Graduation date: 2003

Thèse (M.Sc.)--Université Laval, 2007. / Bibliogr.: f. 66-73. Publié aussi en version électronique dans la Collection Mémoires et thèses électroniques.

La gale argentée, causée par le champignon Helminthosporium solani, est une maladie importante affectant le tubercule de pomme de terre. Cette étude avait pour objectif d'évaluer l'influence du Fe, Cu, Mn, Zn et Mo, sous différentes formes chimiques, sur le développement de H. solani et de la gale argentée de la pomme de terre. Les résultats obtenus ont permis de démontrer que ces minéraux affectent la croissance mycélienne et la germination des conidies de ce champignon. L'addition de doses élevées des minéraux à l'étude dans le milieu de culture a généralement eu un effet inhibiteur sur la croissance mycélienne et la germination des conidies. Appliqués sur le tubercule, ces minéraux ont également affecté le développement de la gale argentée. Cependant, les travaux réalisés n'ont pas permis de révéler que la composition du substrat de culture en ces minéraux avait un effet sur le développement de la gale argentée ainsi que sur la quantité de H. solani détectée à la surface du tubercule par PCR en temps réel.

Double-stranded RNA fungal virus Helminthosporium victoriae virus 190S (genus Victorivirus, family Totiviridae) contains two large open reading frames (ORFs) that overlap in the tetranucleotide AUGA. Translation of the downstream ORF, which encodes the RNA-dependent RNA polymerase (RdRp), was previously proposed to depend on ribosomal reinitiation following termination of the upstream ORF, which encodes the capsid protein. In this study, I provided evidence to confirm that coupled termination-reinitiation (stop-restart) is indeed used. A dual-fluorescence method was established to define the RNA sequence determinants for RdRp translation. Stop-restart depends on a 32-nt stretch of RNA sequence immediately upstream of the AUGA motif, including a predicted pseudoknot structure. The presence of similar sequence motifs and predicted RNA structures in other victoriviruses suggest that they all share a related stop–restart strategy for RdRp translation. The close proximity of the secondary structure to the AUGA motif appears to be especially important for promoting translation of the downstream ORF. Normal strong preferences for AUG start codons and canonical sequence context for translation initiation of the downstream ORF appear somewhat relaxed. With dual-fluorescence system, reinitiation efficiency of the downstream ORF was determined to be ~3.9%. Pseudoknot swapping between the one in HvV190S and those predicted from other victoriviruses showed that reinitiation from the downstream ORF of HvV190S is quite tolerant to varying primary sequences of the various pseudoknots. Mutational analysis by introducing different combinations of nucleotide mutations into pseudoknot stems reproducibly confirmed the determinant role of pseudoknot on reinitiation using two different experimental systems. Together, these results provide the first example of coupled termination-reinitiation regulated by a simple pseudoknot stucture. These data expanded the understanding of coupled termination-reinitiation mechanism employed by RNA viruses and refined a new model for genus victorivirus, the largest genus in the family Totiviridae. The dual fluorescence system used in this study represented the first application of an efficient in vivo assay for recording low-frequency events in filamentous fungi.

Submitted by (edna.saturno@ufrpe.br) on 2017-05-18T13:59:13Z No. of bitstreams: 1 Tatiana Neres de Oliveira.pdf: 1588049 bytes, checksum: 1bec51e391cc99844e14b24b53268967 (MD5) / Made available in DSpace on 2017-05-18T13:59:13Z (GMT). No. of bitstreams: 1 Tatiana Neres de Oliveira.pdf: 1588049 bytes, checksum: 1bec51e391cc99844e14b24b53268967 (MD5) Previous issue date: 2007-03-26 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq / The work was conducted at the Itambé Experimental Station of the Pernambuco State Agricultural Research Enterprise – IPA, to characterize clones and estimate heritability and character correlation, besides estimate repeatability coefficients and evaluate adaptability and stability of eye spot incidence in Pennisetum sp. clones under pasture. Sixteen Pennisetum sp. clones were studied under pasture at 42 days intervals, and after-grazing residual of 40 cm, under the randomized blocks design, with five replicates. Characters evaluated before grazing were forage availability, average plant height, disease incidence, desirability, uncovered soil, above and below 40 cm forage mass. Residual biomass above and below 40 cm, average plant height and losses were evaluated after grazing. Heritability was estimated on the ample sense, and averages were compared by theTukey test at five percent significance. Clones Taiwan A 25 P 18 (3.8), Pusa Napier 1 P 32 (1.8), SEA P 35 (1.8), SEA P 36 (3.4), SEA P 37 (3.2), RENACE CNPGL 93F41.1 (2.0), hybrids HV 241 (1.8) and Pioneiro (2.4) had the highest Helminthosporium susceptibility notes. Except for leaf production, below 40 cm residual biomass, and after grazing losses, all evaluated variables had highheritability value (64.75 to 93.40%). Choosing higher plants leads to simultaneous selection for higher above 40 cm forage mass, desirability, lower disease incidence and higher soil coverage index. Repeatability coefficients were estimated by: analysis of variance, principal components – correlation matrix, principal components – covariance matrix, and structural analysis – correlation matrix. Maximum heritability for leaf spot was 95 %. Repeatability coefficients by the four methods ranged from 0.75 to 0.78. With regards to genotype adaptability, Mineirão (0.31), Taiwan A 25 P 18 (0.50), SEA P 36 (0.28), SEA P 37 (0.38) and Gigante de Pinda P 73 (0.46) had regression coefficients below population average (β1i), indicating unfavorable environment adaptability. Genotypes Pusa Napier 1 P 25 (1.58), Pusa Napier 1 P 27 (1.55), Pusa Napier 1 P 28 (1.47), Pusa Napier 1 P 32(1.28), Pusa Napier 1 P 33 (1.22), SEA P 35 (1.60), HV 241 (1.41) and Pioneiro (1.36) had better response in favorable environments, and Pusa Napier 1 P 31 and Roxo de Botucatu P 80 had ample adaptability. Hybrid HV 241 and Pioneiro had significant deviations from regression by the F test (P<0.05), indicating instability and unpredictability to environmental alterations. / O trabalho foi realizado na Estação Experimental de Itambé da Empresa Pernambucana de Pesquisa Agropecuária – IPA, objetivando caracterizar clones e estimar a herdabilidade e correlações, além de estimar coeficientes de repetibilidade e avaliar a adaptabilidade e estabilidade de clones de Pennisetum sp. sob pastejo a incidência de mancha ocular. Foram estudados 16 clones de Pennisetum sp. sob pastejo a intervalos de 42 dias e resíduo pós pastejo de 40 cm, num delineamento em blocos ao acaso, com cinco repetições. Os caracteres avaliados no pré pastejo foram disponibilidade de forragem, altura média das plantas, incidência de doença, desejabilidade, solo descoberto, massa de forragem acima e abaixo de 40 cm. Biomassa residual acima e abaixo de 40 cm, altura média das plantas e perdas foram avaliadas no pós pastejo. Os coeficientes de repetibilidade foram estimados por:análise de variância, componentes principais – matriz de correlação, componentes principais – matriz de covariância e análise estrutural – matriz de correlação. A herdabilidade foi estimada no sentido amplo e as médias comparadas pelo teste de Tukey a 5% de probabilidade. Os clones Taiwan A 25 P 18 (3,8), Pusa Napier 1 P 32 (1,8), SEA P 35 (1,8), SEA P 36 (3,4), SEA P 37 (3,2), RENACE CNPGL 93F41.1(2,0), o híbrido HV 241 (1,8) e o Pioneiro (2,4) apresentaram maiores notas para susceptibilidade ao Helminthosporium. Com exceção de produção de folhas, biomassa residual abaixo de 40 cm e perdas pós pastejo, todas as variáveis analisadas apresentaram valores altos para herdabilidade (64,75 a 93,4%). A escolha de plantas mais altas leva à seleção simultânea para maior produção de massa de forragem acima de 40 cm e desejabilidade, menor incidência de doenças e maior índice de cobertura do solo. O valor máximo da herdabilidade para mancha ocular foi de 95%. Os coeficientes de repetibilidade estimados pelos quatro métodos variaram de 0,75 a 0,78. Com relação à adaptabilidade dos genótipos, o Mineirão (0,31), Taiwan A 25 P 18 (0,50), SEA P 36 (0,28), SEA P 37 (0,38) e Gigante de Pinda P 73 (0,46) apresentaram coeficientes de regressão abaixo da média populacional (β1i), indicandoadaptabilidade a ambientes desfavoráveis. Os genótipos Pusa Napier 1 P 25 (1,58), Pusa Napier 1 P 27 (1,55), Pusa Napier 1 P 28 (1,47), Pusa Napier 1 P 32 (1,28), Pusa Napier 1 P 33 (1,22), SEA P 35 (1,60), HV 241 (1,41) e Pioneiro (1,36) responderam melhor em ambientes favoráveis, e o Pusa Napier 1 P 31 e Roxo de Botucatu P 80 apresentaram ampla adaptabilidade. O híbrido HV 241 e o Pioneiro apresentaram desvios significativos da regressão pelo teste F (P<0,05), sugerindo instabilidade e imprevisibilidade às alterações ambientais.

Tableau d’honneur de la Faculté des études supérieures et postdoctorales, 2010-2011 / Le but de cette étude était d'en apprendre davantage sur les relations antagonistes entre Helminthosporium solani et les souches E30 et 94-19 de Pseudomonas putida. Les travaux présentés dans ce mémoire montrent que la souche 94-19 produit des composés antifongiques quel que soit le milieu de culture utilisé alors que la souche E30 produit des composés antifongiques seulement en présence de cellules fongiques vivantes, en particulier en présence de cellules vivantes de H. solani. La présence des gènes de voies de biosynthèse de la pyrrolnitrine, de la pyolutéorine et du 2,4-diacétylphloroglucinol chez la souche 94-19 suggère l'implication de ces molécules dans l'activité antagoniste de cette bactérie envers H. solani. Aucun de ces gènes n'a été retrouvé chez la souche E30. Les travaux réalisés suggèrent plutôt qu'un composé thermostable de faible poids moléculaire serait impliqué dans l'activité antagoniste de la souche E30 envers H. solani.