammes de conditions bien délimitées en termes de propriétés du sol (disponibilité en nutriments et toxicité de certains éléments) et d’intensité lumineuse. Par exemple, certaines espèces sont plus tolérantes à l’ombrage (espèces « sciaphiles ») que d’autres qui ne peuvent s’établir que dans des trouées forestières offrant suffisamment de lumière (espèces « héliophiles »). En Afrique centrale, les communautés d’arbres sont aujourd’hui en grande partie composées de ces espèces dites « héliophiles », alors que les ouvertures forestières naturelles sont rares. Il est fortement suspecté que la dominance de ces espèces soient la conséquence de trouées générées par l’homme qui, jusqu’au début de la période coloniale (vers 1900), occupait de vastes surfaces de forêt où il pratiquait l’agriculture sur brûlis. Cependant, peu d’études ont jusqu’à présent déterminé dans quelle mesure ces pratiques agricoles ont influencé la composition spécifique des forêts à l’échelle régionale comme à l’échelle locale.<p>L’objectif du présent travail est de faire la lumière sur l’impact de ces perturbations humaines mais aussi plus généralement sur l’influence relative de la niche écologique des espèces d’arbres par rapport à d’autres facteurs (dispersion limitée et facteurs stochastiques) sur leur distribution spatiale. Pour cela nous avons utilisé des données botaniques et environnementales provenant d’inventaires réalisés dans une forêt tropicale située en République Démocratique du Congo (quatre transects parallèles mesurant chacun 500 à 600 m de long), ainsi que des données similaires complémentées d’inventaires anthracologiques (estimation de la quantité de charbons de bois dans le sol, utilisée comme indicateur de feux passés d’origine anthropique) récoltées dans trois régions du sud du Cameroun (208 parcelles de 0,2 ha chacune). <p>Les données récoltées nous ont permis de mettre en évidence un impact significatif des propriétés physico-chimiques du sol sur la composition en espèces d’arbres. Plus précisément, nous avons pu constater une différence floristique marquée entre deux habitats très contrastés (sol sableux vs. sol argileux, Rép. Dém. Du Congo), et cela à une échelle spatiale locale (< 1 km²) où l’on pensait que de l’influence des facteurs stochastiques et de dispersion limitée étaient prépondérante. Mes analyses ont également démontré que cette différence était plus marquée pour les arbres de la canopée que pour les arbres des strates inférieures (« sous-canopée »), ce qui est sans doute lié au fait que de nombreux individus de la sous-canopée sont composés de juvéniles régénérant la canopée, parmi lesquels de nombreux arbres subissent une exclusion compétitive en cours (brouillant ainsi les signaux d’association espèce-habitat). <p>À une échelle spatiale beaucoup plus large cette fois (de 5 à 100 km, inventaires du Sud Cameroun), nous avons démontré que la diversité floristique était également influencée de manière significative par l’hétérogénéité spatiale de propriétés abiotiques du sol, notamment par les concentrations en (i) certains nutriments essentiels pouvant présenter des valeurs potentiellement limitantes (K, Mg, Ca et P) ainsi qu’en en (ii) élements pouvant être présents en quantités toxiques (Al et Mn). Cependant, alors que le signal environmental a été clairement détecté à l’échelle communautaire, seule les abondances d’une minorité d’espèces (< 15%) ont répondu significativement à la variation des conditions de sol. En outre, le nombre de réponses significatives a augmenté avec l’échelle d’observation ainsi qu’avec le degré d’hétérogénéité environnementale et/ou floristique. Pour mettre en évidence cet effet du sol, nous avons introduit une nouvelle approche permettant de tester la fraction d’une analyse de partition de variance correspondant à la part de variation floristique expliquée par l’effet de conditions édaphiques spatialement structurées (co-variation entre effets spatiaux et édaphiques), en combinant l’analyse de partition de variance avec des vecteurs propres de Moran (« Moran’s eigenvector maps ») et des translations toroïdales. Bien que cette méthode nous ait permis de déterminer si la fraction en question était significative, nous avons également mis en doute son interprétation habituelle suggérant que cette fraction représente une structure floristique directement induite par des structures spatiales de conditions de sol. Grâce à des simulations de populations végétales liées à des propriétés environnementales, nous avons mis en évidence que la valeur de la fraction étudiée ne semble finalement pas influencée par le degré de structuration spatiale des conditions environnementales, remettant donc en question l’utilité de l’analyse de partition de variance pour inférer des effets de processus écologiques sous-jacents sur la distribution spatiale des espèces d’arbres.<p>Enfin, les données floristiques et anthracologiques du Sud Cameroun ne nous ont pas permis de démontrer statistiquement l’hypothèse que les perturbations humaines passées sont en partie responsables de la dominance actuelle des espèces héliophiles. L’absence de corrélation significative entre l’abondance relative de ces espèces et la quantité de charbons de bois dans le sol peut s’expliquer par le fait que la majorité de ces charbons (60%) étaient trop vieux (1500 à 3000 ans) pour refléter des perturbations ayant influencé la diversité végétale présente. <p>Les conclusions générales de ma thèse de doctorat soutiennent que la niche écologique des espèces d’arbres des forêts tropicales africaines contribue de manière significative à déterminer leur assemblage dans l’espace, mais aussi que ces effets de niche dépendent fortement du contexte environnemental étudié ainsi que de l’échelle spatiale d’observation. Ce travail lève donc en partie un voile sur l’écologie des écosystèmes forestiers d’Afrique centrale qui restent largement méconnus par rapport à ceux d’Asie du Sud-Est et des régions néotropicales.<p> / Doctorat en sciences, Spécialisation biologie végétale / info:eu-repo/semantics/nonPublished