Historical background The State Institute for Viticulture and Enology (WBI, Freiburg, Germany), was founded in 1920 under the direction of Karl Müller. Karl Müller continued his earlier work on grapevine downy mildew (Plasmopara viticola) and dealt intensively with the conditions for the outbreak of the disease and the germination behaviour of the sporangia of the pathogen. His work provided precise data on the relationship between incubation time and temperature. Further studies on the development of oil spots and the formation of sporangia at the end of the incubation period also revealed a dependence of these events on temperature, humidity and time of day. The incubation curve created using these data has made the incubation calendar more precise. From now on it allowed the presentation of potential infection conditions as well as the prediction of the duration of the incubation period and dates of outbreaks based on weather observations. This was the first time that targeted treatments against grapevine downy mildew could be planned based on its biological development (Müller and Rabanus, 1923; Müller and Sleumer, 1934). Research on grapevine downy mildew is still one of the main topics in plant protection at WBI. While the search for uncompromisingly safe control methods was at the forefront in the early days, today the focus is on safe protection of the grapevine with the minimum possible use of pesticides. Since the very first studies on grapevine downy mildew, the basic idea has always been: plant protection strategies achieve the best effectiveness when they take into account the biology of the pathogen. To this day, this idea shapes the work of WBI. Consequently, further studies from Freiburg and other institutes carried out during the 1920s, 1930s, 1970s (Blaeser, 1978) and 1980s (Gehmann, 1987) provided even more precise data on the relationship between weather conditions and the biology of downy mildew. At the end of the 1980s until the beginning of the 2000s, the first forecasting models were operated with small electronic weather stations. During this time, an intensive exchange about models took place on an international level, on the one hand at the Workshops on Grapevine Downy and Powdery Mildew and on the other hand at the IOBC (International Organisation for Biological Control) meetings. Recent background From the early and mid-2000s, the internet was used more intensively to provide model results. The precondition for the rapid dissemination of decision support systems was thus created. In parallel, the desire to reduce the use of pesticides grew in the European Community and in the individual member countries. In consequence during the last years, plant protection in the EU and in Germany is increasingly influenced by new laws and regulations. The directive 2009/128/EC, for example aims for a sustainable use and a reduction of the risks and impacts of pesticides use in the European Community (EC) (https://ec.europa.eu/food/plants/pesticides/sustainable-usepesticides_de). One tool for low pesticide use in crop protection is the Integrated Pest Management (IPM). IPM must be implemented by all professional users and promoted by EU countries, as specified in Annex III of the abovementioned directive. Based on the directive, all EU countries developed own National Action Plans (NAP) for sustainable use of pesticides. An essential goal of the National Action Plan on Sustainable Use of Plant Protection Products in Germany (NAP Germany) is the reduction of pesticide treatments to necessary levels (https://www.nappflanzenschutz.de/en/about-the-national-actionplan/regulations/european-regulations/directive-2009128ec/ . Forecasting models, expert software and decision support systems are key factors to promote this process. A modern an intensively used platform for forecasting models, weatherand monitoring data for viticulture in the South-West of Germany (Baden-Wuerttemberg) is “VitiMeteo” (VM; www.vitimeteo.de). The basic science underlying the “VitiMeteo” platform has been continuously published (Bleyer et al., 2008; Bleyer et al., 2011; Bleyer et al., 2014, Bleyer et al., 2020a; Dubuis et al., 2012). The platform is a cooperative project between WBI, Agroscope (Changins, Switzerland) and the company GEOsens GmbH (Schallstadt, Germany). The working group is supported by other research institutes. Besides Baden-Wuerttemberg, RhinelandPalatinate, Bavaria and Switzerland VM Models are widely used in other countries in Europe, such as France and Austria. “VM Plasmopara” was the first VM module, created in 2002. It calculates the most important steps of the infection cycle of downy mildew (Bleyer et al. 2008; Dubuis et al., 2012). The growth model “VM Growth”, which was programmed for trellising systems in cooperation with H.-R. Schultz from Geisenheim University (Geisenheim, Germany) was the next component (Schultz, 1992). In 2004 “VM Growth” was implemented in the downy mildew model. The weather forecast of the company Meteoblue (Basel, Switzerland) was embedded in the software modules since 2009. The integration of the weather forecast in all models was a milestone in the development of the system. This innovation allowed the calculation of incubation curves, total temperature, infection risk, leaf area and number of leaves as well as several other important parameters seven days in advance. On the basis of this implementation it was possible to make the first real predictions on plant protection applications in viticulture depending on weather conditions.

Bei den Sorten Gewurztraminer und Weiser Burgunder wurde in den Jahren 1977 und 1978 die Entwicklung der Samenanlagen in normalen und verrieselten Fruchtknoten untersucht. Die Fruchtknoten verrieselten, wenn alle vier Samenanlagen degeneriert waren. Es wurden zwei Typen der Degeneration gefunden: Degeneration normal ausgebildeter Embryosacke infolge Ausbleibens der Befruchtung. Fruchtknoten mit solchen Samenanlagen wurden vom 9. d nach dem Aufbluhen an abgeworfen, nachdem zwischen dem 4. und 6. d ein Trenngewebe ausgebildet worden war. In signifikant unterschiedlicher Haufigkeit traten bei beiden Sorten Samenanlagen ohne Embryosack auf. Im Gegensatz zum Degenerationstyp 1 zeigten deren Nucelli bis zum 20. d nach dem Aufbluhen keine Anzeichen von Degeneration. Fruchtknoten, in denen solche Samenanlagen auftraten, wuchsen nur wenig, bildeten kein saftiges Pericarp und blieben bis zur Reife der normal entwickelten Beeren an der Infloreszenz hangen. Wahrscheinlich wird das geringe Wachstum der Fruchtknoten durch das anfanglich mehr oder weniger normale Wachstum der Nucelli ausgelost. Cytological investigations about the causes of shedding and limited growth of pistils in Vitis In the years 1977 and 1978, investigations of the cvs. Gewurztraminer and Weisser Burgunder were carried out on the ovules in normal ovaries and in those of shedded or undeveloped pistils. Shedding and limited growth of pistils occurred, if all four ovules were aborted. Two types of abortion were found: Normally formed embryo sacs aborted due to nonfertilization. Ovaries enclosing such ovules dropped beginning with the 9th d after bloom, an abscission layer being developed between the 4th and 6th d. Ovules without embryo sac occurred, their frequency differing significantly between both cultivars. In contrast to abortion type 1, their nucelli showed no signs of degeneration until the 20th d after bloom. The ovaries in which such ovules occurred showed only minimal growth, formed no juicy pericarp and adhered to the clusters until maturity of the normally developed berries. It is suggested that the reduced growth of the ovaries was initiated by the more or less normal growth of the nucelli at the beginning of the development.

Impact of abiotic factors has been recently discussed in grapevine trunk diseases such as Esca. Emphasis of the present study lies on the relation between different water regime ("normal" and "stress") on one side and growth characters as well as Esca-related wood symptoms on the other side. Trials were conducted in the greenhouse with cuttings of the cultivars 'Muller-Thurgau' and 'Riesling', part of which artificially infected with Phaeomoniella chlamydospora. During a 12 month incubation period the following characters were evaluated: shoot length, weight of stem, expression of wood symptoms, and survival rate of plants. For evaluation of wood symptoms a numerical system was developed that is applied here for the first time. The obtained results indicate that water supply plays a statistically significant role, with plants under "stress" regime shown to be more affected. No strict spatial correlation was found to exist between wood symptoms and physical presence of the pathogen.

Stilbenic phytoalexins have been associated with disease resistance. In Vitis spp., stilbene synthesis can be induced by UV irradiation, treatment with a variety of substance extracts, and inoculation with Botrytis cinerea or Plasmopara viticola. The aim of the present work was to examine the relationship between stilbene production and the level of resistance of different Vitis genotypes to P. viticola. The ability of different grapevine genotypes (Vitis vinifera L. cvs. Tempranillo, Touriga Nacional, Pinot noir, and Cabernet Sauvignon and Vitis riparia cv. Gloire de Montpellier) to resist Plasmopara viticola infection was assessed via their potential to accumulate toxic stilbenic phytoalexins. Leaf discs taken from plants belonging to these genotypes were inoculated with P. viticola sporangia and disease severity was determined five days later. Stilbene production was quantified in similar leaf material at 6, 24, 48, and 72 hr postinoculation. After P. viticola infection, the resistant genotype V. riparia showed high production of the phytotoxic stilbenes ɛ- and δ-viniferin, which limited the development of the pathogen and prevented it from producing spores. Indeed, this genotype was associated with the lowest sporulation values. No relationship was observed, however, between resistance and these compounds in the V. vinifera genotypes. Further study is required to define the role of stilbenic phytoalexins in resistance to P. viticola.

Chemical and natural resistance-inducing substances may be used to decrease the susceptibility of plants to various pathogens, thus reducing the application of pesticides in agriculture. This study evaluated the potential of biocontrol products and of plant extracts. The invoked mode of induced resistance was verified to control downy mildew on grapevine plants using leaf discs and potted vines. Induced resistance was determined by the increase of pathogenesis-related (PR) proteins, including peroxidase, polyphenol oxidase, β-1,3-glucanase, phenylalanine ammonia-lyase, stilbene synthase, β-1,3-glucanase, PR-1 protein, and caffeoyl-coenzyme A 3-O-methyltransferase. Candidate resistance inducers, including Solidago canadensis (CanG) extract, mycelium extract of Penicillium crysogenum (PEN), linoleic acid (LIN), and biocontrol agent Aureobasidium pullulans (Aureo), and chemical elicitors 3-dl-β-aminobutyric acid (BABA) and benzothiadiazole (BTH) were tested against Plasmopara viticola in potted vines grown outdoors. BABA, BTH, and CanG provided a protection of more than 80%, whereas PEN, LIN, and Aureo provided minimal protection. BABA and Aureo were not able to inhibit zoospores, whereas a concentration-dependent inhibition of zoospore mobility was observed for all other tested substances. BTH, CanG, PEN, and LIN induced the production of a broad spectrum of resistance-related metabolites, whereas Aureo did not cause any response. BABA provoked formation of necrotic spots and PR proteins immediately after inoculation. These results indicate the potential to partly induce natural resistance metabolites to enhance tolerance of grapevine plants to P. viticola, thus offering a synergistic effect when used with fungicides and aiding in reducing their ecological burden, even if they are not effective enough to replace them fully.

This work reports the leaf morphology of six grapevine genotypes, five belonging to Vitis vinifera and one to Vitis riparia. Earlier studies on these genotypes showed different levels of susceptibility to grapevine downy mildew (Plasmopara viticola). The aim of this work was to detect differences between the leaf morphology of these cultivars at the macro- and microscopic levels, and to characterize morphological traits which could be associated with susceptibility and resistance to downy mildew. An ampelographic description of each genotype was used-to develop a scheme illustrating the characteristic leaf morphology. The density and morphology of the trichomes and the stomatal index was assessed by means of microscopical techniques. Distinct macro and microscope differences among the genotypes were seen. No clear relation between ampelographic characteristics and susceptibility to downy mildew was observed. The two cultivars that in earlier studies were found to be the least susceptible to downy mildew were the most similar in terms of their spongy mesophyll. Both showed very little or no wax oil the abaxial surface of their leaves.

3 paginas.- Trabajo presentado al 6o GDPM celebrado en Burdeos (Francia) del 4 al 9 de Julio de 2010.

In order to obtain insight into host responses to grapevine downy mildew (Plasmopara viticola), we compared pathogen development on a panel of Vitis species from North America, Asia and Europe. Leaf discs from different host species were inoculated in parallel, and the colonisation of the mesophyll was visualised by aniline blue staining and quantified with respect to infection incidence and mycelial growth. In parallel, the morphology of guard cells was screened for the presence of an internal cuticular rim after staining with acridine orange and using low-temperature scanning electron microscopy. We observed three response patterns: (i) inhibition of pathogen development early after attachment of zoospores; (ii) successful colonisation of the mesophyll by the pathogen; and (iii) aberrant development, where the pathogen does not attach to guard cells, but produces hyphae on the leaf surface without formation of viable sporangiophores. Inhibition is observed in the North American and Siberian species, successful colonisation prevails in the European hosts, and surface hyphae are found on non-Siberian Asiatic species. We propose that the interaction between host and pathogen is under control of specific signals that have been subject to evolutionary diversification.

8 paginas, 5 figuras, 1 tabla.- Este trabajo se presento en el Congreso celebrado en Zagreb (Croacia) entre el 28 de junio y el 3 de julio de 2009.