Esca Complex Research Articles

Interactions between bois noir and the esca disease complex in a Chardonnay vineyard in Italy

Grapevine yellows bois noir (BN) and the grapevine trunk disease esca complex (EC) cause serious yield losses in European vineyards and are often widespread in the same vineyard. In a Chardonnay vineyard in north-eastern Italy, evolution of the two diseases from 2007 to 2020 was compared and their possible interaction was investigated. Evolution of symptomatic grapevines over the 16 years was very different between the two diseases, with a substantial linear increase for BN and an exponential increase for EC. The BN increase from one year to another was associated with the abundance of Hyalesthes obsoletus, the BN-phytoplasma vector, whereas the exponential increase in EC was likely due to the amount of inoculum and the increased size of pruning cuts over time. The courses of the two diseases were also very different, with a much greater occurrence of dead grapevines from EC than from BN. Some grapevines showed symptoms of both diseases, but the probability was less that a grapevine symptomatic for BN or EC showed symptoms of the other disease. Examinations of the spatial distribution of the two diseases showed dissociation between them. Data indicated that mechanisms of induced defense were involved in the lower probability that a grapevine affected by one showed symptoms of the other.

Role of Rain in the Spore Dispersal of Fungal Pathogens Associated with Grapevine Trunk Diseases.

Grapevine trunk diseases are caused by a complex of fungi that belong to different taxa, which produce different spore types and have different spore dispersal mechanisms. It is commonly accepted that rainfall plays a key role in spore dispersal, but there is conflicting information in the literature on the relationship between rain and spore trapping in aerobiology studies. We conducted a systematic literature review, extracted quantitative data from published papers, and used the pooled data for Bayesian analysis of the effect of rain on spore trapping. We selected 17 papers covering 95 studies and 8,778 trapping periods, concerning a total of 26 fungal taxa causing Botryosphaeria dieback (BD), Esca complex (EC), and Eutypa dieback (ED). Results confirmed the role of rain in the spore dispersal of these fungi but revealed differences among the different fungi. Rain was a good predictor of spore trapping for ED (AUROC = 0.820) and BD (0.766) but not for the ascomycetes involved in EC (0.569) and not for the only basidiomycetes, Fomitiporella viticola, studied as for spore discharge (AUROC not significant). Prediction of spore trapping was more accurate for negative prognosis than for positive prognosis; a rain cutoff of ≥0.2 mm provided an overall accuracy of ≥0.61 for correct prognoses. Spores trapped in rainless periods accounted for only <10% of the total spores. Our analysis had some drawbacks, which were mainly caused by knowledge gaps and limited data availability; these drawbacks are discussed to facilitate further research.

Seasonal Periodicity of the Airborne Spores of Fungi Causing Grapevine Trunk Diseases: An Analysis of 247 Studies Published Worldwide.

Grapevine trunk diseases (GTDs) are among the most devastating grapevine diseases globally. GTDs are caused by numerous fungi belonging to different taxa, which release spores into the vineyard and infect wood tissue, mainly through wounds caused by viticultural operations. The timing of operations to avoid infection is critical concerning the periodicity of GTD spores in vineyards, and many studies have been conducted in different grape-growing areas worldwide. However, these studies provide conflicting and fragmented information. To synthesize current knowledge, we conducted a systematic literature review, extracted quantitative data from published papers, and used these data to identify trends and knowledge gaps that need to be addressed in future studies. Our database included 26 papers covering 247 studies and 3,529 spore sampling records concerning a total of 29 fungal taxa responsible for Botryosphaeria dieback (BD), Esca complex (EC), and Eutypa dieback (ED). We found a clear seasonality in the presence and abundance of BD spores, with a peak from fall to spring, more in the northern hemisphere than in the southern hemisphere, but not for EC and ED. Spores of these fungi were present throughout the growing season in both hemispheres, possibly because of higher variability in spore types, sporulation conditions, and spore release mechanisms in EC and ED fungi than in BD. Our analysis has limitations because of knowledge gaps and data availability for some fungi (e.g., basidiomycetes, which cause EC). These limitations are discussed to facilitate further research.

Temperature-Dependent Growth and Spore Germination of Fungi Causing Grapevine Trunk Diseases: Quantitative Analysis of Literature Data.

Grapevine trunk diseases (GTDs) are serious threats in all viticultural areas of the world, and their management is always complex and usually inadequate. Fragmented and inconsistent information on the epidemiology and environmental requirements of the causal fungi is among the reasons for poor disease control. Therefore, we conducted a quantitative analysis of literature data to determine the effects of temperature on mycelial growth and the effects of temperature and moisture duration on spore germination. Using the collected information, we then developed mathematical equations describing the response of mycelial growth to temperature, and the response of spore germination to temperature and moisture for the different species and disease syndromes. We considered 27 articles (selected from a total of 207 articles found through a systematic literature search) and 116 cases; these involved 43 fungal species belonging to three disease syndromes. The mycelial growth of the fungi causing Botryosphaeria dieback (BD) and the esca complex (EC) responded similarly to temperature, and preferred higher temperatures than those causing Eutypa dieback (ED) (with optimal temperature of 25.3, 26.5, and 23.3°C, respectively). At any temperature, the minimal duration of the moist period required for 50% spore germination was shorter for BD (3.0 h) than for EC (17.2 h) or ED (15.5 h). Mathematical equations were developed accounting for temperature-moisture relationships of GTD fungi, which showed concordance correlation coefficients ≥0.888; such equations should be useful for reducing the risk of infection.

First Description of Non-Enzymatic Radical-Generating Mechanisms Adopted by Fomitiporia mediterranea: An Unexplored Pathway of the White Rot Agent of the Esca Complex of Diseases.

Fomitiporia mediterranea (Fmed) is the primary Basidiomycota species causing white rot in European vineyards affected by the Esca complex of diseases (ECD). In the last few years, an increasing number of studies have highlighted the importance of reconsidering the role of Fmed in ECD etiology, justifying an increase in research interest related to Fmed's biomolecular pathogenetic mechanisms. In the context of the current re-evaluation of the binary distinction (brown vs. white rot) between biomolecular decay pathways induced by Basidiomycota species, our research aims to investigate the potential for non-enzymatic mechanisms adopted by Fmed, which is typically described as a white rot fungus. Our results demonstrate how, in liquid culture reproducing nutrient restriction conditions often found in wood, Fmed can produce low molecular weight compounds, the hallmark of the non-enzymatic "chelator-mediated Fenton" (CMF) reaction, originally described for brown rot fungi. CMF reactions can redox cycle with ferric iron, generating hydrogen peroxide and ferrous iron, necessary reactants leading to hydroxyl radical (•OH) production. These observations led to the conclusion that a non-enzymatic radical-generating CMF-like mechanism may be utilized by Fmed, potentially together with an enzymatic pool, to contribute to degrading wood constituents; moreover, indicating significant variability between strains.

Effects of Temperature and Moisture Duration on Spore Germination of Four Fungi that Cause Grapevine Trunk Diseases.

Grapevine trunk diseases (GTDs) are serious threats worldwide and are difficult to control, in part because the environmental requirements for epidemiological processes of the causal fungi are poorly understood. Therefore, we investigated the effects of temperature and moisture duration on spore germination of four fungi associated with two GTDs (esca complex and Eutypa dieback): Phaeomoniella chlamydospora, Phaeoacremonium minimum, Cadophora luteo-olivacea, and Eutypa lata. Conidia of Phaeomoniella chlamydospora, Phaeoacremonium minimum, and C. luteo-olivacea were similar: conidia of these fungi germinated profusely (>90%) between 20 and 30°C; Phaeomoniella chlamydospora and Phaeoacremonium minimum tended to germinate at higher temperatures (up to 40°C for P. minimum), and C. luteo-olivacea at lower temperatures (as low as 5°C). E. lata ascospores germinated between 10 and 30°C. The required duration of moist periods for germination was shortest for C. luteo-olivacea (about 6 h), followed by P. minimum and E. lata (about 12 h) and Phaeomoniella chlamydospora (about 24 h). Further research on the environmental requirements of GTD fungi may increase our ability to predict infection periods and, thereby, improve disease control.

Susceptibility of pruning wounds to grapevine trunk diseases: A quantitative analysis of literature data.

Pruning wounds are the main entry points for fungi causing grapevine trunk diseases (GTDs). Several studies identified factors influencing the temporal dynamics of wound susceptibility, which include the fungal species and inoculum dose, weather conditions, grape variety, pruning date, and so forth. Here, we conducted a quantitative analysis of literature data to synthesise outcomes across studies and to identify the factors that most affect the length of pruning wound susceptibility. We extracted data on the frequency at which the inoculated wounds showed GTD symptoms or an inoculated pathogen was reisolated following artificial inoculation at the time of pruning or in the following days. A negative exponential model was fit to these data to describe changes in wound susceptibility as a function of time since pruning, in which the rate parameter changed depending on specific factors. The results show that wound susceptibility is high at the time of pruning, and they remain susceptible to invasion by GTD fungi for months after pruning. Infection incidence on wounds was higher for fungi associated with Botryosphaeria dieback than those associated with Eutypa dieback or Esca complex, and wound susceptibility decreased faster for Eutypa dieback than for other GTD agents. Grapevine variety and pruning season also affected the wound susceptibility period. Sauvignon Blanc remains susceptible to GTDs longer than other varieties. We also found that the time of pruning can affect infection dynamics, especially for more susceptible varieties. The results increase our understanding of GTD epidemiology and should help growers control infections.

Tannins-lignin mixed nanoformulations for improving the potential of neem oil as fungicide agent.

Sustainability and circular economy are increasingly pushing for the search of natural materials to foster antiparasitic treatments, especially in the case of economically relevant agricultural cultivations, such as grapevine. In this work, we propose to deliver neem oil, a natural biopesticide loaded into novel nanovectors (nanocapsules) which were fabricated using a scalable procedure starting from Kraft lignin and grapeseed tannins. The obtained formulations were characterized in terms of size and Zeta potential, showing that almost all the nanocapsules had size in the suitable range for delivery purposes (mean diameter 150-300nm), with low polydispersity and sufficient stability to ensure long shelf life. The target microorganisms were three reference fungal pathogens of grapevine (Botrytis cinerea, Phaeoacremonium minimum, Phaeomoniella chlamydospora), responsible for recurrent diseases on this crop: grey mold or berry rot by B. cinerea and diseases of grapevine wood within the Esca complex of diseases. Results showed that grapeseed tannins did not promote inhibitory effects, either alone or in combination with Kraft lignin. On the contrary, the efficacy of neem oil against P. minimum was boosted by more than 1-2 orders of magnitude and the parasite growth inhibition was higher with respect to a widely used commercial pesticide, while no additional activity was detected against P. chlamydospora and B. cinerea.

Phytotoxic Metabolites Produced by Fungi Involved in Grapevine Trunk Diseases: Progress, Challenges, and Opportunities.

Grapevine trunk diseases (GTDs), caused by fungal pathogens, are a serious threat to vineyards worldwide, causing significant yield and economic loss. To date, curative methods are not available for GTDs, and the relationship between the pathogen and symptom expression is poorly understood. Several plant pathologists, molecular biologists, and chemists have been investigating different aspects of the pathogenicity, biochemistry, and chemical ecology of the fungal species involved in GTDs. Many studies have been conducted to investigate virulence factors, including the chemical characterization of phytotoxic metabolites (PMs) that assist fungi in invading and colonizing crops such as grapevines. Moreover, multidisciplinary studies on their role in pathogenicity, symptom development, and plant-pathogen interactions have also been carried out. The aim of the present review is to provide an illustrative overview of the biological and chemical characterization of PMs produced by fungi involved in Eutypa dieback, Esca complex, and Botryosphaeria dieback. Moreover, multidisciplinary investigations on host-pathogen interactions, including those using cutting-edge Omics techniques, will also be reviewed and discussed. Finally, challenges and opportunities in the role of PMs for reliable field diagnosis and control of GTDs in vineyards will also be explored.

Xylem anatomy and hydraulic traits in Vitis grafted cuttings in view of their impact on the young grapevine decline.

Grapevine grafting is an essential practice in viticulture and over the years, various bench grafting techniques have been developed to mechanize the nursery process and to increase the yield in number of viable cuttings. Bench grafting is a fundamental nursery practice that can potentially affect the quality of propagation material also in young decline associated to grapevine trunk diseases and has been recently reported to influence leaf symptoms development associated with diseases of Esca complex. The study aimed to investigate how three bench grafting methods [i.e., (i) Omega graft as mechanical technique, (ii) Whip and Tongue graft as manual technique and (iii) Full Cleft graft as semi-mechanical technique] can influence these phenomena. Specifically, the different methods were compared for their effect on the anatomical development of the grafting point and the functionality of the xylem, also considering two factors: the grapevine cultivar (Cabernet Sauvignon, Glera and Teroldego) and the scion/rootstock diameter (thin and large). Observations by light microscopy on the anatomical evolution and measurements on the xylem morphology and hydraulic traits were correlated with the grafting methods and the investigated varieties. The anatomical observations revealed that the mechanical (Omega) and semi-mechanical (Full Cleft) grafting methods have a faster callusing response while the manual technique (Whip and Tongue) has a slower but greater vascularization of the differentiated callus. Significant differences between cultivars and/or grafting types were also detected in necrotic area on the grafted tissues. Statistical analysis of the grapevine vessels suggested differences in xylem parameters between cultivars, while grafting type had no significant effects. On the other hand, the grafting type significantly affected the intrinsic growth rate. The study confirms the potential incidence of lesions and dysfunctionalities correlated with the grafting method applied, which can potentially induce grafted vine declines in vineyards due to the necrotic area detected on the grafted tissues.

Oxygen Radical-Generating Metabolites Secreted by Eutypa and Esca Fungal Consortia: Understanding the Mechanisms Behind Grapevine Wood Deterioration and Pathogenesis.

Eutypa dieback and Esca complex are fungal diseases of grape that cause large economic losses in vineyards. These diseases require, or are enhanced by, fungal consortia growth which leads to the deterioration of the wood tissue in the grapevine trunk; however, pathogenesis and the underlying mechanisms involved in the woody tissue degradation are not understood. We examined the role that the consortia fungal metabolome have in generating oxygen radicals that could potentially play a role in trunk decay and pathogenesis. Unique metabolites were isolated from the consortia fungi with some metabolites preferentially reducing iron whereas others were involved in redox cycling to generate hydrogen peroxide. Metabolite suites with different functions were produced when fungi were grown separately vs. when grown in consortia. Chelator-mediated Fenton (CMF) chemistry promoted by metabolites from these fungi allowed for the generation of highly reactive hydroxyl radicals. We hypothesize that this mechanism may be involved in pathogenicity in grapevine tissue as a causal mechanism associated with trunk wood deterioration/necrosis in these two diseases of grape.

Understanding the control strategies effective against the esca leaf stripe symptom: the edge hypothesis

A peculiar symptom that may develop in grapevines affected by wood pathogens involved in the esca complex of diseases is the leaf stripe symptom, which also gives the name to the Grapevine Leaf Stripe Disease. Multiple studies have revealed strong links between fungal presence, wood symptomatology and expression of the leaf stripe symptom. However, numerous other factors have been shown to play roles in symptom onset, incidence, severity and yearly fluctuation of this disease. While the factors triggering the leaf stripe symptom are still under investigation, three control strategies have been proven effective for substantially reducing its expression, namely trunk surgery, and applications of sodium arsenite or a fertilizer mixture. These control strategies are examined here, including their (putative or confirmed) modes of action, and how they may influence the leaf stripe symptom development. In this article, we also propose the ‘edge’ hypothesis to tentatively explain symptoms onset, keeping in consideration past knowledge and recent advances in the understanding of the esca leaf stripe symptom. Ultimately, it is our intention to offer food-for-thought and stimulate debate within the phytopathological community.

Activity of Trichoderma asperellum Strain ICC 012 and Trichoderma gamsii Strain ICC 080 Toward Diseases of Esca Complex and Associated Pathogens.

Grapevine trunk diseases are widespread in all grape-growing countries. The diseases included in the Esca complex of diseases are particularly common in European vineyards. Their distinctive foliar symptoms are well known to be associated not only with losses in quantity, as with all grapevine wood diseases, but also with losses in the quality of the crop. Protection of pruning wounds is known to reduce infections in artificial inoculations and, to some extent, reduce the external leaf symptoms. The application of biological control agents in the field is typically started at the first appearance of symptoms. In this article, the two strains belonging to two different species, Trichoderma asperellum ICC 012 and T. gamsii ICC 080, which are present in a commercial formulation, were tested in vitro, in vivo in artificial inoculation, and in the field in long-term experiments where the wounds on four young asymptomatic vineyards were protected since 1 or 2 years after planting. The in vitro trials highlighted the different temperature requirements of the two strains, the direct mycoparasitizing activity of T. asperellum, and the indirect activity shown by both Trichoderma strains. The in vivo trials confirmed the ability of the two strains to reduce the colonization following artificial inoculations with the high, unnatural concentration of spores used in artificial infections, even if with variable efficacy, and with long persistence as they could be reisolated 7 months post-application. The preventive applications carried out over 9 years showed a very high reduction in symptom development in the treated vines, on annual and cumulated incidence and on the death of vines, with disease reduction varying from 66 to almost 90%. Early and annual application of protection to the pruning wounds appears to be the best method for reducing damages caused by grapevine leaf stripe disease (a disease of the Esca complex of diseases). Trichoderma appears to offer an efficient, environmentally friendly, and long-lasting protection in the presence of a natural inoculum concentration.

Trunk Surgery as a Tool to Reduce Foliar Symptoms in Diseases of the Esca Complex and Its Influence on Vine Wood Microbiota.

In the last few years, trunk surgery has gained increasing attention as a method to reduce foliar symptoms typical of some of the Esca complex diseases. The technique relies on the mechanical removal of decayed wood by a chainsaw. A study on a 14-year-old Cabernet Sauvignon vineyard was carried out to validate the efficacy of trunk surgery and explore possible explanations behind it. Three levels of treatment were applied to three of the most characteristic symptoms associated with some diseases of the Esca complex, such as leaf stripe symptoms (LS), wilted shoots (WS) and apoplexy (APP). The most promising results were obtained by complete trunk surgery, where the larger decay removal allowed lower symptom re-expression. According to the wood types analyzed (decay, medium and sound wood), different changes in microbiota were observed. Alpha-diversity generally decreased for bacteria and increased for fungi. More specifically, main changes were observed for Fomitiporia mediterranea abundance that decreased considerably after trunk surgery. A possible explanation for LS symptom reduction after trunk surgery could be the microbiota shifting caused by the technique itself affecting a microbic-shared biochemical pathway involved in symptom expression.

Fomitiporia punicata and Phaeoacremonium minimum associated with Esca complex of grapevine in China

The Esca disease complex includes some of the most important trunk diseases of grapevines (Vitis spp.) and causes serious yield losses in grape production worldwide. However, there has been no detailed study on its presence and associated pathogens in China. During 2017–2019, a preliminary field survey was conducted in eight vineyards in Hebei and Ningxia provinces, China when unusual foliar symptoms were observed. Symptoms were distinct tiger striped leaves, which are typical of grapevine leaf stripe disease (GLSD), one of the most common diseases in the Esca complex. Tiger-stripe leaf symptoms were found in four vineyards, and incidence was cultivar dependent varying with vineyard and year. A total of 266 fungal isolates were obtained from wood tissues of grapevines with typical foliar symptoms of GLSD. Based on morphological characters and multigene-combined phylogenetic analyses, the Ascomycete Phaeoacremonium minimum, one of the pathogens associated with Esca complex was identified. The basidiomycete Fomitiporia punicata, which has never been reported infecting grapevine, was also identified and found to be associated with wood rot in grapevine. The remaining isolates included some known wood pathogens, such as Neofusicoccum species and Diaporthe species. Koch’s postulates were performed in the greenhouse, confirming that both F. punicata and P. minimum caused leaf interveinal chlorosis and necrosis that resembled the GLSD symptoms of the Esca complex observed in the field. The present study provides the first detailed report of the Esca complex in China. In addition, this is the first record of F. punicata associated with Esca complex of grapevine worldwide. The results of this study provide new insights into the knowledge of the Esca complex.

A Lipidomic Analysis of Leaves of Esca-Affected Grapevine Suggests a Role for Galactolipids in the Defense Response and Appearance of Foliar Symptoms.

Both qualitative and quantitative changes occur in the lipid composition of Vitis vinifera L. tissues, which may compromise the defense response against Esca complex disease, a widespread and damaging trunk disease. In this study, a lipidomic analysis of grapevine leaves is conducted to assess how lipid membrane remodeling relates to the emergence and progression of Esca foliar symptoms. In total, 208 molecular species (including lipids, four hormones, and some other compounds of the metabolism of lipids) were detected. Lipid species were readily assigned to the classes fatty acyls, glycerolipids, glycerophospholipids, sphingolipids, sterols, and prenol lipids. Using different clustering analyses, distinct metabolic pathways stimulated at different stages of disease development were characterized. These analyses revealed consistent changes in the abundance of 13 galactolipids and two diacylglycerolipids. Overall, the observations indicated an increment in the levels of these lipid species in leaves of asymptomatic vines and a progressive drop with increasing foliar symptom severity in symptomatic vines. Five fatty acids also appear to exert a central role in the etiopathogenesis of Esca complex disease because of their accumulation in leaves of asymptomatic vines, namely, heptadecanoic, linoleic, γ-linolenic, arachidonic, and stearic acids. Symptomatic leaves were characterized by high levels of all lipid classes, except for galactolipids, lyso-galactolipids, and compounds relevant to the biosynthesis of chlorophylls and carotenoids, that exhibited decreased levels. The data also suggested a jasmonic acid-associated signaling mechanism activation upon the invasion of woods by Esca-associated fungi, compared with abscisic and salicylic acids. Further research is required for validation of these results with additional molecular analyses using more vine cultivars.

Long-term effects of Trichoderma asperellum and Trichoderma gamsii on the prevention of esca in different vineyards of Northeastern Italy

Among wood diseases, esca complex has increased over the last decades around Europe, and there are no chemical solutions that can limit its spread in vineyards. During a 7-year trial in 3 vineyards, half of the surface was sprayed every season with a solution of Trichoderma asperellum and Trichoderma gamsii at the phenological stage of bleeding, and half of the vineyard remained untreated. During August and September every year, the fate of esca symptoms on the single vines was monitored, distinguishing light, medium-to-severe leaf tiger stripe symptoms, and acute symptoms, including apoplexy. During the 7-year period, the vines affected by esca (all symptoms) increased over time in both the control and the sprayed treatments. Among the symptoms, Trichoderma was demonstrated to reduce the impact of both light tiger-stripe symptoms and apoplexy, while no significant differences were shown in the medium-to-severe symptoms A 22% reduction in the incidence of infected vines was ascertained after seven years of Trichoderma application. Regarding meteorological conditions, a significant positive correlation was found between the amount of rain in May and the occurrence of Esca in the field at the end of the season.

Grapevine Trunk Diseases Management in Vineyards from Central Transylvania

Grapevine trunk diseases (GTD) are among the most important diseases reported in vineyards in central Transylvania. On average, up to 5% of the vineyards are affected by the GTD although there are also vineyards where the incidence of the attack exceeds 15%. Recent studies show that the importance of pathogens in wood is so great that they are considered limiting factors that affect the stability of the world’s vineyards. The main objective of this study is to develop new sustainable management alternatives for the GTD control. For this purpose, an agroecological variant including prophylactic and cultural measures and two treatments with biofungicides based on: Trichoderma atroviride strain 8, Trichoderma atroviride strain B11 and Trichoderma harzianum, were tested. The frequency of the attack of the main four GTD diseases (Esca complex, Phomopsis dieback, Eutypa dieback and Crown gall) on the SCDVV Blaj homologated grapevine varieties, ‘Astra’, ‘Amurg’, ‘Brumariu’, ‘Blasius’ ‘Radames’, ‘Rubin’ and ‘Selena’, was assessed showing that these had a lower frequency of the symptoms compared with the widely cultivated variety ‘Feteasca regala’. Also the effect of training system (Classical versus semi-high Guyot) on GTD is presented. The classical system had decreased the frequency of crown gall and Phomopsis dieback, and the semi-high Guyot system had decreased Eutypa dieback’s frequency, indicating that the training system is an important tool of the agroecological system in maintaing the health of grapevine. Biofungicides tested help reduce the symptoms of GTD, but not enough to help reduce the premature death of grapevine.

Exhibition of Local but Not Systemic Induced Phenolic Defenses in Vitis vinifera L. Affected by Brown Wood Streaking, Grapevine Leaf Stripe, and Apoplexy (Esca Complex).

Balance between constitutive and induced responses provides plants flexibility to cope with biotic stresses. This study tested the hypothesis that invasion of grapevine wood by esca-associated fungi induces the production of defensive compounds as part of locally- and systemically-induced responses. In a vineyard, different symptomatic expressions of “Esca complex” in Vitis vinifera L. ‘Malvasia’ were evaluated in annual inspections. Then, levels of phenolics and fatty acids were determined in asymptomatic leaves of brown wood streaking (BWS) and grapevine leaf stripe (GLSD) vines, and in symptomatic leaves of GLSD and apoplectic vines; the results were compared with levels in healthy vines. In asymptomatic leaves of BWS and some GLSD vines, levels of phenolics decreased, independent of the total phenolic group. Such responses were usually associated with an increase in levels of linoleic, γ-linolenic and arachidonic acids, well-known signal transduction mediators. In symptomatic leaves, levels of phenolics increased, which is consistent with a locally-induced response; the onset of symptoms coincided with the highest increases e.g., 35% for quercetin-3-O-glucuronide. Thus, the long latency period between trunk invasion by fungi and visible foliar damage and the year-to-year fluctuation in symptomatic expressions observed with “Esca complex” might be partially attributed to a better utilization of constitutive defenses.

The Esca complex in German vineyards: does the training system influence occurrence of GLSD symptoms?

The Esca complex is one of the most destructive grapevine trunk diseases (GTDs) worldwide. Several factors, such as plant age, grapevine cultivar, or pattern of precipitation have been identified as possible driving forces of the disease. In the present study, a 4-year monitoring of grapevine leaf stripe disease (GLSD) symptoms in vineyards located in three areas in Rhineland-Palatinate was conducted. Vineyards of different age and planted with different cultivars, both traditional and new ones tolerant against Powdery and Downy Mildew, were chosen. All vineyards were equally subdivided into minimally and intensively pruned sections. The following aspects with regard to the training system were investigated: i) the occurrence of GLSD over the season; ii) the possible influence of cultivar, plant age and precipitation on symptom development; and iii) the possible impact of the training system on the incidence of GLSD. The seasonal patterns of symptom appearance in general were identical for the years 2015, 2016 and 2017. In 2018, however, the maximum peak of newly affected vines was reached about 4 weeks earlier, which is probably linked to the fast phenological development of the vines in this particular year. The training system did not affect the seasonal symptom appearance. All investigated parameters, i.e. cultivar, plant age and precipitation, were shown to have at least some influence on symptoms incidence, even though some of the results were inconsistent over the period of monitoring. Concerning the influence of the training system, in 2015 no differences between minimally pruned (1.8%) and intensively pruned (1.9%) vines were found. However, in the following year minimally pruned vines (6.9%) expressed significantly more symptoms than intensively pruned vines (4.9%). In the years 2017 and 2018 the opposite was the case. 2.6% and 2.4%, respectively, of the minimally pruned vines showed GLSD symptoms, while for the intensively pruned vines the mean values were 4.5% and 3.6%, respectively. Our study represents the first systematic GLSD related data collection in German vineyards over an extended period of time.