Plasmopara Viticola Research Articles

Exploring the association between latent Plasmopara viticola infection and downy mildew epidemic in commercial vineyards: Application of qPCR assay

AbstractIt is critical to quantify latent Plasmopara viticola infections in commercial vineyards rapidly and accurately to estimate the potential for grapevine downy mildew (GDM) epidemics. In this study, a well‐established quantitative PCR (qPCR) assay was employed to quantify the amount of P. viticola in asymptomatic grapevine leaves from various commercial vineyards in the Ningxia Hui Autonomous Region (Ningxia), China. The qPCR revealed efficient detection of P. viticola, with 56.6% and 95.8% of the asymptomatic leaves testing positive to the pathogen in 2018 and 2019, respectively. The molecular disease index (MDI), which offers insights into the progression of latent infection preceding the appearance of visible GDM symptoms, showed relatively modest values in the initial phases. However, it increased variably as grapevines grew. The disease index progress curve and the relative area under the disease progress curve revealed that all assessed vineyards experienced different degrees of epidemics after the initial GDM observation, with most vineyards experiencing more severe GDM epidemics in 2019 than in 2018. Bayesian and non‐linear regression analyses demonstrated that MDI data matched well with occurrence of GDM at early, mid and late stages of disease, and the overall accuracy of predictions exceeded 50%, 64% and 70%, respectively. Furthermore, latent infection levels were positively correlated with subsequent assessments of disease progression (p < 0.001). This study provides evidence for the interrelation between latent P. viticola infections and development of GDM epidemics under field conditions. This insight has substantive implications for the formulation of effective disease management strategies.

Fighting Tomato Fungal Diseases with a Biocontrol Product Based on Amoeba Lysate.

New solutions to reduce the use of chemical pesticides to combat plant diseases and to meet societal and political demands are needed to achieve sustainable agriculture. Tomato production, both in greenhouses and in open fields, is affected by numerous pathogens. The aim of this study is to assess the possibility of controlling both late blight and powdery mildew in tomatoes with a single biocontrol product currently under registration. The biocontrol product AXP12, based on the lysate of Willaertia magna C2c Maky, has already proved its efficacy against downy mildew of grapevine and potato late blight. Its ability to elicit tomato defenses and its efficacy in the greenhouse and in the field were tested. This study establishes that AXP12 stimulates the tomato genes involved in plant defense pathways and has the capacity to combat in greenhouse and field both late blight (Phytophtora infestans) and powdery mildew (Oidium neolycopersici and Leveillula taurica) of tomato.

Predictive models for grape downy mildew (Plasmopara viticola) as a decision support system in Mediterranean conditions

Plasmopara viticola (Peronosporales: Peronosporaceae) is a highly destructive disease that can cause very serious damage under favorable conditions. Cultural practices, disease-tolerant varieties, and phytosanitary treatments have been effective tools to control this disease. However, predictive models such as decision support systems (DSS) could help reduce the need for phytosanitary treatments. In this study, we aimed to develop, adjust, and validate a customized predictive model at the plot level, comparing it with the other three existing models (Milvit, VitiMeteo-Plasmopara, and Goidanich) in Mediterranean conditions. Downy mildew symptoms were observed in the field and predicted using the four mentioned models in eight plots during the 2018 and 2019 campaigns. All tested models predicted possible daily infection cycles, which were grouped into infection blocks every 5–7 days to validate predicted data with in-field observations. In Mediterranean conditions, Milvit and VitiMeteo-Plasmopara models provided both over-prediction and under-prediction infection blocks compared to field observations. However, the Goidanich model only provided over-prediction infection blocks with very few matches to field observations. The UR-model was successfully improved to adjust it to Mediterranean conditions, and it matched observed and predicted infection blocks in 56,25% of the plots and years. However, the UR-model was more accurate (75% matching) in humid years like 2018 than in dryer years like 2019 (37,5% matching), although in both cases it was the most accurate model to be used as a decision support system.

Field and In vitro Study of Pronos and Dormulin against Downy Mildew and Powdery Mildew Diseases of Grape

Downy mildew and powdery mildew are destructive diseases of grapes which require application of fungicides. Fungicides are expensive and cause ecological contamination and resistance. Pronos and Dormulin are 'Multi nutrient fertilizers' which were evaluated against the diseases. The field experiments were conducted against powdery mildew (Sangli, Maharashtra) and downy mildew (Theni, Tamil Nadu) in grapes. In vitro experiment against downy mildew conducted at ICAR-National Research Centre for Grapes laboratory. In vitro study comprised of 12 treatments. In the case of downy mildew, a field experiment was set with 7 treatments. The foliar application of Dormulin flowering @ 5 g/L of water, and Pronos @ 1.5 g/L of water recorded the lowest percent disease index on leaves, and they were at par with Dormulin (vegetative) followed by 3 sprays of Dormulin (flowering) @ 5 g/L ofwater. In the case of powdery mildew, experiment was set with 10 treatments. On leaves, Pronos (curative) and Pronos (Prophylactic) @ 1.5 g/L of water and Dormulin 1 flowering (curative) @ 5 g/L of water showed the lowest percent disease index on leaves than the untreated control. Therefore, Dormulin flowering @ 5 g/L and Pronos @ 1.5 g/L for downy mildew and Pronos (curative) and Pronos (Prophylactic) @ 1.5 g/L water and Dormulin 1 flowering (curative) @ 5 g/L for powdery mildew were claimed to be effective for controlling diseases. In vitro study showed that Dimethomorph at 1g/L of water was found to be superior over all the treatments with high disease suppression followed by Pronos @1.5gm/L, Dormulin-V1- Flowering grade, and Dormulin-V2- Flowering grade @ 10g/L with slight sporulation. Marketable yield was significantly higher with Pronos (curative) which was on par with Dormulin application as compared to control and fungicide treatment. Use of mineral nutrients in an appropriate proportion is one of the new approaches for plant disease management.

TaqMan-MGB PCR Method for Rapid Detection of QoI Fungicide Resistance in Chinese Populations of Plasmopara viticola.

Grape downy mildew caused by Plasmopara viticola is one of the most devastating diseases of grapevine worldwide. Quinone outside inhibitor (QoI) fungicides are commonly used for the control of the pathogen in grape fields across China. However, their recurrent use could lead to the emergence of resistance against these compounds. Based on the most common mutation in resistant isolates, a glycine to alanine substitution at amino acid position 143 (G143A) in the cytochrome b protein, a TaqMan-MGB PCR was developed for the rapid detection of resistance to the QoI fungicide azoxystrobin in P. viticola. Specificity and sensitivity of this method showed it could specifically detect the point mutations linked with QoI resistance in P. viticola, and the detection limit was 0.2 pg. It could also quantify the resistance allele even in isolate mixtures containing as little as 5% QoI-resistant P. viticola strains. With this method, a large P. viticola population (n = 2,373) was screened, and QoI-resistant isolates were identified for the first time in China. The average frequencies of the resistant genotype from eight major-grapevine regions were up to 66%. Taken together, the results not only provide a novel tool for the rapid distinction and quantification of the QoI-resistant allele in P. viticola but also provide important references for fungicide selection and application, which will facilitate resistance management of grape downy mildew and improve grape production systems in Chinese vineyards.

First report of quinone outside inhibitor stigmatellin binding type (QoSI) resistance in Plasmopara viticola in India

First report of quinone outside inhibitor stigmatellin binding type (QoSI) resistance in <i>Plasmopara viticola</i> in India

Development of hypothetical infection model based on environmental variables for Plasmopara viticola (Berk. &amp; M.A. Curtis) Berl. &amp; De Ton

Development of a hypothetical infection model for Plasmopara viticola based on environmental variables was applied to black grape variety Vranec. The infected leaves were digitally quantified using the software platform 'ImageJ' to determine disease severity. The resulting data, along with inputs of average temperature and leaf wetness duration, were used to establish a regression relationship. Downy mildew infection reaches its maximum when we have an average of 2 hours and 29 minutes of leaf wetness duration and an average daily temperature of 26.8 ° C. The regression relationship then by used to describe the results, and based on this, a hypothetical infection model for P. viticola was developed.

Evaluation of grapevines for resistance to downy mildew (Plasmopara viticola) under greenhouse conditions

Evaluation of grapevines for resistance to downy mildew (Plasmopara viticola) under greenhouse conditions

Remote detection of fungal pathogens in viticulture using laser-induced fluorescence: an experimental study on infected potted vines

IntroductionPathogenic fungi, such as Plasmopara viticola and Erysiphe necator, severely threaten the annual yield of grapes in both quantity and quality. In contrast to other crop production systems, fungicides are intensively applied in viticulture as a countermeasure. The goal of precision viticulture is to optimize vineyard performance as well as the environmental impact by reducing fungicides and applying different techniques and combined strategies. Therefore, new emerging technologies are required, including non-invasive detection, as well as monitoring and tools for the early and in-field detection of fungal development. MethodsIn this study, we investigated leaves of potted vines (Vitis vinifera cv. ‘Riesling’) and traced the development of the inoculated leaves using our new remote detection system vinoLAS®, which is based on laser-induced fluorescence spectroscopy. We ran a measurement campaign over a period of 17 days.ResultsWe were able to detect a leaf infection with P. viticola, the causal agent of downy mildew, between 5 and 7 days after inoculation. Our results provide evidence for a successful application of laser-based standoff detection in vineyard management in the future. Thus, the vinoLAS system can serve as a model technology for the detection of pathogenic disease symptoms and thus monitoring complete vineyard sites. This allows for early countermeasures with suitable crop protection approaches and selected hot-spot treatments.DiscussionAs P. viticola is considered one of the most damaging fungi in European viticulture, disease mapping via this monitoring tool will help to reduce fungicide applications, and will, therefore, support the implementation of the European Green Deal claims.

Unravelling molecular mechanisms involved in resistance priming against downy mildew (Plasmopara viticola) in grapevine (Vitis vinifera L.)

Downy mildew (DM; Plasmopara viticola) is amongst the most severe fungal diseases in viticulture and the reason for the majority of fungicide applications. To reduce synthetic and copper-based fungicides, there is an urgent need for natural alternatives, which are being increasingly tested by the industry and the research community. However, their mode of action remains unclear. Therefore, our study aimed to investigate the transcriptomic changes induced by oregano essential oil vapour (OEOV) in DM-infected grapevines. OEOV was applied at different time points before and after DM infection to differentiate between a priming effect and a direct effect. Both pre-DM treatment with OEOV and post-infection treatment resulted in a significant reduction in DM sporulation. RNA-seq, followed by differential gene expression and weighted gene co-expression network analysis, identified co-expressed gene modules associated with secondary metabolism, pathogen recognition and response. Surprisingly, the molecular mechanisms underlying the efficiency of OEOV against DM appear to be independent of stilbene synthesis, and instead involve genes from a putative signalling pathway that has yet to be characterized. This study enhances our understanding of the molecular regulation of innate plant immunity and provides new insights into the mode of action of alternative natural antifungal agents.

Peptide analogs of a Trichoderma peptaibol effectively control downy mildew in the vineyard.

Plasmopara viticola, the agent of grapevine downy mildew, causes enormous economic damage and its control is primarily based on synthetic fungicides. The European Union (EU) policies promote reducing reliance on synthetic plant protection products. Biocontrol agents (BCA) such as Trichoderma constitute a resource for the development of biopesticides. Trichoderma species produce secondary metabolites such as peptaibols, whose poor water solubility hampers their practical use as agrochemicals. To identify new bio-inspired molecules effective against P. viticola, some water-soluble peptide analogs of the peptaibol trichogin were synthesized. In grapevine leaf disk assays, various peptides at 50 µM completely prevented P. viticola infection after zoosporangia inoculation. Microscopic observations carried out with one of the most effective peptides showed that it causes membrane lysis and cytoplasm granulation of both zoosporangia and zoospores. Among the effective peptides, 4r was selected for a two-year field trial experiment. In the vineyard, the peptide administered at 100 µM (equivalent to 129.3 g/ha) overall reduced significantly disease incidence and severity on both leaves and bunches, allowing protection levels similar to those obtained with a cupric fungicide. In the second-year trial, reduced dosages were also tested, and results indicated that even by reducing the peptide concentration by 50 or 75%, a significant decrease in the disease level was obtained at the end of the trial. The peptide did not show any phytotoxic effect. Previously, peptide 4r had been demonstrated to be active against other fungal pathogens, including the grapevine fungus Botrytis cinerea. Thus, this peptide may be a candidate for broad-spectrum fungicide whose biological properties deserve further investigation.

Volatile linalool activates grapevine resistance against downy mildew with changes in the leaf metabolome

Volatile organic compounds (VOCs) are produced by plants in response to biotic and abiotic stimuli. In grapevine, volatile terpenoids are triggered by downy mildew infection (caused by Plasmopara viticola), suggesting their involvement in plant defense responses. In particular, linalool was detected in leaves of downy mildew-resistant genotypes, but no information is available on its involvement in the defense mechanisms against P. viticola. The aim of this study was to investigate the defense mechanisms activated by linalool in grapevine leaves against P. viticola and to identify metabolic changes associated with linalool-induced resistance. Linalool treatment reduced downy mildew severity on leaf disks of susceptible grapevines (cultivar Pinot noir) and stimulated callose deposition at the sites of P. viticola infection. Moreover, the upregulation of defense-related genes was found in linalool-treated leaf disks, indicating the activation of grapevine defense mechanisms of salicylic acid and jasmonic acid pathways. Linalool treatment caused changes in the leaf metabolome of mock-inoculated and P. viticola-inoculated samples at one and six days post inoculation, as revealed by ultra-high pressure liquid chromatography-electrospray ionization-high-resolution quadrupole time of flight-mass spectrometry. Pathway analysis of annotated features with significant increases and decreases in abundance revealed the reprogramming of amino acid, phenylpropanoid, and terpenoid metabolisms in response to linalool treatment and P. viticola inoculation. In particular, features with significant increases in abundance in linalool-treated samples mainly belonged to putative phenylpropanoids, putative terpenoids, putative lipids, and lipid-like compounds, including molecules possibly associated with plant defense against pathogens, such as 2-phenylethanol, 2,4-heptadienal, α-terpineol, citral, and geraniol. These results demonstrated that linalool induces grapevine resistance against downy mildew, acting as a signaling molecule for plant resistance induction.

Plant Resistance Inducers Affect Multiple Epidemiological Components of Plasmopara viticola on Grapevine Leaves.

Plant resistance inducers (PRIs) harbor promising potential for use in downy mildew (DM) control in viticulture. Here, the effects of six commercial PRIs on some epidemiological components of Plasmopara viticola (Pv) on grapevine leaves were studied over 3 years. Disease severity, mycelial colonization of leaf tissue, sporulation severity, production of sporangia on affected leaves, and per unit of DM lesion were evaluated by inoculating the leaves of PRI-treated plants at 1, 3, 6, 12, and 19 days after treatment (DAT). Laminarin, potassium phosphonate (PHO), and fosetyl-aluminium (FOS) were the most effective in reducing disease severity as well as the Pv DNA concentration of DM lesions on leaves treated and inoculated at 1 and 3 DAT; PHO and FOS also showed long-lasting effects on leaves established after treatment (inoculations at 6 to 19 DAT). PRIs also prevented the sporulation of Pv on lesions; all the PRI-treated leaves produced fewer sporangia than the nontreated control, especially in PHO-, FOS-, and cerevisane-treated leaves (>75% reduction). These results illustrate the broader and longer effect of PRIs on DM epidemics. The findings open up new perspectives for using PRIs in a defense program based on single, timely, and preventative field interventions.

Genome Resource of Streptomyces atratus PY-1, a Broad-Spectrum Antimicrobial Strain in Particular Antagonistic Against Plasmopara viticola.

Streptomyces atratus PY-1 exhibited promising antimicrobial properties; in particular, it is highly inhibitory to Plasmopara viticola, which causes downy mildew of grape. It is very necessary to carry out systematic and in-depth research on the PY-1 strain for the improvement, application, and promotion of biocontrol agents. The PY-1 genome was fully sequenced and assembled. We present the draft genome sequence of PY-1, with a size of 9, 254, and 781 bp. Preliminary analysis on the PY-1 genome sequence shows that at least 35 gene clusters are involved in the biosynthesis of polyketides, terpenes, and nonribosomally synthesized peptides.

A Bayesian model for control strategy selection against Plasmopara viticola infections.

Plant pathogens pose a persistent threat to grape production, causing significant economic losses if disease management strategies are not carefully planned and implemented. Simulation models are one approach to address this challenge because they provide short-term and field-scale disease prediction by incorporating the biological mechanisms of the disease process and the different phenological stages of the vines. In this study, we developed a Bayesian model to predict the probability of Plasmopara viticola infection in grapevines, considering various disease management approaches. To aid decision-making, we introduced a multi-attribute utility function that incorporated a sustainability index for each strategy. The data used in this study were derived from trials conducted during the production years 2018-2020, involving the application of five disease management strategies: conventional Integrated Pest Management (IPM), conventional organic, IPM with substantial fungicide reduction combined with host-defense inducing biostimulants, organic management with biostimulants, and the use of biostimulants only. Two scenarios were considered, one with medium pathogen pressure (Average) and another with high pathogen pressure (Severe). The results indicated that when sustainability indexes were not considered, the conventional IPM strategy provided the most effective disease management in the Average scenario. However, when sustainability indexes were included, the utility values of conventional strategies approached those of reduced fungicide strategies due to their lower environmental impact. In the Severe scenario, the application of biostimulants alone emerged as the most effective strategy. These results suggest that in situations of high disease pressure, the use of conventional strategies effectively combats the disease but at the expense of a greater environmental impact. In contrast to mechanistic-deterministic approaches recently published in the literature, the proposed Bayesian model takes into account the main sources of heterogeneity through the two group-level effects, providing accurate predictions, although precise estimates of random effects may require larger samples than usual. Moreover, the proposed Bayesian model assists the agronomist in selecting the most effective crop protection strategy while accounting for induced environmental side effects through customizable utility functions.

The pivotal role of high-resolution mass spectrometry in the study of grape glycosidic volatile precursors for the selection of grapevines resistant to mildews.

A breeding program to produce new grape varieties tolerant to main vine fungal pathogens (Plasmopara viticola and Erysiphe necator) is carrying out by crossing Vitis vinifera cv. "Glera" with resistant genotypes such as "Solaris," "Bronner," and "Kunleany." Firstly, resistance gene-based markers analyses allowed the identification of five genotypes, which have inherited the resistance loci against mildews. To select those that also inherited the phenotype as close as possible to 'Glera' suitable to be introduced in the Prosecco wine production protocols, the grape glycosidic derivatives were studied by UHPLC/QTOF mass spectrometry. Targeted identification of the metabolites was performed using a database expressly constructed by including the glycosidic volatile precursors previously identified in grape and wine. A total of 77 glycosidic derivatives including many aroma precursors and some variety markers, were identified. Original resistant genotypes had distinct metabolomic profiles and different to 'Glera', while the crossings showed varying similarity degrees to V. vinifera parent. Findings demonstrated the Glera × Bronner and Glera × Solaris crossings are more suitable to produce high-sustainable Prosecco wines. Coupling of glycosidic volatile precursors profilingto multivariate statistical analysis was effective for phenotypic characterization of grapes and to evaluate their enological potential.

Variation in Susceptibility to Downy Mildew Infection in Spanish Minority Vine Varieties.

Downy mildew is one of the most destructive diseases affecting grapevines (Vitis vinifera L.). Caused by the oomycete Plasmopara viticola (Berk. and Curt.) Berl. and de Toni, it can appear anywhere where vines are cultivated. It is habitually controlled by the application of phytosanitary agents (copper-based or systemic) at different stages of the vine growth cycle. This, however, is costly, can lead to reduced yields, has a considerable environmental impact, and its overuse close to harvest can cause fermentation problems. All grapevines are susceptible to this disease, although the degree of susceptibility differs between varieties. Market demands and European legislation on viticulture and the use of phytosanitary agents (art. 14 of Directive 128/2009/EC) now make it important to know the sensitivity of all available varieties, including minority varieties. Such knowledge allows for a more appropriate use of phytosanitary agents, fosters the commercial use of these varieties and thus increases the offer of wines associated with different terroirs, and helps identify material for use in crop improvement programmes via crossing or genetic transformation, etc. Over 2020-2021, the susceptibility to P. viticola of 63 minority vine varieties from different regions of Spain was examined in the laboratory using the leaf disc technique. Some 87% of these varieties were highly susceptible and 11% moderately susceptible; just 2% showed low susceptibility. The least susceptible of all was the variety Morate (Madrid, IMIDRA). Those showing intermediate susceptibility included the varieties Sanguina (Castilla la Mancha, IVICAM), Planta Mula (Comunidad Valenciana, ITVE), Rayada Melonera (Madrid, IMIDRA), Zamarrica (Galicia, EVEGA), Cariñena Roja (Cataluña, INCAVI), Mandrègue (Aragón, DGA) and Bastardo Blanco (Extremadura, CICYTEX). The highly susceptible varieties could be differentiated into three subgroups depending on sporulation severity and density.

Combining Trichoderma koningiopsis and chitosan as a synergistic biocontrol and biostimulating complex to reduce copper rates for downy mildew control on grapevine

Plasmopara viticola, causal agent of downy mildew and one of the most severe grapevine diseases, is commonly controlled by multiple fungicide applications, primarily based on copper compounds in organic viticulture. Biostimulants and biocontrol agents could make a major contribution to pesticide reduction. A synergistic biocontrol and biostimulating complex consisting of Trichoderma sp. and chitosan was investigated to achieve copper fungicide reduction in the control of P. viticola. To ensure complex efficacy, the interactions and effects of all agents need to be investigated at the tri-trophic level of grapevine, downy mildew, and biocontrol and biostimulating complex. To guarantee the compatibility of Trichoderma sp. and chitosan, the chitosan tolerance of different copper-tolerant Trichoderma isolates was investigated in mycelial growth and germination tests. A T. koningiopsis isolate proved to be highly chitosan-tolerant was identified for further studies. The timing of spray application with T. koningiopsis and various chitosans was evaluated for efficacy against P. viticola. In the period 0 to 1 day before inoculation with the pathogen, the formation of the sporangia number was significantly reduced by the tested agents. To further describe the mode of action and efficacy of T. koningiopsis and chitosan against P. viticola, the application of single agents on upper and lower grapevine leaves inoculated with the pathogen in comparison to resistance inducers and copper fungicide were tested. Moreover, the combination of T. koningiopsis with different chitosans and a reduced copper rate was investigated on the respective leaf sides of greenhouse plants. Both, a direct and indirect mode of action against downy mildew was demonstrated. Regardless of the treated leaf side, sporulation of downy mildew was clearly inhibited compared to the untreated control. Moreover, microscopic images showed successful establishment of T. koningiopsis and uniform distribution of chitosan on leaves. The tested biocontrol and biostimulating complex might show a promising combatting tool against P. viticola while simultaneously reducing copper rate.

The Influence of Climatic Conditions on Downy Mildew and Powdery Mildew in Târnave Vineyard

The main diseases that affect the vineyards in the Târnave vineyard are: grapevine downy mildew caused by Plasmopara viticola and grapevine powdery mildew caused by Uncinula necator. The present study aimed to address the relationship between grapevine cultivars and the main diseases, downy mildew and powdery mildew, according to climatic variability and treatments applied. The analysis was carried out over two consecutive years 2021 and 2022 on five new cultivars, the creation of SCDVV Blaj: Selena, Blasius, Rubin, Radames and Brumăriu. Disease attack was determined during the vegetation period, until harvest. Cultivar susceptibility varied, some cultivars were relatively tolerant and no cultivar was highly resistant to both diseases. In addition, a difference between foliar and grape berry susceptibility to the two diseases was observed for several cultivars. This data provide a basis for developing low-treatment disease management strategies for specific grapevine cultivars based on downy mildew and powdery mildew susceptibility/tolerance.

Use of a real-time PCR method to quantify the primary infection of Plasmopara viticola in commercial vineyards

Grapevine downy mildew (GDM) caused by Plasmopara viticola is a recurrent disease of wine grapes in the Ningxia Hui Autonomous Region (Ningxia) of northwestern China. However, the primary infectious pathogen in this region has not been thoroughly investigated. In this study, a multiplex real-time PCR assay was utilized to quantify P. viticola in soil, leaf residues, and asymptomatic leaf samples from ten commercial vineyards in two consecutive years to better understand the epidemiological significance of overwintering primary inoculum and its inoculum potential before the appearance of the first visual GDM symptoms. The DNA primers and multiplex real-time PCR assays that had been established exhibited specificity towards P. viticola within the test samples. The majority of the asymptomatic leaves (60%), leaf residues (80%), and soil samples (100%) tested positive for P. viticola. In addition, the amount of primary inoculum of P. viticola was found to be lower in soil than in leaf residues. The area under the disease progress curve in terms of the molecular disease index (AUDPC-MDI) was used to evaluate the overall latent P. viticola infection in asymptomatic leaves. Asymptomatic leaves were found to have different levels of P. viticola infection, and high AUDPC-MDIs correlated with a high AUDPC in terms of disease index (AUDPC-DI), with a significant correlation relationship between them (P < 0.01). Additionally, a well-correlated relationship was observed between the disease progress in the previous year and the MDIs of leaf residues and asymptomatic leaves in the following year, as well as the AUDPC-DI (Spearman’s correlation coefficient ρ = 0.643, 0.498, and 0.595, respectively) (P < 0.01). These findings provide valuable information for quantifying the primary infection of P. viticola in commercial vineyards.