Apple Scab Research Articles (Page 1)

The cultivated apple is a traditional crop for Abkhazia. However, the humid subtropical climate here promotes the intensive development of fruit diseases, such as scab (caused by Venturia inaequalis (Cooke) G. Winter) and moniliosis (caused by Monilinia fructigena (Pers.) Honey). Research efforts today are aimed at searching for formulations capable of enhancing the natural immunity of plants against these diseases. In this work, we assess the possibility of extending the protection system against apple scab and monilial rot by including a single treatment with growth regulators during the budding phase. The studies were conducted in 2022–2024 in Golden Rangers apple tree plantations in the Gulrypsh district of the Republic of Abkhazia using a generally accepted methodology. The immune-stimulating effect of the Zerebra agro©, Biosil©, and Stimmunol EF© growth regulators against fruit scab was observed in the second and third years of application. With regard to monilial rot, the effect was observed in the third year of application. Yantarin BAU© demonstrated an increased biological effectiveness against scab and moniliosis already after the first application. A single application of the Zerebra agro©, Biosil©, Stimmunol EF©, and Yantarin BAU© growth regulators during the budding period did not increase the apple yield. Energiya-M, KRP© did not exhibit an immune-stimulating effect against either scab or moniliosis. However, a single treatment of the plants with this preparation during the budding period resulted in a 23.4 % increase in the apple yield compared to the control.

Apple production, a cornerstone of global agriculture, faces significant threats from diseases such as apple scab, fire blight, powdery mildew, and cedar apple rust, which reduce yield, quality, and sustainability. Early and accurate disease classification is essential to mitigate economic losses and ensure food security. This paper evaluates traditional and modern approaches to apple plant disease classification, including manual visual diagnosis, image-based techniques, and molecular methods like PCR and ELISA. While traditional methods are accessible but error-prone, advanced technologies such as machine learning, deep learning, and sensor-based systems offer high accuracy and scalability, achieving up to 95% detection rates in controlled settings. Challenges, including limited labeled datasets, high computational costs, and poor model generalization across apple varieties and regions, hinder widespread adoption. Emerging trends, such as generative AI, explainable AI, drone-based monitoring, and edge computing, promise to enhance real-time diagnostics and accessibility. The paper also explores opportunities for integrating these technologies with precision agriculture to optimize orchard management and promote sustainability. By synthesizing current methods, technologies, and research gaps, this paper provides a comprehensive roadmap for researchers, farmers, and policymakers to advance apple disease management, fostering sustainable agricultural practices and global food security.

ABSTRACTApple scab, caused by Venturia inaequalis, is the most economically important fungal disease impacting apple production globally. Most commercial apple cultivars are susceptible to scab, although several sources of genetic resistance have been identified. The availability of genetic markers tightly linked with the functional resistance alleles is one of the factors limiting the breeding of scab‐resistant cultivars. ‘Honeycrisp’, one of the popular North American apple cultivars, is a source of Vhc1 scab resistance on linkage group 1, but the associated locus spans 12.6 cM and harbours over 200 genes. Here, we present the fine‐mapping of the Vhc1 locus, the development of haplotype‐specific simple sequence repeat (SSR) markers and the identification of candidate resistance alleles. Chromosome‐level phased genome assemblies of the scab‐resistant parent ‘Honeycrisp’ and scab‐susceptible ‘Gala’ were used to design nine novel polymorphic markers, along with two previously reported markers, spanning the Vhc1 QTL region. An F1 population derived from the two cultivars was developed and was evaluated for scab resistance across two consecutive years using the V. inaequalis isolate Vi‐19‐004 collected from Malus floribunda 821. Broad‐sense heritability was estimated at 0.66 across experiments. Phenotype–genotype association analysis fine‐mapped a moderate‐effect apple scab resistance QTL, explaining 5.2%–11.8% of phenotypic variance, to a 4.2‐cM genetic interval and a corresponding 0.85‐Mb physical region. SSR markers mdCu_2500, mdCu_3000 and CH‐Vf1 collocated with the Vhc1 QTL and can be used in future marker‐assisted selection studies for Vhc1. Six LRR‐encoding genes underlying the QTL region with enhanced expression upon inoculation with V. inaequalis were identified as scab resistance candidate alleles. These newly developed markers and candidate genes will accelerate the development of ‘Honeycrisp’ based scab‐resistant cultivars.

Triazole compounds are members of the demethylation inhibitor class of systemic agents used to combat the most widespread apple diseases worldwide, namely apple scab and powdery mildew. The dissipation kinetics of difenoconazole, mefentrifluconazole, myclobutanil, penconazole, tebuconazole and tetraconazole from commercial products in two apple cultivars (Rosana and Selena) were studied over four years. Pesticide residues in the apples were determined using the QuEChERS extraction procedure, followed by liquid chromatography–mass spectrometry analysis. Triazoles applied 84–100 days before harvest dissipated faster than those applied 44–55 days before harvest, with half-lives of 4.0–22.3 days and 7.1–43.9 days, respectively. Except for tebuconazole, all triazoles were found to be well below 30% of the maximum residue levels at the end of the pre-harvest interval, which is mandatory for products in use. The dissipation of five triazoles was evaluated during cold storage over two subsequent years. Residues of difenoconazole, myclobutanil and tebuconazole were detected at levels above 0.01 mg/kg after more than five months. The calculated risk intake values were lower than the established acceptable daily intake and acute reference dose values, indicating that the acute and chronic risks of pesticide exposure from consuming apples are not expected.

Venturia inaequalis, a hemibiotrophic ascomycete, is the causal agent of apple scab, a major disease affecting apple production worldwide. The widespread use of fungicides in orchard management has led to the selection of resistant strains. To limit the spread of these resistant strains, it is essential to understand their competitive fitness within the population. In this study, we evaluated the resistance profiles and fitness components of 23 V. inaequalis isolates from both treated and untreated orchards in Northern Italy, focusing on five fungicides: dodine, cyprodinil, trifloxystrobin, boscalid, and myclobutanil. Fitness parameters, including mycelial growth, conidia number, and conidia size, were assessed in relation to fungicide resistance and environmental factors, such as altitude. The results revealed that, overall, resistant and sensitive strains showed no significant differences in fitness, except for cyprodinil-resistant strains, which exhibited enhanced mycelial growth and increased conidia size, and dodine-resistant strains, which produced smaller conidia. Additionally, altitude influenced conidial size, with higher elevation sites correlating with smaller conidia. These findings suggest that both genetic and environmental factors contribute to conidial variation, which may impact pathogen dispersal and infection dynamics. This study highlights the resilience and potential for spread of fungicide-resistant strains and underscores the need for integrated resistance management strategies to maintain sustainable and high quality apple production.

BackgroundApple scab, caused by the hemibiotrophic fungus Venturia inaequalis (cooke) Wint., is a globally prevalent disease that severely threatens apple yield and fruit quality. Although the key resistance gene Rvi6 (resistance to Venturia inaequalis 6) has been widely deployed in apple scab-resistant breeding programs, the molecular mechanisms underlying its resistance phenotype remain poorly characterized.ResultsIn this study, we generated transgenic apple calli overexpressing Rvi6 and systematically investigated both its resistance phenotype and underlying molecular mechanisms. The Rvi6 gene presented high expression levels in leaves and fruits throughout the growth cycle, and aligning with the infection window of V. inaequalis. Rvi6 overexpression significantly reduced the levels of IAA (indole-3-acetic acid), ABA (abscisic acid), and JA (jasmonic acid), and auxin signaling, as well as the callus growth, which directly evidencing the “growth-defense trade-off” hypothesis on Rvi6-mediated apple scab resistance. The marked inhibition of V. inaequalis infection in Rvi6-overexpressing calli was attributed to increased ROS (reactive oxygen species) scavenging capacity, increased osmolyte accumulation, and maintenance of plasma membrane integrity. Additionally, Rvi6 induction depressed apple growth by reducing auxin accumulation and attenuating auxin signaling. Transcriptome analysis revealed that multiple biological processes and signaling pathways are involved in Rvi6-mediated disease resistance. Pathways related to plant‒pathogen interactions, lipid and amino acid metabolism, and flavonoid biosynthesis were significantly enriched among the upregulated pathways. Conversely, plant hormone signal transduction, protein processing and modification, and carbohydrate metabolism were enriched predominantly in the downregulated pathways.ConclusionsRvi6 exhibits high expression in leaves and fruits across the growth cycle, aligning with the infection window of V. inaequalis. Rvi6 enhances ROS scavenging capacity, osmolyte accumulation, and plasma membrane integrity, as well as suppresses apple growth, thereby restricting V. inaequalis invasion. Plant immune responses mediated by Ca2⁺ or MAPK cascade reactions, plant hormone signaling and multiple secondary metabolic mechanisms, contribute to Rvi6-mediated resistance against apple scab. This study provides novel insights into the biological functions of Rvi6.Supplementary InformationThe online version contains supplementary material available at 10.1186/s12870-025-07117-1.

Control of diffuse abaxial apple scab by the systemic fungitoxicity of fluopyram and the defense enhancement of fosetyl-Al

Abstract Grapevine (Vitis vinifera L.) synthesizes many secondary metabolites within its woody tissues, which act as a chemical defence against pathogens. The annual pruning of mature woody shoots of grapevine (also referred to as grapevine canes) from vineyards represents a renewable source of natural fungicides. We produced an extract of grapevine cane waste (Antoferine®) to evaluate its efficacy on apple scab disease in the field over three seasons from 2018 to 2020. The application of grapevine cane extract ranging from 2.5 g/L (1.25 kg/ha) to 15 g/L (7.5 kg/ha) on cider‐apple trees significantly protected apple shoots and fruits from scab disease, regardless of application time at low or high Photosynthetically Active Radiation (PAR) levels. Its efficacy was comparable to commonly used fungicides under moderate pathogen pressure in 2018 and 2019. Under a high pathogen pressure in 2020, its effect was lower than that of the commonly used fungicides while still providing protection against disease. An optimal dose of 5 g/L (2.5 kg/ha) of grapevine cane extract is suitable for use in crop protection from an industrial perspective. Under the financial support of the European Union, we submitted the dossier for approval of grapevine cane extract as a commercial biocontrol to contribute to sustainable agriculture.

In Poland, the main causal agent of sooty blotch and flyspeck disease is the fungus Microcyclosporella mali J.Frank, Schroers et Crous, which is most commonly isolated from the spots found on apples. The aim of the paper was to study the effects of essential oils extracted from Greek oregano, thyme and costmary on M. mali. Analysis of the essential oils was conducted using gas chromatography–mass spectrometry (GC–MS) with a flame ionization detector (FID). The Greek oregano essential oil was classified to the carvacrol chemotype, while the thyme and costmary were classified to the thymol and the β-thujone chemotypes, respectively. The influence of these essential oils on the viability of the M. mali conidia was analysed cytometrically. The Greek oregano oil was characterised by the significantly highest activity against the M. mali spores. The regression analysis performed showed the occurrence of a significant linear relationship between the viability of the conidia and the concentration of the essential oils, which was then the basis for the determination of MICs and MFCs. The values of these parameters in the case of the Greek oregano oil were 0.9 and 0.4%, respectively, and for the thyme oil they were 1.2 and 2.4%.

Sooty blotch and fl yspeck (SBFS) is one of the most harmful diseases of fungal origin developing on the surface of apple fruits and endangering industrial plantations in Krasnodar Krai. For a long time, fl yspeck was believed to be caused by Schizothyrium pomi (Mont. & Fr.) Arx.; however, over the past 15 years, 12 pathogens from the Schizothyrium and Zygophiala genera have been identifi ed. Data on the biological characteristics of fl yspeck-causing fungi obtained in the USA, Europe, China, Turkey, and other countries indicate signifi cant diff erences in their development depending on the weather conditions of the year and the climate of the area. In connection with the increasing harmfulness of these pathogens in Russia, we set out to study the bioecological characteristics of pathogens of the Schizothyrium genus developing in fruit agrocenoses. The studies were conducted in 2021–2024 in the Black Sea horticultural zone of Krasnodar Krai. The infection was found to persist in the form of thyriothecia on 16 plant species from 11 families (Cornaceae, Rosaceae, Staphyleaceae, Salicaceae, Sapindaceae, Betulaceae, Ranunculaceae, Fagaceae, Ulmaceae, Smilacaceae, and Caprifoliaceae). Blackberry was identifi ed as the main reservoir plant due to its widespread distribution in the study area. The level of over-wintering infection during the study period varied from 5.3 to 12.3 thyriothecia per cm of blackberry shoot. It was established that from 22.3 to 44 % of the fungus fruiting bodies do not survive the winter period. The development of thyriothecia begins in March–April followed by spreading of ascospores in April–May, up to the second or third ten-day period of June. The fi rst symptoms of apple fruit damage by fl yspeck are noted from the second ten-day period of July to the fi rst ten-day period of August. The prevalence of the disease during the harvest period varied from 1 to 50 % in cultivated areas and from 10.3 to 76.3 % in uncultivated areas. The analysis of weather conditions allowed us to conclude that air humidity, precipitation amount, and hydrothermal coeffi cient (HTC) in the summer months of vegetation determine the harmfulness of Schizothyrium sp

Apple (Malus × domestica Borkh.) production is threatened by scab, caused by the fungus Venturia inaequalis. One defense mechanism of apple trees against fungal pathogens such as V. inaequalis is the biosynthesis of antifungal compounds. Amongst these, phenolic compounds are particularly hypothesized to correlate with scab resistance, thereby offering a putative route to breed new apple cultivars with enhanced resistance. To characterize the involvement of phenolics in scab resistance, as conferred by either the Rvi6 resistance gene or through increased somatic ploidy, we monitored the phenolics profile in the leaves of apple genotypes harboring Rvi6 or increased ploidy that show enhanced levels of scab resistance compared to susceptible genotypes. Our study revealed differences in total and specific phenolic contents across the tested genotypes with significant correlation to Rvi6-based resistance and a minor effect of polyploidy herein. In particular, procyanidin dimer levels appeared positively correlated with the level of resistance, indicating a putative functional role in scab resistance. In contrast, the majority of other phenolics were negatively correlated with the resistance. Finally, our study did not identify a significant correlation between reduced phloridzin:flavanol ratio and Rvi6 resistance. These findings are discussed in the context of the role of phenolic metabolism in apple scab resistance.

Diffuse apple scab symptoms on the abaxial leaf surface are caused by the fungal pathogen Venturia inaequalis and occur even in well-managed orchards. The disease is challenging to manage, as the symptoms emerge on aging leaves later in the season and only develop on some leaves, suggesting the involvement of intrinsic defense mechanisms. We studied the development of diffuse abaxial scab symptoms on 'Jonagold' leaves in an orchard at three different shoot positions and at four different time points during the growing season to identify leaf-specific defense mechanisms. We identified infection moments by tracking the ascospore load and formation of new shoot leaves and determined the period required for proliferation of diffuse abaxial scab symptoms. Then, we correlated gene expression and phenolics profiles with the V. inaequalis DNA content to identify those inhibiting scab proliferation in asymptomatic leaves. Leaves in the middle of shoots showed higher symptom expression compared with shoot base and tip leaves. Disease inhibition in asymptomatic leaves was negatively correlated with several defense-related genes and phenolics. Altogether, our observations highlight that diffuse abaxial scab is one of the key challenges in apple growing and that the leaf ontogenic status during the infection process affects the development of these symptoms, with putative regulation by phenolic metabolism and ontogeny-related defense genes.

Malus sieversii, the primary progenitor of domesticated apples and a vital genetic resource in Kazakhstan, faces increasing threats from aging, degradation, diseases, and insect infestations despite ongoing conservation efforts and the establishment of genetic reserves. The aim of our work was to examine genetic variability, population structure and characterize the alleles of resistance loci for fire blight, apple scab and powdery mildew from M. sieversii and Malus niedzwetzkyana populations in Kazakhstan. We genotyped 352 accessions of M. sieversii and M. niedzwetzkyana sampled from various regions in Kazakhstan using Axiom JKI50kMd SNP array. Wild apple populations from Zhongar Alatau exhibited reduced genetic diversity, with expected heterozygosity (He) of 0.21, and minimal gene flow. In contrast, populations from Ile Alatau demonstrated higher genetic variability, with expected heterozygosity reaching 0.32, likely influenced by gene flow from cultivated apple varieties. Principal component analysis (PCA), clustering, and phylogenetic tree reconstruction consistently identified distinct population groupings corresponding to their geographic origin. Populations from Zhongar Alatau and Tarbagatai formed a relatively homogeneous group, while populations from Ile Alatau and Ketmen clustered into another group, reflecting a higher degree of genetic mixing and heterogeneity. M. niedzwetzkyana emerged as a separate and genetically divergent cluster and demonstrated a higher frequency of polymorphic disease resistance markers compared to M. sieversii, reinforcing its potential as a valuable genetic resource for breeding disease-resistant apple varieties. These findings provide critical insights for conservation strategies, emphasizing the importance of preserving genetic diversity in wild apple populations to support long-term breeding and disease management efforts.

Apple scab, caused by Venturia inaequalis, remains a major challenge for apple production in Morocco, where disease management heavily depends on fungicide applications. However, increasing reports of resistance have raised concerns about the long-term efficacy of commonly used products and the economic sustainability of apple orchards. In this study, we evaluated the sensitivity of five V. inaequalis isolates from the Fes-Meknes region, a key apple-producing area in Morocco, to three fungicides: difenoconazole, trifloxystrobin, and thiophanate-methyl. The identity of the isolates was confirmed based on both morphological characteristics and by molecular analysis of the ITS region. In vitro and in vivo assays revealed significant differences in isolate responses. Difenoconazole consistently showed the highest efficacy, with EC50 values ranging from 0.05 to 1.46 µg/mL, and preventive applications reducing disease severity by up to 85.8% at 10 µg/mL. In contrast, trifloxystrobin and thiophanate-methyl exhibited much higher EC50 values (2.94–29.62 µg/mL and 14.84–1237.20 µg/mL, respectively), indicating widespread resistance, particularly to thiophanate-methyl, whose curative and preventive efficacy rarely exceeded 44%. Preventive treatments were significantly more effective than curative applications for all fungicides tested. These findings highlight the urgent need to revise apple scab management strategies in Morocco, including the rotation of fungicides with different modes of action and the integration of non-chemical approaches. Broader sensitivity monitoring and the use of molecular diagnostics are recommended to better inform sustainable disease control programs.

Venturia inaequalis, the cause of apple scab, readily develops resistance to fungicides with specific modes of action. Knowledge of the spatial and temporal pattern of resistance development is therefore relevant to fruit producers and their consultants. In the Lower Elbe region of Northern Germany, a two-year survey based on a conidial germination test was conducted, examining fungicide resistance in 35 orchards under Integrated Pest Management (IPM), 16 orchards of susceptible cultivars as well as a further 12 orchards of scab-resistant (Vf) cultivars under organic management, and 34 abandoned or unmanaged sites. No evidence of resistance to SDHI compounds (fluopyram, fluxapyroxad) was found after >5 yr of their regular use. Resistance to anilinopyrimidines (cyprodinil, pyrimethanil) had disappeared 15 yr after its widespread occurrence. Isolates from a few IPM orchards showed a reduced sensitivity to dodine. Double resistance to the MBC compound thiophanate-methyl and the QoI trifloxystrobin was rare in V. inaequalis strains that had achieved breakage of Vf-resistance, but very common (>50%) on scab-susceptible cultivars in IPM, organic and abandoned orchards in the 'Altes Land' core area of the Lower Elbe region, and in IPM orchards in the periphery. We conclude that resistance to QoI and MBC fungicides is persistent even decades after their last use, and that the core area harbours a uniform population adapted to intensive crop protection, whereas isolated orchards in the periphery are colonised by discrete populations of V. inaequalis.

Efficacy of biofungicides based on Bacillus against apple scab (Venturia inaequalis) and their influence on rhizosphere fungal communities

The root-derived syringic acid and shoot-to-root phytohormone signaling pathways play a critical role in preventing apple scab disease.

Phytosanitary treatments are massively used in orchards to fight apple scab, a disease caused by the fungus Venturia inaequalis (Vi). To reduce these treatments, resistant varieties are largely deployed but their effectiveness can decrease over time. The combination of complementary molecular mechanisms within new varieties could enhance the durability of genetic resistance however, the underlying resistance mechanisms remain poorly understood. An apple pseudo-F1 progeny was previously widely investigated for its quantitative trait loci (QTL) controlling resistance to scab and at least three of them seem to act complementarily; notably, one of them is specific to some Vi isolates while the others have a broader spectra of action. The aim of this approach is to better understand the underlying molecular mechanisms and metabolites associated with resistance alleles by exploring apple leaf specialized metabolism. A total of three experiments was conducted: one experiment included non-inoculated leaves whereas in the two other experiments, leaf samples were collected five days after inoculation with two different Vi isolates, including one known to overcome one QTL. Metabolic content was extracted in aqueous methanol before performing an untargeted metabolomic analysis using an Orbitrap IDXTM mass spectrometer, allowing high-resolution mass spectrometry (HRMS) detection. This approach without a priori enables the detection of potentially new chemical families involved in resistance to apple scab. The current data article includes 1) the protocol of plant sample production with a table summarizing key elements of the experimental designs, 2) overview of the raw metabolomic profiles from all three experiments and 3) assessment of metabolic feature reproducibility between replicates in each dataset through Principal Component Analysis. The raw data files are available on the recherche.data.gouv repository (10.57745/XJBD8V). These datasets are valuable resources to further investigate the molecular mechanisms underlying genetic resistance to apple scab, with a focus on specialized metabolism. In the long term, it should improve apple breeding strategies by informing on how to combine appropriate genetic and biochemical factors in new varieties to ensure a more durable resistance.

Apple scab is a disease caused by Venturia inaequalis; it alters the vegetative cycle of apple trees and affects the fruits in orchards or during post-harvest storage. Utilizing rotten apples in cidermaking is a promising technique to mitigate crop losses; nonetheless, uncertainties persist regarding the beneficial effects of damaged fruits. This study involves a thorough chemical analysis of cider produced from both healthy and scab-infected fruits to identify compositional changes caused by microbial proliferation and to assess their impact on cider quality. Apples infected by post-harvest apple scab, as opposed to uninfected apples, were employed in cidermaking. The peel microbiota was described by plate count, and next-generation sequencing-based metabarcoding methods were used to describe the peel microbiota, while HPLC and GC MS-MS were used to characterize the cider compositions. Apples infected with post-harvest scab host a specific fungal consortium with higher biodiversity, as evidenced by the Shannon evenness index, especially in the fungi kingdom. The presence of apple scab slows fermentation by up to 23%, lowers ethanol accumulation by up to 0.4%, and affects certain cider constituents: sugars, alcohols, amino acids, fatty acids, and esters. The statistical treatment of data relative to the chemical profile (PLS and PCA on the 31 compounds with VIP > 1) distinguishes ciders made from altered or safe fruits. Scab-infected apples can be valorized in the agri-food industry; however, microbiota alterations must not be underestimated. It is necessary to implement adequate mitigation strategies.

One of the world’s most important economic crops, apples face numerous disease threats during their production process, posing significant challenges to orchard management and yield quality. To address the impact of complex disease characteristics and diverse environmental factors on detection accuracy, this study proposes a multimodal parallel transformer-based approach for apple disease detection and classification. By integrating multimodal data fusion and lightweight optimization techniques, the proposed method significantly enhances detection accuracy and robustness. Experimental results demonstrate that the method achieves an accuracy of 96%, precision of 97%, and recall of 94% in disease classification tasks. In severity classification, the model achieves a maximum accuracy of 94% for apple scab classification. Furthermore, the continuous frame diffusion generation module enhances the global representation of disease regions through high-dimensional feature modeling, with generated feature distributions closely aligning with real distributions. Additionally, by employing lightweight optimization techniques, the model is successfully deployed on mobile devices, achieving a frame rate of 46 FPS for efficient real-time detection. This research provides an efficient and accurate solution for orchard disease monitoring and lays a foundation for the advancement of intelligent agricultural technologies.