Much research has been published on Mycosphaerella spp. causing Mycosphaerella Leaf Disease (MLD) on Eucalyptus spp. The first chapter of this thesis presents a review of the literature on this topic and focuses on the taxonomy, phylogeny and population biology of Mycosphaerella spp. occurring on Eucalyptus. From the published literature, it is clear that the majority of research conducted on MLD has focussed on the epidemiology and taxonomy of Mycosphaerella spp and the susceptibility of Eucalyptus hosts to species of Mycosphaerella. Advances in DNA-based technologies have, however, lead to extensive DNA sequence datasets of Mycosphaerella spp occurring on Eucalyptus. These datasets have provided substantial insight into species concepts for Mycosphaerella and have led to the realisation that many morphological species are complexes of several cryptic phylogenetic taxa. Furthermore, a recent application to the study of Mycosphaerella spp. occurring on Eucalyptus is that concerning their population dynamics. Such studies will aid in our understanding of the genetic structure of Mycosphaerella populations and their movement between countries. These population-based studies will aid forestry companies in establishing Eucalyptus breeding programmes to produce tolerant Eucalyptus genotypes that may be deployed in commercial forestry operations. Mycosphaerella spp. are difficult to identify, due to their conserved teleomorph morphology and the lack of natural occurrences of anamorph structures. DNA sequence data have, therefore, become the definitive technique used to identify Mycosphaerella spp. The Internal Transcribed Spacer (ITS) region of the ribosomal RNA operon has traditionally been targeted for DNA sequence comparisons. However, this gene region does not offer sufficient resolution to discriminate cryptic taxa or resolve deeper nodes within Mycosphaerella. Results presented in chapter two of this thesis present a multi-gene phylogeny for the identification of Mycosphaerella spp. occurring on Eucalyptus. This is based on DNA sequence data from four nuclear gene regions. The generation of these sequence datasets has allowed for competent elucidation of cryptic taxa, species complexes and the greater resolution of deeper nodes within Mycosphaerella. Furthermore, these results have also led to recognising that Mycosphaerella ambipyhlla and M. vespa is a synonym of Mycosphaerella molleriana and Pseudocercospora epispermogonia is recognised as the asexual state of Mycosphaerella marksii. A serious foliar disease of Eucalyptus camaldulensis and hybrids of this species has been known from Thailand and Vietnam for many years. This disease has been known to be caused by a species of Pseudocercospora and was attributed to the cosmopolitan Pseudocercospora eucalyptorum. Results of a study presented in chapter three of this thesis have, however, clearly shown that P. eucalyptorum is not the causal agent of the disease observed on E. camaldulensis in Thailand. By employing classical morphological techniques and DNA sequence data from four nuclear gene regions, I have shown that an undescribed species of Pseudocercospora is responsible for epidemics of this leaf disease. This species is formally described as Pseudocercospora flavomarginata. P. flavomarginata is only known from Thailand and Vietnam. However, considering that E. camaldulensis is planted in other south-east Asian countries and that E. camaldulensis is the most commonly found Eucalyptus sp. in Australia, further surveys in these areas will most likely lead to the discovery of the pathogen from these countries. Techniques that have been used to identify Mycosphaerella spp. include classical morphological comparisons and analyses of DNA sequence data. These techniques have, however, allowed only for the study of the evolutionary history within Mycosphaerella and for species identification. Recent advances in the field of population biology have led to the study of many fungal pathogens at a population level. One of the main tools used to study population biology involves applying DNA-based microsatellite markers. Chapter four of this thesis focuses on the development of DNA-based microsatellite markers for the Eucalyptus leaf pathogen Mycosphaerella nubilosa. By employing specific enrichment protocols, I was able to develop ten polymorphic microsatellite markers for M. nubilosa. These microsatellite markers exhibit high specificity for M. nubilosa and did not cross amplify with other Mycosphaerella spp. that are closely related to M. nubilosa. Mycosphaerella nubilosa has been extensively studied with respect to its taxonomy and epidemiology. However, nothing is known regarding the population biology of this important Eucalyptus leaf pathogen. Therefore, DNA-based microsatellite markers developed in chapter four of this thesis were used to study the population biology of M. nubilosa from several different geographic locations. Results presented in chapter five of this thesis show that populations of M. nubilosa from eastern Australia are genetically more diverse than those populations from western Australia, Africa and Europe. This indicates that eastern Australia is the likely centre of origin for M. nubilosa. Furthermore, based on shared haplotypes between M. nubilosa populations used in this study, I have proposed a pathway of gene flow of M. nubilosa. This suggests that the pathogen moved from eastern Australia to both western Australia and South Africa and then from South Africa into other countries in Africa and finally into Europe. An interesting result emerging from the population biology study presented in chapter five, is the finding that M. nubilosa appears to employ a homothallic mating strategy. Thus, opportunities exist, in countries with limited genetic diversity of M. nubilosa, to breed for Eucalyptus resistance. From the high number of M. nubilosa haplotypes observed in Australia and South Africa, it is also important that this pathogen be added to quarantine action lists to prevent the movement of contaminated Eucalyptus germplasm. This is necessary to prevent novel M. nubilosa haplotypes from moving into new environments where susceptible Eucalyptus spp. are propagated. Mycosphaerella nubilosa is one of the most pathogenic Mycosphaerella spp. causing MLD on Eucalyptus. Surveys of diseased Eucalyptus plantations from several countries where this pathogen occurs, have resulted in an extensive collection of M. nubilosa isolates. Recently, DNA-based studies have led to the hypothesis that M. nubilosa may represent two distinct taxa. Results of studies presented in chapter six of this thesis indicate that two distinct ITS phylogenetic lineages are represented by M. nubilosa sensu lato. These are characterized by defined geographic distributions and Eucalyptus host associations. M. nubilosa ITS lineage 1 is found exclusively in New Zealand, Tasmania and Victoria, eastern Australia occurring on E. globulus. M. nubilosa ITS lineage 2 has a broader geographic distribution and can be found in Spain, Portugal, Tanzania, Kenya, Ethiopia, South Africa, western Australia, Victoria and New South Wales, eastern Australia, where it occurs on E. globulus and several other Eucalyptus spp. that are used in commercial forestry including E. nitens. It is envisaged that results presented in chapter six will lead to more extensive studies into M. nubilosa sensu lato that may result in the description of a new Mycosphaerella sp. represented by M. nubilosa ITS lineage 1. / Thesis (PhD)--University of Pretoria, 2011. / Microbiology and Plant Pathology / Unrestricted

Accroître la diversité végétale au sein d'une culture par l'utilisation d'associations variétales est une stratégie qui permet de limiter la sévérité des maladies à dispersion éolienne. Les potentialités de cette pratique culturale restent à être caractérisées de manière précise dans le cas des maladies à dispersion pluviale, telle que la septoriose du blé durant sa phase épidémique. Cette maladie foliaire, due au champignon pathogène Mycosphaerella graminicola, est prédominante sur blé et est capable de causer des pertes substantielles de rendement, allant jusqu'à -40 %. Des expérimentations au champ ont été menées durant cinq années, de 2008 à 2012, sur le site INRA de Grignon (Yvelines, France), avec une association constituée de deux variétés de blé ayant des niveaux contrastés de résistance à M. graminicola, et dont les proportions étaient de une plante sensible pour trois assez résistantes. Par rapport à leur culture monovariétale respective, nous avons observé une diminution de la sévérité de la septoriose sur la plus sensible des variétés (en moyenne, 45 % de surface pycnidiale foliaire en moins sur les trois dernières feuilles), sans affecter significativement la variété plus résistante. Une méthodologie originale semi-automatisée a été développée pour quantifier le flux de spores dispersés par la pluie en conditions naturelles. Les mesures expérimentales ont permis de corréler l'intensité de plusieurs épisodes pluvieux avec la dispersion de spores au sein de différents couverts incluant des associations variétales. Un modèle mécaniste et stochastique a été développé afin de décrire la progression du potentiel de maladie au sein d'un couvert végétal hétérogène en trois dimensions. Cette approche théorique combine physique et épidémiologie, d'une part, (i) pour calculer l'interception des gouttes de pluie avec les organes végétaux et la trajectoire des gouttelettes d'éclaboussement au sein du couvert et, d'autre part, (ii) pour prendre en compte les niveaux de résistance variétale et la nature polycyclique de l'épidémie. À partir de ce modèle, il a été mis en évidence pour des associations de deux variétés que les proportions, ainsi que le différentiel de résistance entre les variétés à associer, pouvaient être optimisées pour réduire la sévérité de la maladie. Par ailleurs, ce modèle permet d'évaluer et d'identifier les distributions spatiales des variétés les plus propices à une réduction de la progression d'une maladie à dispersion pluviale. Parmi les précédents travaux traitant des potentialités des associations de variétés pour lutter contre des pathogènes dispersés par l'action mécanique de la pluie, certains avançaient des conclusions souvent contradictoires et peu en faveur de cette pratique. Nous avons montré ici qu'il est possible sous certaines conditions d'association de variétés (proportions, agencement spatial, différentiel de résistance globale) et de pluviométrie d'obtenir un effet significatif en termes de réduction de la maladie. / Increasing plant diversity within a crop by the use of cultivar mixtures is a strategy which allows to reduce severity of windborne diseases. Potentialities of this cropping practice have still to be precisely characterized in the case of rain-borne diseases, such as septoria tritici blotch during its spring epidemiological stage. This disease, due to the pathogen fungus Mycosphaerella graminicola, is prevalent on wheat crops and it may be result in substantial yield losses, up to -40%. Field experiments were carried out during five years, from 2008 to 2012, at the Grignon location (Yvelines, France), with a mixture consisting of two wheat cultivars with contrasted resistance to M. graminicola in a 1/3 susceptible/resistant ratio. In comparison with their pure stands, we observed a severity decrease of septoria tritici blotch for the most susceptible cultivar (on average, less 45% of leaf pycnidial leaf surface on the three upper leaf levels), without significantly affect the more resistant cultivar. An original semi-automated methodology was developed to quantify the splash-dispersed spore flux in outdoor conditions. Experimental measurements allowed to correlate intensity of several rainfall events with spore dispersal within different canopies including a cultivar mixture. A mechanistic and stochastic model was implemented in order to describe disease potential progression within a heterogeneous three-dimensional plant canopy. This theoretical approach combines physics and epidemiology in order to, on one hand, (i) compute interception of raindrops with plant organs and the pathway of splash droplets within the canopy and, on the other hand, (ii) take into account cultivar resistance levels and the polycyclism of epidemics. From this model, we highlighted for two-component cultivar mixtures that the proportions and the difference between resistance levels of cultivars to mix together could be optimized in order to reduce disease severity. Furthermore, this modelling approach makes it possible to assess and identify the cultivar spatial distributions the most favourable to a decrease of progression of a splash-dispered disease. Previous studies about potentialities of cultivar mixtures to control splash-dispersed pathogen agents, led in some cases to conclusions with inconsistent and not in favour of this cropping practice. We showed here that it was possible under certain cultivar designing conditions (proportions, spatial arrangement, difference between resistance levels) and rainfall properties to obtain a consistent significant effect in terms of disease reduction.

La dispersion est un processus clef dans la dynamique et l'évolution des populations naturelles. En plus de son rôle primordial dans les processus de colonisation, la dispersion influence également les processus d'adaptation des organismes. Chez les pathogènes, une meilleure compréhension des processus de dispersion apparaît de ce fait être un enjeu majeur pour mieux les contrôler. Durant cette thèse, nous avons étudié les processus de dispersion et quantifié les flux de gènes qui en découlent chez le champignon parasite du bananier Mycosphaerella fijiensis. Cette étude a été réalisée à l'échelle locale d'un bassin de production du Cameroun (la région dite du Moungo) et nous avons combiné plusieurs approches complémentaires considérant différentes échelles spatio-temporelles. Dans un premier temps, nous avons décrit, à l'aide de marqueurs génétiques neutres, la structuration spatiale des populations de M. fijiensis dans la région du Moungo qui présente différentes barrières potentielles à la dispersion. Nous n'avons décelé aucun effet du paysage ni de la distance géographique sur la structuration génétique. Cependant, une rupture spatiale dans les fréquences alléliques, vraisemblablement de nature historique a été mise en évidence. Ces résultats suggèrent l'existence de grandes populations de M. fijiensis s'écartant de l'équilibre mutation-dérive. Dans un second temps, nous avons utilisé la théorie des clines génétiques pour étudier les forces à l'origine de la mise en en place et de l'évolution de gradients spatiaux de fréquences alléliques. En particulier, l'analyse de la variation spatio-temporelle de la discontinuité génétique précédemment détectée par un modèle de clines neutres nous a permis d'estimer l'intensité des flux géniques ( =1175 m/génération). Finalement, nous avons mesuré la distribution des distances de dispersion des deux types de spores produites par M. fijiensis à partir d'une source d'inoculum primaire. Cette expérimentation nous a permis de confirmer que les ascospores participent à une dispersion à grande distance alors que les conidies sont impliquées dans une dispersion à très courte distance. Nous avons estimé une distance moyenne de dispersion de 3,12 et de 283 mètres/génération respectivement pour les conidies et les ascospores et montré que le noyau de dispersion des ascospores est caractérisé par une queue lourde. Cette thèse a permis de préciser comment M. fijiensis se disperse et les estimations réalisées pourront être intégrées dans des modèles théoriques afin de mieux comprendre l'évolution des résistances aux fongicides et de définir des stratégies durables d'utilisation raisonnée des traitements chimiques. / Dispersal is a key process for both the dynamics and evolution of natural populations. In addition to being crucial for colonization, dispersal also influences the processes occurring during adaptation. For pathogens, a better understanding of dispersal processes may improve our capacity to control the diseases that they cause. In this thesis, we studied dispersal processes and quantified gene flow in the banana plant pathogen Mycosphaerella fijiensis at the local scale of a production area in South-West Cameroon (named Moungo). For this purpose, several approaches differing in the spatio-temporal scale to which they refer were combined. First, neutral markers were used to describe the spatial genetic structure of this pathogen in the Moungo area, which includes several potential ecological barriers to dispersal. No effects on genetic structure of landscape elements or geographical distance were found. However, we detected a spatial break in allelic frequencies that appeared to be explained by an historical event. This result suggests the existence of large M. fijiensis populations out of the mutation-migration-drift genetic equilibrium. Second, genetic cline theory was applied to study the evolutionary forces implicated in the installation and evolution of spatial gradients in allelic frequencies. More specifically, we analysed the spatio-temporal variation of the genetic discontinuity previously detected through a neutral cline model to estimate the intensity of gene flow in this area ( =1175 m/generation). Lastly, we measured the distribution of dispersal distances of M. fijiensis spores from a primary source of inoculum was. Such an experiment allowed us to confirm that conidia are implicated in short-distance dispersal whereas ascospores are responsible for spread of the disease over longer distances. The estimated mean dispersal distance travelled by spores was 3.12 and 283 metres/generation for conidia and ascospores, respectively, and the ascospore dispersal kernel was shown to be fat-tailed. This thesis adds to global knowledge of M. fijiensis dispersal and the measures of dispersal estimated in this work will be useful in parameterizing models aimed at a better understanding of the spatial patterns of fungicide resistance evolution under different management strategies.

La température est un des principaux facteurs climatiques pilotant le développement des champignons pathogènes foliaires pendant les différentes étapes de leur cycle parasitaire. Puisque ces microorganismes se développent à la surface, puis à l’intérieur des feuilles, c’est la température de feuille (« body temperature » en écologie) qui pilote leur développement. En épidémiologie végétale, c’est toutefois la température d’air qui est utilisée pour caractériser l’effet de la température sur le développement des agents pathogènes foliaires. Or, la température de feuille peut différer significativement de la température d’air en fonction des conditions climatiques. La prise en compte de la température d’air pour étudier la dynamique des maladies foliaires ne peut donc s’affranchir de deux biais : la température mesurée n’est pas celle qui est réellement perçue par l’agent pathogène et l’hétérogénéité spatiale des températures au sein du peuplement n’est pas prise en compte. De plus, la relation entre la température et le développement des agents pathogènes est non linéaire, ce qui limite la gamme de validité autorisant l’utilisation des sommes de températures, pourtant largement employées en protestion des cultures. L’objectif général de cette thèse est de reconsidérer la prise en compte de la température pour l’étude du développement des champignons pathogènes foliaires.Le pathosystème blé-Mycosphaerella graminicola a été choisi en tant qu’objet d’étude. La stratégie adoptée pour atteindre les objectifs de la thèse combine deux approches complémentaires, l’expérimentation et la modélisation. Pour la première fois, la loi de réponse d’un agent pathogène foliaire à la température de feuille a été établie. Un dispositif expérimental innovant a permis d’établir la loi de réponse pour trois isolats sur une large gamme de températures foliaires, via la mesure en continu de la température de 191 feuilles (F et F) inoculées et l’utilisation d’un système de forçage thermique par lampe infrarouge. La loi de réponse de la période de latence de la septoriose à la température de feuille s’apparente au concept de courbe de performance thermique développé en écologie. Celle-ci étant non linéaire sur l’ensemble de la gamme de température étudiée, l’impact de l’amplitude de fluctuations de température de feuille a été caractérisé. Une amplitude élévée a conduit à plusieurs effets négatifs pour le développement de M. graminicola : l’augmentation de la durée du cycle de l’agent pathogène, la diminution de la surface sporulante des lésions et de la densité de pycnides. Les différences de cinétique de développement en fonction de l’amplitude des fluctuations ne sont que partiellement expliquées par l’effet Kaufmann (purement mathématiques), suggérant que M. graminicola atténue les conséquences négatives d’amplitudes de fluctuation plus élevées. Enfin, les simulations du développement de la septoriose réalisées à partir de données de températures foliaires diffèrent signicativement de celles réalisées à partir de températures d’air mesurées de façon standard par une station météorologique. Ces simulations ont également souligné le caractère déterminant du pas de temps considéré.Par le transfert de concepts d’écologie vers l’épidémiologie, cette thèse ouvre des pistes pour améliorer la prise en compte de la température dans les modèles épidémiologiques. Elle contribue au développement d’une meilleure compréhension des mécanismes par lesquels l’environnement affecte les microorganismes, point clé pour le développement de modèles mécanistes de réponses possibles au changement climatique / Temperature is a major force for the development of foliar fungal pathogens. Such organisms develop onto and into leaves during their growth cycle. Thus, leaf temperature is the temperature they actually perceive (“body temperature”). However, air temperature has always been used by plant pathologists to study the effect of temperature on the development of foliar fungal pathogens. Leaf temperature may significantly differ from the air temperature according to weather conditions. Therefore, considering the air temperature to study foliar pathogens can potentially cause two biases: the measured temperature is not the temperature such pathogens actually perceive and the spatial heterogeneity of leaf temperatures within the plant canopy is ignored. In addition, the relationship between temperature and the development of foliar pathogens is nonlinear. This challenges the immoderate use of degree-day sums in plant disease epidemiology. The main objective of this thesis is to reconsider the use of temperature for the study of the development of foliar fungal pathogens.The wheat-Mycosphaerella graminicola pathosystem was chosen as the model of study. The strategy to achieve the objectives of the thesis combines two complementary approaches: experimentation and modelling. For the first time, the impact of leaf temperature on the development of a leaf pathogen was characterized. An original experimental device allowed determining the response law for three isolates over a wide range of leaf temperature, using thermal infrared lamps and measuring continuously the temperature of 191 inoculated leaves (F1 and F2). The response law of M. graminicola latent period to leaf temperature is similar to the concept of thermal performance curve (TPC) developed in ecology. As this TPC is non-linear over the entire leaf temperature range investigated, the impact of the amplitude of leaf temperature fluctuations has been characterized. A high amplitude led to several negative effects on M. graminicola development: an increase in the duration of the pathogen cycle, a decrease in the final sporulating area in the pycnidium density. Differences in kinetics of development depending on the amplitude of the fluctuations were only partially explained by the Kaufmann effect (purely mathematical), suggesting that M. graminicola mitigates the negative consequences of higher amplitudes of temperatures fluctuation. Finally, simulations of the development of M. graminicola performed using leaf temperature data differed significantly from those performed using air temperatures measured in a standard way, by a weather station. Simulations also underlined the importance of the time step considered. By transferring concepts from ecology to epidemiology, this thesis provided guidelines to better take into account temperature in epidemiological models. It helped to develop a better understanding of the mechanisms by which the environment affects micoorganisms, the cornerstone for the development of mechanistic models of possible responses to climate change.

No description available.

Zymoseptoria tritici is an ascomycete fungus that causes Septoria tritici leaf blotch disease, which is one of the most devastating diseases of wheat. The lack of molecular tools has withheld functional genomics and consequently has left extensive gaps in the knowledge of the biology of infection by Z. tritici. The current research was conducted to develop molecular tools in order to facilitate forward and reserves genetic screens in Z. tritici. These tools include an optimised genetic manipulation protocol, the Z. tritici strains that provide high frequency targeted genome manipulations, a strategy for gene overexpression and protein tagging, and regulatable promoters for controlled gene expression in Z. tritici. The regulatable promoters served to reveal that the Z. tritici β-(1,3)- glucan synthase (BGS1) gene encoded an essential protein, which regulated cell wall stress tolerance and was therefore, a potential drug target. In addition, these molecular tools revealed a virulence-associated role of the glyoxylate cycle in Z. tritici as inactivation of this pathway impeded pre-penetration morphogenesis, which was restored by exogenous glucose application. This result implied that Z. tritici engaged the glyoxylate cycle to produce energy though gluconeogenesis by channelling the by-products of lipolysis. This significance of the glyoxylate cycle during initiation of the bi-phasic infection cycle suggests that Z. tritici is not a hemibiotroph, but a necrotrophic pathogen with an extended asymptomatic phase of infection. Overall, the molecular tools developed in this study will facilitate large-scale functional genomic analyses to interrogate the biology of infection by Z. tritici. The resulting data will inform the development of durable control strategies to combat Z. tritici outbreaks.

Submitted by Marco Antônio de Ramos Chagas (mchagas@ufv.br) on 2017-04-24T12:31:48Z No. of bitstreams: 1 texto completo.pdf: 486412 bytes, checksum: ea7846af4d8a5809764bfecb46fb6ed2 (MD5) / Made available in DSpace on 2017-04-24T12:31:48Z (GMT). No. of bitstreams: 1 texto completo.pdf: 486412 bytes, checksum: ea7846af4d8a5809764bfecb46fb6ed2 (MD5) Previous issue date: 2003-12-17 / A sigatoka negra, causada pelo fungo Mycosphaerella fijiensis, ocasiona perdas que oscilam entre 50 a 100% na produção de bananeira e bananeira-da-terra. Visando obter informação sobre epidemias da sigatoka negra em ambas as musáceas, realizaram-se dois experimentos. No primeiro, avaliaram-se os componentes epidemiológicos: períodos de incubação e latente médio; severidade aos 24 e 40 dias; freqüência de infecção; intervalo, em dias, para atingir a severidade máxima; dias transcorridos do aparecimento de sintomas até atingir a severidade máxima; e as áreas abaixo da curva da severidade e da porção necrosada. Verificou-se que M. fijiensis não foi específico para bananeira ou bananeira-da-terra e que as populações variam quanto à agressividade. A inoculação artificial em mudas pode ser usada para avaliar componentes de resistência de diferentes genótipos à doença. No segundo experimento, estudou-se o progresso da doença em plantações comerciais de bananeira 'Williams' e bananeira-da-terra 'Barraganete', durante as épocas seca e chuvosa. Independentemente da época avaliada, os valores de área abaixo da curva da severidade estimados para bananeira foram maiores que para bananeira-da-terra. Na época chuvosa, o progresso da doença foi maior que na época seca. Em bananeira-da-terra, detectou-se correlação significativa da severidade e o número de horas semanais com temperatura entre 24 e 28°C e umidade relativa maior de 90%, quando se consideraram os valores das variáveis climatológicas registrados quatro e três semanas antes da severidade, nas épocas seca e chuvosa, respectivamente. Não se detectou correlação significativa de severidade e intensidade de precipitação pluviométrica, nas duas épocas avaliadas. Este é o primeiro relato de estudos de sigatoka negra em bananeira-da-terra no Equador, nas épocas seca e chuvosa. É, também, o primeiro estudo de componentes epidemiológicos de isolados equatorianos de M. fijiensis. Os resultados obtidos serão importantes para subsidiar o manejo da sigatoka negra, bem como programas de melhoramento que visem obter resistência a M. fijiensis. / Black sigatoka, caused by the fungus Mycosphaerella fijiensis, is the most important leaf disease of banana and plantain crops, causing 50 to 100% production losses. To generate information regarding black sigatoka epidemics on both Musacea, two experiments were conducted. In the first, isolates of M. Fijiensis obtained from diseased leaves of banana and plantain from several regions of Ecuador, were inoculated in banana and plantain plantlets. The following epidemic components were evaluated: mean incubation and latent periods, initial severity, infection frequency, number of lesions/leaf area, days to reach maximum severity, area under disease progress curve for severity, and area under disease progress curve of leaf necrosis. Regarding all components, it was found that M. fijiensis was not specific for either banana or plantain, and that there is variability in fungal aggressiveness. It was concluded that artificial inoculation of M. fijiensis in plantlets can be used in evaluating disease resistance components of different genotypes. In the second experiment, disease progress was studied in commercial crops of banana 'Williams' and plantain 'Barraganete', during dry and rainy seasons. In both seasons, area under disease progress curve (AUDPC) on banana was higher than AUDPC for iplantain. Values of AUDPC in plantain were higher in the rainy season than in the dry season. Correlation analysis was done between weather variables and disease severity in plantains. Disease severity was not correlated with temperature, relative humidity, or precipitation. Significant correlation was detected between severity and both number of hours with temperature ranging from 24 to 28° C and relative humidity higher than 90%, when these variables were registered four or three weeks before severity assessment, in either dry or rainy seasons, respectively. This is the first report of epidemiological studies of Black Sigatoka in plantains in the dry and rainy seasons, in Ecuador. It is also the first study of aggressiveness components of M. fijiensis, which may become important to assist future breeding programs to obtain resistance against the pathogen. / Dissertação importada do Alexandria

Submitted by (lucia.rodrigues@ufrpe.br) on 2017-03-22T16:19:02Z No. of bitstreams: 1 Otacilio Monteiro da Rocha Junior.pdf: 493982 bytes, checksum: 6eac9d2040ce61a3f47221fcd1d41acc (MD5) / Made available in DSpace on 2017-03-22T16:19:02Z (GMT). No. of bitstreams: 1 Otacilio Monteiro da Rocha Junior.pdf: 493982 bytes, checksum: 6eac9d2040ce61a3f47221fcd1d41acc (MD5) Previous issue date: 2007-07-27 / Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq / Yellow Sigatoka disease or leaf spot Banana caused by fungus Mycosphaerella musicola (anamorph Pseudocercospora musae), it is an important disease of banana disseminated throughout in Brazilian territory. This work aimed to determine the spatial pattern of the Sigatoka disease in the field and appropriate sample’s size for quantification of the disease in different planting areas and severity levels. The spatial pattern of the disease was investigated in three areas of banana’s planting, being delimited in each planting a portion of thirty contiguous lines, with 30 covas/line. Yellow Sigatoka disease was evaluated in each plant-mother and, considering the respective location, the analysis of space spatial’s autocorrelation was made. The three areas presented aggregate pattern of diseased plants, with predominance of the three areas presented pattern of diseased plants, with predominance of the aggregation inside of the lines aggregation inside of the lines. To determinate the appropriate sizes of the samples, it was made pilot’s sampling in 30 plantings, being established in each planting a sub-area of 2 ha, where 50 plants were selected by systematic sampling and evaluated by disease’severity. The severity of the Sigatoka yellow in the 30 plantingareas submitted to pilot’s sampling varied from 5,3% to 46,7%, not being verified significant correlations between the severity levels and the plantings’ age, as well as of these last ones with the sizes of the samples. The samples’ size for quantification of Sigatoka yellow banana’s severity were determinated considering the aggregate pattern of diseased plants. Obtained data were analyzed by method that specifies the acceptable mistake, with a aggregate pattern of diseased plants. The sample’s size were correlated negatively with the levels of disease’ severity (r = -0,60). Considering the planting area’ average, in futures studies of the severity of the Sigatoka yellow, at which excellent precision’ level is demanded (error = 5%), the sampling of 66 plants is recommended for each 2 ha cultivated, with the evaluation of the nine leaves more young/plant. The results obtained in this study serve as base for futures epidemic studies of the Sigatoka yellow banana, as data were originated from fields under different conditions and estimated considering growing needs of precision.Yellow Sigatoka disease or leaf spot Banana caused by fungus Mycosphaerella musicola (anamorph Pseudocercospora musae), it is an important disease of banana disseminated throughout in Brazilian territory. This work aimed to determine the spatial pattern of the Sigatoka disease in the field and appropriate sample’s size for quantification of the disease in different planting areas and severity levels. The spatial pattern of the disease was investigated in three areas of banana’s planting, being delimited in each planting a portion of thirty contiguous lines, with 30 covas/line. Yellow Sigatoka disease was evaluated in each plant-mother and, considering the respective location, the analysis of space spatial’s autocorrelation was made. The three areas presented aggregate pattern of diseased plants, with predominance of the three areas presented pattern of diseased plants, with predominance of the aggregation inside of the lines aggregation inside of the lines. To determinate the appropriate sizes of the samples, it was made pilot’s sampling in 30 plantings, being established in each planting a sub-area of 2 ha, where 50 plants were selected by systematic sampling and evaluated by disease’severity. The severity of the Sigatoka yellow in the 30 plantingareas submitted to pilot’s sampling varied from 5,3% to 46,7%, not being verified significant correlations between the severity levels and the plantings’ age, as well as of these last ones with the sizes of the samples. The samples’ size for quantification of Sigatoka yellow banana’s severity were determinated considering the aggregate pattern of diseased plants. Obtained data were analyzed by method that specifies the acceptable mistake, with a aggregate pattern of diseased plants. The sample’s size were correlated negatively with the levels of disease’ severity (r = -0,60). Considering the planting area’ average, in futures studies of the severity of the Sigatoka yellow, at which excellent precision’ level is demanded (error = 5%), the sampling of 66 plants is recommended for each 2 ha cultivated, with the evaluation of the nine leaves more young/plant. The results obtained in this study serve as base for futures epidemic studies of the Sigatoka yellow banana, as data were originated from fields under different conditions and estimated considering growing needs of precision. / A Sigatoka-amarela, causada pelo fungo Mycosphaerella musicola (anamorfo Pseudocercospora musae, é uma importante doença da bananeira e encontra-se disseminada em todo o território brasileiro. Este trabalho teve como objetivos determinar o padrão espacial da Sigatoka-amarela no campo e os tamanhos ideais das amostras para quantificação da doença em diferentes áreas de plantio e níveis de severidade. O padrão espacial da doença foi investigado em três áreas de plantio de bananeira, sendo em cada plantio delimitada uma parcela de 30 linhas contíguas, com 30 covas/linha. A severidade da Sigatoka-amarela foi avaliada em cada planta-mãe e, considerando a respectiva localização, foi efetuada a análise de autocorrelação espacial. As três áreas apresentaram padrão agregado de plantas doentes, com predominância da agregação dentro das linhas. Na determinação dos tamanhos ideais das amostras, foram efetuadas amostragens-piloto em 30 plantios, sendo em cada plantio estabelecida uma sub-área de 2 ha, onde 50 plantas foram selecionadas por amostragem sistemática e avaliadas quanto à severidade da doença. A severidade da Sigatoka-amarela nas 30áreas de plantio submetidas às amostragens-piloto variou de 5,3% a 46,7%, não sendo constatadas correlações significativas entre os níveis de severidade e as idades dos plantios, bem como destas últimas com os tamanhos das amostras. Os tamanhos das amostras para quantificação da severidade da Sigatoka-amarela da bananeira foram determinados considerando o padrão agregado de plantas doentes. Os dados obtidos foram analisados pelo método que especifica o erro aceitável, com um padrão agregado de plantas doentes. Os tamanhos das amostras correlacionaram-se negativamente com os níveis de severidade da doença (r = -0,60). Considerando a média das áreas de plantio, em futuros levantamentos da severidade da Sigatoka-amarela, nos quais seja exigido excelente nível de precisão (erro = 5%), recomenda-se a amostragem de 66 plantas para cada 2 ha cultivados, com a avaliação das nove folhas mais jovens/planta. Os resultados obtidos nesse estudo servem como base para futuros levantamentos epidemiológicos da Sigatoka-amarela da bananeira, uma vez que os dados foram originados de campos sob diferentes condições e estimados considerando necessidades crescentes de precisão.

Please read the Summary in the section 03chapter3 of this document / Dissertation (MSc)--University of Pretoria, 2005. / Plant Science / Unrestricted

La maladie des raies noires (MRN), causée par le champignon ascomycète Mycosphaerella fijiensis, est l'une des maladies les plus dévastatrices du bananier (Musa spp.). Elle constitue une contrainte majeure à sa production, particulièrement dans les pays des tropiques humides où le bananier est une culture alimentaire de base. L'objectif de cette thèse a été de caractériser les populations de M. fijiensis et d'étudier l'épidémiologie de la MRN dans la région de Kisangani (RDC) en vue d'évaluer les stratégies de protection intégrée à développer dans les cultures de bananiers et bananiers plantains. La particularité de notre approche réside en la combinaison d'études en laboratoire, selon des approches classique et moléculaire, et des expérimentations sur le terrain pour mieux connaître les caractéristiques épidémiologiques de la maladie selon les saisons et les systèmes de cultures. Les caractéristiques phénotypiques des souches isolées de Kisangani sur milieu PDA étaient typiques de l'espèce M. fijiensis. Cette identification a été confirmée selon une approche moléculaire sur base du séquençage d'une partie de l'ADN ribosomal incluant les régions ITS (internal transcribed spacers) et le gène 5,8S. L'existence des deux types de croisement Mat1-1 et Ma1-2 au sein de la population a été révélée mais un déséquilibre entre les deux idiomorphes a été remarqué. L'évaluation de la pathogénicité des souches a montré que toutes les souches testées ont un pouvoir pathogène vis-à-vis du cultivar Cavendish " Grande Naine ". Notre étude a aussi permis de ressortir des différences de virulence selon les souches. Les tests de sensibilité aux fongicides ont montré que les souches de la RDC sont sensibles aux triazoles et au carbendazime, mais certaines souches seraient résistantes à l'azoxystrobine. Sur le plan épidémiologique, notre étude a révélé que les deux formes fongiques (anamorphe et téléomorphe) sont présentes non seulement en saison des pluies mais également en saison subsèche. Elles jouent donc un rôle important dans l'épidémiologie de la maladie. L'incidence de la maladie 6 Résumé a été légèrement moindre en saison subsèche qu'en saison humide. Une comparaison de la progression de la maladie pendant les deux saisons selon le système de culture a révélé que le développement de la MRN a été plus lent en forêt secondaire qu'en jachère et en jardin de case et l'incidence et la sévérité ont été plus grandes sur les plantains que sur les bananes. La meilleure tolérance du cultivar Yangambi Km5 a été confirmée. Ces résultats ont apporté des éléments nouveaux sur l'épidémiologie de la maladie dans la région de Kisangani et sur les caractéristiques de la population en présence. Ils ont été exploités pour établir une liste de recommandations visant à mieux gérer les dégâts de M. fijiensis, un pathogène au potentiel évolutif important.