Apple Scab Research Articles

Cost-Benefit Analysis of Apple Scab Sanitation Practices for ULO-Stored Apple Fruit in Integrated and Organic Production Systems

ABSTRACT The economic viability of orchard sanitation practices, is crucial for sustainable apple production. However, our knowledge in this area is limited, particularly after the fruit is stored in the high-energy-consuming ultra-low oxygen (ULO) storage system. The objective of this 3-year study was to investigate the cost-benefit ratios of five sanitation treatments (lime sulfur-Lime-S, leaf collection-Collect-L, mulching-Mulch-C, lime sulfur + leaf collection, leaf collection + mulching) in integrated and organic apple orchards, considering the sale of apples after 6-month ULO storage. Cost-benefit analyses determined cost, total revenue, revenue for class 1 fruit (fruits without scab infection) and income surplus. Costs of ULO storage were twice higher in the integrated orchard (mean 3,064 EUR ha−1) than in the organic one (mean 1,512 EUR ha−1). Direct costs of the two combined sanitation treatments were significantly higher than the Lime-S and Collect-L treatments across all years and orchard systems. Analysis of variance for total revenue, revenue for class 1 fruit and income surplus revealed significant differences among years, sanitation treatments, and orchard systems. The total revenue and revenue for class 1 fruit were significantly higher in the integrated orchard (10,787 and 10,557 EUR ha−1, respectively) than in the organic one (8,713 and 7,742 EUR ha−1, respectively). The lowest total revenue and revenue for class 1 fruit were obtained in the non-sanitized control, while highest were recorded in the Collect-L or Collect-L + Mulch-C treatments. Collect-L and Collect-L + Mulch-C treatments provided the highest income surplus in all years and orchard systems. Kernel density estimations and frequency distributions indicated the widest variability for total revenue and revenue for class 1 fruit in the integrated orchard system. Correlation and linear regression analyses revealed significant relationship between total revenue and revenue for class 1 fruit in both orchard systems. In conclusion, our study demonstrates that Collect-L and Collect-L + Mulch-C treatments offer the greatest economic benefit after 6-month ULO storage regardless of the orchard system employed.

Biocontrol of plant pathogens by Lysobacter enzymogenes isolate LEC: efficacy of shake flask broth, fermentation broth and dried preparations

ABSTRACT The aim of our study was to upscale the production of Lysobacter enzymogenes strain LEC from shake flasks to a laboratory bioreactor. The obtained fermentation broth was to be downstream-processed by lyophilisation and fluidised bed-drying, followed by testing of the dried preparations against plant pathogens. Different batches of broth from shake flasks and from individual fermenter runs were characterised and compared. Number of viable cells, in vitro efficacy (ED90 value) against the apple scab pathogen Ventura inaequalis, as well as efficacy against Phytophthora infestans on potato plants were all reproducible and not impaired by upscaling the production volume from shake flask to the bioreactor. Fermentation broth was processed by lyophilisation and fluidised bed-drying. In bioassays, the activity against downy mildew (Pseudoperonospora cubensis) on cucumber were comparable for the unformulated fermentation broth and the fluidised bed-dried product, while the lyophilised product was significantly more effective. Strain LEC showed reproducible pathogen suppressive activity, independent from production scale and batch. Production upscaling and formulation by drying are possible without loss of efficacy.

Comparative Analysis of Some Morpho-cultural Characters of Venturia inaequalis (Apple Scab Pathogen) under Kashmir Conditions

Apple (Malus × domestica Borkh.) represents one of the most widely cultivated and economically important temperate fruit crops in the world. However, its cultivation faces significant challenges due to various fungal pathogens, particularly apple scab inflicted by Venturia inaequalis, which has a profound impact on the yield and quality of apple, resulting in substantial economic loss. The pervasive nature of V. inaequalis and its ability to damage crops poses a serious threat to sustainable apple production. In this study, the morpho-cultural characteristics of V. inaequalis were systematically analyzed and compared between the Shopian and Baramullah districts of the Kashmir Valley. Ten isolates from each district were grown on Malt Extract Agar (MEA) and Potato Dextrose Agar (PDA) for comparative analysis. The colonies were characterized by a compact hue ranging from greyish-green to blackish and exhibited a densely velvety texture. Mycelial growth was predominantly aerial, with some isolates displaying partial irregularity in colony margins, while others exhibited greater uniformity. The mean colony radii for potato dextrose agar and malt extract agar media was measured as 23.01 mm and 28.50 mm for the Shopian district, and 28.09 mm and 33.33 mm for the Baramullah district, respectively. The mean conidial spore density was recorded at 27.87 spores/cm² for the Baramullah district and 34.67 spores/cm² for the district Shopian, respectively. This variation could be attributed to several factors, including genetic diversity within the pathogen populations, differences in altitude, climate, and other environmental factors, the selection pressure exerted by fungicide applications, the emergence of novel pathogen races, and phenotypic plasticity driven by the differing agricultural practices and microclimatic conditions in the respective regions.

Classifying early apple scab infections in multispectral imagery using convolutional neural networks

Multispectral imaging systems combined with deep learning classification models can be cost-effective tools for the early detection of apple scab (Venturia inaequalis) disease in commercial orchards. Near-infrared (NIR) imagery can display apple scab symptoms earlier and at a greater severity than visible-spectrum (RGB) imagery. Early apple scab diagnosis based on NIR imagery may be automated using deep learning convolutional neural networks (CNNs). CNN models have previously been used to classify a range of apple diseases accurately but have primarily focused on identifying late-stage rather than early-stage detection. This study fine-tunes CNN models to classify apple scab symptoms as they progress from the early to late stages of infection using a novel multispectral (RGB-NIR) time series created especially for this purpose.This novel multispectral dataset was used in conjunction with a large Apple Disease Identification (ADID) dataset created from publicly available, pre-existing disease datasets. This ADID dataset contained 29,000 images of infection symptoms across six disease classes. Two CNN models, the lightweight MobileNetV2 and heavyweight EfficientNetV2L, were fine-tuned and used to classify each disease class in a testing dataset, with performance assessed through metrics derived from confusion matrices. The models achieved scab-prediction accuracies of 97.13 % and 97.57 % for MobileNetV2 and EfficientNetV2L, respectively, on the secondary data but only achieved accuracies of 74.12 % and 78.91 % when applied to the multispectral dataset in isolation. These lower performance scores were attributed to a higher proportion of false-positive scab predictions in the multispectral dataset. Time series analyses revealed that both models could classify apple scab infections earlier than the manual classification techniques, leading to more false-positive assessments, and could accurately distinguish between healthy and infected samples up to 7 days post-inoculation in NIR imagery.

Aerial dispersal of Venturia inaequalis ascospores with under-canopy sprinkler irrigation for apple scab management

AbstractSprinkler irrigation systems can release ascospores of Venturia inaequalis, the cause of apple scab, from infected leaves on the ground under conditions unsuitable for infection, and thus reducing the primary inoculum. Under-canopy irrigation was carried out for two hours in the middle of the day over overwintered apple leaves heavily infected with scab, either in a wind-protected enclosure or in a wind-exposed orchard. Ascospores were captured with rotating-arm spore traps at heights ranging from 0.3 m to 3.0 m above the ground. Ascospores dispersed above the irrigated layer and were detected at all heights above the sprinklers. Wind played a critical role in spore transport, evident from the set-up where wind interference was minimised by a wind fence, resulting in higher airborne spore numbers across all measured heights compared with the orchard exposed to unrestricted wind conditions. Furthermore, vertical temperature gradients significantly correlated with spore distributions, particularly where negative gradients at heights between 0.3 m and 0.05 m and positive gradients at heights between 1.0 m and 0.3 m led to spore retention within the irrigated zone. The findings highlight that ascospores, dispersed above the irrigated layers, could settle on susceptible tissues. It thus becomes imperative to ensure a rain-free period of at least 24 h post-irrigation and, if a rainfall shortly occurs after irrigation, the application of curative fungicides becomes essential following unexpected rain. Reliable weather forecasts are therefore crucial in determining the effectiveness of under-canopy irrigation to reduce apple scab incidence.

Comparing Apples and Oranges: Advances in Disease Resistance Breeding of Woody Perennial Fruit Crops.

Apple and citrus are perennial tree fruit crops that are vital for nutritional security and agricultural economy and to achieve the Sustainable Development Goals of the United Nations. Apple scab and fire blight, along with Huanglongbing, canker, and tristeza virus, stand out as their most notorious diseases and annually destabilize fruit supply. An environmentally sound approach to managing these diseases is improving tree resistance through breeding and biotechnology. Perennial fruit tree germplasm collections are distributed globally and offer untapped potential as sources of resistance. However, long juvenility, specific pollination and flowering habits, and extensive outcrossing hinder apple and citrus breeding. Advances in breeding approaches include trans- and cis-genesis, genome editing, and rapid-cycle breeding, which, in addition to conventional crossbreeding, can all facilitate accelerated integration of resistance into elite germplasm. In addition, the global pool of available sources of resistance can be characterized by the existing genetic mapping and gene expression studies for accurate discovery of associated loci, genes, and markers to efficiently include these sources in breeding efforts. We discuss and propose a multitude of approaches to overcome the challenges of breeding for resistance in woody perennials and outline a technical path to reduce the time required for the ultimate deployment of disease-resistant cultivars.

Harnessing Trichoderma spp.: A Promising Approach to Control Apple Scab Disease.

Apple scab, caused by the pathogenic fungus Venturia inaequalis, can result in significant economic losses. The frequent use of fungicidal products has led to the emergence of isolates resistant to commonly used active substances. Therefore, biological control offers a sustainable alternative for managing apple scab. In this study, eight Trichoderma isolates were evaluated against five different isolates of V. inaequalis isolated from the Fes-Meknes region. The biocontrol potential of these Trichoderma isolates had previously been demonstrated against other pathogens. The results indicated that the inhibition rate of mycelial growth of V. inaequalis obtained with Trichoderma spp. isolates ranged from 50% to 81%, with significant differences observed among the pathogenic isolates after 5 and 12 days of incubation. In addition, the in vitro tests with Trichoderma cell-free filtrates showed inhibition rates ranging from 2% to 79%, while inhibition rates ranged from 5% to 78% for volatile compound tests. Interestingly, the inhibition of spore germination and elongation was approximately 40-50%, suggesting the involvement of antifungal metabolites in their biocontrol activities. The in vivo bioassay on detached apple leaves confirmed the biocontrol potential of these Trichoderma isolates and demonstrated their ability to preventively control apple scab disease. However, their efficacies were still lower than those of the fungicidal product difenoconazole. These findings could contribute to the development of an effective biofungicide based on these Trichoderma isolates for reliable and efficient apple scab control.

Apple scab: resistance to chemical fungicides

The review highlights the situation with the development of resistance to various systemic fungicides in Venturia inaequalis around the world and in Russia, with an assessment of the prospects for their further use. Information is provided on all fungicides used in Russia against apple scab, their effectiveness at a given time, and a description of each chemical class. Data on the mechanisms of resistance to chemicals in the pathogen, including at the molecular level, are presented. The problem of the development of resistance in V. inaequalis and possible ways of its solution at the present level of scientific knowledge are discussed.

Control of a phytopathogenic infection in an apple orchard in the forest-steppe of Samara Oblast

The study evaluates a protection system by selecting and alternating fungicides having different mechanisms of action to exclude the emergence of resistant populations of apple tree pathogens. The experiments were started at Koshelevsky Posad LLC (Syzransky District, Samara Oblast) in 2022-2023. The orchard was planted in 2013-2014, with trees arranged in a 3.5×1.5 m grid; the 62-396 rootstock was used. The biological effectiveness of fungicide protection against apple scab (Venturia inaequalis (Cooke) Wint.) and fruit rot (Monilia fructigena Pers.) was analyzed using ‘Berkutovskoye,’ ‘Kulikovskoye,’ ‘Kuibyshevskoye,’ ‘Lobo,’ and ‘Northern Sinap’ varieties. The protection system including contact and systemic agents having different mechanisms of action was developed according to the FRAC diagram for assessing the combined risk of fungicide resistance developing in phytopathogens, which takes into account the adaptation rate of organisms (emergence of new resistant types) to changing environmental conditions. An analysis of the correlation between the growth rate of apple-specific phytopathogens and weather conditions shows no significant relationship (0.032-0.245). In these studies, the anthropogenic factor-chemical treatment with fungicides – had a predominant effect on the development of scab and monilia in apple orchards along with weather factors. The yield of marketable apples in the experimental quarter of the orchard differed insignificantly from year to year. In 2023, the yield was lower; however, this fact can be probably attributed to the return of late frosts during apple blossom in Samara Oblast. Noteworthy is that for the ‘Berkutovskoye’ and ‘Lobo’ varieties, unmarketable apples did not exceed 5 and 12 %, respectively, in the studied quarter of the orchard. The protection system using fungicides (GC Shans) helped to optimize the phytosanitary condition of the orchard, thus reducing the amount of fallen fruit and providing a stable harvest of marketable apples.

Deciphering the mechanisms involved in reduced sensitivity to azoles and fengycin lipopeptide in Venturia inaequalis

Apple scab, caused by the hemibiotrophic fungus Venturia inaequalis, is currently the most common and damaging disease in apple orchards. Two strains of V. inaequalis (S755 and Rs552) with different sensitivities to azole fungicides and the bacterial metabolite fengycin were compared to determine the mechanisms responsible for these differences. Antifungal activity tests showed that Rs552 had reduced sensitivity to tebuconazole and tetraconazole, as well as to fengycin alone or in a binary mixture with other lipopeptides (iturin A, pumilacidin, lichenysin). S755 was highly sensitive to fengycin, whose activity was close to that of tebuconazole. Unlike fengycin, lipopeptides from the iturin family (mycosubtilin, iturin A) had similar activity on both strains, while those from the surfactin family (lichenysin, pumilacidin) were not active, except in binary mixtures with fengycin. The activity of lipopeptides varies according to their family and structure. Analyses to determine the difference in sensitivity to azoles (which target the CYP51 enzyme involved in the ergosterol biosynthesis pathway) showed that the reduced sensitivity in Rs552 is linked to (i) a constitutive increased expression of the Cyp51A gene caused by insertions in the upstream region and (ii) greater efflux by membrane pumps with the involvement of ABC transporters. Microscopic observations revealed that fengycin, known to interact with plasma membranes, induced morphological and cytological changes in cells from both strains. Sterol and phospholipid analyses showed a higher level of ergosta-7,22-dien-3-ol and a lower level of PI(C16:0/C18:1) in Rs552 compared with S755. These differences could therefore influence the composition of the plasma membrane and explain the differential sensitivity of the strains to fengycin. However, the similar antifungal activities of mycosubtilin and iturin A in the two strains indirectly indicate that sterols are probably not involved in the fengycin resistance mechanism. This leads to the conclusion that different mechanisms are responsible for the difference in susceptibility to azoles or fengycin in the strains studied.

Comparative expression profile of selected genes in Venturia inaequalis Cooke (Wint.) infecting apple fruits and leaves

Scab is a noxious fungal disease of apples (Malus domestica Borkh) in all apple producing regions caused by a host-specific phytopathogen Venturia inaequalis Cooke (Wint.). Its symptoms include black or brown lesions on leaves as well as on fruits, and causes fruit deformation. In this study, V. inaequalis was isolated from infected fruit samples and expression level of selected pathogenesis related genes in scab infected fruits and leaves was studied. The isolated fungus formed a brown coloured mat-like colony having septate mycelium and produced acute ovoid shaped conidia. Molecular characterization of the fungus was done by amplification and sequencing of internal transcribed spacer (ITS) and Cytochrome (CYP51A1) regions of the isolate. The Sanger sequencing of amplicons and sequence analysis using BLAST tool of the NCBI against GenBank database confirmed that the obtained sequence of ITS and CYP51A1 regions had 99.6 % and 98 % sequence identity with the reference V. inaequalis, respectively. The isolated strain of V. inaequalis was submitted in the fungal repository of Microbial Type Culture Collection (MTCC), India. The phylogenetic analysis of ITS region of the isolate revealed that the isolated strain of V. inaequalis was more closely related to Fusicladium eriobotryae compared to other Venturia species. The expression levels of pathogenesis related genes viz. CIN1, CE5 and VICE16 were higher in infected leaves as compared to infected fruits. Whereas expression of VICE12 and GH28 were higher in infected fruits compared to infected leaves. VICE4 gene showed equal level of expression during infection in both fruits and leaves, which was also maximum as compared to the control treatment. The transcript analysis of aforementioned genes of V. inaequalis gives the insights of the pathogen's expression profile during pathogenesis in fruits and leaves. This expression analysis can form a basis selecting pathogenesis related genes as targets for developing dsRNA expressing constructs with an aim to reduce RNAi mediated silencing of specific genes, in a futuristic biotechnological based solution to deal with apple scab disease.

Irrigation Targeted to Provoke Ejection of Ascospores of Venturia inaequalis Shortens the Season for Ascospore Release and Results in Less Apple Scab.

Trials were carried out in apple orchards of Emilia-Romagna and Trentino-Alto Adige in northern Italy to investigate the effects of sprinkler irrigation on possible reduction in inoculum and subsequent disease pressure of Venturia inaequalis, the ascomycete causing apple scab. In spring, volumetric spore traps were placed above apple leaf litter containing pseudothecia with ascospores of the fungus. Pseudothecia matured more rapidly in irrigated plots, and 95% of the total number of spores trapped in a season was reached on average 164 degree days (base temperature 0°C) earlier in irrigated compared with nonirrigated plots. On average for seven location/year combinations, more than 50% of the ascospores were trapped following irrigations carried out for 2 h on sunny days before a forecasted rainfall. Subsequently, a much lower number of spores were trapped on rainy days following irrigation. Field trials with scab-susceptible apple cultivars were carried out in the two regions to evaluate the efficacy of sprinkler irrigation on disease. Irrigated and nonirrigated plots were either treated with different fungicide control strategies or not treated. Irrigation significantly reduced the incidence of apple scab at both sites, and the overall number of infected leaves and fruit was reduced by more than 50%. Midday sprinkler irrigation can significantly reduce the inoculum pressure of V. inaequalis in apple orchards. This may be a sustainable management strategy, especially in areas with extended dry periods.

Apple Fruit Disease Classification using Naive Bayes Algorithm

Apples are one of the most productive varieties of fruit in the world, with a high nutritional and medicinal value. However, numerous diseases affect apple production on a wide scale, resulting in significant economic losses. These diseases often go overlooked until just before, after, or after fruit has been processed. Many pathogens can be avoided with cultural traditions and (optional) fungicides, even if there are no cures for tainted fruit. However, accurate diagnosis is essential for determining the right management practices and preventing further losses. Apple scab, apple rot, and apple blotch are some of the most prevalent diseases that affect apples. The proposed approach will greatly aid in the automated identification and classification of apple diseases, according to our test results. We discovered that normal apples were easy to discern from diseased apples in our trial, and that the texture-based GLCM function produced more reliable results for apple disease classification, with a classification accuracy of more than 96.43 percent. This demonstrates that combining the GLCM extraction function with naive bayes classification will greatly improve accuracy. Key Words: Naive bayes, Apple Diseases, Classifier

Prediction of Disease in Apple Leaf Using Convolution Neural Networks

Abstract: Apple tree diseases can significantly impact fruit quality and yield, making early detection and intervention crucial for orchard management. To avoid the impact on apple production a novel approach is required for the early and accurate prediction of apple leaf diseases through Convolutional Neural Networks (CNNs). Our proposed system contains a comprehensive dataset of high-resolution pictures of apple leaves exhibiting various disease symptoms, including common issues like apple scab, apple rust, and powdery mildew. The dataset was carefully annotated to train and validate the CNN model effectively. The proposed CNN model makes use of its ability to automatically learn applicable features from images, making it highly suitable for the task of disease prediction in apple leaves. This model contributes to the field of precision agriculture by offering a cost-effective and efficient tool for apple disease detection.

Integrating Biological Control Agents for Enhanced Management of Apple Scab (Venturia inaequalis): Insights, Risks, Challenges, and Prospects

Apple scab incited by the ascomycete Venturia inaequalis poses a significant threat to apple cultivation, necessitating a reassessment of existing disease management strategies. Attempts to manage apple scab include diverse approaches like developing disease forecasting models and the extensive application of synthetic chemical fungicides. However, the efficacy of these methods is compromised by inconsistencies, environmental concerns, and the pathogen’s resistance, necessitating the exploration of alternative sustainable strategies. Addressing the challenges associated with apple scab management, this review strongly supports a shift towards the integration of biological control agents (BCAs). Emphasising the transformative synergy between BCAs and their bioactive secondary metabolites, we highlight their efficacy in advancing precision disease control through innovative and sustainable solutions. The review effectively presents a strong justification for the integration of BCAs and their by-products into apple scab management, offering insights into associated benefits, risks, and challenges while outlining promising prospects. Ultimately, it is expected to drive the adoption of environmentally conscious practices for effective apple scab management.

<i>In Vitro</i> Study of Fitness Parameters in Fungicide-Resistant and -Sensitive <i>Venturia inaequalis</i> Isolates

The developing resistance of Venturia inaequalis to toxicants commonly used in systemic fungicides against apple scab has reduced their effectiveness, causing substantial fruit loss in orchards. To improve the situation and manage the resistance, a thorough analysis of the fitness potential among different pathogen biotypes, particularly those resistant to fungicides, is needed. In this study, the mycelial growth of V. inaequalis isolates with baseline sensitivity and resistance to one or more fungicides was assessed in vitro at four temperatures (6, 18, 27, and 30°C) and three agar concentrations in the nutrient medium (2, 4, and 6% m/V). Except for the mycelial growth at 27°C, the indicators of fitness predicted in vitro did not differ significantly between the V. inaequalis isolates with multiple resistance to fungicides and the biotypes with baseline sensitivity.

Biological method of apple trees protection against scamb (Venturia inaequalis (Cooke) Wint.) in the conditions of Precarpathian province of the Carpathian mountain zone of Ukraine

It was established that the investigated systems of biological protection of apple trees in the conditions of Precarpathian province of Carpathian mountain zone of Ukraine in 2016–2020 showed high effectiveness against apple scab. The highest efficiency was obtained when using protection system No. 4 (Fit Doctor, p., Haubsyn, p. and Trikhodormin, p. and MAStech nutrition technology): the effectiveness against scab on apple leaves was on average 71.6% and against scab on fruits — 73.5%. The biological protection system of apple tree No. 1 (four application of Planryz, vs.) showed 65.7% effectiveness against scab on leaves and 62.7% against scab on fruits. When using the biological protection system No. 2 (four times application of Planryz, vs. and immunoprotect or Bai-Si), the effectiveness against scab on apple leaves was on average 67.2% and against scab on fruits — 66.7%. When using the biological protection system No. 3 (four-time application of Planryz, vs. and Stoller feeding technology), the effectiveness against scab on apple leaves was on average 70.1% and against scab on fruits — 72.5%. The yield of apple fruits when using the biological protection system No. 1 in 2016–2020 averaged 17.1 t/ha, when using the biological protection system No. 2 it was 17.5 t/ha, when using the biological protection system No. 3 the yield was level of 18.3 t/ha and for the use of biological protection system No. 4 — 18.1 t/ha. When applying the biological protection system No. 1 in 2016–2020, they received an average profitability of 322.1% and the income from its use was UAH 6,410.0 from ha. From the application of system No. 2, we received conditional net income in the amount of UAH 8,110.0 from ha and profitability of 262.5%. By using system No. 3, conditional net income was obtained in the amount of UAH 10,932.0 from ha and the profitability of protective measures when using it was 186.3%. When applying the biological system No. 4, they obtained a profitability of 69.2% and an income from its use of UAH 6,300.0 from ha.

The Effectiveness of Synthetic and Inorganic Substances in Different Apple Scab Control Strategies

A two-year trial (2021 and 2022) was performed with five different fungicide and foliar fertiliser application strategies to control apple scab (Venturia inaequalis) in integrated apple orchards in Latvia. A strategy of using inorganic fungicides or combining them with synthetic fungicides was compared to a strategy of applications with only synthetic fungicides and untreated control. Furthermore, two strategies included foliar fertilisers to determine whether they may affect apple scab used alone or combined with synthetic fungicides. The timing of the fungicide applications was based on the risk forecasted by the decision support system RIMpro, and fertilisers were used at certain growth stages of the crop. The disease incidence on untreated fruits on cv. Auksis ranged from 38.3% to 59.6%, and on cv. Ligol from 99.3% to 99.5%. Strategies including synthetic fungicides were the most effective against scab on shoot leaves and fruits. The strategy using only inorganic fungicides was effective for low-inoculum orchards. Combining synthetic and inorganic fungicides provided the best apple scab control strategy on fruits, likely helping reduce the resistance selection pressure and residues of synthetic fungicides. Foliar fertilisers were insufficient to control apple scab; they would supplement existing scab fungicide programs.

Screening of Apple Cultivars for Scab Resistance in Kazakhstan

Scab, caused by Venturia inaequalis, is the most destructive fungal disease of apple worldwide. Apple scab incidence was studied in apple orchards in the south and southeast of Kazakhstan, including the Almaty, Zhambyl, and Turkestan regions, during 2022 and 2023. Disease incidence was higher in the Zhambyl region than in the Turkestan and Almaty regions in both years. The field evaluation suggested that 19 genotypes showed resistance to apple scab. Molecular screening was carried out using eight gene-specific molecular markers (AM19, CH05e03, OPL19, Hi07f02, AL07, K08, HB09, and CH02f06). The results of the molecular screening revealed that in 38 of the 45 studied cultivars, which included 11 Kazakh cultivars and 34 foreign cultivars, the Rvi (Rvi2, Rvi4, Rvi5, Rvi6, Rvi8, Rvi9, Rvi11, Rvi14, and Rvi15) resistance genes were amplified. Resistance genes such as Rvi2, Rvi4, Rvi6, and Rvi9 are still useful for breeding, but their use is recommended only in extended pyramids of multiple resistance genes. Several cultivars will be strong candidates for further breeding programs against apple scab and for the pyramiding of scab resistance genes in new cultivars.

Phenotyping, genetics, and "-omics" approaches to unravel and introgress enhanced resistance against apple scab (Venturia inaequalis) in apple cultivars (Malus × domestica).

Apple scab disease, caused by the fungus Venturia inaequalis, endangers commercial apple production globally. It is predominantly managed by frequent fungicide sprays that can harm the environment and promote the development of fungicide-resistant strains. Cultivation of scab-resistant cultivars harboring diverse qualitative Rvi resistance loci and quantitative trait loci associated with scab resistance could reduce the chemical footprint. A comprehensive understanding of the host-pathogen interaction is, however, needed to efficiently breed cultivars with enhanced resistance against a variety of pathogenic strains. Breeding efforts should not only encompass pyramiding of Rvi loci and their corresponding resistance alleles that directly or indirectly recognize pathogen effectors, but should also integrate genes that contribute to effective downstream defense mechanisms. This review provides an overview of the phenotypic and genetic aspects of apple scab resistance, and currently known corresponding defense mechanisms. Implementation of recent "-omics" approaches has provided insights into the complex network of physiological, molecular, and signaling processes that occur before and upon scab infection, thereby revealing the importance of both constitutive and induced defense mechanisms. Based on the current knowledge, we outline advances toward more efficient introgression of enhanced scab resistance into novel apple cultivars by conventional breeding or genetic modification techniques. However, additional studies integrating different "-omics" approaches combined with functional studies will be necessary to unravel effective defense mechanisms as well as key regulatory genes underpinning scab resistance in apple. This crucial information will set the stage for successful knowledge-based breeding for enhanced scab resistance.