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In table grapes (cv. Thomson Seedless), the antifungal activity against Botrytis cinerea was further analysed and compared between two high potential bacterial biological control agent (BCA) strains, Bacillus velezensis BUZ-14 and B. ginsengihumi S38. Two commercial biocontrol products (BPs), served as standards of comparison, Amylo-X® and Serenade Max®, also based on Bacillus BCA strains. The main mode of action quantified for all the strains was antibiosis due to hydrosoluble and volatile metabolites and their combinations. The BUZ-14 strain was the most active BCA strain, demonstrating significant disease reduction exceeding 60 % when used in the culture form grown in 863 medium, including living cells (LCs) and cell-free supernatant (CFS). Both BPs exhibited significantly reduced efficacy of their CFS fraction (< 10 %) compared with that of the two BCA strains, confirming their high antibiosis potential. The novel methodology allowed us to demonstrate the significant effect of the BCA culture medium on volatilome (VOC) antagonist efficacy. The S38 strain achieved the highest disease reduction (90 %) owing to the greatest production of VOCs in the richest MOLP (Medium Optimum Lipopetide Production) culture medium, whereas grape juice was the least favourable medium for VOC efficacy for both bacterial strains (BUZ14 and S38). The overall poor activity of living Bacillus cells in all the BCA and BPs tested is discussed based on the low capacity of the BCA strains to grow in the berry. Then, the presence of living cells is also discussed with the possibility that these cells are not required in field applications of such BCA strains in this genus. Moreover, different environmental suboptimal conditions, including temperature (22 and 27 °C) and relative humidity (RH) (100 and 85–95 %), were tested, and BUZ-14 exhibited the highest Botrytis reduction at both temperatures and RH values. However, no significant differences were observed between temperatures or RH values for the same BCA. Further studies in vineyard conditions and applications, such as biofumigation or active packaging, will be performed to confirm the new findings reported in this investigation.

The contamination of grape berries by Botrytis cinerea can drastically damage wine quality, in particular causing colour degradation. In musts obtained from botrytised grapes, SO2 addition is the main means of avoiding oxidation damage due to laccases excreted by the pathogen. However, consumers are becoming increasingly reluctant to accept SO2 addition to wine. Oenological tannins are used for fining wines because of their colloidal properties, and for wine colour stabilisation due to their ability to condense with anthocyanins. They are also known for their antioxidant and antioxidasic properties. They were thus investigated in the present study for their potential as an alternative to SO2 against laccase oxidation.The impact of various types of oenological tannins on musts and wines was studied once added to musts obtained from the Merlot cultivar, comprising 20 % and 50 % botrytised grapes. Laccase activity, antioxidant capacity, composition of phenolic compounds, spectrophotometric and CIELAB colour parameters were assessed in the musts and wines. Sensory analyses were also performed on 3-month-old wines to evaluate the visual, olfactory and gustative consequences of tannin addition. At a 50 % botrytisation rate, the addition of any type of oenological tannins (at a concentration of 100 g/hL) had no effect on laccase activity and did not protect phenolic compounds. However, at the same concentration and at a 20 % botrytisation rate, proanthocyanidin tannins from grape skin were found to be the most promising tannins with simultaneous protective effects, such as an inhibitory effect on laccase enzymes, protection of colour from complete degradation and preservation of some procyanidin compounds.Oenological tannins are promising candidates for protecting wines from Botrytis damage and they induce a differential effect according to their origin and structure. They could be used to reduce the amount of SO2 that is added during vatting. More research is needed to confirm and better understand the mode of action of various tannins at levels lower than the 20 % botrytised rate tested in the present study.

Onologische Tannine werden aus unterschiedlichen Grunden in der Weinherstellung verwendet (Versari et al., 2013; Vignault et al., 2018), insbesondere jedoch wegen ihrer hemmenden Eigenschaften gegenuber der Aktivitat der Laccase. Die Verwendung ist besonders in denjenigen Jahrgangen sinnvoll, die von der Botrytis-Traubenfaule betroffen sind, um die Weine vor Braunfarbung zu schutzen. Dieser Anti-Laccase-Effekt der Tannine beruhte bis vor Kurzem nur auf Beobachtungen, ohne wissenschaftliche Beweise. Die OIV hatte aus diesem Grund eine spezielle Arbeitsgruppe gegrundet, die sich mit der praktischen Anwendung onologischer Tannine beschaftigt. Die Ergebnisse dieser Untersuchungen werden in diesem Artikel vorgestellt und zeigen die Effektivitat, mit der onologische Tannine die Laccaseaktivitat inhibieren und somit die Farbe der Weine schutzen (Vignault et al., 2019; Vignault et al., 2020).

Stem end rot (SER) caused by Botrytis cinerea is the primary postharvest disease in the Chilean kiwifruit industry. Relationships between the postharvest occurrence of SER in ‘Hayward’ kiwifruit and the temporal dynamics of earlier B. cinerea colonization of the floral parts (petals, sepals, receptacles, styles) was studied in five orchards over two consecutive seasons in Chile. Weather conditions in the first season favored B. cinerea infection with roughly constant colonization of floral parts up to about 120 days after full bloom, but colonization then increased up until harvest. In the second season, colonization was roughly constant throughout. Latent infections of the fruit occurred in both seasons but were high in the first season and low in the second. Incidence of latent infections at harvest were the best predictors (r > 0.8) of postharvest SER. The number of preharvest infection periods calculated using temperature, leaf wetness, and relative humidity satisfactorily predicted SER incidence by an exponential model, R2 = 0.90, P < 0.001. Results indicated environmental variables play key roles in the temporal dynamics of B. cinerea colonization. Quantification of latent B. cinerea infections in asymptomatic fruit close to harvest, is a practicable way to predict later incidence of SER during storage.

Stem end rot (SER) caused by

International audience; The dual performance, both economic and environmental, is a major challenge for the wine industry, which remains highly dependent on the use of pesticides. Fungicide control alone accounts for 80% of inputs in France. A DSS (DeciTrait®) gathering all the information necessary for the implementation of a low pesticides protection against the main fungal diseases (downy mildew - powdery mildew - black-rot - grey mould) was conceived in a collaborative approach within a CASDAR project. This DSS is easy to use and offers the user a protection strategy at the plot level based on the information and knowledge collected. The bioassays carried out within the CASDAR project clearly demonstrate the potential for reduction of phytosanitary inputs allowed by this DSS, for reducing both the number of treatments and the dose applied.; La double performance, économique et environnementale, constitue un enjeu majeur pour la filière viticole qui demeure très dépendante de l’utilisation des pesticides. A elle seule, la lutte fongicide représente 80% des intrants. Un OAD (DeciTrait®) regroupant l’ensemble des informations nécessaires à la mise en œuvre d’une protection économe en intrants vis-à-vis des principales maladies cryptogamiques (mildiou - oïdium - black-rot - botrytis) a été conçu dans une démarche collaborative ausein d’un projet CASDAR. Cet OAD est simple à utiliser et propose à l’utilisateur une stratégie de protection personnalisée sur la base des informations et connaissances recueillies. Les essais biologiques conduits au sein du projet CASDAR mettent clairement en évidence le potentiel deréduction des intrants phytosanitaires permis par cet OAD, tant sur la réduction du nombre de traitements que sur la dose appliquée.

Botrytis bunch rot (BBR) is a major disease occurring in vineyards worldwide. Its control is still largely based on the use of synthetic fungicide sprayings at predetermined intervals, which often produces negative residues in grapes and wines that may affect the environment and/or human health. To rationalize BBR management, disease risk indicators were developed and evaluated in a set of field experiments carried out between 2010 and 2019 in France and Chile. Key indicators include early grapevine vegetative growth, i.e. ground-based normalized difference vegetation index (NDVI), and the potential berry susceptibility to Botrytis cinerea, which is driven by tannin content in the skin. Under these contrasting weather and cropping conditions, regression analyses, including weather information, showed a highly significant positive correlation between the early NDVI, measured at berry pea size stage, and BBR incidence or severity at harvest, whereas the opposite was demonstrated for tannin content in the berry skin measured at an early herbaceous fruit stage. The exponential relationship between the final disease severity and the early NDVI allowed us to identify a possible threshold NDVI value, i.e. between 0.5 and 0.6, under which the BBR severity should be lower or close to 5% at harvest (BBR tolerance threshold for wine quality). Accordingly, in a leaf-removal vineyard experiment in France, the NDVI level at berry pea size stage was strictly controlled to correspond to three different increasing index values: 0.45, 0.60, and 0.78. Following this increase in NDVI, a significant increase in final BBR severity was noticeable, i.e. 2.4%, 6.6% and 9.9%, respectively. Very interestingly, the NDVI increase was also related to a significant decrease in the tannin content in the skin of herbaceous berries at veraison, from 47 to 22 mg tannin/g skin. All regression analyses explaining BBR development were highly significant, showing the weather conditions before harvest as the primary factor. They also show that some of the disease risk indicators chosen, especially early NDVI, could be used in the future as tools in decision support systems for deciding to spray and/or scheduling optimized fungicide applications during the season.

International audience; With only a few biocontrol products currently registered against Botrytis bunch rot (BBR) of grapes, there is a crucial need for new antagonistic strains that are able to survive and efficiently suppress B. cinerea under vineyard conditions. The aim of this study was to establish and follow a pre-selection process among potential antagonistic bacterial strains, previously identified in vivo for efficacy, and to carry out a further field screening assay using a reduced strain number. Ten bacterial strains were pre-selected and tested, in vitro and in vivo, to characterise their mode of action and population dynamics under simulated climatic regimes. Four candidate strains were then selected and characterised for high efficacy in vivo, known mode of action and marked survival ability. Some suitable additives for increasing strain adherence on grape berry surface were tested prior to field applications, indicating one commercial adjuvant for potential improved bacterial persistence in the field. The four strains were applied separately in an experimental Merlot vineyard near Bordeaux (SW France), either at five key phenological stages, or following a specially developed Disease Risk Index (DRI). The Bacillus ginsengihumi S38 strain treatments significantly reduced BBR incidence by 72-75% compared to the control, whereas sprays applied according to the DRI decision support system tended to improve disease control. The study validates a laboratory pre-selection process followed by a field screening step, resulting in a candidate B. ginsengihumi strain S38 with a high potential for BBR biocontrol and future development in vineyards.

International audience; The development of biological control agents (BCAs) is a promising and environmentally friendly method to control plant pathogens. In a grapevine nursery greenhouse and for the first time on grafted cuttings (scion cv. Cabernet sauvignon), this two-year study demonstrated the significant efficacy of the oomycete Pythium oligandrum as a BCA against two major aggressive fungal pathogens, Neofusicoccum parvum and Phaeomoniella chlamydospora, which are involved in grapevine trunk diseases (GTDs). By considering the reduction in necrosis lengths within the scion stem, treatments with P. oligandrum alone showed the greatest efficacy against the two pathogens (overall average efficacy of 48.3%). This major result was obtained during the two-year bioassay and in cuttings grafted on the two widely used rootstocks, 101-14 and SO4. The biocontrol efficacies of two bacterial strains previously isolated from vineyards, Pantoea agglomerans and Bacillus pumilus, were also assessed, separately or in combination with P. oligandrum. Treatments with each bacterial strain were less effective than treatments with P. oligandrum, and the efficacies were not improved when they were applied in combination with the oomycete.

Background and Aims The susceptibility of winegrape cultivars to Botrytis cinerea is a debated topic, and the available classifications are based on professional experience rather than on experimental data. The main aim of this study was to compare and classify the susceptibility of several winegrape cultivars to B. cinerea and its relation to fruit maturity under two contrasting climatic and cropping conditions. Methods and Results Between 2011 and 2015, three field trials were undertaken in Chile and France, including 13 common cultivars. Both the incidence and severity of the disease were evaluated at harvest, and indices of susceptibility and maturity were calculated on a per site basis. The significant difference in incidence and severity observed among cultivars led to a similar susceptibility classification in both countries. Cabernet Sauvignon, Cabernet Franc, Grenache Noir and Petit Verdot were the most resistant cultivars, whereas Gewurztraminer and Sauvignon Blanc were the most susceptible. Moreover, an exponential and positive relationship was established between indexes of susceptibility and maturity. Conclusions The classification of cultivars according to the susceptibility to B. cinerea was similar in both countries, despite the contrasting climatic conditions and cropping practices. Significance of the Study These findings might be of interest for choosing cultivars that are more resistant to B. cinerea to reduce the number of fungicide applications.

Botrytis bunch rot, caused by Botrytis cinerea, is an important fungal disease of grapevine with high economic importance in wine grape production and postharvest storage of table grapes. Biological control by antagonistic bacteria is a promising strategy for reducing the common use of synthetic fungicides to control this pathogen. A total of 45 bacterial strains, isolated from grapevine tissues in 'Bordeaux' vineyards were screened in vitro for their potential antifungal activity against two major vineyard subpopulations of B. cinerea, i.e., transposa and vacuma. These two transposon genotypes differ significantly in virulence on grape berries. The inhibitory effects of the bacterial strains on the mycelial growth were tested in vitro for detecting the potential production of diffusible metabolites and volatile organic compounds. Furthermore, ten strains among the most effective ones were selected and evaluated in vivo on detached grapevine host organs: leaf discs and grape berries. We showed that some of the bacterial strains strongly inhibited B. cinerea mycelial growth under in vitro conditions, and also significantly reduced rot severity in vivo. The results suggest the potential to control postharvest gray mold by some of the bacterial strains tested.

International audience; Enzymatic parameters (KM and Vmax), residual activity, effect of bentonite and electrophoresis characterization of laccase in the presence of different oenological tannins (OT) were investigated in relation to B. cinerea negative effects in grapes and musts. Five OT were tested (gallotannin, ellagitannin, quebracho, grape-skin and grape-seed) in comparison with ascorbic acid (AA), sulfur dioxide (SO2) and bentonite. We added OT, AA, SO2 and bentonite to botrytized must obtained by inoculation of grapes with B. cinerea strain 213. Laccase activity was measured by the syringaldazine method at different concentrations of substrate. Enzymatic parameters were determined using Michaelis-Menten and Lineweaver-Burk plots. The B. cinerea strain was also grown in a liquid medium for laccase production. Molecular weight of laccases and effect of OT upon these laccases were studied by SDS-PAGE. Results confirm that bentonite, contrary to OT, did not permit to reduce laccase activity. Regardless the tannin considered, Vmax, KM and laccase activity were reduced and gallotannin, grape-skin and grape-seed tannin presented the greatest ability. Efficiency of grape-seed tannin addition in order to reduce the laccase activity, was comparable to that of AA or SO2 at the typical doses employed in oenology for each one. Oenological tannins appear to be excellent processing aids to prevent laccase effects and contribute to reduce the use of SO2 in grapes and musts.

Aims: The aim of this research was to determine and quantify the ability of enological tannins to reduce laccase activity and, consequently, to protect wine color against enzymatic browning and/or oxidasic haze. Methods and results: Botrytized grape juice with laccase activity was obtained by inoculating Botrytis cinerea in healthy mature grapes. Laccase activity was determined in grape juice before and after supplementation with enological tannins using the syringaldazine method. White micro-fermentations were performed in the presence or not of laccase activity and supplemented or not with enological tannins in order to determine how the color was affected. Similarly, red micro-fermentations were performed using white grape juice supplemented with malvidin-3-O-glucoside. All enological tannins inhibited laccase activity and protected the wine color. Conclusion: Supplementation with enological tannins is an interesting tool to inhibit laccase activity and protect the color of white wines from browning and the color of red wines from oxidasic haze. Significance and impact of the study: This is the first scientific study evidencing the inhibitory effect of enological tannins on laccase activity in winemaking conditions. Keywords: enological tannins, Botrytis cinerea, grey mould, laccase activity, contact time, dose effect

Background and Aims Social, environmental and regulatory evolution encourages grapegrowers to reduce chemical use. Organic production is one possible answer, but controlling pests and diseases by products allowed in organic production is less easy than with chemicals. We integrated disease severity levels (Botrytis bunch rot, powdery and downy mildews) and pest incidence (grape berry moths) to develop an indicator of pests and disease damage in grape bunches, named assessment indicator of damage in grape bunches (AIDB), which can be used to assess pest incidence in networks of grower vineyards. Methods and Results In 2011 and 2012, we tested AIDB by monitoring damage at key phenological stages in 20 vineyards in the Bordeaux and Languedoc regions in the south of France, under three modes of production: conventional production, organic production and in conversion to organic production. The indicator proved accurate in describing the total damage on grape bunches under all conditions tested. Conclusions Irrespective of the mode of production, the AIDB value was negatively correlated with yield parameters and the technical expertise of the grower. This indicator proved to be an innovative tool to estimate the multipest damage on grapevines over a range of conditions. Significance of the Study The AIDB enables grapegrowers and advisors to assess the integrated impact of their treatment strategies on grape production, which is necessary when reducing pesticide use.

Background and Aims The presence of viable sources and of conditions favourable for conidial production, dispersal and deposition is essential for a high number of Botrytis cinerea conidia to be available at host infection sites. This study investigated the effect of environmental conditions, growing media and grape organs on the sporulation of ten strains of different genotypes and geographical origin. Method and Results Media of different water activity and similar to berry juice at several maturity stages, grape bunch trash or mature berries were inoculated with B. cinerea and incubated under variable conditions of temperature and relative humidity. Optimal conditions for sporulation were: temperature between 15 and 20°C, relative humidity >65.5%; water activity=0.971; and medium similar to the juice of softening berries. Conidia produced on bunch trash and mature berries were significantly correlated with those on artificial media. Conclusions Differences among strains did not change the response pattern of sporulation to the environmental conditions. Equations were then developed for describing the effect of temperature and relative humidity on sporulation, and of degree-days on the length of latent period. Significance of the Study When combined with predictive models for infection, our equations could contribute to the development of an effective disease prediction system for Botrytis bunch rot.

Botrytis bunch rot (BBR), caused by the necrotrophic fungus Botrytis cinerea, is a major disease of wine and table grapes worldwide. Due to negative effects of pesticides on the environment and human health, alternative control strategies against BBR, such as biological control agents (BCAs), are required to produce high-quality grapes and wines with high standards of food safety. However, few biological control products against BBR are available, and their efficacy is sometimes variable. This study aimed to evaluate and compare (1) the efficacy of new bacterial BCA strains developed at INRA Bordeaux and (2) the BBR reductions achieved by commercial biocontrol products that are already registered or close to being registered. During three consecutive seasons, 10 field experiments were established in six different experimental vineyards in southwestern France. Spray applications were performed at key phenological stages (five or six during the season), or at high BBR-risk periods late in the season according to a Disease Risk Index model. At harvest, BBR incidence and severity (% of symptomatic berries per bunch) were visually determined. The experiments included four bacterial strains at an early experimental stage, particularly Bacillus ginsengihumi (S38). Nine commercial BCA products were also tested, including Bacillus subtilis, Bacillus amyloliquefaciens, Aureobasidium pullulans, Ulocladium oudemansii, and Candida sake. Among the four experimental bacterial strains, only B. ginsengihumi S38 significantly controlled the BBR, presenting reductions in the average severity ranging from 35 to 60%, compared to untreated control, throughout the three seasons. Several commercial BCAs achieved significant reductions in BBR severity ranging from 21 to 58%, although not in every trial. The treatments that achieved higher reductions in severity rates were based on C. sake (45%), B. subtilis (54%), and B. amyloliquefaciens (58%). The efficacy of those BCAs was consistent throughout the studied seasons. The results confirmed the suitability of several biological control products under the conditions in vineyards in southwestern France, while also highlighting the good performance of the novel experimental BCA B. ginsengihumi S38 strain, which achieved similar control rates to the products registered for commercial use. The major factors involved in the variability in the results are also discussed.

International audience; Botrytis cinerea causes one of the most serious diseases in grapevines namely Botrytis Bunch Rot (BBR). A classification of different grapevine cultivars (cvs.) according to their susceptibility to B. cinerea is an essential management indicator in Integrated Pest Management. Although such classifications are available, they are based mostly on professional experience rather than experimental results. The aim of this study was to compare and classify different wine-grape cvs.according to their susceptibility to B. cinerea and to study the influence of fruit maturity on this classification. Between 2011 and 2015, three field trials were carried out under two contrasting climatic and cropping conditions, in Chile and France, including 13 common cvs. Both incidence and severity of the disease were evaluated at harvest and indices of susceptibility (SI) and maturity (FMat) were calculated on a per-site basis. The significant differences in disease incidence and severity observed among cvs. led to a similar susceptibility classification in both countries, despite the contrasting climatic conditions and cropping practices. Cabernet Sauvignon, Cabernet Franc, Grenache Noir, Petit Verdot and Mourvèdre were the most resistant cvs., whereas Gewürztraminer and Sauvignon Blanc were the most susceptible ones. Moreover, an exponential and positive relationship was established between SI and maturity. These findings might be of interest for choosing cultivars more resistant to B. cinereain order to reduce the number of specific anti-Botrytis fungicide applications.; Botrytiscinerea provoca una de las enfermedades más importantes en vides, llamada Pudrición gris(BBR). Contar con una clasificación de diferentes cultivares (cvs.) de vid de acuerdo a su susceptibilidad a B. cinerea es una información esencial en el manejo integrado de enfermedades. Aunque en literatura es posible encontrar ciertas clasificaciones, ellas están basadas en la experiencia profesional más que en resultados experimentales. El objetivo de este estudio fue comparar y clasificar diferentes cvs. de vid vinífera de acuerdo con su susceptibilidad a B. cinerea y estudiar la influencia de la madurez de fruta en esta clasificación. Entre 2011 y 2015, tres ensayos de campo fueron llevados a cabo bajo dos condiciones contrastantes de clima y manejo, en Chile y Francia, incluyendo 13 cultivares en común. La incidencia y la severidad de la enfermedad fueron evaluadas a la cosecha, además de calcular un índice de susceptibilidad (SI) y otro de madurez (FMat) en cada sitio. Diferencias significativas en incidencia y severidad entre los cultivares, hicieron que la clasificación de susceptibilidad fuera similar en ambos países, a pesar de las condiciones contrastantes de clima y cultivo. Cabernet Sauvignon, Cabernet Franc, GrenacheNoir, PetitVerdot y Mourvècre fueron los cvs. más tolerantes, mientras que Gewürztraminer y SauvignonBlanc fueron los más susceptibles. Además, una relación exponencial y positiva fue establecida entre SI y la madurez. Estos resultados podrían ser de interés como un criterio importante en la elección de un cultivar, con el fin de disminuir el número de aplicaciones fungicidas específicas contra B. cinerea.

The effect of temperature and wetness duration on infection of Vitis vinifera inflorescences (from “inflorescence clearly visible” to “end of flowering” stages) and young berry clusters (at “fruit swelling” and “berries groat-sized” stages) by Botrytis cinerea was investigated. Artificial inoculations were carried out using conidial suspensions of eight B. cinerea strains belonging to the transposon genotypes transposa and vacuma. Infection incidence was significantly affected by strain but not by transposon genotype (transposon genotype accounted for only 6.5% of the variance). Infection incidence was also affected by the interaction between strain and growth stage of the inflorescence or berry cluster (overall accounting for approximately 57% of the experimental variance). Thus, under our experimental conditions, the ability to cause infection was a strain rather than a transposon genotype attribute. Across all strains, infection incidence was lowest when inflorescences were clearly visible or fully developed, highest at flowering (from beginning to end of flowering), and intermediate at the postflowering fruit stages (fruit swelling and berries groat-sized). One transposa strain, however, was highly virulent on all grapevine growth stages tested. The effects of temperature and wetness duration on infection incidence were similar for all fungal strains and grapevine growth stages; infection incidence was highest at 20°C and lowest at 30°C, and was also low at 5°C. Similar results were obtained for mycelial growth and conidial germination. Based on the pooled data for all strains and grapevine growth stages, an equation was developed that accounted for the combined effects of temperature and wetness duration on relative infection incidence. This equation should be useful for developing decision-making systems concerning B. cinerea control at early grapevine growth stages.

International audience; Botrytis bunch rot (BBR) is a major fungal disease of grapevine worldwide caused by Botrytis cinerea. The pathogen presents a complex life cycle in the vineyard with a great genetic variability, multiple biological forms and various infection pathways highly dependent on meteorological conditions. Losses at harvest can be very important quantitatively as well as qualitatively by modifying wine quality from 5% of rotted berries upwards.Extensive research on BBR epidemiology has been carried out at INRA Bordeaux-Aquitaine evaluating and developing disease risk indicators. An interesting case of study is the B. cinerea floral calyptras infection rate as a potential early indicator of disease development and losses at harvest. From 2011 to 2015, B. cinerea infection of calyptras from an experimental Bordeaux vineyard (cv. Merlot) was evaluated at the end of flowering. The potential relationships between the infection on calyptras and the climatic conditions are analysed and discussed. However, no significant correlation was observed between the indicator and BBR disease incidence or severity.Additionally, alternative strategies to chemical fungicides have been evaluated in different Bordeaux organic vineyards in 2015. Natural products, already commercialized for their use in organic viticulture, were applied at key phenological stages or following a disease risk index. Results indicated the reduced interest of a wicker tea product, whereas potassium bicarbonate, kaolin and a fatty acid products showed BBR reduction and may be good candidates as alternative strategies for BBR control.

Summary Understanding the causes of population subdivision is of fundamental importance, as studying barriers to gene flow between populations may reveal key aspects of the process of adaptive divergence and, for pathogens, may help forecasting disease emergence and implementing sound management strategies. Here, we investigated population subdivision in the multihost fungus Botrytis cinerea based on comprehensive multiyear sampling on different hosts in three French regions. Analyses revealed a weak association between population structure and geography, but a clear differentiation according to the host plant of origin. This was consistent with adaptation to hosts, but the distribution of inferred genetic clusters and the frequency of admixed individuals indicated a lack of strict host specificity. Differentiation between individuals collected in the greenhouse (on Solanum) and outdoor (on Vitis and Rubus) was stronger than that observed between individuals from the two outdoor hosts, probably reflecting an additional isolating effect associated with the cropping system. Three genetic clusters coexisted on Vitis but did not persist over time. Linkage disequilibrium analysis indicated that outdoor populations were regularly recombining, whereas clonality was predominant in the greenhouse. Our findings open up new perspectives for disease control by managing plant debris in outdoor conditions and reinforcing prophylactic measures indoor.

National audience

International audience; The antagonistic activity of 46 bacterial strains isolated from Bordeaux vineyards were evaluated against Phaeomoniella chlamydospora, a major grapevine pathogen involved in Esca. The reduction of the necrosis length of stem cuttings ranged between 31.4% and 38.7% for the 8 most efficient strains. Two in planta trials allowed the selection of the two best strains, Bacillus pumilus (S32) and Paenibacillus sp. (S19). Their efficacy was not dependent on application method; co-inoculation, prevention in the wood and soil inoculation were tested. The involvement of antibiosis by the secretion of diffusible and/or volatile compounds in the antagonistic capacity of these two strains was assessed in vitro. Volatile compounds secreted by B. pumilus (S32) and Paenibacillus sp. (S19) were identified by gas chromatography/mass spectroscopy (GC/MS). The volatile compounds 1-octen-3-ol and 2,5-dimethyl pyrazine were obtained commercially and tested, and they showed strong antifungal activity against P. chlamydospora, which suggested that these compounds may play an important role in the bacterial antagonistic activity in planta. Furthermore, the expression of 10 major grapevine defense genes was quantified by real-time polymerase chain reaction, which demonstrated that the two strains significantly affected the grapevine transcripts four days after their application on the plants. High expression levels of different genes associated with P. chlamydospora infection in B. pumilus pre-treated plants suggests that this strain induces systemic resistance in grapevine. For the first time, we demonstrated the ability of two bacterial strains, B. pumilus and Paenibacillus sp., isolated from grapevine wood, to control P. chlamydospora via direct and/or indirect mechanisms.

Background and Aims: The impact of grey mould (Botrytis cinerea (B. cinerea)) was quantified on chemical, phenolic and sensory qualities of grapes, derived musts and wines. Methods and Results: Analyses were carried out by using naturally or artificially infected grape berries at ripeness or overripeness. In grape seeds, chemical analyses revealed no major differences between healthy and rotten grapes. In grape skins of Botrytis-affected berries, concentrations of all the phenolic compounds (anthocyanins and proanthocyanidin monomers, dimers and trimer) decreased drastically. Mean degree of polymerization of the proanthocyanidin polymeric fraction was also affected in skins. Chemical analyses of musts and wines made with different percentages of rotten berries showed a moderate impact of the pathogen on their phenolic composition. Nevertheless, sensory analyses underlined a loss of wine sensory quality perceptible from a threshold as low as 5% of Botrytis-affected grapes onwards. Conclusion: Phenolic variations and the associated negative impact in grapes, derived musts and wines may be related to oxidation phenomena from B. cinerea. The main effects of severity/age of grey mould and the level of berry maturity are also discussed. Significance of the Study: B. cinerea drastically affects the phenolic and organoleptic properties of grape skins and derived wines. Therefore, prophylactic actions early in the vineyard, evaluation of the sanitary status of the harvested grapes and berry sorting are primordial even under low disease pressure.

International audience; This work investigated the structural and biochemical changes during grape berry development which account potentially for the onset and increase in susceptibility to Botrytis cinerea. Using the cv. Sauvignon blanc, we quantified at seven developmental growth stages from herbaceous to over-mature berries: (1) fruit ontogenic resistance using three strains (II-transposa), (2) the morphological and maturity fruit characteristics and (3) preformed biochemical compounds located in the berry skin. From the mid-colour change stage onwards, susceptibility of unwounded fruit increased sigmoidally in both rot and sporulation severities at the berry surface. A principal component analysis identified a very close connection between fruit susceptibility and the level of fruit maturity. Berry susceptibility was significantly and positively correlated with the phenolic compounds in the skin cell walls and negatively correlated with the total tannin content in the skin and with water activity (Aw) at the fruit surface. On the berry, Aw decreased from 0.94 at bunch closure to 0.89 at berry maturity, with a relatively low value (0.90) at the stage of mid-colour change. Using artificial media, different Aw levels led to significant differences in mycelial growth (Aw ≤0.95 resulted in the lowest growth rate ≤0.34 mm day−1). Thus, besides the level of fruit maturity, both water activity on the fruit and the total tannin content in the skin may affect fungal growth and berry colonisation. The potential of these variables for use as indicators of grape berry susceptibility as well as associated mechanisms for the development of disease are discussed.

The dominant strategy followed by vine-growers in Chile to control powdery mildew (Erysiphe necator) involves schedule phytosanitary applications resulting between 9 to 18 fungicide sprays depending on the grape cultivar and the geographical area, mainly with sulphur applications. This large application of chemicals generates many environmental and human health risks To solve this, the present study aimed at evaluating the effectiveness of a Phytosanitary Decision Rule (PDR) proposed by French pathologists to rationalize fungicide applications against powdery mildew in grapevine. The PDR was evaluating in two irrigated vine fields, one of cultivar Cabernet sauvignon (CS, 1.56 ha) and another of Chardonnay (CH, 1.66 ha), in the Mediterranean climatic conditions of Talca Region, Chile. The experiment was carried out between 2009 and 2013. For the two experimental fields, two strategies to control powdery mildew were distributed in a randomized block design with four replicates: i) “Optimized traditional management” (OPT), which consisted in periodic applications (mainly sulphur), but with no more than nine treatments per season, ii) Application of a PDR based on field observations but with no more than four treatments per season. Untreated vines were left in each block to assess disease pressure at each studied season. Finally, a survey was conducted to know the practices of crop protection of traditional vine-growers (TVG) in the area, who carry out a “zero risk” strategy without limiting the number of phytosanitary applications. At veraison stage, clusters were observed to assess disease severity. The results show that powdery mildew control based on a PDR was as effective as schedule applications used by the OPT at experimental station for both vine fields. In the OPT and PDR treatments disease severity was lower than 5 %, which was considered as a threshold value for avoid in gloss of wine quality. For both cultivars disease severity was lower than that observed in untreated vines (close to 10% and 40 % for CS and CH, respectively). In the OPT treatment 7 to 9 applications per season independent of cultivar were made, whereas in the PDR treatment only 2-4 application were carried out. The differences are even greater when comparing the PDR with the TVG strategy in which, independent of the season and the cultivar, performed an average of 14 fungicide applications. Finally in the OPT and PDR treatments the cost per season was similar and fluctuated between US $ 322 and 415 per hectare independent of the cultivar. This value is 60% lower than the cost of the traditional "zero risk" strategy of vine-growers.; La principale stratégie de contrôle de l'oïdium (Erysiphe necator) suivie par les viticulteurs chiliens se fait par applications phytosanitaires périodiques. Selon le cépage et la zone géographique, cela se traduit par 9 à18 applications de fongicides par saison, principalement sous forme de soufre. Cette utilisation importante de produits chimiques entraîne d’importants risques pour la santé humaine et l'environnement. Pour résoudre ce problème, cette étude vise à évaluer l'efficacité d'une règle de décision phytosanitaire(PDR) proposé par des pathologistes français. Cette PDR a pour objectif de rationaliser les applications de fongicides contre l'oïdium de la vigne. La PDR a été évalué sur deux parcelles viticoles irriguées, une avec le cépage Cabernet-Sauvignon (CS, 1,56 ha) et l’autre avec Chardonnay (CH, 1,66 ha), dans les conditions climatiques méditerranéennes de la région de Talca au Chili. L'étude a été réalisée de 2009 à 2013. Pour les deux parcelles expérimentales, deux stratégies de lutte contre l'oïdium ont été mises en oeuvre en blocs aléatoires avec quatre répétitions: i) “Gestion traditionnelle optimisée" (OPT), qui consiste en des applications périodiques(principalement soufre), mais avec un maximum de neuf traitements par saison, ii) Application d'une PDR basée sur des observations de terrain, avec un maximum de quatre traitements par saison. Des plantes non traitées ont été laissées au sein de chaque bloc pour évaluer la pression de la maladie à chaque saison étudiée. Enfin, une enquête a été menée pour connaître les pratiques de protections traditionnelles des vignerons dans la région, qui effectuent une stratégie de “risque zéro” sans limite du nombre de traitements fongicides. Au stade véraison, les grappes ont été observées pour évaluer la sévérité de la maladie. Les résultats montrent que pour les deux parcelles de l’étude, le contrôle de l'oïdium avec la PDR est aussi efficace que la OPT.. Dans les traitements OPT et PDR la sévérité de la maladie est inférieure à 5%, ce qui est considéré comme une valeur seuil au-dessus de laquelle la qualité du vin est altérée. Pour les deux cépages la sévérité de la maladie sur les vignes traitées a été inférieure à celle observée sur les vignes non traitées (près de 10% et 40% respectivement pour CS et CH). Indépendamment du cépage, 7-9 applications par saison ont été effectuées pour le traitement OPT, alors que seulement 2-4 applications ont été réalisées pour le traitement PDR. Les différences sont encore plus importantes lorsque l'on compare la PDR à la stratégie de protections “risque zéro” menées par les viticulteurs de la région pour laquelle, indépendamment de la saison et le cépage, 14 applications par saison ont été effectuées en moyenne. Enfin pour les traitements OPT et PDR le coût par saison était similaire et a fluctué entre US $ 322 et 415 par hectare, valeur qui est 60% inférieure au coût de la stratégie “risque zéro” de viticulteurs.

International audience; La Yesca es hoy la enfermedad de la madera la más preocupante en Francia. Su progreso desde el final del siglo XX, incluso antes de la prohibición de arsenito de sodio, fue tal que algunos la han considerado como una “enfermedad emergente”. Después de recordar los principales datos del Observatorio Nacional para evaluar la situación de las principales “Enfermedades de la Madera de la Vid” durante la última década, este artículo sugiere varias hipótesis que pueden explicar la progresión de este síndrome. Se complementa con una sección sobre los síntomas y la dinámica de su aparición, que no había sido revisado durante casi un siglo. Los resultados de las observaciones finas y regulares en viñedo en Francia o en el extranjero, dan lugar a una redefinición de los síntomas de la yesca y conducen a nuevas preguntas. Este texto está inspirado en gran parte de un artículo publicado en 2012 y presentado en una conferencia del AFPP (Asociación Francesa para la Protección de las Plantas).

National audience

Effects of environment, Botrytis cinerea strain, and their interaction on the infection of mature grape berries were investigated. The combined effect of temperature (T) of 15, 20, 25, and 30°C and relative humidity (RH) of 65, 80, 90, and 100% was studied by inoculating berries with mycelium plugs. Regardless of the T, no disease occurred at 65% RH, and both disease incidence and severity increased with increasing RH. The combined effect of T (5 to 30°C) and wetness duration (WD) of 3, 6, 12, 24, and 36 h was studied by inoculating berries with conidia. At WD of 36 h, disease incidence was approximately 75% of affected berries at 20 or 25°C, 50% at 15°C, and 30 to 20% at 30 and 10°C; no infection occurred at 5°C. Under favorable conditions (100% RH or 36 h of WD) and unfavorable conditions (65% RH or 3 h of WD), berry wounding did not significantly affect disease incidence; under moderately favorable conditions (80% RH or 6 to 12 h of WD), disease incidence was approximately 1.5 to 5 times higher in wounded than in intact berries. Our data collectively showed that (i) T and RH or WD were more important than strain for mature berry infection by either mycelium or conidia and (ii) the effect of the environment on the different strains was similar. Two equations were developed describing the combined effect of T and RH, or T and WD, on disease incidence following inoculation by mycelium (R2 = 0.99) or conidia (R2 = 0.96), respectively. These equations may be useful in the development of models used to predict and control Botrytis bunch rot during berry ripening.

Mature grapevine berries at the harvesting stage (MB) are very susceptible to the gray mold fungus Botrytis cinerea, while veraison berries (VB) are not. We conducted simultaneous microscopic and transcriptomic analyses of the pathogen and the host to investigate the infection process developed by B. cinerea on MB versus VB, and the plant defense mechanisms deployed to stop the fungus spreading. On the pathogen side, our genome-wide transcriptomic data revealed that B. cinerea genes upregulated during infection of MB are enriched in functional categories related to necrotrophy, such as degradation of the plant cell wall, proteolysis, membrane transport, reactive oxygen species (ROS) generation, and detoxification. Quantitative-polymerase chain reaction on a set of representative genes related to virulence and microscopic observations further demonstrated that the infection is also initiated on VB but is stopped at the penetration stage. On the plant side, genome-wide transcriptomic analysis and metabolic data revealed a defense pathway switch during berry ripening. In response to B. cinerea inoculation, VB activated a burst of ROS, the salicylate-dependent defense pathway, the synthesis of the resveratrol phytoalexin, and cell-wall strengthening. On the contrary, in infected MB, the jasmonate-dependent pathway was activated, which did not stop the fungal necrotrophic process.

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National audience