No description available.

Foot rot disease of wheat is caused by the pathogens Fusarium cuImorum, F.avenaceum and Microdochium nivale. Symptoms of foot rot are a general browning of the stem base and leaf sheath. There is a discrepancy between the ability of fungicides to control these pathogens in vivo and in vitro, and no relationship between disease symptom severity and yield loss has been established in wheat. The identification of the causal agents of foot rot disease is not possible from examination of disease symptoms alone. This work showed that the azole fungicides flusilazole and prochloraz inhibited the germination of conidia and mycelial growth of F. culmonon, F. avenaceum and M. nivale in vitro to a varying extent. However, no consistent control of these pathogens in wheat was observed in the field using the same fungicides. Further studies employing a semicontrolled outdoor experiment showed a relationship between density and timing of inoculum application, disease symptom severity and yield loss in wheat artificially inoculated with F. culmorum and M. nivale. Molecular marker systems were used to address the problem of pathogen detection and identification. A Random Amplified Polymorphic DNA (RAPD) assay was developed to differentiate F.culmorum, F.avenaceum and two types of M.nivale (M.nivale var.nivale and M. nivale var .majus) in vitro. Selected RAPD products were cloned and sequenced and species specific primers constructed from this sequence infonnation. These primers were used in the polymerase chain reaction (peR) and were shown to detect the pathogens in host tissue. This technique was adapted by addition of a competitor fragment to the peR reaction resulting in a quantifiable competitive peR assay. Using this method the fungal biomass of each pathogen present in the host tissue could be estimated. The development of these techniques for the identification, detection and quantification of F. cuimorum, F.avenaceum, M.nivale var.nivale and M.nivale var.majus in plant tissue will allow more extensive studies of the epidemiology of these species, the competition between species and the effect of fungicides on these pathogens can be carried out.

Universiẗat, Diss., 2003--Bonn.

No description available.

Doctor of Philosophy / Department of Biology / Ari M. Jumpponen / Dark septate endophytes (DSE) are darkly pigmented microfungal ascomycetes commonly observed in the healthy plant roots. Studying the functional roles of DSE is challenging as fundamental information about their identity, nutritional requirements, host range or host preference are lacking. Objective 1: root colonizing fungi were isolated from Konza plants roots and DSE fungi were identified by testing Koch’s postulates using leek plants. Periconia macrospinosa and Microdochium sp., were identified as DSE as they produced microsclerotia and chlamydospores in the root cortex. Select DSE were tested for their enzymatic capabilities and ability to utilize nitrogen sources: fungi tested positive for amylase, cellulase, polyphenol oxidases and gelatinase. Periconia isolates utilized organic and inorganic nitrogen suggesting facultative biotrophic and saprotrophic habits. Objective 2: a Microdochium isolate and three Periconia isolates were screened on 16 plant species (six native grasses and forbs, four crops) in a resynthesis system to test host range. DSE colonized all plant species, albeit to varying degrees. Host biomass and nutritional levels to DSE colonization varied within and among host species confirming the broad host range. Based on % responsiveness to DSE colonization, a metric similar to ‘mycorrhizal dependency’, grasses responded positively, while forbs and crops responded negatively. To test this observed ‘host preference’ under natural conditions, Konza roots from seven grass and nine forb species were surveyed for DSE colonization. Grasses hosted 50% greater DSE than forbs, supporting the broad host range and host preference of DSE fungi. Objective 3: three conspecific Arabidopsis ecotypes, Col-0, Cvi-0 and Kin-1 were inoculated with 25 P. macrospinosa isolates in resynthesis system. The three ecotypes responded differently to inoculation: Col-0 and Cvi-0 responded negatively, while Kin-1 response was neutral. Despite the negative or neutral response, each ecotype responded positively to one or two isolates. The outcomes were along the mutualism-parasitism continuum precluding an unambiguous assignment to any particular life-style. This study shows that the outcomes along this continuum are dictated by host and fungal genotypes. However, the more important question about their function remains. Additional studies with Arabidopsis microarrays are likely to provide unique insights into the potential roles of DSE.

Le travail présenté s'inscrit dans une double préoccupation de protection intégrée des cultures et de sécurité sanitaire. L'objectif est d'étudier comment les pratiques culturales dans les champs de blé influent sur le développement de la fusariose de l'épi et la production de mycotoxines fusariennes. Les procédures d'échantillonnage pour le dosage des toxines ont d'abord été évaluées. Puis, nous avons analysé les corrélations éventuelles entre pratiques culturales, symptômes de fusariose sur l'épi, contamination en mycotoxines des grains, et infection de la parcelle par telle ou telle combinaison des différentes espèces (ou souches) de pathogènes. Deux dispositifs ont été suivis: un réseau comparant 30 parcelles cultivées en agriculture biologique dans des milieux différents, pendant deux ans, et un essai comparant différents systèmes de culture (biologique, conventionnel, intégré, et sans travail du sol avec couverture permanente) dans un même lieu, pendant quatre ans. Pour que les prélèvements au champ permettent de caractériser de façon fiable le niveau de contamination de la parcelle, nous avons établi quelques règles concernant la procédure de prélèvement: prélever une quantité suffisante d'épis (au moins 1 kg de grains), bien répartis dans la parcelle (quadriller la parcelle, par 10 botillons par exemple), broyer les grains pour homogénéiser au mieux l'échantillon sur lequel les toxines seront analysées. Avant même le broyage, une séparation soigneuse des grains et des organes végétatifs est essentielle pour que le niveau de contamination en toxines des premiers ne soit pas surévalué à cause de la présence de résidus des seconds, beaucoup plus fortement contaminés en termes de µg de toxine par kg de matière végétale. Aucune relation stable entre les symptômes visibles sur les épis et la contamination des grains par les mycotoxines n'a été observée dans nos conditions expérimentales, où les niveaux d'attaque et de contamination de nos parcelles sont restés en moyenne relativement modérés. Il ne semble donc pas possible d'établir un modèle prédisant la teneur en mycotoxines à la récolte à partir des symptômes observés auparavant sur les épis. Aucune des hypothèses simples de la littérature concernant un effet des pratiques culturales sur la fusariose de l'épi n'a été vraiment validée. En revanche, une corrélation positive a été observée entre un paramètre nutritionnel du blé, le rapport des quantités d'azote sur celles de fructose dans les épis à la floraison, et le taux d'infection des grains par les agents du complexe fusarien ou les symptômes visibles de la fusariose (intensité ou gravité). En ce qui concerne la production de mycotoxines fusariennes (et non plus les symptômes visibles de la maladie), nous avons trouvé qu'elle était corrélée à la présence de résidus de la culture précédente -pour autant que cette culture précédente soit sensible elle-même à la fusariose-, et à des valeurs faibles du rapport du taux d'azote sur celui de potassium dans les épis à la floraison. F. culmorum semble être une espèce très importante tant pour la production de déoxynivalénol que de nivalénol; sa plus forte présence dans les systèmes sans travail du sol pourrait expliquer les plus forts taux de contamination dans ce système. Cependant, la production de mycotoxines semble en partie résulter d'interactions complexes, de compétition ou de synergie, entre les différentes espèces de Fusarium productrices de toxines, ou entre elles et les espèces non productrices de toxines (faisant ou non partie du complexe fusarien); ces interactions probables contribuent à minimiser l'effet d'éventuels traitements fongicides de cultures. Ce travail suggère l'intérêt d'un travail à l'interface de l'agronomie et de la pathologie, à l'échelle du champ comme à l'échelle de la souche de pathogène, et appelle des études complémentaires à l'interface de ces champs d'activité.

Submitted by Reginaldo Soares de Freitas (reginaldo.freitas@ufv.br) on 2016-05-31T09:26:57Z No. of bitstreams: 1 texto completo.pdf: 1453980 bytes, checksum: a906f0c2ee1673a4173cbe5af072a89a (MD5) / Made available in DSpace on 2016-05-31T09:26:57Z (GMT). No. of bitstreams: 1 texto completo.pdf: 1453980 bytes, checksum: a906f0c2ee1673a4173cbe5af072a89a (MD5) Previous issue date: 2013-07-05 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / A escaldadura, causada pelo fungo Microdochium oryzae, é uma das principais doenças do arroz (Oryza sativa) no Brasil. Considerando que até o momento, informações sobre a interação arroz-M. oryzae são escassas, buscou-se, neste trabalho investigar a fotossíntese, o metabolismo antioxidativo e as respostas de defesa de plantas de arroz da cultivar Primavera, supridas ou não com silício (Si) durante o processo infeccioso de M. oryzae. No primeiro estudo, uma abordagem a fim de avaliar a diversidade de eventos que ocorrem próximo à área infectada numa mesma folha durante a infecção por M. oryzae foi realizada, a fim de contribuir para um maior entendimento na dinâmica fotossintética durante a interação planta- hospedeiro. Para esta finalidade, foi realizada a avaliação de parâmetros e imagens de fluorescência da clorofila a em diferentes áreas próximas a lesão, associando-as, às trocas gasosas e a avaliação dos pigmentos fotossintéticos em plantas de arroz inoculadas ou não inoculadas com M. oryzae. Em plantas não inoculadas com M. oryzae os valores da fotossíntese (A), da condutância estomática (gs) e da taxa transpiratória (E) foram maiores em relação às plantas inoculadas, evidenciando o efeito negativo causado pelo fungo nas trocas gasosas, principalmente em A. A utilização da energia para os processos fotossintéticos e a capacidade de dissipação do excesso de energia na maquinaria fotossintética demonstrados pelos parâmetros de fluorescência de imagem da clorofila a foi comprometida durante a infecção, reduzindo o rendimento fotoquímico e induzindo a inibição do aparato fotossintético nas áreas lesionadas, evidenciando que a infecção tinha efeito local sobre A. Houve diminuição das áreas verdes na superfície do tecido foliar, ocasionado pela expansão das lesões e aumento de tecido necrótico. As concentrações de pigmentos fotossintéticos diminuíram significativamente com o progresso da escaldadura o que limitou a absorção da radiação fotossinteticamente ativa. No segundo estudo, buscou-se investigar a atividade das enzimas antioxidativas ascorbato peroxidase (APX), peroxidase (POX), catalase (CAT), superóxido dismutase (SOD) e glutationa redutase (GR), os danos causados à membrana celular através da concentração de aldeído malônico (MDA), as concentrações de peróxido de hidrogênio (H2O2) e de pigmentos fotossintéticos, bem como trocas gasosas em folhas de plantas de arroz durante o processo infeccioso de M. oryzae. O progresso da doença promoveu redução da A, gs e E. Houve também incrementos na concentração interna de CO2 e redução na concentração de pigmentos fotossintéticos ocasionados pela expansão das lesões, comprometendo a absorção da radiação fotossinteticamente ativa e limitando a fotossíntese. As atividades das enzimas envolvidas no sistema antioxidativo nas plantas de arroz infectadas por M. oryzae aumentaram na tentativa de impedir o acúmulo de H2O2, principalmente APX, POX e GR, não sendo, entretanto, eficientes na remoção do excesso de H2O2, resultando em dano oxidativo. As concentrações de MDA nas plantas inoculadas mantiveram-se elevadas no final do processo infeccioso, como resultado da peroxidação lipídica. No terceiro estudo, buscou-se, investigar o efeito do Si sobre as trocas gasosas, a eficiência fotoquímica do fotossistema II e a concentração de pigmentos fotossintéticos em plantas de arroz infectadas por M. oryzae. Para esta finalidade plantas de arroz da cultivar Primavera foram cultivadas em solução nutritiva contendo 0 ou 2 mmol L-1 de Si e não inoculadas ou inoculadas com M. oryzae. A infecção por M. oryzae reduziu o rendimento fotossintético, o qual esteve associado com a menor concentração de pigmentos fotossintéticos nas folhas. Na presença de Si, a atividade fotossintética e a eficiência de utilização da energia luminosa e sua conversão em energia química foram potencializados, conforme demonstrado pelos parâmetros de fluorescência de imagem da clorofila a, independente da inoculação com M. oryzae, confirmando assim, que o Si é um elemento importante no rendimento fotossintético em plantas de arroz infectadas por M. oryzae. No quarto estudo, buscou-se, investigar o papel do Si na resistência de plantas de arroz infectadas por M. oryzae. Para esta finalidade, plantas de arroz da cultivar Primavera foram cultivadas em solução nutritiva contendo 0 ou 2 mmol L-1 de Si e inoculadas com M. oryzae. A concentração foliar de Si aumentou nas plantas supridas com esse elemento em relação às plantas não supridas o que contribui para reduzir a expansão das lesões. A extensão dos danos celulares em resposta a infecção por M. oryzae foi reduzida nas plantas supridas com Si, evidenciado pelos menores valores da concentração de MDA. Maiores concentrações de compostos fenólicos solúveis totais (CFST) e de derivados da lignina-ácido tioglicólico (DLATG) nos tecidos foliares das plantas supridas com Si, contribuíram para a resistência à escaldadura. Maiores atividades das enzimas peroxidases (POX), polifenoloxidases (PFO), fenilalanina amônia-liases (FAL) e lipoxigenases (LOX), mas não de quitinases (QUI) e β-1,3-glucanases (GLU), nos tecidos foliares das plantas de arroz supridas com Si foram importantes para a resistência à escaldadura. Em conclusão, os resultados do presente estudo evidenciam que o Si pode aumentar a resistência à escaldadura em plantas de arroz, melhorando o rendimento fotossintético e potencializando mecanismos bioquímicos de defesa ao invés de agir apenas como uma barreira física na tentativa de conter a penetração de M. oryzae. / The scald caused by the fungus Microdochium oryzae is a major disease of rice (Oryza sativa) in Brazil. Whereas until now, information on the interaction rice-M. oryzae are scarce, we sought in this paper to investigate photosynthesis, metabolism antioxidative and defense responses of rice plants of cultivar Primavera, or not supplied with silicon (Si) during the infection process of M. oryzae. In the first study, an approach to assess the diversity of events that occur near the infected area on one sheet when the infection with M. oryzae was carried out in order to contribute to a greater understanding of the dynamics during photosynthetic plant-host. For this purpose, we analyzed the fluorescence parameters and images of chlorophyll a in different areas around the injury, associating them, gas exchange and evaluation of photosynthetic pigments in rice plants inoculated or not with M. oryzae. Not in plants inoculated with M. oryzae values of photosynthesis (A), stomatal conductance (gs) and transpiration rate (E) were higher than those inoculated plants, indicating the negative effect caused by the fungus in gas exchange, especially in A. The use of energy for photosynthetic processes and dissipation of excess energy in the photosynthetic machinery demonstrated by fluorescence parameters and images of chlorophyll a was compromised during the infection, reducing the yield and photochemical induced inhibition of the photosynthetic apparatus in the injured areas, showing that the infection had local effect on A. There was decrease in the surface areas of the green leaf tissue, caused by the expansion of lesions and necrotic tissue augmentation. The photosynthetic pigments decreased significantly with the progress of scalding which limited the absorption of photosynthetically active radiation. In the second study, we sought to investigate the activity of antioxidant enzymes ascorbate peroxidase (APX), peroxidase (POX), catalase (CAT), superoxide dismutase (SOD) and glutathione reductase (GR), damage to the cell membrane through concentration malondialdehyde (MDA), the concentrations of hydrogen peroxide (H2O2) and photosynthetic pigments as well as gas exchange in leaves of rice plants during the infectious process of M. oryzae. The progress of the disease promoted reduction of the A, gs and E. There were also increases in internal CO2 concentration and reduction in the concentration of photosynthetic pigments caused by the expansion of lesions affecting the absorption of photosynthetically active radiation and limiting photosynthesis. The activities of enzymes involved in the antioxidant system in rice plants infected by M. oryzae increased in an attempt to prevent accumulation of H2O2, especially APX, POX and GR is not, however, efficient removal of excess H2O2, resulting in oxidative damage. The concentration of MDA in the inoculated plants remained high at the end of the infection as a result of lipid peroxidation. In the third study, we sought to investigate the effect of Si on gas exchange, photochemical efficiency of photosystem II and the concentration of photosynthetic pigments in rice plants infected by M. oryzae. For this purpose the rice plants Primavera were grown in nutrient solution containing 0 or 2 mmol L-1 of Si and not inoculated or inoculated with M. oryzae. Infection with M. oryzae reduced the photosynthetic yield, which was associated with the lowest concentration of photosynthetic pigments in leaves. In the presence of Si, photosynthetic activity and efficiency of utilization of light energy and its conversion into chemical energy were potentiated, as demonstrated by f fluorescence parameters and images of chlorophyll a, regardless of inoculation with M. oryzae, thus confirming that Si is an important element in quantum yield in rice plants infected by M. oryzae. In the fourth study, we sought to investigate the role of Si in resistance of rice plants infected by M. oryzae. For this purpose, the rice plants Primavera were grown in nutrient solution containing 0 or 2 mmol L-1 of Si and inoculated with M. oryzae. The Si concentration increased in the leaf of plants supplied with this element in relation to unmet plants which contributes to reduce the spread of lesions. The extent of cellular damage in response to infection with M. oryzae was reduced in plants supplied with Si, evidenced by lower values of MDA concentration. Higher concentrations of total soluble phenolics (TSP) and derivatives of lignin-thioglycolic acid (DLATG) in the leaves of plants supplied with Si, contributed to resistance to scald. Major activities of the enzymes peroxidase (POX), polyphenol oxidases (PPO), phenylalanine ammonia-lyase (PAL) and lipoxygenase (LOX) but not chitinase (CHI) and β-1, 3- glucanases (GLU) in leaf tissues of rice plants were supplied with Si important for resistance to leaf scald. In conclusion, the results of this study indicate that the Si can increase resistance to scald in rice plants, improving performance and enhancing photosynthetic biochemical defense mechanisms rather than merely acting as a physical barrier in an attempt to contain the penetration of M . oryzae.

Submitted by Reginaldo Soares de Freitas (reginaldo.freitas@ufv.br) on 2015-11-11T13:18:35Z No. of bitstreams: 1 texto completo.pdf: 340314 bytes, checksum: d3df035dc1f7a0bc3479518b1ee91de2 (MD5) / Made available in DSpace on 2015-11-11T13:18:35Z (GMT). No. of bitstreams: 1 texto completo.pdf: 340314 bytes, checksum: d3df035dc1f7a0bc3479518b1ee91de2 (MD5) Previous issue date: 2015-07-27 / Fundação de Amparo à Pesquisa do Estado de Minas Gerais / O arroz (Oryza sativa) é um dos grãos mais consumidos no mundo, no entanto, as perdas proporcionadas por patógenos têm de reduzido grandemente sua produtividade. Dentre estes, a escaldadura, causada pelo fungo Microdochium oryzae, se destaca por ser uma das principais doenças encontradas no arroz. É sabido ainda que, o Silício (Si) é responsável por conferir resistência a uma grande gama de patógenos, em especial na cultura do arroz, incluindo M. oryzae. Para investigar o que proporciona essa maior resistência, plantas de arroz foram crescidas em solução nutritiva, supridas e não supridas com Si, inoculadas e não inoculadas com M. oryzae. Foi encontrado que plantas supridas com Si possuíam menores severidades a escaldadura do arroz, que foi relacionada aos maiores teores desse elemento nessas plantas. As plantas supridas com Si e inoculadas, apresentaram maiores taxas fotossintéticas (A), além de maiores rendimento fotoquímico máximo do fotossistema II (FSII) (F v/F m), a eficiência na captura da energia de excitação pelos centros de reação do FSII (F v’/F m’) e taxa de transporte de elétrons (ETR), demonstrando que nas plantas supridas com Si, a eficiência na captura e transformação da energia luminosa em química era menos afetada quando o Si era suplementado. A análise da taxa aparente de carboxilação máxima (Vcmax) e da taxa de carboxilação que é limitada pelo transporte de elétrons (J max) em base Cc, permitiu inferir que, o Si não mitigou os danos bioquímicos proporcionados pela presença do fungo M. oryzae, uma vez que nenhuma diferença estatística foi encontrada. Desta forma, os dados conduzem a interpretação de que a suplementação com Si permite melhores A através da manutenção de maiores condutâncias mesofílicas (gm), proporcionando assim, menores limitações difusivas nas plantas inoculadas, uma vez que a gm é grandemente afetada pela presença do patógeno na ausência deste elemento. Ainda, a análise quantitativa das limitações à fotossíntese, corrobora com os resultados encontrados, uma vez que as fortes limitações mesofílicas observadas quando o Si não era adicionado. Desta forma conclui-se que o fornecimento do Si à cultura do arroz mitiga os efeitos deletérios proporcionados pela infecção causada por M. oryzae, através da manutenção da condutância do CO2 presente nas câmaras subestomáticas até os sítios de carboxilação da Rubisco. / Rice (Oryza sativa) is one of the most consumed grains in the world, however, losses provided by pathogens have greatly reduced productivity. Among these, scald, caused by the fungus Microdochium oryzae, stands out as a major disease found in rice. It is also known that, Silicon (Si) is responsible for conferring resistance to a wide range of pathogens, especially in rice crops, including M. oryzae. To investigate what this provides greater resistance, rice plants were grown in nutrient solution, supplied and not supplied with Si, inoculated and not inoculated with M. oryzae. It was found that plants supplied with Si had lower severities to scald of rice, which was related to higher levels of aluminum in these plants. The plants supplied with Si and inoculated, had higher photosynthetic rates (A), as well as higher maximum photochemical efficiency of photosystem II (PSII) (F v/F m), the efficiency of excitation energy capture by PSII reaction centers (F v’/F m’) and electron transport rate (ETR), demonstrating that plants supplied with Si, the efficiency in the capture and transformation of light energy into chemical was less affected when Si was supplemented. The analysis of the apparent maximum rate of carboxylation (Vcmax) and carboxylation rate that is limited by the transport of electrons (J max) in Cc base, allowed to infer that the Si not mitigated the biochemical damage provided by the fungus M. oryzae presence, since no statistical difference was found. Thus, the data lead to the interpretation that supplementation with Si allows better by maintaining the largest mesophyll conductance (gm), thus providing smaller diffusive limitations on inoculated plants, since gm is greatly affected by the presence of the pathogen in the absence of this element. Furthermore, the quantitative analysis of limitations to photosynthesis corroborates the results, since the mesophyll strong limitations observed when the Si was not added. Thus, it is concluded that the supply of the Si in rice culture mitigates the deleterious effects provided by the infection caused by M. oryzae, by the maintenance of the CO2 present conductance substomatic to the sites of carboxylation of Rubisco.