Made available in DSpace on 2016-05-02T13:55:22Z (GMT). No. of bitstreams: 1 Marcio de Souza Dias Dissertacao.pdf: 1130526 bytes, checksum: 33886098250a3d16ad0626a969014e45 (MD5) Previous issue date: 2015-03-06 / Coordenacao de Aperfeicoamento de Pessoal de Nïvel Superior / The objective of this research was to analyze the diversity of nitrogen fixing bacteria associated and endophytic B. brizantha, study the potential the solubility of inorganic phosphates of iron and aluminum, produce acid-3-indole acetic (AIA) and to evaluate the effect of inoculation of these isolates in Brachiaria brizantha cv MG 05 Victoria. The bacteria were isolated from soil samples grown under Brachiaria and parts of plant tissue this grass, the dry and wet periods in the municipalities of Alfenas and Machado, southern Minas Gerais. Five semisolid culture media and semi-selective were used: FAM (Azospirillum amazonense), JMV (Burkholderia sp.), JNFb (Herbaspirillum spp.), LGI (A. amazonense) and NFb (Azospirillum spp.). The phosphate solubilization tests and AIA production were performed in vitro and were used as of 22 bacterial isolates selection criteria used in the inoculation of B. brizantha cv MG 5 Victoria, grown in pots containing 20 dm3 of soil. There were two cuts, in what form evaluated the following parameters: height (Al), width (LF) and leaf length (CF), number of tillers (NP), length (CR) and root dry mass (MSR) dry matter (DM), dry matter yield (PMS), neutral detergent fiber (NDF) and acid (ADF) and crude protein in dry matter (PBMS). A total of 332 isolates were obtained, most endophytic. The greatest number and diversity were from the city of Alfenas. During the rainy season was verified greater number and diversity of isolates in both municipalities, when compared to the dry season. Thirty-five isolates solubilized iron phosphate and 78 produced AIA, especially the isolated UNIFENAS 100-17, 21, 40 and 78, able to do both simultaneously. The inoculation of nitrogen fixing strains of endophytic origin and rhizospheric influenced the development of B. brizantha cv MG 5 victory, contributing to the production of MS, PMS and PBMS in the two cutting heights highlighting the UNIFENAS-100-16 isolated, 21, PBMS 78 whose content was more than 7%. / O objetivo desta pesquisa foi analisar a diversidade de bactérias diazotróficas associadas e endofíticas de Brachiaria brizantha, estudar o potencial destas em solubilizar fosfatos inorgânicos de ferro e alumínio, produzir ácido-3-indolacético (AIA) e avaliar o efeito da inoculação destes isolados em Brachiaria brizantha cv MG 05 Vitória. As bactérias foram isoladas de amostras de solos cultivados sob B. brizantha e partes de tecido vegetal desta gramínea, nos períodos seco e chuvoso, nos municípios de Alfenas e Machado, Sul de Minas Gerais. Foram utilizados cinco meios de cultura semissólidos e semisseletivos: FAM (Azospirillum amazonense), JMV (Burkholderia sp.), JNFb (Herbaspirillum spp.), LGI (A. amazonense) e NFb (Azospirillum spp.). Os testes de solubilização de fosfato e produção de AIA foram realizados in vitro e foram utilizados como critério de seleção dos 22 isolados bacterianos utilizados na inoculação de B. brizantha cv MG 5 Vitória, cultivada em vasos contendo 20 dm3 de solo. Foram realizados dois cortes, em que foram avaliados os seguintes parâmetros: altura (Al), largura (LF) e comprimento da folha (CF), número de perfilhos (NP), comprimento (CR) e massa seca da raiz (MSR), matéria seca (MS), produtividade de matéria seca (PMS), fibra em detergente neutro (FDN) e ácido (FDA) e a proteína bruta na matéria seca (PBMS). Foi obtido um total de 332 isolados, sendo a maioria endofíticos. O maior número e diversidade foram provenientes do município de Alfenas. No período chuvoso foi verificado maior número e diversidade de isolados em ambos os Municípios, quando comparado ao período da seca. Trinta e cinco isolados solubilizaram fosfato de ferro e 78 produziram AIA, destacando-se os isolados UNIFENAS 100-17, 21, 40 e 78, capazes de desempenhar ambas as funções simultaneamente. A inoculação de estirpes diazotróficas de origem endofíticas e rizosféricas influenciaram no desenvolvimento de B. brizantha cv MG 5 Vitória, contribuindo para a produção de MS, PMS e PBMS nas duas alturas de corte destacando-se os isolados UNIFENAS-100-16, 21, 78 cujo teor de PBMS foi superior a 7%.

Submitted by Michele Mologni (mologni@unoeste.br) on 2018-05-11T18:40:49Z No. of bitstreams: 1 Rita de Cássia Lima Mazzuchelli.pdf: 967240 bytes, checksum: b50abc610a188a8f6408500562f11123 (MD5) / Made available in DSpace on 2018-05-11T18:40:49Z (GMT). No. of bitstreams: 1 Rita de Cássia Lima Mazzuchelli.pdf: 967240 bytes, checksum: b50abc610a188a8f6408500562f11123 (MD5) Previous issue date: 2017-05-16 / The objective of this study was to evaluate drying times of the previous pasture to soybean cultivation, associated with physical intervention (scarification), through impacts on soil microbial activity in soil and grain yield in the livestock farming system integration. The experiment was conducted in soil classified as Acrisol dystrophic. The experimental area was occupied by the species Urochloa brizantha (cv Marandu) with five years of implementation. The experimental design was a split tracks, onstituting a double factorial 5x2. The plots consisted of five periods of desiccation of grassland (150 DBS - days before soybean sowing; 120 DBS, 60 DBS, 30 DBS and 15 DBS) and the subplots, with and without soil scarification. Were grown two production cycles of soybean and maize, soil samples being collected at the beginning of each production cycle for biological, chemical and physical analysis of fertility. plants were collected for nodulation analysis. At the end of each production cycle crops were evaluated for productivity parameters. The longer periods of early pasture desiccation provided gains in microbial activity in the soil, the first year of cultivation of soybeans and corn. There were also improvements in soil fertility indicators. In the second year of cultivation of soybeans and corn gains in quality indicators were lower compared to the first year of cultivation. Early pasture desiccation in 150 days before the soybean crop yielded considerable nodulation and soybean yield gains. The yield of corn after the first crop of soybeans, was significantly influenced by longer periods of anticipation desiccation performed before soybean cultivation. / O objetivo do presente trabalho foi o de avaliar épocas de dessecação da pastagem anteriores ao cultivo da soja, associado com intervenção física (escarificação), através de impactos na atividade microbiana no solo e rendimento de grãos dentro do sistema de integração lavoura pecuária. O experimento foi desenvolvido em solo classificado como Argissolo Vermelho distroférrico. A área experimental estava ocupada com a espécie Urochloa brizantha (cv Marandu) com cinco anos de implantação. O delineamento experimental foi em faixas subdivididas, constituindo um fatorial duplo, 5x2. As parcelas foram constituídas por cinco épocas de dessecação da pastagem (150 DAS - dias antes da semeadura da soja; 120 DAS; 60 DAS; 30 DAS e 15 DAS) e as subparcelas, com e sem escarificação do solo. Foram cultivados dois ciclos produtivos de soja e milho, sendo coletadas amostras de solo ao início de cada ciclo produtivo para análises biológicas, químicas de fertilidade e físicas. Foram coletadas plantas para análise de nodulação. Ao final de cada ciclo produtivo as culturas foram avaliadas para os parâmetros de produtividade. Os maiores períodos de dessecação antecipada da pastagem proporcionaram ganhos na atividade microbiana no solo, no primeiro ano de cultivo da soja e milho. Ocorreram também melhorias em indicadores de fertilidade do solo. No segundo ano de cultivo da soja e milho os ganhos nos indicadores de qualidade foram menores, comparando-se ao primeiro ano de cultivo. A dessecação antecipada da pastagem em 150 dias antes do cultivo da soja proporcionou ganhos consideráveis de nodulação e rendimento da soja. O rendimento do milho, após o primeiro cultivo da soja, foi influenciado significativamente pelos maiores períodos de antecipação da dessecação efetuada antes do cultivo da soja.

Objetivou-se estudar a substituição do milho por polpa cítrica peletizada no concentrado de vacas leiteiras em lactação, durante a estação chuvosa do ano, em pastejo de capim-elefante. Os trabalhos foram conduzidos no Departamento de Zootecnia da ESALQ/USP. O delineamento estatístico foi em Quadrado Latino 4 x 4, analisados utilizando-se o Proc GLM (SAS, 1999). Foi utilizada uma área de 7,8 ha de pastagem dividida em 39 piquetes de 0,2 ha cada, adubada com 80 kg N ha mês-1. Experimento I: Foram utilizadas oito vacas Holandesas com média de 82 dias de lactação e 522,9 kg de PV, no início do período experimental. Os tratamentos continham as seguintes proporções de milho e polpa cítrica: 100:0 (T0); 75:25 (T25); 50:50 (T50); 25:75 (T75). As vacas receberam 7,00 kg de concentrado dia-1 (6,3 kg MS), fracionado em duas vezes ao dia. A pastagem foi adubada com 80 kg N ha.mês-1. Não houve diferença (P>0,05) no tempo de pastejo (7h22’), ruminação (8h36’), ócio (5h56’) e taxa de bocados (34,4 movimentos min-1). A temperatura retal (38,74 e 39,64ºC) e freqüência respiratória (47,44 e 61,20 movimentos min-1), mensuradas as 8:00 e as 15:30 horas, respectivamente, não foram afetadas pelos tratamentos (P>0,05). Não houve diferença (P>0,05) na produção de leite corrigida para 3,5% de gordura (18,5 kg vaca dia-1), percentagens de gordura (3,5%), proteína (3,06%), lactose (4,40%), sólidos totais (13,02%), N-uréico (15,01 mg dL-1) e contagem de células somáticas (203.000 mL-1). O peso vivo (536,8 kg), condição corporal (2,51), glicose plasmática (75,90 mg dL-1), N-uréico plasmático (16,96 mg dL-1) e ácidos graxos livres no plasma (456,12 mEq L-1) também não foram afetados pelos tratamentos (P>0,05). Experimento II: Foram utilizadas 11 vacas (7 Holandesas e 4 Jersey), com 427,5 kg de PV e 153,22 dias de lactação, no início do período experimental. Os concentrados continham 21,8% de PB e as respectivas proporções de milho e polpa cítrica: 100:0 (T0); 75:25 (T25); 50:50 (T50); 25:75 (T75). As vacas receberam 6,1 kg de concentrado dia-1 (5,5 kg de MS), fracionado em duas vezes ao dia, fornecido após cada ordenha. A pastagem era adubada com 80 kg N ha mês-1. Não houve diferença (P>0,05) na produção de leite corrigida para 3,5% de gordura (13,7 kg vaca dia-1), percentagens de gordura (3,8%), proteína (3,37%), sólidos totais (13,27%), N uréico (14,34 mg dL-1) e contagem de células somáticas (140.450 mL-1). A percentagem de lactose foi diferente (P<0,05) para a maior dose de substituição. O peso vivo (427,2 kg), condição corporal (2,74), glicose plasmática (74,63 mg dL-1), N uréico plasmático (16,74 mg dL-1), e ácidos graxos livres no plasma (417,81 mEq L-1) não foram afetados pelos tratamentos (P>0,05). Não houve diferença (P>0,05) no tempo de pastejo (7h51’), ruminação (7h59’), ócio (6h) e taxa de bocados (37,91 movimentos min-1). A Temperatura retal (38,76 e 39,61ºC) e freqüência respiratória (53,57 e 71,50 movimentos min-1), mensuradas às 8:00 e às 15:30 horas, respectivamente, não foram afetadas pelos tratamentos (P>0,05). O milho pode ser substituído pela polpa cítrica sem depreciar a produção e composição do leite. / Two experiments were conducted to study the partial substitution of fine ground corn by peleted pulp citric in the concentrate of lactating cows in middle lactation (Experiment I) and in late lactation (Experiment II), grazing elephant – grass pasture. The trials were conducted at the Animal Science Department of ESALQ/USP. In both experiments, the animals were grouped according to milk yield, days in milk and parturition order. The statistical designs were repeated 4 x 4 Latin Square. The data were analysed using the Proc GLM of SAS (1999). Experiment I: Eight Holstein cows (82 DIM and 522.9 kg LBW), at the beginning of the trial were used. The concentrates contained the following corn:peleted citrus pulp proportions: 100:0 (T0); 75:25 (T25); 50:50 (T50); 25:75 (T75). The cows received 7 kg of concentrate day-1 (6.3 kg of DM), fractionated in 2 daily meals. The pasture was fertilized with 80 kg N ha.month-1. The forage offer was of 33,6 kg DM of green leaves cow day-1. There was not difference (P>0.05) in the grazing time (7h22’), rumination time (8h36’), leisure time (5h56’) and biting rate (34.4 movements min-1). The rectal temperature (38.74 and 39.64ºC) and respiratory frequency (47.44 and 61.20 movements min-1), measured at 8:00 AM and at 3:30 PM, respectively, were not affected by treatments (P>0.05). There was not difference (P>0.05) in 3.5 % FCM yield (18.5 kg cow day-1), in the contents of milk fat (3.5%), protein (3.06%), lactose (4.40%) and total solids (13.02%), milk urea-N (15.01 mg dL-1) and of somatic cells (203.000 mL-1) were not affected by treatments (P>0.05). The LBW (536.8 kg), BCS (2.51), plasma glucose (75.90 mg dL-1), plasma urea-N (16.96 mg dL-1) and plasma free fat acids (456.12 mEq L-1) were not affected by treatments (P>0.05). Experiment II: Eleven cows were used, 7 Holstein and 4 Jersey (427.5 kg LBW and 153.22 DIM), at the beginning of the trial. The concentrates were 21.8% of CP (DM bases), and the respective corn:peleted citric pulp ratio were: 100:0 (T0); 75:25 (T25); 50:50 (T50); 25:75 (T75). The cows were fed 6.1 kg day-1 of concentrate (5.5 kg of DM), fractionated in 2 daily meals, after each milking. There was not difference (P>0.05) in 3.5 FCM yield (13.7 kg cow day-1), in the content of milk fat (3.8%), protein (3.37%) and total solids (13.27%), milk urea-N (14.34 mg dL-1) and somatic cells (140,450 mL-1). The lactose content was lower (P<0.05) for the 25:75 diet. The LBW (427.2 kg), BCS (2.74), plasma glucose (74.63 mg dL-1), plasma urea-N (16.74 mg dL-1), and plasma free fat acids (417.81 mEq L-1) were not affected by treatments (P>0.05). There were no difference (P>0.05) in the grazing time (7h51’), rumination time (7h59’), leisure time (6h) and biting rate (37.91 movements min-1). The rectal temperature (38.76 and 39.61ºC) and respiratory frequency (53.57 and 71.50 movements min-1), measured at 8:00 and at 15:30 hours, respectively, were not affected by treatments (P>0.05). The corn can be substituted by the citric pulp without depreciating the milk yield and content.

O presente experimento foi conduzido no Departamento de Produção Animal da ESALQ/USP, em Piracicaba (SP), entre 15/12/98 e 04/07/99. Os tratamentos foram constituídos pelas combinações entre três cultivares de Cynodon spp. (Tifton-85, Florakirk e Coastcross) e quatro alturas de pasto (5, 10, 15 e 20 cm) mantidas por pastejo de ovinos em regime de lotação contínua e taxa de lotação variável. O delineamento experimental utilizado foi o de blocos completos casualizados em arranjo de parcelas subdivididas com quatro repetições. As parcelas corresponderam aos cultivares e as subparcelas (unidades experimentais) às alturas de pasto. Foram analisadas as seguintes variáveis: biomassa na área total, densidade populacional de perfilhos, massa por perfilho, massa de folha por perfilho e área foliar por perfilho. A partir dessas medições foram realizados cálculos de índice de área foliar do pasto (IAF), volume por perfilho, relação folha:haste por perfilho e relação área foliar:volume por perfilho (R). O mecanismo de compensação tamanho/densidade populacional de perfilhos operou em pastagens de Cynodon spp.. No entanto, as inclinações das retas foram consistentemente maiores que a proposição teórica de 3/2. Perfilhos individuais de Cynodon spp. apresentaram um padrão de crescimento isométrico e parecem agruparse em clones para assegurar estratégia competitiva e otimização de IAF. Pastos mantidos a 5 cm durante o outono apresentaram densidades populacionais reduzidas, indicando um padrão de tolerância ao pastejo dependente da época do ano. Tifton-85 e Coastcross apresentaram uma capacidade de aumento em biomassa que pode ir além da altura de 20 cm, enquanto que para o cultivar Florakirk essa capacidade situou-se em torno de 20 cm. O estádio reprodutivo das plantas interferiu de forma significativa nos processos de competição intra-específica e dinâmica populacional de perfilhos. / The experiment was conducted at the Department of Animal Production, ESALQ/USP, Piracicaba (SP), from 15/12/98 until 04/07/99. Treatments were combinations of three Cynodon spp. cultivars (Tifton-85, Florakirk and Coastcross) and four sward surface heights (SSH) (5, 10, 15 and 20 cm) maintained by sheep under continuous stocking and variable stocking rate. A complete randomised block design was used, with treatments arranged in split-plot and replicated four times. Grass cultivars were assigned to plots and SSH to sub-plots. Pastures responses evaluated were: total biomass above ground level, tiller population density, tiller weight, leaf mass and leaf area per tiller. From these measurements calculations of sward leaf area index (LAI), tiller volume, tiller leaf:stem ratio and tiller leaf area:volume ratio (R) were derived. A tiller size/population density mechanism operated in Cynodon spp. However, a slope steeper than the theoretical expectation of 3/2 was observed. Individual tillers presented an isometric pattern of growth and seemed to demonstrate a clonal integration among tillers in order to enhance competitive ability and optimise LAI. Swards maintained at 5 cm during autumn presented reduced tiller population densities, indicating a pattern of grazing tolerance dependent of time of the year. Tifton-85 and Coastcross pastures showed a capacity to increase total biomass that could go beyond 20 cm, while Florakirk stabilised around that SSH. Reproductive development of plants interfered with the processes related to intra-specific competition and tiller population dynamics.

No description available.

<p>Wheat is a major source of calories and protein for humans worldwide. Wheat is the most widely grown crop, with cultivation areas and production systems on every continent. The cultivated land area is vast because of its importance and adaptability to various environmental conditions. Global wheat production has not kept up with the growing population, provoking the need to develop new methods and techniques to increase genetic gains. The first research chapter of this Ph.D. dissertation involves performing genome-wide association studies (GWAS) to identify and examine transferability of marker-trait associations (MTAs) across environments. I evaluated yield and yield components traits among 270 soft red winter (SRW) wheat varieties. The population consists of experimental breeding lines adapted to the Midwestern and eastern United States and developed by public university breeding programs. Phenotypic data from a two-year field study and a 45K-SNP marker dataset were analyzed by FarmCPU model to identify MTAs for yield related traits. Grain yield was positively correlated with thousand kernel weight, biomass, and grain weight per spike while negatively correlated with days to heading and maturity. Sixty-one independent loci were identified for agronomic traits, including a region that with <i>–logP</i> of 16.35, which explained 18% of the variation in grain yield. Using 12 existing datasets from other states and seasons, in addition to my own data, I examined the transferability of significant MTAs for grain yield and days to heading across homogenous environments. For grain yield and days to heading, I only observed 6 out of 28 MTAs to hold up across homogenous environments. I concluded that not all marker-trait associations can be detected in other environments.</p><p>In the second research chapter of this Ph.D. dissertation, I dissected yield component traits under contrasting nitrogen environments by using field-based low-throughput phenotyping. I characterized grain yield formation and quality attributes in soft red winter wheat. Using a split-block design, I studied responses of 30 experimental lines, as sub-plot, to high nitrogen and low nitrogen environment, as main-plot, for two years. Differential N environments were imposed by the application, or lack thereof, of spring nitrogen application in a field, following a previous corn harvest. In this study, I measured agronomic traits, in-tissue nitrogen concentrations, nitrogen use efficiency, nitrogen harvest index and end-use quality traits on either all or subset of the germplasm. My data showed that biomass, number of spikes and total grain numbers per unit area were most sensitive to low nitrogen while kernel weight remained stable across environments. Significant genotype x N-environment interaction allowed me to select N-efficient germplasm, that can be used as founding parents for a potential breeding population specifically for low-N environments. I did this selection on the basis of superior agronomic traits and the presence of the desirable gluten quality alleles such as <i>Glu-A1b </i>(<i>2*</i>) and <i>Glu-D1d </i>(<i>5+10</i>).</p>

Im Rahmen des Pilotprojektes Mulde wurde die Schwermetallbelastung landwirtschaftlich und gärtnerisch genutzter Böden untersucht. Als Ergebnis der Bodenuntersuchungen und der Boden-Pflanze-Beziehungen wurden Belastungskarten der untersuchten Gebiete angefertigt.

Food insecurity and nutrition are two of the biggest challenges facing our society. Urban agriculture can help address these challenges, though lack of awareness about opportunities for engagement and degraded soils are two barriers that could prevent people from realizing the benefits that these operations can provide. Soils in urban areas are often highly degraded due to development activities and lack the structure and microbial life needed to sustain healthy, productive plants. Many lifelong habits such as healthy eating and engagement in community gardening are best established during young adulthood. Graduate school is a particularly unique time period, as many students are living on their own for the first time with modest incomes and some have young families that are particularly vulnerable to food insecurity. Consequently, the first objective of this project was to identify which barriers, if any, Purdue graduate students face when purchasing and consuming fresh produce and participating in local urban agriculture initiatives as Purdue’s campus and much of the surrounding area are characterized as food deserts by the USDA. We also sought to determine how the COVID-19 pandemic influenced food access and motivations for healthy eating and community garden engagement. To answer these questions, we distributed a voluntary 33 question online Qualtrics® survey to all Purdue graduate students via mass email blast. Results indicate that many Purdue graduate students face individual and structural barriers to accessing fresh fruits and vegetables. International respondents, in particular, were particularly vulnerable to structural barriers. Not having access to a personal vehicle appears to be the primary predictor of who was most vulnerable, especially during the pandemic. Results also indicate that students are interested in participating in local urban agriculture initiatives, but most are unaware of their existence. Students indicated that e-mails were the best method for increasing awareness and engagement. The second objective of this study was to determine whether leaf mold compost could improve the health and productivity of degraded urban soils. In addition, we aimed to determine whether the leaf compost could better support a beneficial microbial inoculant to further enhance crop productivity, as well as the extent to which plant genotype moderates these beneficial plant-soil-microbial relationships. To answer these questions, leaf compost was obtained from a local grower and applied to experimental plots at the Purdue University Farm. Two tomato varieties, Wisconsin 55 and Corbarino, were inoculated with Trichoderma harzianum T-22 or a sterile water control, and transplanted into the field trials. 15 Survival following transplanting, vigor, disease ratings and the yield and quality of tomato fruit were quantified over the course of two growing seasons. Results indicated that several measures of soil health were significantly increased in compost-amended soils and the health and productivity of tomato plants greatly improved. The microbial inoculant dramatically reduced transplant stress, especially in Wisconsin 55. Other more subtle differences among the tomato varieties indicated that urban agriculture systems could be improved through varietal selection. These studies highlight the fact that graduate students are not immune to food insecurity and proper nutrition and they are interested in connecting with urban agriculture initiatives to address these challenges. Pairing of the two groups could prove to be a successful mutualistic symbiosis as graduate students provide the enthusiasm and manpower that urban gardens need while urban gardens offer access to low-cost fresh produce that many graduate students desire. Leaf mold compost can aid in these initiatives by providing a cost-effective approach to improve the health and productivity of urban soils and crops, while at the same time providing further benefits such as reduced accumulation of valuable carbon sources in municipal landfills. Results like these provide stark evidence that agriculture, particularly urban agriculture, can continue to improve access to nutritious foods through green initiatives and innovations.

Many studies show that large herbivores can have an important impact on the composition of vegetation. With the establishment of a year round, low density grazing regime, plant ecologists and nature managers expect that through selective grazing, herbivores will create a mosaic of different vegetation communities varying in structure and plant species composition. It is believed that such a mosaic in the end will guarantee a high degree of biodiversity. Grazing will, therefore, seem to be a suitable means to maintain grass. Also important is the ability of herbivores affect vegetation through endozoochory. In this thesis I have tried to find out what species of diet horses prefer regarding to plant species and what plant species they can spread through out endozoochory. I have compared this knowledge with the composition of pasture and meadow vegetation at the researched locality in Malenice and Hoslovice. With the purpose of finding out the preferences I established spots where I registered data on vegetation before pasture and the time intervals during the pasture. Afterwards, I researched the amount of sprouts and the composition of seedlings in excrements that I let germinate. I had to create phytocenologic shots from the pastures and meadows to compare the species of composition of grazed and...

Please read the abstract in the section 00front of this document / Thesis (DPhil)--University of Pretoria, 2000. / Veterinary Tropical Diseases / unrestricted