Bibliography: leaves 140-158 / ix, 158 leaves, [23] leaves of plates : ill., 1 map ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.1985) Dept. of Plant Pathology, University of Adelaide

A região noroeste do estado de São Paulo é um importante pólo produtor de uvas de mesa, porém possui condições ambientais muito propícias à ocorrência de doenças fúngicas durante todo o ciclo da videira. Alternativas como o uso de coberturas plásticas e de sistemas de alerta fitossanitário têm se mostrado bastante vantajosas para tal, porém, ainda com poucos estudos sobre isso na região. Deste modo, objetivou-se com este estudo avaliar a eficácia de sistemas de alerta fitossanitário no controle do míldio (Plasmopara viticola) em videiras cultivadas sob coberturas plásticas, e, consequentemente, na produtividade e na qualidade das uvas, no Noroeste Paulista. O experimento foi realizado na Estação Experimental de Viticultura Tropical (EVT) da Embrapa Uva e Vinho, localizada no município de Jales, SP, durante os anos de 2012 e 2013. Foram conduzidas três ruas de 120 m de videiras, cultivar apirênica \'BRS Morena\', em espaçamento de 3,0 m entre plantas. Metade do vinhedo foi coberto com filme plástico de polipropileno trançado sobre estrutura metálica em forma de arco (PPT) e a outra metade com tela preta, com 18% de sombreamento (TP18%). O delineamento experimental foi o de blocos casualizados compostos por cinco tratamentos, com seis repetições por ambiente coberto. Os tratamentos foram determinados a partir de diferentes manejos de controle do míldio da videira: TE - Testemunha (sem controle fitossanitário para o míldio); CA - Controle convencional (calendário); BA - Alerta fitossanitário denominado \'Regra 3-10\' (BALDACCI et al., 1947); MA25 - Alerta fitossanitário com eficiência de infecção baixa - i0 > 25% (MADDEN et al., 2000); e MA75 - Alerta fitossanitário com eficiência de infecção alta - i0 >75% (MADDEN et al., 2000). De acordo com os resultados, sob o PPT a transmissividade média da radiação solar global foi de 82,4% em 2012 e 67,3% em 2013 e sob a TP18%, da ordem de 90% nos dois anos estudados. Os ambientes sob as coberturas apresentaram temperaturas máximas do ar superiores aos valores observados a céu aberto, sendo as diferenças da ordem de 0,7 °C sob ao PPT e de 1,0 °C sob a TP18%. Sob o PPT, a duração do período de molhamento foliar foi 34% superior do que sob TP18%. Os tratamentos baseados nos sistemas de alertas fitossanitários (BA, MA25 e MA75) revelaram níveis baixos de severidade do míldio da videira sob PPT, semelhantes aos verificados no tratamento com base no calendário (CA). Os tratamentos BA, MA25 e MA75 sob TP18% indicaram um número de pulverizações similar aos realizados sob o PPT, porém foram menos eficientes em relação a CA. Houve uma significativa redução no número de pulverizações entre o tratamento CA e os tratamentos BA, MA25 e MA75, da ordem de 70%. As videiras, sob o PPT, pulverizadas com base em BA, MA25 e MA75 apresentaram características produtivas e qualitativas semelhantes às das videiras pulverizadas de acordo com CA. Conclui-se que o cultivo de videiras sob cobertura plástica de polipropileno, aliado à adoção de sistemas de alertas fitossanitários, resultou em excelentes níveis de controle do míldio da videira no Noroeste Paulista. / The Northwest region of the state of São Paulo is one of the main producers of table grapes in Brazil, however has a very favorable environmental conditions to fungal diseases during the growing season. The use of disease warning systems and plastic covers are promising alternatives for disease control, but there are not many researches about that in this region of the state. Thus, the objective of this study was to evaluate the efficacy of warning systems for managing downy mildew (Plasmopara viticola) in vineyards cultivated under plastic coverings, and, consequently, their impact on vine productivity and quality, in the northwest region of São Paulo State, Brazil. The experiment was carried out at the EMBRAPA - Tropical Viticulture Experimental Station (EVT/Embrapa Uva e Vinho), located in Jales, SP, Brazil. Three rows of 120 m of the seedless grape cultivar \'BRS Morena\', spaced with 3.0 m between plants were conducted during 2012 and 2013 growing seasons. Half of the vineyard was covered with braided polypropylene plastic film installed over a metallic arc-shaped structure (PPT) and the other half with black screen, with 18% of shading (TP18%). The experimental design was randomized blocks composed of five treatments, with six repetitions per covered environment. The treatments were defined by the different grapevine downy mildew management : (TE) Control (no sprays against downy mildew); (CA) Conventional control (calendar); (BA) Warning system \'Rule 3-10\' (BALDACCI et al., 1947); (MA25) Warning system with low-infection efficiency - i0 > 25% (MADDEN et al., 2000); and (MA75) Warning system with high infection efficiency - i0 > 75% (MADDEN et al., 2000). According to the results, under the PPT the average global solar radiation transmissivity was 82.4% in 2012 and 67.3% in 2013 and under TP18%, around 90% along the two growing seasons. The microclimate under the plastic covers showed maximum air temperatures higher than the values observed in the external environment, and the differences was around 0.7 °C under the PPT and 1.0 °C under TP18%. In the PPT, leaf wetness duration (LWD) was about 34% higher in relation to the TP18%. The treatments based on warning systems (BA, MA25 and MA75) revealed low levels of severity of grapevine downy mildew under PPT, similar to those observed in the treatment based on a calendar spray (CA). The treatments BA, MA25 and MA75 under TP18% indicated a number of sprays similar to those obtained under the PPT, but less efficient in relation to the CA. There was a significant reduction in the number of sprays between the CA and BA, MA25 and MA75 treatments, about 70%. The vines under the PPT and sprayed based on BA, MA25 and MA75 had productive and quality characteristics similar to those sprayed according to the CA. It is concluded that the association of cultivation under polypropylene plastic cover and the use of disease warning systems resulted in excellent levels of downy mildew control in vineyards in the Northwest region of São Paulo state.

Un déploiement optimal de variétés résistantes nécessite une excellente connaissance des relations entre la vigne et P. viticola. Ces connaissances fondamentales pourront ensuite alimenter les stratégies pour le développement de variétés durablement résistantes au vignoble. Bianca est une variété de vigne résistante au mildiou qui possède le gène résistance Rpv3. Cette variété est résistante à la plupart des souches de P. viticola. Cependant, une souche virulente capable de l’infecter a été isolée. Dans ce projet, un pathosystème original, fondé sur la variété Bianca confrontée à une souche avirulente et à une souche virulente de P. viticola, a été utilisé pour obtenir une image complète de l'impact sur la vigne de l'infection par P. viticola en situation compatible et incompatible, en combinant des études de physiopathologie avec des analyses métabolomiques par spectrométrie de masse à haute résolution et par résonance magnétique nucléaire. Parallèlement, l'identification de métabolites et de séquences géniques spécifiques de P. viticola a permis le développement de méthodes de suivi dynamique de l'infection, grâce à la PCR quantitative et à la quantification de lipides caractéristiques de l'agent pathogène. / Optimal deployment of resistant varieties requires an excellent knowledge of the relationship between grapevine and P. viticola. This fundamental knowledge can then feed the strategies for the development of grapevine varieties with sustainable resistance. Bianca is a downy mildew-resistant grapevine variety, due its Rpv3 resistance gene. This variety is resistant to most strains of P. viticola. However, a virulent strain capable of infecting Bianca has recently been isolated. In this project, we use this original pathosystem to obtain a complete picture of the impact P. viticola infection on grapevine, by combining physiopathological studies with metabolomic analyses. In addition, the identification of specific metabolites and gene sequences from P. viticola has allowed the development of original methods for dynamic monitoring of the infection process, through quantitative PCR and quantification of specific lipids.

Le cucurbitacee possono essere attaccate da più di 200 malattie, una corretta gestione è dunque fondamentale per ridurre il rischio di perdite di produzione, sia in termini di quantità sia in termini di qualità. Tra le malattie più importanti che attaccano le cucurbitacee ci sono l’oidio e la peronospora delle cucurbitacee. Podosphaera xanthii e Golovinomyces cichoracearum sono gli agenti causali dell’oidio. È stato studiato l’effetto della temperature sulla germinazione dei conidi in ambiente controllato a 6 temperature costanti (da 10 a 35°C, ad intervalli di 5C°) da 3 a 72 ore. La temperature ottimale per la germinazone, l’infezione e la sporulazione è risultata essere rispettivamente 24.4, 25.7 e 21.3°C per P. xanthii e 17.9, 17.3 e 16.2°C per G. cichoracearum. Un modello meccanicistico è stato sviluppato per il rischio che i due agenti patogeni causassero un attacco di oidio. Il modello simula la germinazione su foglie infettate sulla base delle condizioni ambientali di temperatura e umidità relativa. Le equazioni che calcolano la germinazione delle dei conidi di entrambi i funghi sono state sviluppate sulla base di dati presenti in bibliografia. Un secondo modello meccanicistico è stato sviluppato per Pseudoperonospora cubensis, agente causale della peronospora delle cucurbitacee. Il modello calcola la data di comparsa dei sintomi e la probabilità del superamento di determinate soglie di gravità della malattia, sulla base di sotto-processi dell’infezione. Il passaggio da uno stato dell’infezione al successivo è dipendente dalle condizioni ambientali. Entrambi i modelli sono stati validati confrontando i dati ottenuti dai modelli con dati indipendenti rilevati in coltivazioni del nord Italia. / Cucurbits are potentially affected by more than 200 diseases of diverse etiologies, so a good disease management is crucial to reduce the risk of high yield losses in terms of quantity and quality. Among the more important diseases there are powdery and downy mildew. Podosphaera xanthii and Golovinomyces cichoracearum are the causal agents of cucurbit powdery mildew. The effect of temperature on conidial germination was studied in controlled condition at 6 constant temperature (from 10 to 35°C, step 5°C) for 3 to 72 hours. Optima temperature for conidial germination, infection and sporulation were 24.4, 25.7 and 21.3°C respectively for P. xanthii and 17.9, 17.3 and 16.2°C for G. cichoracearum. A mechanistic model was developed for the risk posed by P. xanthii and G. cichoracearum to cause cucurbit powdery mildew. The model simulates germination on infected leaves on the base of environmental conditions of temperature and relative humidity. Equation regulating spore germination of both fungi were developed using published data. Another mechanistic model was develop also for Pseudoperonospora cubensis, causal agent of cucurbit downy mildew. The model calculates the symptoms appearance and the probability of overtaking severity threshold based on sub-processes of infection. Changes from one state of the infection to the following one depend on environmental conditions. Both models were validated by comparing model outputs with independent data sets collected in fields located in the north of Italy.

This study was undertaken to determine the sensitivity of grape downy mildew (DM, Plasmopara viticola) and powdery mildew (PM, Erysiphe necator) to commonly used single-site fungicides in Virginia and nearby states. DM and PM isolates were collected from 2005 to 2007. In grape leaf disc bioassays, 92% of the DM isolates were QoI (azoxystrobin)-resistant, but none were resistant to mefenoxam. Eighty-two percent of the PM isolates were QoI-resistant, but none were resistant to boscalid and quinoxyfen. The frequency of the G143A point mutation, which confers high levels of QoI resistance, was quantified in DM and PM isolates by real-time PCR. Most of the QoI-resistant DM and PM isolates contained >95% of the 143A allele. QoI-sensitive DM isolates contained less than 1% of 143A. One out of 145 and 14 out of 154 QoI-resistant DM and PM isolates (able to grow on azoxystrobin concentration ï ³ 1 µg/ml), respectively, contained less than 1% 143A. Most PM isolates exhibited reduced sensitivity to five DMI fungicides when compared to a sensitive subgroup (n=9) and compared to published reports for unexposed populations; the resistance factor (median EC50 of the entire isolate collection divided by median EC50 of sensitive subgroup) was highest for tebuconazole (360) and myclobutanil (350), followed by triflumizole (79), triadimefon (61), and fenarimol (53). Sensitivities to all five DMI fungicides, but also azoxystrobin, were moderately to strongly correlated (pairwise r-values ranging from 0.60 to 0.88). / Master of Science in Life Sciences

Development of fungicide resistance in fungal and oomycete pathogens is a serious problem in grape production. Quinoxyfen is a fungicide widely used against grape powdery mildew (Erysiphe necator). In 2013, E. necator isolates with reduced quinoxyfen sensitivity (designated as quinoxyfen lab resistance or QLR) were detected in Virginia. Field trials were conducted in 2014, 2015, and 2016 at the affected vineyard to determine to what extent quinoxyfen might still contribute to disease control. Powdery mildew control by quinoxyfen was good, similar to, or only slightly less, than that provided by myclobutanil and boscalid in all three years. The frequency of QLR in vines not treated with quinoxyfen declined only slowly over the three years, from 65% to 46%. Information about the mode of action of quinoxyfen is limited; previous research suggests that quinoxyfen interferes with the signal transduction process. We profiled the transcriptomes of QLR and sensitive isolates in response to quinoxyfen treatment, providing support for this hypothesis. Additional transcriptional targets of quinoxyfen were revealed to be involved in the positive regulation of the MAPK signaling cascade, pathogenesis, and sporulation activity. Grape downy mildew (Plasmopara viticola), another important grape pathogen, is commonly controlled by phosphite fungicides. A field trial and laboratory bioassays were conducted to determine whether P. viticola isolates from vineyards with suspected control failures showed reduced sensitivity against phosphite fungicides. Prophyt applied at 14-day intervals under high disease pressure provided poor downy mildew control in the field. Next-generation sequencing technologies were utilized to identify 391,930 single nucleotide polymorphisms (SNPs) and generated a draft P. viticola genome assembly at ~130 megabase (Mb). Finally, field isolates of P. viticola collected from a Virginia vineyard with suspected mandipropamid control failure were bioassayed. The EC50 values of the isolates were >240 μg.ml-1 for mandipropamid, well above the field rate. The PvCesA3 gene of two resistant isolates was sequenced revealing that these isolates had a GGC-to-AGC substitution at codon 1105, the same mutation that has been found associated with CAA resistance elsewhere. / PHD / Powdery and downy mildew are two diseases of grapes that can cause large yield losses, and are usually controlled by regular fungicide applications. Development of fungicide resistance has been a growing challenge. Quinoxyfen is a protectant fungicide commonly used against powdery mildews. Unusual grape powdery mildew isolates that grew well on quinoxyfen-treated plants in the laboratory (designated as quinoxyfen lab resistance or QLR) were detected in a Virginia vineyard. In 2014, the first year of this study, 65% of powdery mildew isolates from parts of this vineyard that received no further quinoxyfen treatments had the QLR type of resistance, and this declined only slowly to 46% by the third year. Field trials were conducted in 2014, 2015, and 2016 to determine the efficacy of quinoxyfen in the presence of QLR. Powdery mildew control by quinoxyfen on both grape clusters and leaves was similar to, or only slightly less, than that provided by the standard anti-powdery mildew fungicides myclobutanil and boscalid in all three years. In order to gain a better understanding of the mode(s) of action and resistance mechanism(s) of quinoxyfen, gene expression of QLR and sensitive isolates, both in the presence and absence of quinoxyfen, was analyzed by nucleic acid sequencing. This study confirms previous research suggesting that quinoxyfen interferes with the important biological process signal transduction, and revealed additional gene targets of quinoxyfen. The phosphites are a group of fungicides commonly used to control grape downy mildew. Control failures after phosphite application have occasionally been suspected, and downy mildew isolates from vineyards with and without suspected control failures were tested in laboratory bioassays to determine if any level of resistance could be demonstrated. There was a limited range of sensitivity, and none of the isolates showed a notable loss of sensitivity. A field trial was conducted to determine the efficacy of one phosphite fungicide, Prophyt, applied at 14-day intervals under conditions favorable for disease development. Prophyt provided poor downy mildew control, suggesting that it has to be applied more frequently. Next-generation sequencing technologies were utilized to identify genetic markers for clade identification and generated a draft genome assembly of grape downy mildew, which improves the understanding of grape downy mildew genome. Grape downy mildew isolates collected from a vineyard in Virginia where mandipropamid provided poor control of downy mildew were bioassayed. The isolates tolerated mandipropamid rates well above the field rate, showing that they were indeed resistant. The mutation that confers mandipropamid resistance on other continents was found in the PvCesA3 gene of two resistant isolates.

Maîtriser l’impact des maladies sur les cultures est un défi majeur de l’agriculture moderne. Cette préoccupation est un aspect important de l’optimisation de la productivité, notamment en viticulture. En France, le mildiou de la vigne causé par Plasmopara viticola est une des maladies cryptogamiques responsable des épidémies les plus dévastatrices et les plus redoutées. Les traitements reposent sur l’utilisation préventive, systématique et onéreuse de composés chimiques antifongiques dont l’utilisation massive constitue un risque à la fois pour l’homme et l’environnement. La réduction de l’utilisation de fongicide implique le développement d’outils de diagnostic au champ, qui requiert la compréhension des interactions entre la plante et les agents pathogènes. Les travaux de cette thèse pluridisciplinaire ont porté sur le pathosystème Plasmopara viticola - Vitis vinifera, notamment pour répondre à l’intérêt croissant pour un outil de diagnostic en temps réel de la maladie utilisable au vignoble. Les stilbènes sont des phytoalexines impliqués dans la défense de certaines plantes supérieures vis-à-vis de stress biotiques et abiotiques. L’autofluorescence de ces composés phénoliques, dont la biosynthèse est induite dans les feuilles de vigne par P. viticola, en fait un potentiel marqueur naturel de l’infection. En effet, la faible autofluorescence bleu-verte des feuilles de vigne saines est considérablement renforcée par l’autofluorescence violet-bleue des stilbènes à la surface de feuilles de vigne infectée par P. viticola. Cette étude a montré que quelque soit le niveau de résistance du génotype, l’autofluorescence violet-bleue des stilbènes induit par l’infection est présente au niveau des parois des cellules de l’épiderme. En dehors de la concentration, la viscosité s’est révélé être la principale variable physico-chimique influençant l’intensité de l’autofluorescence des stilbènes dans les différents compartiments cellulaires des feuilles de vigne. Ceci explique la fluorescence intense des parois, particulièrement rigides, des cellules de garde (stomates) des feuilles infectées. Le suivi cinétique journalier a révélé la nature transitoire de l’autofluorescence des stilbènes lors de l’infection. La robustesse et l’intérêt de ce signal a également été validée par la mesure à différentes échelles (de la cellule à la feuille entière) et avec différentes méthodes fluorimétriques. Les résultats de ce travail ont permis des avancées sur la connaissance du rôle de composés phénoliques induits et constitutifs dans la défense contre P. viticola. En plus de la localisation de l’autofluorescence des stilbènes en surface des feuilles, la microscopie confocale couplée à la microspectrofluorimetrie a révélé différentes localisations de ces phytoalexines dans la profondeur des tissus en corrélation avec le niveau de résistance des génotypes. L’utilisation de l’autofluorescence des stilbènes comme marqueur de l’infection a permis de mettre en évidence : 1) le fait que les flavonols constitutifs des feuilles de V. vinifera retardent le développement de l’infection par P. viticola; et 2) le fait que les acides hydroxycinnamiques constitutifs ne semble pas participer à la défense contre P. viticola. Enfin, une nouvelle méthode de diagnostic non-destructive du mildiou sur feuille basée sur l’autofluorescence des stilbènes a été développée. Elle a montré une détection pré-symptomatique du mildiou sur les feuilles de vigne entières dès le premier jour après l’infection sur la face abaxiale et le troisième jour sur la face adaxiale. Cette méthode de diagnostic du mildiou a été validée au laboratoire notamment grâce à un prototype de capteur proximal développé en collaboration avec la société Force-A. La validation de la méthode au vignoble dans le cadre d’infection naturelle est la prochaine étape pour une utilisation de ce capteur optique dans le cadre de l’agriculture durable et de la sélection variétale. / Controlling the impact of diseases on crops is a major challenge of modern agriculture. This concern is an important aspect of optimizing productivity, notably in viticulture. In France, downy mildew caused by Plasmopara viticola is a fungal disease responsible for the most devastating epidemics. The preventive and systematic treatments are expensive, while the massive use of antifungal chemicals is a risk to both humans and the environment. Reducing the use of fungicide involves the development of diagnostic tools in the field, which requires understanding the interactions between plants and pathogens. The work of this multidisciplinary thesis focused on the pathosystem Plasmopara viticola - Vitis vinifera, especially to meet the growing interest in a real-time diagnostic tool of disease applicable in the vineyard. Stilbenes are phytoalexins involved in the defense of certain higher plants against biotic and abiotic stresses. The autofluorescence of these phenolic compounds, whose biosynthesis is induced in grapevine leaves by P. viticola, makes it a potential marker of natural infection. Indeed, the low blue-green autofluorescence of grapevine leaves is greatly enhanced by the violet-blue autofluorescence of stilbenes on the surface of leaves infected by P. viticola. This study showed that whatever the level of resistance in various genotypes, violet-blue autofluorescence induced by stilbene is present in the walls of epidermal cells. In addition to their concentration, viscosity proved the main physico-chemical variable affecting the intensity of the autofluorescence of stilbenes in different compartments of vine leaves. This explains the intense fluorescence of the walls, particularly rigid, of guard cells (stomata) of infected leaves. Daily monitoring revealed a kinetic with a transient rise of the autofluorescence of stilbenes during infection. The robustness and value of this signal was also validated by measuring at different levels (cellular to whole leaf) and with various fluorimetric methods (imaging, spectroscopy, proximal sensing). These results advance our understanding of the role of constitutive and induced phenolic compounds in plant defence against P. viticola. In addition to a common location of the autofluorescence of stilbenes on the leaf surface, confocal microscopy coupled with microspectrofluorometry revealed distinctive localizations of these phytoalexins in the deep tissue correlated with the level of resistance in genotypes. This aspect no doubt needs broader testing. The use of autofluorescence of stilbene as a marker of infection allowed us to ascertain that: 1) constitutive flavonols of the leaves of V. vinifera retard the development of infection by P. viticola and 2) the constitutive hydroxycinnamic acids do not seem to participate in the defence against P. viticola. Finally, a new method for the non-destructive diagnosis of leaf infection based on the autofluorescence of stilbenes has been developed. We have demonstrated a pre-symptomatic detection of downy mildew on whole grape leaves from the first day after infection on the abaxial surface and from the third day on the adaxial surface. This method of diagnosis has been validated in the laboratory thanks to a proximal sensor prototype developed in collaboration with the company Force-A. The validation of the method in the vineyard in a context of natural infections is the next step for use of this optical sensor as a tool for sustainable agriculture and for genetic screening.

Maîtriser l'impact des maladies sur les cultures est un défi majeur de l'agriculture moderne. Cette préoccupation est un aspect important de l'optimisation de la productivité, notamment en viticulture. En France, le mildiou de la vigne causé par Plasmopara viticola est une des maladies cryptogamiques responsable des épidémies les plus dévastatrices et les plus redoutées. Les traitements reposent sur l'utilisation préventive, systématique et onéreuse de composés chimiques antifongiques dont l'utilisation massive constitue un risque à la fois pour l'homme et l'environnement. La réduction de l'utilisation de fongicide implique le développement d'outils de diagnostic au champ, qui requiert la compréhension des interactions entre la plante et les agents pathogènes. Les travaux de cette thèse pluridisciplinaire ont porté sur le pathosystème Plasmopara viticola - Vitis vinifera, notamment pour répondre à l'intérêt croissant pour un outil de diagnostic en temps réel de la maladie utilisable au vignoble. Les stilbènes sont des phytoalexines impliqués dans la défense de certaines plantes supérieures vis-à-vis de stress biotiques et abiotiques. L'autofluorescence de ces composés phénoliques, dont la biosynthèse est induite dans les feuilles de vigne par P. viticola, en fait un potentiel marqueur naturel de l'infection. En effet, la faible autofluorescence bleu-verte des feuilles de vigne saines est considérablement renforcée par l'autofluorescence violet-bleue des stilbènes à la surface de feuilles de vigne infectée par P. viticola. Cette étude a montré que quelque soit le niveau de résistance du génotype, l'autofluorescence violet-bleue des stilbènes induit par l'infection est présente au niveau des parois des cellules de l'épiderme. En dehors de la concentration, la viscosité s'est révélé être la principale variable physico-chimique influençant l'intensité de l'autofluorescence des stilbènes dans les différents compartiments cellulaires des feuilles de vigne. Ceci explique la fluorescence intense des parois, particulièrement rigides, des cellules de garde (stomates) des feuilles infectées. Le suivi cinétique journalier a révélé la nature transitoire de l'autofluorescence des stilbènes lors de l'infection. La robustesse et l'intérêt de ce signal a également été validée par la mesure à différentes échelles (de la cellule à la feuille entière) et avec différentes méthodes fluorimétriques. Les résultats de ce travail ont permis des avancées sur la connaissance du rôle de composés phénoliques induits et constitutifs dans la défense contre P. viticola. En plus de la localisation de l'autofluorescence des stilbènes en surface des feuilles, la microscopie confocale couplée à la microspectrofluorimetrie a révélé différentes localisations de ces phytoalexines dans la profondeur des tissus en corrélation avec le niveau de résistance des génotypes. L'utilisation de l'autofluorescence des stilbènes comme marqueur de l'infection a permis de mettre en évidence : 1) le fait que les flavonols constitutifs des feuilles de V. vinifera retardent le développement de l'infection par P. viticola; et 2) le fait que les acides hydroxycinnamiques constitutifs ne semble pas participer à la défense contre P. viticola. Enfin, une nouvelle méthode de diagnostic non-destructive du mildiou sur feuille basée sur l'autofluorescence des stilbènes a été développée. Elle a montré une détection pré-symptomatique du mildiou sur les feuilles de vigne entières dès le premier jour après l'infection sur la face abaxiale et le troisième jour sur la face adaxiale. Cette méthode de diagnostic du mildiou a été validée au laboratoire notamment grâce à un prototype de capteur proximal développé en collaboration avec la société Force-A. La validation de la méthode au vignoble dans le cadre d'infection naturelle est la prochaine étape pour une utilisation de ce capteur optique dans le cadre de l'agriculture durable et de la sélection variétale.

Quality protein maize (QPM) has high nutritional value, but production is threatened by downy mildew (DM) and maize streak virus disease (MSVD) among other constraints. There are few studies of DM and MSVD resistance in QPM cultivars. The objective of this study was to improve resistance to DM and MSVD in three QPM populations. This was realized through ascertaining farmers’ key production constraints and special preferences for cultivars; determining the utility of recurrent selection method for improvement of three QPM populations (SussumaS2, ZM521Q and Pop62SRQ); and determining grain yield potential. The study was conducted in Mozambique for DM and in Zimbabwe for MSV, during 2003 to 2006. Surveys were conducted in Manica and Angonia districts in Mozambique to ascertain farmers’ perceptions and preferences for maize varieties, especially QPM. Participatory rural appraisal tools that included semi-structured questionnaires and focus group discussions were used to collect data. Results showed that farmers predominantly grew open pollinated varieties and fewer normal maize hybrids (non-QPM), and grain yield was estimated to be very low (0.2 to 0.6 t ha-1). Results showed that drought and insect pests were the dominant constraints to maize productivity in Mozambique, while diseases were ranked third. Downy mildew disease and MSVD were considered to be the most important diseases reducing maize productivity. Farmers also showed high preference for high yielding and early maturity cultivars in all areas. Predominantly, farmers were still using their local landraces because of sweet taste, particularly for home consumption and flint grain for storage. Farmers’ access to improved cultivars was limited due to high seed prices on the local market. Research priorities as perceived by the farmers included breeding for resistance to drought, grain weevils and diseases and sweetness. Generally, farmers showed little knowledge of QPM varieties and the importance of this trait, but they observed that the few QPM varieties they knew had some weaknesses such as poor storability and susceptibility to DM and MSVD which required improvement. These results should be considered in breeding new cultivars, both normal and QPM. To improve DM and MSV disease resistance in QPM varieties, S1 recurrent selection was conducted in three QPM populations, Sussuma, ZM521Q and Pop62SRQ at Umbeluzi Research Station in Mozambique and at CIMMYT-Harare Research Quality protein maize (QPM) has high nutritional value, but production is threatened by downy mildew (DM) and maize streak virus disease (MSVD) among other constraints. There are few studies of DM and MSVD resistance in QPM cultivars. The objective of this study was to improve resistance to DM and MSVD in three QPM populations. This was realized through ascertaining farmers’ key production constraints and special preferences for cultivars; determining the utility of recurrent selection method for improvement of three QPM populations (SussumaS2, ZM521Q and Pop62SRQ); and determining grain yield potential. The study was conducted in Mozambique for DM and in Zimbabwe for MSV, during 2003 to 2006. Surveys were conducted in Manica and Angonia districts in Mozambique to ascertain farmers’ perceptions and preferences for maize varieties, especially QPM. Participatory rural appraisal tools that included semi-structured questionnaires and focus group discussions were used to collect data. Results showed that farmers predominantly grew open pollinated varieties and fewer normal maize hybrids (non-QPM), and grain yield was estimated to be very low (0.2 to 0.6 t ha-1). Results showed that drought and insect pests were the dominant constraints to maize productivity in Mozambique, while diseases were ranked third. Downy mildew disease and MSVD were considered to be the most important diseases reducing maize productivity. Farmers also showed high preference for high yielding and early maturity cultivars in all areas. Predominantly, farmers were still using their local landraces because of sweet taste, particularly for home consumption and flint grain for storage. Farmers’ access to improved cultivars was limited due to high seed prices on the local market. Research priorities as perceived by the farmers included breeding for resistance to drought, grain weevils and diseases and sweetness. Generally, farmers showed little knowledge of QPM varieties and the importance of this trait, but they observed that the few QPM varieties they knew had some weaknesses such as poor storability and susceptibility to DM and MSVD which required improvement. These results should be considered in breeding new cultivars, both normal and QPM. To improve DM and MSV disease resistance in QPM varieties, S1 recurrent selection was conducted in three QPM populations, Sussuma, ZM521Q and Pop62SRQ at Umbeluzi Research Station in Mozambique and at CIMMYT-Harare Research. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2007.

La vigne est soumise à la pression de nombreux bioagresseurs dont des parasites obligatoires tels que l’oïdium et le mildiou. La lutte contre les maladies causées par les pathogènes biotrophes nécessite une utilisation souvent intensive de fongicides. Le vignoble consomme à lui seul 16% des fongicides commercialisés chaque année en France. Pour réduire leur impact environnemental qui conduit à l’acquisition de la résistance aux pesticides des pathogène et la présence de résidus dans les vins et dans l’atmosphère, des efforts doivent être entrepris pour développer des stratégies de protection innovante de remplacement ou complémentaire permettant de réduire les intrants pesticides.Les stimulateurs des défenses des plantes permettent de limiter le développement des bioagresseurs en conditions contrôlées. Toutefois, leurs efficacités in natura sont variables et souvent décevantes. Suite au grand nombre de produits potentiellement stimulateurs des défenses des plantes, et à l’intérêt que leur portent les viticulteurs, il est nécessaire de disposer de connaissances et d’outils qui permettent d’évaluer leus efficacités et mieux connaitre leurs potentiels de protection du vignoble. Pour ce faire, une méthode d’évaluation de l’efficacité de produits potentialisateurs ou éliciteurs a été développée au niveau biologique, moléculaire (expression de gènes impliqués dans les défenses) et biochimique (analyses qualitatives et quantitatives des polyphénols), nommée "BioMolChem". Cette méthode a permis d’évaluer l’efficacité de deux phosphonates et d’un analogue de l’acide salicylique, sur différents génotypes et phénotypes de mildiou de la vigne et d’oïdium. Cette approche méthodologique "BioMolChem" a permis d’établir des corrélations entre l’expression de gènes de défense, la présence de certains stilbènes et une efficacité des défenses de Vitis vinifera cv. Cabernet-Sauvignon vis-à-vis de l’oïdium et du mildiou. Les modifications des patrons d’expression des 19 gènes suivis dans les feuilles de vigne et les profils HPLC de polyphénols révèlent des mécanismes de défense multigéniques et complexes. Ainsi, les réactions de défense de la plante sont-elles modulées, en fonction de l’éliciteur considéré, mais aussi en fonction de la diversité phénotypique et génétique des agents pathogènes contre lesquels elle se défend. Ces défenses se caractérisent par une sur-expression d’un ensemble de gènes de défense et une accumulation de composés phénoliques spécifiques.Les marqueurs (gènes et molécules) ainsi identifiés, la méthode "BioMolChem" a été appliquée in natura et a conforté, pour partie, les résultats obtenus au laboratoire. Dans des conditions de fortes pressions parasitaires, il est donc possible de protéger les feuilles et les grappes, à l’aide de SDP et des essais d’association ou d’alternance avec des fongicides conventionnels montrent l’intérêt potentiel de l’emploi des SDP au vignoble. Chemin faisant, dans le cadre d’une viticulture innovante et durable, les SDP et la méthode "BioMolChem" ont été appliqués sur des génotypes hybrides (Vitis vinifera x Muscadinia rotundifolia). Nous révélons que selon le niveau de résistance intrinsèque des génotypes (plus ou moins résistants à l’oïdium et au mildiou), il est possible d’augmenter le niveau de la résistance exprimée par élicitation. Ainsi, les SDP pourraient-ils s’avérer des alliés d’intérêt pour l’utilisation de variétés partiellement résistantes et limiter potentiellement le contournement des QTL de résistance. L’ensemble de ce travail, à but appliqué, a conduit à l’obtention de résultats qui nous permettent de mieux comprendre comment la vigne réagit aux SDP dans son environnement agronomique. Leur exploitation et leur finalisation devraient nous permettre d’exploiter et de mettre en place une utilisation des éliciteurs mieux adaptée, à des stratégies alternatives ou complémentaires de la gestion des bioagresseurs de la vigne. / Powdery (Erysiphe necator) and downy mildew (Plasmopara viticola) are very important grapevine diseases (Vitis vinifera). These two biotrophic pathogens, which are native to the United States, infect green vine tissues and cause significant economic loss as well as environmental damage through the repetitive applications of fungicides. To reduce their environmental impact efforts should be made to develop strategies to protect innovative alternative or complementary to reduce pesticide inputs.In this study, the efficacy and the role of Benzothiadiazole (BTH), a salicylic acid analogue, and two phosphonate derivatives strengthen plant defence mechanisms against various isolates of downy and powdery mildews (Plasmopara viticola and Erysiphe necator). These compounds showed differences in their efficacy depending on the variability of mildews and highly dependent on plant genetics, environmental conditions and selection pressure. The plant defense stimulation could be an alternative or additional method to traditional pest management in the grapevine.Tools “BioMolChem” were developed to better assess the defence status of the plant defences in vitro and in natura. Transcript kinetics of selected defence-related genes and polyphenol contents profiles, during Vitis vinifera-biotrophic pathogen interaction, were characterized, and the impact of pathogen diversity was investigated in the absence or presence of elicitation. In vineyard, under strong pathogen pressures, it is thus possible to protect leaves and clusters, with SDP and assays of association or alternation with conventional fungicides show the potential interest of the use of these SDP in the vineyard.The grapevine defense mechanisms are complex, depending on the elicitor, leading to the coordinated accumulation of pathogenesis-related proteins (PR), the production of phytoalexins, and the reinforcement of plant cell walls.On the way, within the framework of an innovative and sustainable viticulture, the SDP was applied to hybrid genotypes (V. vinifera x M. rotundifolia). We reveal that according to the level of intrinsic resistance of the genotypes (more or less resistant to powdery and to downy mildew), it is possible to increase the level of the expressed resistance. The SDP could become allies of interest in the use of partially resistant grapevine varieties.The present findings provide insights into the potential use of transcripts and stilbenes as markers of the defense status of grapevine leaves with or without elicitation or infection, which should allow us to exploit and develop a better use of elicitors in alternative or complementary strategies in grapevine pest management.