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International audience; Horses are gregarious and fearful animals that undergo many stressful situations by humans. Simple and soft means are needed to manage their stress. This study was set up to investigate the relaxing effects of some EO on horses. The calming and soothing effects of Lavender (Lavandula angustifolia Mill.) essential oil (LaEO) have been widely demonstrated. The LaEO mode of action is essentially due to two major active molecules: linalool and linalyl acetate. The objective of this study was to develop an experimental protocol to highlight the effects of EO on equine stress response and to validate the effects of LaEO applied ante stress. Twenty-eight Welsh fillies were divided into two groups: one treated with 2 ml of vegetable oil (control), the other treated with 10% LaEO applied with a roll-on around the nostrils. The fillies were subjected to a series of tests of 30 min during which the heart rate (HR) and different behavioral indicators of stress were noted. Salivary cortisol was also measured. Indicators of stress such as HR, alert postures and defecations measured during some tests are significantly lower in the LaEO group than in the control group. These results and salivary cortisol content show that the application of LaEO reduced the level of stress of animals placed in stressful situations. Furthermore, blood samples taken from 6 horses show that the pharmacokinetics of linalool in plasma presented a peak 20 min after LaEO application, agreeing with the effect of LaEO during the tests. In addition, a peak of antioxidant effectiveness appeared in the plasma 50 min after LaEO application. These data should encourage the use of this protocol with LaEO in further studies to optimize the effective dose, and possibly to assess other EO which could help horses to manage stressful situations.

International audience; The need for environmentally friendly practices in animal husbandry, in conjunction with the reduction of the use of synthetic chemicals, leads us to reconsider our agricultural production systems. In that context, grassland secondary metabolites (GSMs) could offer an alternative way to support to livestock health. In fact, grasslands, especially those with high dicotyledonous plant species, present a large, pharmacologically active reservoir of secondary metabolites (e.g., phenolic compounds, alkaloids, saponins, terpenoids, carotenoids, and quinones). These molecules have activities that could improve or deteriorate health and production. This Review presents the main families of GSMs and uses examples to describe their known impact on animal health in husbandry. Techniques involved for their study are also described. A particular focus is put on antioxidant activities of GSMs. In fact, numerous husbandry pathologies, such as inflammation, are linked to oxidative stress and can be managed by a diet rich in anti-oxidants. The different approaches and techniques used to evaluate grassland quality for livestock health highlight the lack of efficient and reliable technics to study the activities of this complex phytocoektail. Better knowledge and management of this animal health resource constitute a new multidisciplinary research field and a challenge to maintain and valorize grasslands.

International audience; Plant response to their environment stresses is a complex mechanism involving secondary metabolites. Stilbene phytoalexins, namely resveratrol, pterostilbene, piceids and viniferins play a key role in grapevine (Vitis vinifera) leaf defense. Despite their well-established qualities, conventional analyses such as HPLC-DAD or LC-MS lose valuable information on metabolite localization during the extraction process. To overcome this issue, a correlative analysis combining mass spectroscopy imaging (MSI) and fluorescence imaging was developed to localize in situ stilbenes on the same stressed grapevine leaves. High-resolution images of the stilbene fluorescence provided by macroscopy were supplemented by specific distributions and structural information concerning resveratrol, pterostilbene, and piceids obtained by MSI. The two imaging techniques led to consistent and complementary data on the stilbene spatial distribution for the two stresses addressed: UV-C irradiation and infection by Plasmopara viticola. Results emphasize that grapevine leaves react differently depending on the stress. A rather uniform synthesis of stilbenes is induced after UV-C irradiation, whereas a more localized synthesis of stilbenes in stomata guard cells and cell walls is induced by P. viticola infection. Finally, this combined imaging approach could be extended to map phytoalexins of various plant tissues with resolution approaching the cellular level.

Simple and soft means are needed to manage horse stress. For instance, essential oils such as lavender oil contain active principles that may mitigate stress responses in humans and animals. Here we developed a protocol to test the effects of essential oil on equine stress response. We tested the effect of lavender oil on horse stress. Twenty-eight Welsh horse fillies were divided into two groups: horses treated with a roll-on with 2 mL of vegetable oil (control) and horses treated with 2 mL of 10% lavender essential oil in vegetable oil. Horses were then subjected to a series of stress tests. Heart rates and stress behavioral indicators were monitored during the 30 min of the stress tests. Saliva was collected. Blood from six horses was sampled after lavender essential oil application to follow plasma linalool content and antioxidant efficiency. Results show that stress indicators such as heart rate, alert postures and defecations are lower in lavender oil-treated horses. Lavender essential oil also modified salivary cortisol. Pharmacokinetics of linalool in plasma displayed a peak 20 min after lavender essential oil application, thus confirming the effect of lavender oil. Overall, our findings demonstrate that lavender essential oil reduces the response to stress of horses placed in stressful situations.; Des moyens simples et doux sont nécessaires pour gérer le stress du cheval. Par exemple, les huiles essentielles telles que l'huile de lavande contiennent des principes actifs qui peuvent atténuer les réactions au stress chez les humains et les animaux. Ici, nous avons développé un protocole pour tester les effets de l'huile essentielle sur la réponse au stress équin. Nous avons testé l'effet de l'huile de lavande sur le stress du cheval. Vingt-huit pouliches galloises ont été divisées en deux groupes: les chevaux traités avec un rouleau avec 2 mL d'huile végétale (témoin) et les chevaux traités avec 2 mL d'huile essentielle de lavande à 10% dans de l'huile végétale. Les chevaux ont ensuite été soumis à une série de tests de résistance. Les rythmes cardiaques et les indicateurs comportementaux de stress ont été suivis pendant les 30 min des tests de résistance. La salive a été recueillie. Le sang de six chevaux a été prélevé après application de l'huile essentielle de lavande pour suivre la teneur en linalol plasmatique et l'efficacité antioxydante. Les résultats montrent que les indicateurs de stress tels que la fréquence cardiaque, les postures d'alerte et les défécations sont plus faibles chez les chevaux traités à l'huile de lavande. L'huile essentielle de lavande a également modifié le cortisol salivaire. La pharmacocinétique du linalol dans le plasma a montré un pic 20 min après l'application de l'huile essentielle de lavande, confirmant ainsi l'effet de l'huile de lavande. Dans l'ensemble, nos résultats démontrent que l'huile essentielle de lavande réduit la réponse au stress des chevaux placés dans des situations stressantes.

International audience; Accurate localization of phytoalexins is a key for better understanding their role. This work aims to localize stilbenes, the main phytoalexins of grapevine. The cellular localization of stilbene fluorescence induced by Plasmopara viticola, the agent of downy mildew, was determined in grapevine leaves of very susceptible, susceptible, and partially resistant genotypes during infection. Laser scanning confocal microscopy and microspectrofluorimetry were used to acquire UV-excited autofluorescence three-dimensional images and spectra of grapevine leaves 5-6 days after inoculation. This noninvasive technique of investigation in vivo was completed with in vitro spectrofluorimetric studies on pure stilbenes as their fluorescence is largely affected by the physicochemical environment in various leaf compartments. Viscosity was the major physicochemical factor influencing stilbene fluorescence intensity, modifying fluorescence yield by more than two orders of magnitude. Striking differences in the localization of stilbene fluorescence induced by P. viticola were observed between the different genotypes. All inoculated genotypes displayed stilbene fluorescence in cell walls of guard cells and periclinal cell walls of epidermal cells. Higher fluorescence intensity was observed in guard-cell walls than in any other compartment due to increased local viscosity. In addition stilbene fluorescence was found in epidermal cell vacuoles of the susceptible genotype and in the infected spongy parenchyma of the partially resistant genotype. The very susceptible genotype was devoid of fluorescence both in the epidermal vacuoles and the mesophyll. This strongly suggests that the resistance of grapevine leaves to P. viticola is correlated with the pattern of localization of induced stilbenes in host tissues.

Analysis of grapevine phytoalexins at the surface of Vitis vinifera leaves has been achieved by laser desorption/ionisation time-of-flight mass spectrometry (LDI-ToFMS) without matrix deposition. This simple and rapid sampling method was successfully applied to map small organic compounds at the surface of grapevine leaves. It was also demonstrated that the laser wavelength is a highly critical parameter. Both 266 and 337 nm laser wavelengths were used but the 266 nm wavelength gave increased spatial resolution and better sensitivity for the detection of the targeted metabolites (resveratrol and linked stilbene compounds). Mass spectrometry imaging of grapevine Cabernet Sauvignon leaves revealed specific locations with respect to Plasmopara viticola pathogen infection or light illumination.

International audience; Plasmopara viticola, the causal agent of grapevine downy mildew, is an obligate biotrophic oomycete that grows in the intercellular spaces of host tissues and develops haustoria in the cells. Histological observations are the most effective methods to visualize and quantify the development of the infection structures. We chose two staining techniques leading to high resolution and contrast between parasite structures and host-plant tissues with a minimum of sample preparation: Blankophor and KOH-aniline blue fluorescent stainings. Blankophor (50 ppm in water or 15% KOH) staining was used to study the zoospore encystement on the leaf surface after release from sporangia. The aniline blue dye (0.05% in 0.067 M K2HPO4, pH 9-9.5, after hot KOH whitening) was used to observe the invasive structures inside host tissues that lead to the production of sporangiophores and infectious sporangia. We tested modifications of some parameters of the procedures to determine the most appropriate for high throughput analyses adapted to our pathosystem and equipment facilities.

The alkaloids colchicine and colchicoside contained in meadow saffron (Colchicum autumnale L.) seeds are used, respectively, in drugs to treat gout and relax muscles. A two year study at two sites demonstrated the concentration and yields of these two seed constituents involves the transformation of colchicine into colchicoside during plant growth. The optimum harvest date for meadow saffron could be selected for the highest total alkaloid or colchicoside content and for the highest dry matter, and alkaloid yields. Differences in alkaloid yields and concentrations in different plant parts strongly suggest that alkaloids can be translocated in the plant.

International audience; Downy mildew is a major disease of grapevine caused by the oomycete Plasmopara viticola. It is at the origin of numerous fungicide treatments. In order to optimize these treatments and reduce their number, an early detection of the disease in the field is sought-after, preferably by non-destructive means for a precision agriculture approach. Stilbenes, the main phytoalexin of grapevine, are not present in healthy leaves. Their synthesis and accumulation is induced by P. viticola. They are fluorescent phenolic compounds, displaying violet-blue fluorescence (VBF). In the laboratory, VBF was used to assess stilbenes in vivo in grapevine leaves or as an indicator of the development of the infection by P. viticola. So, this fluorescence signal could potentially be used as a non-invasive proxy for the presence of downy mildew. A new portable sensor for stilbene VBF, Mx-330, was developed by the company FORCE-A (Orsay, France). The present study confirmed that this new sensor could be used in the vineyards to detect downy mildew. Thanks to its presence also on the adaxial leaf side, P. viticola-induced stilbene VBF is suitable for vehicle-mounted proximal sensing.

International audience; To investigate the in-situ response to a stress, grapevine leaves have been subjected to mass spectrometry imaging (MSI) experiments. The Matrix Assisted Laser Desorption/Ionisation (MALDI) approach using different matrices has been evaluated. Among all the tested matrices, the 2,5-dihydroxybenzoic acid (DHB) was found to be the most efficient matrix allowing a broader range of detected stilbene phytoalexins. Resveratrol, but also more toxic compounds against fungi such as pterostilbene and viniferins, were identified and mapped. Their spatial distributions on grapevine leaves irradiated by UV show their specific colocation around the veins. Moreover, MALDI MSI reveals that resveratrol (and piceids) and viniferins are not specifically located on the same area when leaves are infected by Plasmopara viticola. Results obtained by MALDI mass spectrometry imaging demonstrate that this technique would be essential to improve the level of knowledge concerning the role of the stilbene phytoalexins involved in a stress event.

A new, fast and reliable procedure for the quantification of the major compounds of Hypericum perforatum L. has been developed. Four naphthodianthrones (protopseudohypericin, pseudohypericin, protohypericin, hypericin) and two phloroglucinols (hyperforin, adhyperforin) were assayed by HPLC using a short (17 min) linear gradient, with hypericin and hyperforin as external standards. Extraction of dried plant material with methanol in the dark at room temperature for 2 h led to a complete recovery of phloroglucinols but only a partial recovery of the naphthodianthrone derivatives. Treatment of plant material with water:ethanol (40:60, v/v) in a water bath shaker at 80°C led to the total extraction of hypericins, but a 10% loss of total hyperforins was also observed. The two extraction methods, applied successively to the same sample, allowed the complete extraction of all compounds of interest. A 5 min exposure of the crude extract of H. perforatum to sunlight (1 E/m2) induced a 96% loss of hyperforins, whereas the dry plant material lost only 20% of hyperforins after 2 h exposure to sunlight (24 E/m2). Copyright © 2001 John Wiley & Sons, Ltd.

Meadow saffron (Cotchicum autumnale) is an undomesticated plant from whose seeds the alkaloids coichicine and colchicoside are extracteil and usai pharmaceutically. Research was conducted towards domesticating meadow saffron in which interand intns-genetic variability of accessions was studied. Colchicine, 3-dernethylcolchicine and colchicoside were assayed in plants of six accessions collected from natural sites in eastern Rance. These were cultivated at two sites ami studied during I or 2 yn Plants from 70 initial transplanted conns of one accession were studied individually for 4 yrto determined intra-accession variability and, as spontaneous vegetative multiplication of conus occurreil, comparisons arnong plants from one initial transplanted conn were also made. For the main characteristics, seed dry weïght (SDW) per plant, alkaloid content and colchicine:colcbicoside ratio, the inter- accession variability was Iower than die infra-accession variability. The results suggest that vegetative propagation of sclected genotypes could isnprnve alkaloid content by about 80% and improve SDW per plant by about 300%., Le colchique (Colchicwn autunznale) est une plante à alcaloïdes non domestiquée. La colchicine et le colchicoside extraits des graines sont utilisés dans plusieurs médicaments. Un programme de recherche a été développé pour domestiquer cette plante et produire des graines pour l’industrie pharmaceutique. La variabilité inter et infra origine(s) de caractères agronomiques et chimiques aété étudiée. La colchicine, la 3-demethylcolchicine et te colchicoside ont été dosés en chromatographie en phase liquide. Six origines ont été prélevées sur des sites naturels & l’Est & la Fiance et cultivées sur deux sites pendant un ou deux ans. Des plantes provenant de soixante dix connus repiqués ont été étudiées individuellement pendant quatre ans en vue d’évaluer la variabilité lutin origine. Du fait de la multiplication végétative spontanée de certains connus, une comparaison entre plusieurs plantes issues d’un connus a été possible. La variabilité inter origines était moins élevée que la variabilité infra origine pour les principaux caractères étudiés. La multiplication végétative des génotypes sélectionnés pourrait améliorer la teneur en alcaloïdes d’environ 80% et le rendement en poids sec de graines par plante de 300%. Des recherches sur la micropropagation de cette plante doivent être entreprises afin de cultiver des génotypes à haut potentiel.

International audience; Grapevine is of worldwide economic importance due to wine production. However, this culture is often affected by pathogens causing severe harvest losses. Understanding host-pathogen relationships may be a key to solve this problem. In this paper, we evaluate the direct flow injection by electrospray - Fourier transform ion cyclotron resonance mass spectrometry (MS) of leaf extracts as a rapid method for the study of grapevine response to downy mildew (Plasmopara viticola) attack. The comparison of MS profiles obtained from control and infected leaves of different levels of resistant grapevines highlights several classes of metabolites (mainly saccharides, acyl lipids, hydroxycinnamic acids derivatives and flavonoids) which are identified using high resolution MS and tandem MS (MS/MS). Statistical analyses of 19 markers show a clear segregation between inoculated and healthy samples. This study points out relative high levels of disaccharides, acyl lipids and glycerophosphoinositol in inoculated samples. Sulfoquinovosyl diacylglycerols also emerge as possible metabolites involved in plant defense.

National audience

National audience

International audience; A 15-day survey of autofluorescence has been conducted upon infection by downy mildew [Plasmopara viticola (Berk. & M.A. Curtis) Berl. & de Toni] of leaves of a susceptible grapevine genotype. Different autofluorescence signals were followed from the cellular to the whole-leaf level by using four types of devices for fluorosensing: a macroscope, a spectrofluorimeter, a portable field optical sensor (the Multiplex 3), and a field fluorescence sensor prototype with 335 nm excitation. It was shown for the first time, by the three different techniques and at three different scales, that the stilbene-dependent violet-blue autofluorescence (VBF) had a transitory behaviour, increasing to a maximum 6 days post-inoculation (DPI) and then decreasing to a constant lower level, nevertheless significantly higher than in the control leaf. This behaviour could be sensed from both sides of the leaf. On the abaxial side, VBF could discriminate the presence of infection from 1 DPI, and on the adaxial side from 3 DPI. There was a constant increase in blue-excited green fluorescence starting from 8 DPI, concomitant with a decrease in leaf chlorophyll content sensed by one reflectance and two fluorescence indices available on the Multiplex 3 sensor. These results show that a pre-symptomatic and symptomatic sensing of downy mildew is possible by autofluorescence-based sensors, and this is potentially applicable in the field.

International audience; Flavonols and hydroxycinnamic acids are known to contribute to plant resistance against pathogens, but there are few reports on the implication of flavonols in the resistance of grapevine against Plasmopara viticola, and none on the involvement of hydroxycinnamic acids. In order to analyze the effect of flavonols on P. viticola infection, variable amounts of flavonols were induced by different light conditions in otherwise phenologically identical leaves. Differences in content of leaf hydroxycinnamic acids were induced at the same time. A non-invasive monitoring of flavonols and hydroxycinnamic acids was performed with Dualex leaf-clip optical sensors. Whatever the light condition, there were no significant changes in flavonol or in hydroxycinnamic acid contents for control and inoculated leaves during the development of P. viticola until 6 days after inoculation. The violet-blue autofluorescence of stilbenes, the main phytoalexins of grapevine that accumulate in inoculated leaves, was used as an indicator of infection by P. viticola. The implication of leaf constitutive flavonols and hydroxycinnamic acids in the defence of Vitis vinifera against P. viticola could be investigated in vivo thanks to this indicator. The increase in stilbene violet-blue autofluorescence started earlier for leaves with low flavonol content than for leaves with higher content, suggesting that constitutive flavonols are able to slow down the infection by P. viticola. On the contrary, constitutive hydroxycinnamic acids did not seem to play a role in defence against P. viticola. The non-destructive nature of the methods used alleviates the major problem of destructive experiments: the large variability in leaf phenolic contents.

International audience

International audience

International audience

International audience; The current strategy to control grapevine downy and powdery mildew relies on chemical treatments. An alternative solution to the use of chemicals is the development of varieties resistant to pathogens. Therefore a program to create new grapevine varieties with a durable resistance to downy and powdery mildew and with a berry quality suitable for high quality wine production was launched in 2000. The situation seemed very favourable to start up such a program: plenty of resistance sources were available, and several resistance QTLs with various effects had already been discovered. Nevertheless a first case of downy mildew resistance breakdown was described in the cultivar 'Bianca'. Even if resistance durability is a retrospective judgment, some principles can be considered to monitor the risk of resistance breakdown: pyramiding resistance genes, taking into account the evolutionary potential of the pathogen or assessing the cost of virulence, from a practical point of view, a durable management of resistance meaning to reduce the selection pressure applied by the resistance genes on the pathogen population. Therefore we chose to use multiple sources of resistance as genitors. The genetic determinism of most of them was analysed and the molecular markers derived from these studies were quickly integrated to assist with selection. Concerning the shortening of the breeding process, we developed a greenhouse growing method allowing to go from seed to seed in one year and a resistance phenotyping platform to get the precise plant phenotype as early as possible in the process. Moreover all the field trials have been performed through an experimental network, which allows us to save time and to take into account the differences in environment conditions. The overall process of selection is organized into three steps and takes 16 years. We expect to propose our first varieties for registration in 2016.

International audience

International audience

International audience; Secondary metabolites are known to be involved in the interaction between plants and pathogens (1). Some of them are highly suspected to contribute to resistance against fungi, such as stilbenes (2, 3). Stilbenes are the main phytoalexins in grapevine (4). Downy mildew (Plasmopara viticola, Oomycetes) causes huge damage in vineyards. So the creation of new varieties is expected to reduce phytochemical applications. These varieties will be obtained by the pyramiding of complementary resistance genes. Thereby, a better knowledge of the effect of these genes on the plant response is important to acquire. Two populations derived from the American species Muscadinia rotundifolia and previously phenotyped for their resistance to downy mildew were studied for their ability to synthesize stilbenes. The first population called 41528 possesses two major resistance genes: Rpv1 which slows down the progression of the pathogen in the leaves and Rpv2 which blocks it at a very early stage. The second population 41524 contains only Rpv1. Mocked and inoculated leaves were studied on about 100 genotypes of each the two populations. One to three plants were studied per genotype. Leaves of level 5 (level 1 corresponded to the first spread leaf at the top of the stem) and 6 were harvested. Level 6 was inoculated with Plasmopara viticola. Leaf discs were sampled at 4 days post infection (dpi) and 5 dpi then extracted with MeOH at 60°C. Stilbenes (piceid cis and trans, resveratrol, viniferins delta and epsilon, pterostilbene) were analyzed with HPLC-DAD and in some cases with HPLC-mass spectrometry (MS-MS). The sum of 6 stilbenes and pterostilbene contents were highly correlated between 4 and 5 dpi (R2 respectively of 0.7 and 0.84); showing a linear activity of stilbene synthase and O-methyl transferase after infection during that period. Quantitative trait loci (QTL) were found for the different molecules studied. In population 41528, a stilbene synthesis QTL found on chromosome 18 co-segregated with Rpv2. Nevertheless, stilbene contents were higher in susceptible genotypes than in the resistant ones. In contrast, in population 41524, a stilbene synthesis QTL co-segregated on chromosome 12 with Rpv1 and their syntheses were positively correlated with the level of resistance.(5)

International audience; Analysis of grapevine phytoalexins at the surface of Vitis vinifera leaves has been achieved by laser desorption/ionisation time-of-flight mass spectrometry (LDI-ToFMS) without matrix deposition. This simple and rapid sampling method was successfully applied to map small organic compounds at the surface of grapevine leaves. It was also demonstrated that the laser wavelength is a highly critical parameter. Both 266 and 337 nm laser wavelengths were used but the 266 nm wavelength gave increased spatial resolution and better sensitivity for the detection of the targeted metabolites (resveratrol and linked stilbene compounds). Mass spectrometry imaging of grapevine Cabernet Sauvignon leaves revealed specific locations with respect to Plasmopara viticola pathogen infection or light illumination. Copyright © 2010 John Wiley & Sons, Ltd.

Analysis of grapevine phytoalexins at the surface of Vitis vinifera leaves has been achieved by laser desorption/ionisation time-of-flight mass spectrometry (LDI-ToFMS) without matrix deposition. This simple and rapid sampling method was successfully applied to map small organic compounds at the surface of grapevine leaves. It was also demonstrated that the laser wavelength is a highly critical parameter. Both 266 and 337 nm laser wavelengths were used but the 266 nm wavelength gave increased spatial resolution and better sensitivity for the detection of the targeted metabolites (resveratrol and linked stilbene compounds). Mass spectrometry imaging of grapevine Cabernet Sauvignon leaves revealed specific locations with respect to Plasmopara viticola pathogen infection or light illumination.

Objectif : L’objectif de ce travail est d’étudier la distribution spatiale et la cinétique de synthèse des stilbènes dans les feuilles de vigne. Ces molécules fortement fluorescentes sont considérées comme étant les principales phytoalexines de la vigne. Méthodes et résultats : Deux techniques complémentaires ont été utilisées pour étudier la synthèse des stilbènes. D’une part, par l’analyse directe de la fluorescence sur les feuilles ce qui permet une évaluation globale de la teneur en stilbènes sur 1,6 mm2 et d’autre part en chromatographie en phase liquide, méthode précise et fiable. Cette dernière technique est longue et nécessite environ 1 cm2 de feuille. Cette étude a été menée sur différents génotypes de vigne cultivés en serre. Conclusion : Les teneurs en stilbène mesurées en HPLC sont fortement corrélées à la fluorescence spécifique des stilbènes. La fluorescence mesurée sur la même surface abaxiale d’une feuille augmente linéairement durant au moins cinq jours après inoculation. Cependant, l’intensité de la fluorescence varie selon la feuille étudiée et n’est pas distribuée de façon homogène sur la face abaxiale de la feuille. Signification et impact de l'étude : Ces résultats montrent que la mesure de la fluorescence des stilbènes in vivo est une méthode efficace, rapide et non destructive permettant d’évaluer la teneur en stilbène dans les feuilles de vigne., Aim: This work aimed at studying the spatial distribution of stilbenes in grapevine leaves of different genotypes and to determine their time course of synthesis. These highly fluorescent molecules are considered as the main phytoalexin in grapevine. Methods and results: Two complementary techniques were used to study the synthesis of stilbenes. On the one hand, direct fluorescence of leaves that allowed local evaluation of stilbenes content on 1.6mm2, and, on the other hand, a well known precise and accurate method: high performance liquid chromatography. The latter is time consuming and requires extraction of about 1 cm2 of leaf. This study was performed on different grapevine genotypes cultivated in greenhouse. Conclusion: Stilbenes content measured by HPLC was highly correlated to the specific fluorescence of stilbene. Fluorescence measured on the abaxial side of the same leaf area increased linearly at least during five days after inoculation. Nevertheless, fluorescence intensity varied depending on the leaf studied and stilbenes are not homogeneously distributed on the abaxial side of the leaf. Significance and impact of study: The results showed that in vivo stilbene fluorometry is an efficient, fast and non destructive tool to evaluate stilbene content of grapevine leaf.

International audience