Orientador: Wagner Bettiol / Resumo: A cultura do tomateiro é severamente atacada por diversas doenças, entre elas pode-se destacar a Murcha-de-Fusário. O objetivo do presente trabalho foi o de avaliar a eficiência de isolados de Fusarium oxysporum não patogênicos (Fnp) 233, 233/1, 245, 245/1, 141/3, 251, 251/2, 251/5, 257, originários da Universidade de Torino, Itália, no controle da Murcha-de-Fusário, causada por Fusarium oxysporum f. sp. lycopersici raças 1 e 2 (Fol). Os isolados patogênicos CA4A (Fol - 1), C-21A (Fol - 2), TO11 (Fol - 2) e TO245 (Fol - 2), bem como os isolados não patogênicos, foram cultivados em meio de cultura BD (batata-dextrose) durante 10 dias à 25ºC, com agitação constante de 150rpm. Para se obter estruturas de resistência do fungo 500 ml de inóculo líquido de cada isolado de Fnp foram adicionados em 1000 g de talco e incubados durante 30 dias. Com o intuito de verificar a patogenicidade dos isolados CA4A, C-21A, TO11 e TO245, plântulas de tomateiro cv. Viradoro foram transplantadas para substrato infestado com inóculo líquido nas concentrações de Fol de 103, 104, 105 e 106 conídios mL-1. Após 35 dias do transplante, as mudas foram avaliadas quanto a severidade da doença (Notas variando entre 1 a 6, onde: 1 planta sadia e 6 planta morta), a altura e as massas secas do sistema radicular e da parte aérea das plantas. As concentrações de 106 e 105 conídios mL-1 dos isolados de Fol promoveram a maior severidade da doença, quando comparadas com a testemunha não inoculada. Após determinar a concentração do patógeno, verificou-se a atividade não patogênica dos isolados de Fnp em plantas de tomateiro onde, raízes foram imersas em uma suspensão de conídios dos... (Resumo completo, clicar acesso eletrônico abaixo). / Abstract: The tomato is severely is affected by several diseases, among them may be detached the Fusarium wilt. The objective this present research was to evaluate the efficacy of the nonpathogenic Fusarium oxysporum strains (Fnp) 233, 233/1, 245, 245/1, 141/3, 251, 251/2, 251/5, 257, from the University of Torino, Italy, on the control of Fusarium wilt, caused by Fusarium oxysporum f. sp. lycopersici (Fol) races 1 and 2. The pathogenic strains CA4A race 1, C-21A race 2, TO11 race 2 and TO245 race 2, as well the nonpathogenic strains were growing in liquid media PD (potato-dextrose) during 10 days at 25ºC, with constant agitation at 150 rpm. To obtain resistant structure of the fungi 500 mL of the liquid inoculum with each the Fnp strain were mixed in 1000 g of talc and incubated for 30 days. To evaluate the pathogenic activity of the strains: CA4A (Fol - 1), C-21A (Fol - 2), TO11 (Fol - 2) e TO245 (Fol - 2), tomato seedlings cv. Viradoro susceptible to race 2 of the pathogen were transplanted into the infested substrate with inoculum suspension in the concentrations of Fol 103, 104, 105 e 106 conidia mL-1. After 35 days of the seedlings transplantation were evaluated the disease severity (Notes between 1 and 6, where: 1 health plant e 6 died plant), the height plants and the weight dry material of the root system and aerial part of the plants. The concentrations 106 e 105 conidia mL-1 of the strains de Fol increased the higher severity, when compared with non inoculated plants. After determination the concentration of the pathogen, observed the nonpathogenic activity of the Fnp strains in tomato plants where, roots were dipped in a conidial suspension in the concentration of the 106 conidia mL-1. The plants were growing into pots for the 500 mL capacity of the substrate and after 35 days of the growing in greenhouse were realized the evaluations. The plant... (Complete abstract, click electronic address below). / Mestre

Tese (doutorado) - Universidade Federal de Santa Catarina, Centro de Ciências Agrárias, Programa de Pós-Graduação em Recursos Genéticos Vegetais, Florianópolis, 2017. / Made available in DSpace on 2017-08-01T04:16:08Z (GMT). No. of bitstreams: 1 347208.pdf: 1255192 bytes, checksum: f8bdc42e9524a9d8a457cb61de8d3e4e (MD5) Previous issue date: 2017 / Existe pouca informação sobre a colonização vascular do feijão comum por Fusarium oxysporum f. sp. phaseoli (Fop), bem como sobre os mecanismos de defesa do hospedeiro frente ao ataque patogênico. Assim, o trabalho objetivou estudar a colonização vascular espaço-temporal de plantas de feijão comum dos genótipos UFSC-01 e Uirapuru por F. oxysporum f. sp. phaseoli e mecanismos físicos e químicos de defesa do hospedeiro. Na primeira parte do trabalho, a incidência e severidade da Murcha de Fusarium (MF), descoloração vascular do hipocótilo, unidades formadoras de colônias (ufc) e ergosterol foram quantificadas em tecidos da raiz, hipocótilo e epicótilo, aos 5, 10, 15, 20, 25 e 30 dias após inoculação (dai). A colonização vascular também foi monitorada em secções dessas partes da planta e na coroa a 1, 3, 5 e 25 dai. Na segunda parte, sintomas externos e internos foram avaliados no sistema radicular e hipocótilos aos 25 dai. No sistema radicular e hipocótilos desses tecidos, foi monitorada a atividade das enzimas guaiacol peroxidase (GPX), fenilalanina amônia-liase (PAL) e polifenol oxidase (PPO) a 0, 1, 2, 3, 4, 5 e 6 dai. Nessas partes, também foi determinado o conteúdo de fenólicos totais, flavonoides e lignina, a 0, 3 e 6 dai. Secções da raiz principal e hipocótilo foram analisadas com microscópio de epifluorescência a 1, 3 e 6 dai. Nesse último tempo, secções ultrafinas desses tecidos foram analisadas por microscopia eletrônica de transmissão. Determinações de cfu e ergosterol conduziram a resultados semelhantes, mostrando que o fungo colonizou mais eficientemente plantas suscetíveis. Fop cresceu intercelularmente até alcançar os vasos do xilema das raízes principais. Depois disso, o patógeno começou a colonizar partes superiores pela produção de uma grande quantidade de conídios dentro dos vasos do xilema. Sintomas precoces e fortes em plantas suscetíveis foram associados a uma rápida colonização e um colapso dos vasos do xilema em tecidos aéreos. Em contraste, vasos de plantas resistentes permaneceram sem ser afetados e o retraso na colonização foi associada com a fraca formação/transporte de conídios em vasos de tecidos da raiz principal e a coroa. Uma precoce, maior e rápida atividade das enzimas GPX, PAL e PPO, aliado a uma parede celular espessa dos vasos do xilema, são importantes na defesa de feijão comum a Fop. As vesículas, além de inibir quimicamente o crescimento do patógeno, podem formar parte do material de oclusão no interior dos vasos do xilema de plantas resistentes.<br> / Abstract : There is a lack of information on the vascular colonization of common bean by Fusarium oxysporum f. sp. phaseoli (Fop), as well as the host defense mechanisms against the pathogen. Thus, this work was aimed to study the space-temporal vascular colonization of UFSC-01 and Uirapuru common bean plants by Fop and physical and chemical defense mechanisms of host. In the first part of the work, incidence and severity of Fusarium wilt (Fw), vascular discoloration in hypocotyls, colony forming units (cfu) and ergosterol were quantified on root, hypocotyl and epicotyl tissues, at 5, 10, 15, 20, 25 and 30 days after inoculation (dai). Fungal colonization was also monitored by light microscopy of cross sections from the mentioned plants parts as well as root crown at 1, 3, 5 and 25 dai. In the second part, external and internal symptoms of Fw were quantified in plants, at 25 dai. guaiacol peroxidase (GPX), phenylalanine ammonia lyase (PAL) and polyphenol oxidase (PPO) activity were monitored in system roots and hypocotyls at 0, 1, 2, 3, 4, 5 and 6 dai. In these tissues, total phenolics, flavonoids and lignin content were determined at 0, 3 and 6 dai. At the last time, ultrafine sections of these tissues were analyzed by transmission electron microscopy. Cfu and ergosterol determinations lead to similar results showing that fungus colonized more efficiently susceptible plants. Fop grew intercellularly until reaching the xylem vessels of taproots. Thereafter, it started to colonize upper parts by producing a large amount of conidia inside plant vessels. Earlier and stronger symptoms on susceptible plants were associated to both faster colonization and collapse of xylem vessels in aerial tissues. In contrast, vessels of resistant plants remained unaffected, and delayed colonization was associated with weak formation/transport of conidia in vessels of taproot and root crown. An early, larger and faster activity of the GPX, PAL and PPO enzymes, together with a thick cell wall of xylem vessels, are important in the defense of common bean to Fop. Vesicles besides inhibiting to chemically the growth of the pathogen, may form part of the occlusion material inside xylem vessels of resistant plants.

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia Química, Florianópolis, 2017 / Made available in DSpace on 2017-09-05T04:13:14Z (GMT). No. of bitstreams: 1 347270.pdf: 2494526 bytes, checksum: bbea18f57e394096de608a8cec11abbe (MD5) Previous issue date: 2017 / As nanopartículas de prata sintetizadas a partir de sistemas microbianos por meio de métodos de produção verde, também conhecido como métodos ecoeficientes são uma realidade do século XXI. O método da biossíntese é considerado uma técnica ecologicamente limpa, não-tóxica e ambientalmente aceitável. Muitos microrganismos atuam diretamente na síntese intracelular ou extracelular de nanopartículas metálicas com diferentes eficiências, além de tamanhos e formas variáveis de nanopartículas. Desse modo, a síntese de nanopartículas de prata (AgNPs) por fungos é um processo alternativo e promissor devido a sua natureza ecoeficiente, segura e rentável. O objetivo deste estudo foi a biossíntese de AgNPs mediada pelo fungo Fusarium oxysporum, bem como a caracterização destas nanopartículas, incluindo a avaliação do controle do tamanho e estabilidade em diferentes condições de tratamento e a verificação de seu potencial como agente antimicrobiano. O tamanho e a estabilidade das AgNPs foram determinados respectivamente pelos métodos de espalhamento de luz dinâmico (DLS) e potencial zeta (PZ). As nanopartículas de prata também foram caracterizadas via espectroscopia na região ultravioleta visível (UV-Vis), espectroscopia no infravermelho por transformada de Fourier (FTIR), espectroscopia de absorção atômica por chama (FAAS), microscopia eletrônica de varredura com emissão de campo (MEV-EC) e microscopia eletrônica de transmissão (TEM). Por fim, o potencial antimicrobiano foi avaliado testando-as contra diferentes cepas bacterianas, medindo os halos de inibição de bactérias tratadas com diferentes quantidades de soluções coloidais contendo nanopartículas de prata. Os resultados mostraram que a biossíntese produziu AgNPs com tamanho médio de 34 nm e valores de potencial zeta inferiores a -30 mV nas condições de tratamento. Os espectros UV-Vis e FAAS confirmaram a presença de íons de prata reduzidos e consequentemente a formação de AgNPs. Já as análises em FTIR detectaram bandas correspondentes a vibrações em ligações químicas de grupamentos tipo amida I e II de proteínas, além da presença de alcanos cíclicos, ciclo-hexano, éteres e hidrocarbonetos aromáticos. As análises em MEV-EC e TEM revelaram a formação de AgNPs com formato esférico e bem dispersos. Por fim, a verificação dos testes de sensibilidade de cepas bacterianas tratadas com AgNPs confirmaram a eficiência das nanopartículas como agente antimicrobiano. / Abstract: Silver nanoparticles synthesized from microbial systems by means of green production or eco-friendly methods are a reality of the 21st century. The synthesis of silver nanoparticles (AgNPs) by fungi is a promising alternative processing due to its eco-friendly, safe, and cost-effective nature. The goal of this study was to evaluate the biosynthesis of AgNPs mediated by the fungus Fusarium oxysporum, as well as the characterization of these nanoparticles, including the evaluation of size control and stability in different treatment conditions and the verification of their potential as an antimicrobial agent. The size and stability of the AgNPs were determined respectively by the methods of dynamic light scattering (DLS) and zeta potential (ZP). Silver nanoparticles were also characterized by visible ultraviolet (UV-Vis) spectroscopy, Fourier transform infrared spectroscopy (FTIR), flame atomic absorption spectroscopy (FAAS), field emission scanning electron microscopy (FE- SEM) and transmission electron microscopy (TEM). Finally, the effectiveness of the antimicrobial potential was evaluated by testing them against different bacterial strains by the antimicrobial susceptibility test, measuring the inhibition halos of bacteria treated with different quantities of colloidal solutions containing silver nanoparticles. The results showed that biosynthesis produced silver nanoparticles with a mean size of 34 nm and zeta potential values below -30 mV under treatment conditions. The UV-Vis and FAAS spectra confirmed the presence of reduced silver ions and consequently the formation of AgNPs, whereas FTIR detected bands corresponding to vibrations in chemical bonds of groupings type: amide I and II of proteins besides the presence of alkanes, cyclohexane, ethers and aromatic hydrocarbons. FE-SEM and TEM revealed the formation of AgNPs with spherical shape and well dispersed. Finally, the verification of the sensitivity tests of bacterial strains treated with AgNPs confirmed the efficiency of the nanoparticles as an antimicrobial agent.

Made available in DSpace on 2014-06-12T15:49:40Z (GMT). No. of bitstreams: 2 arquivo1529_1.pdf: 841640 bytes, checksum: a1668107b89c5355d88180dbb4cb329e (MD5) license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2008 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / Objetivando estudar o efeito de isolados de bactérias promotoras do crescimento de plantas (BPCP) e fungos micorrízicos arbusculares (FMA) foram realizados três experimentos. Primeiramente, bactérias epifíticas e endofíticas foram isoladas de raízes de bananeiras sadias de seis cultivares e caracterizadas quanto à produção de pectinase, celulase, ácido indolacético, &#946;-1,3-glucanase e quitinase. No 1º. experimento, as rizobactérias foram avaliadas quanto à promoção do crescimento de bananeiras micropropagadas cv. Grande Naine em casa de vegetação, sendo 74 tratamentos de bacterização + um tratamento controle, com 8 repetições. Mudas com aproximadamente 10 cm foram transplantadas e bacterizadas em potes contendo 1 kg de solo desinfestado. No 2º. experimento, foi observada a ação antagônica in vitro das RPCP selecionadas, contra Fusarium oxysporum f. sp. cubense. No 3º experimento, em casa de vegetação, foi estudado o efeito da associação RPCP x FMA no desenvolvimento de mudas de bananeiras cv. Grand Naine. Foi aplicado DIC com 7 tratamentos de bacterização com RPCPs (BAN29, BAN36, BAN81, BAN82, S1, S2 e controle) × 3 tratamentos de inoculação com FMAs (Glomus etunicatum, Glomus clarum e controle) × 7 repetições. A inoculação (200 glomerosporos/planta) ocorreu no transplantio das mudas para sacos contendo 1,5 Kg de solo desinfestado. Em seguida, as mudas foram bacterizadas com seis isolados pré-selecionados no Experimento 1. As suspensões bacterianas (50 mL/planta) utilizadas nos experimentos em casa de vegetação foram preparadas e ajustadas em fotocolorímetro (A580) em água destilada esterilizada (ADE) visando obter para 108 UFC/mL. O tratamento controle sem FMA e sem bactérias recebeu ADE. Para o isolamento de bactérias endofíticas foram testados diferentes substâncias desinfestantes e tempos de exposição, com melhor resultado obtido com hipoclorito de cálcio a 5%, por 20 minutos. Foram obtidos 80 isolados bacterianos, com predominância de bactérias epifíticas (53,7%) e de Gram-positivas (67,1%). Nove isolados produziram pectinase, 37 ácido indolacético e dois &#946;-1,3-glucanase. Nenhum dos isolados foi capaz de produzir celulase, ácido cianídrico, quitinase ou solubilizar fosfato. Incrementos no desenvolvimento de mudas micropropagadas de bananeiras cv. Grand Naine foram evidenciados a partir dos 30 dias após bacterização com 40 isolados. Houve incremento de até 82% para a biomassa fresca (BF) da parte aérea e de até 263% para a BF de raízes das mudas associadas com BAN29, BAN36, BAN81, BAN82, S1 e S2 (Experimento 1). A BAN36 foi capaz de inibir o crescimento micelial de Fusarium oxysporum f. sp. cubense em placas de Petri (até 67%) (Experimento 2). Em geral, a inoculação conjunta RPCP × FMA não proporcionou incremento no crescimento, sendo observada interação positiva apenas entre FMAs e os isolados S1 e S2. Apenas na ausência dos FMAs, as mudas tratadas com BAN29, BAN36, BAN81 e BAN82 diferiram em relação ao controle. Houve estímulo na colonização das raízes de bananeiras por G. clarum quando associadas com BAN82. Isolados bacterianos epifíticos e endofíticos de raízes de bananeiras são capazes de produzir substâncias, in vitro, com potencial uso biotecnológico para promoção do crescimento de mudas micropropagadas de bananeira da cultivar Grand Naine visando o controle de F. oxysporum f. sp. cubense. A interação RPCPs e FMAs demonstrou resultados conflitantes, concluindo-se que o efeito associado depende do isolado específico de cada microrganismo

M.Sc. / An increasing problem in subtropical regions, such as South Africa, is the susceptibility of various banana varieties to Fusarium wilt by the soil borne pathogen Fusarium oxysporum tsp. cubense (FOC). In this study the problem of fungal susceptibility of banana was addressed by investigating the biochemical aspects of cell wall strengthening in banana roots. Defence responses were induced in both adult and tissue culture tolerant Goldfinger and susceptible Williams banana cultivars by treatment of the plants with a heat-released elicitor preparation from the mycelial cell walls of FOC race 4 and the crude filtrate. Banana plants were maintained in a hydroponic system, before being inoculated with the elicitor and crude filtrate preparation. Differences in lignin content, callose deposition, phenolics and the enzymes involved in cell wall strengthening; (PAL, CAD, POD and PPO) between the tolerant and susceptible banana cultivars were investigated. Differences in defence responses after treatment with elicitor and with crude filtrate were observed, but it was shown that the former is a more efficient experimental system for the characterisation of susceptible and tolerant responses in banana cultivars. An elicitor concentration of 45 4g/m1 greatly induced cellular POD, PPO, PAL and CAD activity in Goldfinger, whereas no significant increase was observed for Williams. Lignin content increased significantly in Goldfinger compared to Williams. The quantitative determination of induced total phenolics, phenolic glycosides, phenolic esters and cell wall-bound phenolic acids were higher in Goldfinger than in Williams. These increases in the four phenolic subfractions were clearly confirmed by reverse phase HPLC. No significant increase in callose accumulation was observed for both cultivars. The obtained results indicate an important role for cell wall strengthening as an inducible defence mechanism of banana roots against FOC race 4.

Nanoparticles are microscopic particles in the nanometre range of between 1-100 nm. A wide variety of metal nanoparticles have been found to be produced by prokaryotic and eukaryotic organisms including several fungal species, when exposed to solutions containing metal salts. Previous studies have suggested that this bioreduction of metal particles may occur via an active reductase/hydrogenase enzyme process where H2 is the electron donor and positively charged platinum species act as the electron acceptors becoming reduced to a neutral metal nanoparticle. In view of this on going research, the current study investigated the “factors” in the fungus Fusarium oxysporum which were responsible for platinum nanoparticle formation. The fungus F.oxysporum was used in this study as it has been previously shown to produce a variety of nanoparticles including gold and silver. During exposure of the biomass to H2PtCl6 the initial response to the platinum salts was metal internalisation and subsequent reduction of H2PtCI6 to produce platinum nanoparticles. The observed localization and distribution of platinum precipitates provided some evidence for a hydrogenase mediated bioreduction of platinum salts to produce nanoparticles. Factors secreted by the fungus into the extracellular fluids, were shown to be responsible for platinum nanoparticle formation. From the identification, purification and characterisation studies it was concluded that a hydrogenase and other “factors” were responsible for platinum nanoparticle formation in F.oxysporum. Purification of the hydrogenase by freeze-drying and Sephacryl S200 size exclusion- ion exchange chromatography revealed the enzyme to be a dimer with a 29.4 and 44.5 kDa when analysed by a 10 % SDS-PAGE. Characterisation of the enzyme revealed optimal activity at a pH of 7.5 and temperature of 38 °C while it exhibited a poor thermal stability with a half life of 36 minutes. The kinetic parameters Vmax and Km were 3.16 U ml-1 and 3.64 mM respectively. The purified hydrogenase was used in subsequent experiments for the reduction of platinum salts, H2PtCl6 and PtCl2. the results indicated an over 90 % reduction of the platinum salts and TEM micrographs indicated the production of platinum nanoparticles under the various experimental conditions.

In-vitro and greenhouse screening of 78 bacterial isolates from sorghum rhizosphere in Ethiopia and 86 isolates from the rhizosphere of grasses at Nylsvlei Nature Reserve in South Africa was conducted in terms of inhibition of Fusarium oxysporum that causes root rot in sorghum. Among the Ethiopian isolates KBE5-7, KBE5-1, KBE2-5 and NAE5-5 resulted in 100% disease suppression while disease suppressions ranging from 85.6% - 95.8% were rendered by South African isolates KBS9-H, KBS9-B, KFP9-A, NAS6-B and KBS5-F. According to identification by means of API and 16S rDNA sequencing, the majority of the effective isolates belong to members of the genus Bacillus. Other Gram negative isolates effective in this study have been identified as Serratia marcescens, Chryseomonas luteola, Stenotrophomonas maltophilia and Enterobacter sakazaki. Screening of rhizobacterial isolates was also conducted in terms ofin-vitro and in-vivo antagonistic activity against Pythium ultimum Trow, a common soilborne pathogen causing yield reductions in a wide variety of crops including sorghum. Statistically significant disease suppression was achieved by a number of isolates both from Ethiopia and South Africa. Most of the effective isolates maintained themselves in the rhizosphere at a level of ≥ 105 cfu/g four weeks after inoculation. While Bacillus cereus was the predominant isolates from both sites, Brevilbacterium laterosporus, Serratia marcescens and Pseudomonas fluorescens were among the most effective isolates with the potential to suppress Pythium ultimum in-vitro and in-vivo. Modes of action studies assessing production of antibiotics, siderophores, chitinolytic activity and induction of systemic resistance in sorghum were conducted for rhizobacterial isolates effective against F. oxysporum and P. ultimum. The antibiotic substances produced in the culture filtrates of many of these effective bacteria resulted in strong antifungal activity against both pathogens. The antibiotics from Bacillus cereus (KBS5-H) and Bacillus subtilis (KBS6-3) resulted in an efficient antagonistic activity against F. oxysporum and Pythium ultimum respectively. Siderophore production was evident in the Gram-negative strains Serratia marcescens (KBS9-R), C. violaceum (KBE9-1) and E. sakazaki (NAS6-B) with prominent yellow/orange halo development on CAS-agar plates demonstrating the potential by these isolates to produce siderophores under iron stressed conditions. Chitinolytic activity on chitin-agar plates was shown by isolates which mostly (83%) belonged to strains of B. cereus The split root system has also demonstrated that B. cereus (KBS5-H), C. violaceum (KBE9-1) and S. marcescens (KBS9-R) were capable of rendering significant induction of systemic resistance against F. oxysporum in sorghum. The successful in-vitro and in-vivo suppression of F. oxysporum and P. ultimum by the effective rhizobacterial isolates and the presence of various modes of action provide useful information on the potential of these isolates as biocontrol agents against soilborne fungal pathogens. The isolation and screening of rhizobacteria for growth promotion of sorghum has also been conducted under greenhouse condition in pathogen free soils. Three isolates from Ethiopia and 10 isolates from South Africa have been identified as the most effective growth promoting isolates in these studies. The isolates also tested positive for the production of siderophores, production of indoleacetic acid and phosphate solubilization, the direct modes of actions through which bacteria promote plant growth in the rhizosphere of several plants. Of the most effective isolates 44 % were identified as Bacillus cereus, 19 % as Chryseomonas luteola, 13 % as Serratia marcescens, 13 % as Sphingomonas paucimobilis, and 6% each as Stenotrophomonas maltophilia and Brevibacterium laterosporus respectively. The best biocontrol agents were selected out of a total of 24 isolates both from Ethiopia and South Africa. The selection procedure was conducted by using criteria such as the in-vitro and in-vivo suppression of Fusarium oxysporum and Pythium ultimum, the root colonization ability of the bacterial isolates and selected modes of action including production of antibiotic substances and siderophores, chitinolytic activity and induction of systemic resistance in sorghum. According to this procedure five isolates from Ethiopia (KBE5-7, KBE5-1, KBE9-1, NAE1-7 and NAE5-7) and six isolates from South Africa (KBS5-F, KBS9-R, KBS6-H, KBS5-H, KFP9-K and KBE6-17) have been selected as the most efficient biocontrol isolates. The selection of the best performing growth promoting isolates was conducted out of 12 efficient isolates using the following criteria: root colonization, siderophores and indoleacetic acid (IAA) production, phosphate solubilization and bacterial growth profiles in liquid cultures. Two isolates from Ethiopia (KBE7-8 and KBE9-1) and five isolates from South Africa (KBS5-H, KBS5-F, KBS6-H, KBS9-B and NAS4-3) have been selected as the best growth promoting isolates. As the screening and selection of this study are based on laboratory and greenhouse studies, further evaluation of the best isolates under field conditions and additional modes of action studies are warranted to ascertain their full potential as biocontrol and growth promoting agents. / Thesis (PhD (Plant Pathology))--University of Pretoria, 2009. / Microbiology and Plant Pathology / unrestricted

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