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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. [ABSTRACT FROM AUTHOR]

Background: Venturia inaequalis is an apple scab causing fungal pathogen. It is a highly contagious and destructive pathogen which rapidly spreads infection in the surrounding orchards if not managed. The management and control of disease require multiple fungicides to be sprayed at different development stages of the apple. Persistent applications of fungicides also raises environmental concerns. Here, we demonstrate the potential of using spray induced gene silencing (SIGS) by developing target specific gene constructs for the synthesis of corresponding double-stranded RNA (dsRNA). Methods and Results: The exogenous application of dsRNAs was found to reduce mycelial growth and spore formation of V. inaequalis on culture plates. Four genes of V. inaequalis viz. CIN1, CE5, VICE12 and VICE16 which get upregulated during infection, were selected as targets for the development of gene construct expressing the corresponding dsRNA. The effect of exogenously supplied in vitro synthesized dsRNA on V. inaequalis was assessed in culture bioassay experiments with respect to growth, and spore formation. The expression level of the target genes in treated and control fungus was evaluated using quantitative PCR. Fungus treated with VICE12 targeted dsRNA showed maximum reduction in colony size (~ 55%), conidia formation (~ 93%) and expression level of the corresponding gene (2.2 fold), which was followed by CIN1-dsRNA. VICE16-dsRNA treatment was least effective with 32% reduction in growth, the non-significant effect of conidial spore formation and 1.13 fold down regulation of corresponding target gene expression level. Conclusion: The result of this investigation validates the hypothesis that RNAi is evoked in V. inaequalis by exogenously supplied dsRNA and spray induced gene silencing (SIGS) based solutions may reduce burden of fungicide usage on apple crop against apple scab disease in future. [ABSTRACT FROM AUTHOR]

Apple scab, caused by the fungus Venturia inaequalis, is one of the most damaging diseases of cultivated apples (Malus x domestica) worldwide. It results in huge losses as it diminishes fruit quality and impacts tree growth. Current management revolves around the application of fungicides, however the number of sprays required per season is unsustainable and expensive. Further to this, populations of V. inaequalis have developed fungicide resistance. Breeding new cultivars with higher levels of resistance to scab is a priority, however, this process is long, so introducing mixed cultivar orchards may be a faster solution. We reviewed the general principles of using mixtures to manage plant diseases, and then considered specifically using mixed cultivars to manage apple scab in commercial production. Limited field studies have demonstrated the potential of using mixture to suppress apple scab development; but scab super-races that could emerge from mixture can pose a significant risk in commercial production. However, recent research on population genetics of apple scab in monoculture and mixed orchards suggests that the risk of super-race emergence is probably over-stated, because assortative mating among lesions on the same leaves is likely to occur, rather than commonly assumed random mating. Thus, we conclude that cultivar mixtures can contribute towards sustainable scab management, particularly in commercial cider apple production.

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.

ABSTRACT Scab, caused by the biotrophic fungal pathogen Venturia inaequalis, is the most economically important disease of apples. During infection, V. inaequalis colonizes the subcuticular host environment, where it develops specialized infection structures called runner hyphae and stromata. These structures are thought to be involved in nutrient acquisition and effector (virulence factor) delivery, but also give rise to conidia that further the infection cycle. Despite their importance, very little is known about how these structures are differentiated. Likewise, nothing is known about how these structures are protected from host defenses or recognition by the host immune system. To better understand these processes, we first performed a glycosidic linkage analysis of sporulating tubular hyphae from V. inaequalis developed in culture. This analysis revealed that the V. inaequalis cell wall is mostly composed of glucans (44%) and mannans (37%), whereas chitin represents a much smaller proportion (4%). Next, we used transcriptomics and confocal laser scanning microscopy to provide insights into the cell wall carbohydrate composition of runner hyphae and stromata. These analyses revealed that, during subcuticular host colonization, genes of V. inaequalis putatively associated with the biosynthesis of immunogenic carbohydrates, such as chitin and β-1,6-glucan, are downregulated relative to growth in culture, while on the surface of runner hyphae and stromata, chitin is deacetylated to the less-immunogenic carbohydrate chitosan. These changes are anticipated to enable the subcuticular differentiation of runner hyphae and stromata by V. inaequalis, as well as to protect these structures from host defenses and recognition by the host immune system. IMPORTANCE Plant-pathogenic fungi are a major threat to food security. Among these are subcuticular pathogens, which often cause latent asymptomatic infections, making them difficult to control. A key feature of these pathogens is their ability to differentiate specialized subcuticular infection structures that, to date, remain largely understudied. This is typified by Venturia inaequalis, which causes scab, the most economically important disease of apples. In this study, we show that, during subcuticular host colonization, V. inaequalis downregulates genes associated with the biosynthesis of two immunogenic cell wall carbohydrates, chitin and β-1,6-glucan, and coats its subcuticular infection structures with a less-immunogenic carbohydrate, chitosan. These changes are anticipated to enable host colonization by V. inaequalis and provide a foundation for understanding subcuticular host colonization by other plant-pathogenic fungi. Such an understanding is important, as it may inform the development of novel control strategies against subcuticular plant-pathogenic fungi.

Demethylation inhibitor fungicides (DMIs) are widely used against Venturia inaequalis in north western Himalayas. The sensitivity of pathogen populations to DMIs viz., myclobutanil, difenconazole and flusilazole was evaluated. Thirty baseline isolates of V. inaequalis were collected from an orchard never exposed to fungicides and 200 other isolates from fungicide-exposed orchards. To establish the baseline sensitivity, the thirty baseline isolates were tested at seven concentrations viz., 0.001, 0.01, 0.03, 0.1, 0.3, 1.0, and 10.0 µg ml−1 of each fungicide using mycelial growth assays. The mean EC50 values of myclobutanil, difenoconazole and flusilazole for baseline population were 0.17, 0.02 and 0.022 µg ml−1, respectively, and accordingly the respective discriminatory doses of 0.20, 0.03 and 0.03 µg ml−1 were selected. To monitor the shift in fungicide-exposed populations, all the two hundred isolates were tested for their sensitivity at the respective discriminatory doses of different fungicides and the frequency distributions of their relative growth (RG) values were compared to that of the baseline isolates. A major shift towards reduced sensitivity was observed in myclobutanil, flusilazole and difenoconazole. The highest proportion of isolates (35.5%) were 'resistant' to myclobutanil followed by 19.5 per cent isolates resistant to flusilazole while only 7.5 per cent of isolates were resistant to difenoconazole. [ABSTRACT FROM AUTHOR]

The apple scab induced by Venturia inaequalis is an economically significant disease of apples worldwide and is predominantly controlled by multiple fungicide applications. Therefore, resistant apple cultivation is important for long-standing disease control. The knowledge about cultivar resistance is mainly founded on their evaluation in orchard conditions and testing in a greenhouse that is laborious and requires a large space. This study evaluated apple cultivar resistance and the virulence of V. inaequalis strains by inoculating detached leaves and immature fruits. Nine V. inaequalis strains originating from different apple-growing regions and host genotypes were tested on eight apple genotypes. Microscopic and macroscopic symptom development and host tissue reactions were monitored during the experiments. The tested V. inaequalis strains and cultivars showed different levels of virulence and resistance, respectively. Cultivar ‘Lobo’ was scored as partially susceptible, with almost all strains tested. The incompatible interaction with or without host tissue reactions was observed only on the cultivar ‘Priscilla’ with all the strains and field populations tested. The results of this study using detached leaves and immature fruits were concordant with the data obtained in the cultivar evaluation trials in the orchards. [ABSTRACT FROM AUTHOR]

Apple scab is an important disease conventionally controlled by chemical fungicides, which should be replaced by more environmentally friendly alternatives. One of these alternatives could be the use of lipopeptides produced by Bacillus subtilis. The objective of this work is to study the action of the three families of lipopeptides and different mixtures of them in vitro and in vivo against Venturia inaequalis. Firstly, the antifungal activity of mycosubtilin/surfactin and fengycin/surfactin mixtures was determined in vitro by measuring the median inhibitory concentration. Then, the best lipopeptide mixture ratio was produced using Design of Experiment (DoE) to optimize the composition of the culture medium. Finally, the lipopeptides mixtures efficiency against V. inaequalis was assessed in orchards as well as the evaluation of the persistence of lipopeptides on apple. In vitro tests show that the use of fengycin or mycosubtilin alone is as effective as a mixture, with the 50–50% fengycin/surfactin mixture being the most effective. Optimization of culture medium for the production of fengycin/surfactin mixture shows that the best composition is glycerol coupled with glutamic acid. Finally, lipopeptides showed in vivo antifungal efficiency against V. inaequalis regardless of the mixture used with a 70% reduction in the incidence of scab for both mixtures (fengycin/surfactin or mycosubtilin/surfactin). The reproducibility of the results over the two trial campaigns was significantly better with the mycosubtilin/surfactin mixture. The use of B. subtilis lipopeptides to control this disease is very promising. [ABSTRACT FROM AUTHOR]

Apple scab, caused by the fungal pathogen Venturia inaequalis , is the most economically important disease of apple (Malus x domestica) worldwide. To develop durable control strategies against this disease, a better understanding of the genetic mechanisms underlying the growth, reproduction, virulence and pathogenicity of V. inaequalis is required. A major bottleneck for the genetic characterization of V. inaequalis is the inability to easily delete or disrupt genes of interest using homologous recombination. Indeed, no gene deletions or disruptions in V. inaequalis have yet been published. Using the melanin biosynthesis pathway gene trihydroxynaphthalene reductase (THN) as a target for inactivation, which has previously been shown to result in a light-brown colony phenotype when transcriptionally silenced using RNA interference, we show, for the first time, that the CRISPR-Cas9 gene editing system can be successfully applied to the apple scab fungus. More specifically, using a CRISPR-Cas9 single guide RNA (sgRNA) targeted to the THN gene, delivered by a single autonomously replicating Golden Gate-compatible plasmid, we were able to identify six of 36 stable transformants with a light-brown phenotype, indicating an ∼16.7% gene inactivation efficiency. Notably, of the six THN mutants, five had an independent mutation. As part of our pipeline, we also report a high-resolution melting (HRM) curve protocol for the rapid detection of CRISPR-Cas9 gene-edited mutants of V. inaequalis. This protocol identified a single base pair deletion mutation in a sample containing only 5% mutant genomic DNA, indicating high sensitivity for mutant screening. In establishing CRISPR-Cas9 as a tool for gene editing in V. inaequalis , we have provided a strong starting point for studies aiming to decipher gene function in this fungus. The associated HRM curve protocol will enable CRISPR-Cas9 transformants to be screened for gene inactivation in a high-throughput and low-cost manner, which will be particularly powerful in cases where the CRISPR-Cas9-mediated gene inactivation efficiency is low. • First report of CRISPR-Cas9 gene editing in Venturia inaequalis. • Golden Gate-compatible plasmid used for delivery of the sgRNA. • First use of HRM to identify CRISPR-Cas9 gene-edited mutants in fungi. [ABSTRACT FROM AUTHOR]

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Apple scab caused by Venturia inaequalis has the most destructive effects among other phytopathogens in apple crops all over the world. The integration of resistance genes from local and domestic cultivars is a prerequisite for the efficient control of this disease and is a main target in efficient breeding approaches. Across Greece, many domestic apple cultivars are reported without deep knowledge about the presence and diversity of scab resistance genes. In this study, the presence of five resistance genes (Rvi2, Rvi4, Rvi6, Rvi8 and Rvi11) was evaluated across twenty local and domestic apple genotypes, employing twelve molecular markers closely linked to known apple scab resistance loci. Significant differences and polymorphisms among the tested cultivars were detected suggesting that some of them carry a sufficient number of resistance genes. This observed genetic diversity could be exploited in ongoing breeding approaches as a natural source of polygenic resistance against apple scab.

DMIs (sterol demethylation inhibitors) provide an important mode of action for control of Venturia inaequalis. They target the enzyme 14a-demethylase, encoded by the Cyp51 gene, which acts on an essential precursor for ergosterol biosynthesis. One mechanism, which leads to reduced DMI sensitivity of fungi, is based on mutations in Cyp51. In contrast to other phytopathogenic fungi, only little information is available on changes in the Cyp51 gene of V. inaequalis and their potential influence on DMI sensitivity. In this study, 126 monoconidial isolates were generated from field samples of V. inaequalis collected in apple orchards in different countries in 2018 and 2019. The Cyp51 gene of all isolates was sequenced. Furthermore, a new liquid culture method for V. inaequalis was established, which provides strongly sporulating cultures as a basis for the sensitivity tests. The sequence analysis revealed 15 different point mutations, and each of them resulted in an amino acid exchange in the 14α-demethylase. For some of them, corresponding mutations had been reported in other plant pathogens and shown to influence DMI sensitivity. We measured fungal growth in microtiter-plate tests to evaluate the influence of the amino acid changes in the Cyp51 gene on the sensitivity of the isolates towards the DMIs mefentrifluconazole, difenoconazole, and myclobutanil. While some mutations (e.g. those in the YGYG region 443–446) showed little impact on DMI sensitivity, others caused higher EC50 values, in particular Y133F and M141T. The sensitivity reducing effects differed for the three DMIs and were most pronounced for myclobutanil and less for mefentrifluconazole. The variability in the DMI sensitivity in each Cyp51 haplotype suggests the presence of additional resistance mechanisms caused by genetic background. [ABSTRACT FROM AUTHOR]

The large genetic evolution due to the sexual reproduction-mediated gene assortments and propensities has made Venturia inaequalis (causing apple scab) unique with respect to its management strategies. The resistance in apple germplasm against the scab, being controlled for by more than fifteen genes, has limited gene alteration-based investigations. Therefore, a biological approach of bacterial endophyte community dynamics was envisioned across the apple germplasm in context to the fungistatic behavior against V. inaequalis. A total of 155 colonies of bacterial endophytes were isolated from various plant parts of the apple, comprising 19 varieties, and after screening for antifungal behavior followed by morphological, ARDRA, and sequence analysis, a total of 71 isolates were selected for this study. The alpha diversity indices were seen to fluctuate greatly among the isolation samples in context to microflora with antifungal behavior. As all the isolates were screened for the presence of various metabolites and some relevant genes that directly or indirectly influence the fungistatic behavior of the isolated microflora, a huge variation among the isolated microflora was observed. The outstanding isolates showing highest percentage growth inhibition of V. inaequalis were exploited to raise a bio-formulation, which was tested against the scab prevalence in eight apple varieties under controlled growth conditions. The formulation at all the concentrations caused considerable reductions in both the disease severity and disease incidence in all the tested apple varieties. Red Delicious being most important cultivar of the northwestern Himalayas was further investigated for its biochemical behavior in formulation and the investigation revealed different levels of enzyme production, chlorophyll, and sugars against the non-inoculated control. [ABSTRACT FROM AUTHOR]

The material used for composting may contain pathogenic or harmful microorganisms, therefore, it is important issue to eliminate harmful or pathogenic microorganisms during the composting process to be used in plant production. Three different mixtures were prepared at initial C/N ratio of 35.34, 40.10, and 47 fixing the apple scab infected leaves at 62% dry weight basis. Composting study was carried out using three identical cylindrical reactors made of two nested plastic containers with 65 L. Temperature, moisture, carbon/nitrogen ratio, organic matter EC, pH, and O2/CO2 concentrations were monitored during process. Apple scab disease incidence of apple leaves and the colony number during composting, compost microbial population, and germination index of compost mixtures were determined. Except for the temperature rise to 65 °C for a short time at 7 days of composting for Mix‑1, all temperature for three mixes stayed between 24 and 46 °C. Disease severity of apple scab obtained from the compost samples showed that colony of apple scab after 16 days of composting were not detected. Furthermore, the population of beneficial microorganisms such as bacteria, actinomycetes, and fungi was colonized in the finished compost mixes. Germination index at the finished compost were above 80% for Mix‑1, Mix‑2, and Mix-3 at 10−3 dilution rate. In conclusion, composts obtained from apple scab infected leaves with dairy manure can be used reliably in agricultural production. [ABSTRACT FROM AUTHOR]

The resistance level of 90 single lesion conidial isolates of Venturia inaequalis collected from multiple commercial orchards in Shaanxi and Gansu Provinces and Xinjiang Autonomous Region of China to the demethylation inhibitor (DMI) fungicide difenoconazole and quinone outside inhibitor (QoI) fungicide pyraclostrobin was examined. The EC50 values of the 90 isolates to difenoconazole and pyraclostrobin ranged from 0.143 to 6.735 μg/mL and 0.084 to 2.026 μg/mL, respectively. Among the isolates, 19 had resistance, 66 had reduced sensitivity, and five had sensitivity to difenoconazole; eight had resistance, 81 had reduced sensitivity, and one had sensitivity to pyraclostrobin. Although a weak correlation between difenoconazole and pyraclostrobin was detected, four isolates were identified as resistant to difenoconazole and pyraclostrobin. However, isolates with practical resistance were not found widely in our study and were only sporadic in a few places, indicating that at present, difenoconazole and pyraclostrobin are still safe for disease management in the apple-growing areas of Shaanxi, Gansu and Xinjiang. However, the risk of fungicide resistance should be managed with caution, and yearly monitoring of resistance development is necessary. [ABSTRACT FROM AUTHOR]

Bingöl and Isparta are two remote regions with significant differences in terms of apple production in Turkey. In this study, some morphological and physiological characteristics of the apple scab (Venturia inaequalis) were measured and compared between these two regions. Colony colors and boundary lines, mycelial structures, colony growth rates, conidial numbers and sizes of the isolates were measured and compared in controlled conditions. With respect to colony morphologies of Bingöl and Isparta isolates, important differences were observed. On the other hand, coloni development rate of Bingöl isolates in PDA, MEA and CMA media were statistically significant, exhibiting an average of 30% faster growth compared to Isparta isolates. In addition, conidial numbers in 1 cm2 area of PDA were to be higher and significant in Bingöl isolates. However, it has not been determined differences for the dimensions of the conidial isolates developed in PDA belonging to two districts. As a result, it is considered that the morphological and physiological privileges determined by the comparison of the two district isolates of apple black spot is important. These results may be due to the genetic or fungicidal pressure due to the new race formation and the phenotypic characteristics due to different agricultural applications. [ABSTRACT FROM AUTHOR]

BACKGROUND Myclobutanil is one of the most widely used demethylation inhibitor (DMI) fungicides for the management of apple scab, caused by Venturia inaequalis. Strains of V. inaequalis resistant to myclobutanil have been reported across the world. Tebuconazole, another DMI fungicide, has been proposed as an alternative to myclobutanil, and the extent of cross‐resistance with myclobutanil therefore needs to be evaluated. The sensitivity to tebuconazole and myclobutanil of a total of 40 isolates was determined. Half the isolates came from an isolated orchard which had never been sprayed with fungicides and half from orchards sprayed regularly with myclobutanil, but still with disease control problems. The progeny of a tebuconazole resistant (R) × sensitive (S) V. inaequalis cross were analyzed in order to improve understanding of the genetic control of tebuconazole sensitivity. RESULTS: There is cross‐resistance between myclobutanil and tebuconazole (r = 0.91; P < 0.001). Sensitivity to tebuconazole of the progeny of a R × S cross varied quantitatively in a pattern which implied at least two gene loci differing between the parental strains. In addition, the asymmetric distribution of the sensitivity in the progeny implied possible epistatic effects. CONCLUSION: Resistance to myclobutanil and tebuconazole is strongly correlated. At least two genes are involved in the control of tebuconazole resistance in V. inaequalis. [ABSTRACT FROM AUTHOR]

Venturia inaequalis is a notorious fungal pathogen and show classical gene for gene interaction with its apple host. Neutral markers provide clues about history, evolutionary potential, genetic diversity and population structure of V. inaequalis. The genetic diversity and population structure of fungus indicates that the pathogen is highly diverse with the capacity to breach the scab resistance genes. In the present study, we collected 108 V. inaequalis isolates from three apple cultivars differing in Rvi1 resistance gene. Based on the AMOVA, the variation was mostly distributed among the isolates, providing evidence of non-existence of subpopulation in orchards thus founder population is difficult to arise in Kashmir apple orchards. Pair wise genetic differentiation is less due to regular occurrence of gene flow between the populations residing on different orchard as infected material is transported without stringent quarantine measures. Based on principal coordinate analysis and clustering algorithm as implemented in STRUCTURE, we observed admixture between the two subpopulations, which is quite low, suggesting the existence of pre-zygotic and post-zygotic barriers to gene flow and we cannot rule out the existence of other structures shared by accessions belonging to different varieties. Due to the continuous increase in introduction and monoculture of apple varieties, mixed orchard with different host resistance specificities are more suitable for managing the apple scab in Kashmir valley. [ABSTRACT FROM AUTHOR]

Apple scab caused by Venturia inaequalis has the most destructive effects among other phytopathogens in apple crops all over the world. The integration of resistance genes from local and domestic cultivars is a prerequisite for the efficient control of this disease and is a main target in efficient breeding approaches. Across Greece, many domestic apple cultivars are reported without deep knowledge about the presence and diversity of scab resistance genes. In this study, the presence of five resistance genes (Rvi2, Rvi4, Rvi6, Rvi8 and Rvi11) was evaluated across twenty local and domestic apple genotypes, employing twelve molecular markers closely linked to known apple scab resistance loci. Significant differences and polymorphisms among the tested cultivars were detected suggesting that some of them carry a sufficient number of resistance genes. This observed genetic diversity could be exploited in ongoing breeding approaches as a natural source of polygenic resistance against apple scab. [ABSTRACT FROM AUTHOR]

In 2016, a serious outbreak of apple scab (caused by Venturia inaequalis) in Aomori Prefecture, Japan, resulted from reduced fungal sensitivity to sterol demethylation inhibitors (DMIs). In this study, the lanosterol 14α-demethylase (CYP51A1) gene of V. inaequalis isolates from Aomori Prefecture was analyzed. A nonsynonymous nucleotide polymorphism causing an amino acid substitution from tyrosine to phenylalanine at position 133 (Y133F) in CYP51A1 was closely associated with low sensitivity to DMIs. This is first report of a point mutation in CYP51A1 associated with low sensitivity to DMIs in V. inaequalis. [ABSTRACT FROM AUTHOR]

Influence of moisture on maturation rate of the airborne Venturia inaequalis (Cooke) Wint. ascospores was numerically examined using field data collected from spore traps in Skierniewice, Poland, during 2005–2008 and 2010–2014. In order to avoid a bias resulting from different abundance of airborne ascospores in different seasons, the cumulative proportions of mature ascospores observed in the season were analyzed. The maturation rate was expressed with the probit of cumulative proportion which linearized its sigmoidal shape and made the effect of the weather during the entire season of the same importance. The significant, positive association between the probit slope and the moisture indicators related to precipitation, leaf wetness, and high relative humidity were observed. Additionally, the significant, negative relationships with the average and maximal air temperature were found. The results suggested that rain should be treated as the major factor driving the ascospore development and leaf wetness as the second factor. In conclusion, the main sources of moisture should be taken into account in statistical models of ascospore development, but it seems reasonable to take into account different strength of their association with the development rate. [ABSTRACT FROM AUTHOR]

During the recent years, High Resolution Melting (HRM) analysis has been developed as a rapid and accurate tool in plant disease diagnostics, species identification and SNP genotyping. This approach has been applied to analyze the genetic diversity in several plant species with molecular markers, including single sequence repeats (SSR). However, no studies have been carried out to investigate the variation of SSR in plant pathogenic fungi by using the HRM technology. In this report, the genetic structure of Venturia inaequalis populations in Greece was investigated for the first time by using six microsatellite markers. The developed HRM protocol was able to generate genotype-specific melting curves, consistent with the haploid nature of the fungus. Unknown samples were genotyped using standard samples as reference controls among multiple runs. Compared to the more complex genome of diploid plants, several limitations were avoided. The shape of the melting curves revealed differences between the genotypes in each SSR marker and showed that all the genotypes could be easily distinguished. The genetic analysis of apple scab populations revealed high genetic variation within the populations (96%), while only 4% of the total gene diversity was attributed to among-population variation. The isolates were grouped into three higher-level populations according to the principal coordinate analysis (PCoA).

Models of maturation rate of the airborne Venturia inaequalis (Cooke) Wint. ascospores were compared using field data collected from spore traps in Skierniewice, Poland, during 2005–2008 and 2010–2014. Two sets of models describing ascospores maturation rate as a function of cumulative temperature were compared. The first set consisted of the "Stensvand" model with degrees summed during and 147 h after the rainfall, and the "Only" type models accumulating temperature only during hours with observed high moisture level indicated by rain, leaf wetness or high humidity. The second set consisted of more complex "All" type models proposed in the study, with degrees summed each hour, but differently weighted for periods with various sources of moisture such as rain, leaf wetness (LW) and relative air humidity (RH). The "All" type models proved to be superior over the "Only" type models. The "All Rain + LW + RH," "All Rain + LW," "All LW" and the "Stensvand" models gave the best match with the data. The final and most important result of the study is such that all of the examined models had high and unsatisfactory range of models' uncertainty for the data from central Poland. Therefore, further improvements in modeling of ascospore maturation rate are necessary. Low accuracy of the models limits their practical application at the current stage of development. [ABSTRACT FROM AUTHOR]

Venturia inaequalis is a known pathogen for long time as causing apple scab disease or black spots. The extent of the disease expression highly depends on apple cultivars, the presence in orchards of host plants of the pathogen, climatic conditions and agricultural practices. Today it becomes more important to broaden the access to more diverse genetic resources in order to improve the breeding programs including for apple varieties. The scope of this article is to analyse how much are affected apple trees by apple scab in the traditional orchards of Sibiu, Fântânele. These orchards are maintained without any pesticides, only traditional practices being applied for more than 30 years. Therefore, we consider that this hot-spot of apple diversity can be a valuable pool gene for further breeding programmes in Europe. Based on our results we can conclude that ‘Belle de Boskoop’, ‘Winter Pearmain’, ‘London Pepping’, ‘Batul Alma’, ‘Edelborsdorfer’, ‘Boiken’, ‘Yellow Bellflower’, ‘Reinette Ananas’ and ‘Reinette Baumann’ are among the best resisting cultivars against this disease. ‘Golden delicious’ is obviously the most susceptible apple cultivar against V. inaequalis. [ABSTRACT FROM AUTHOR]

The apple scab disease which is caused by the fungus of Venturia inaequalis is a continuous problem to the apple growers. The infection requires immediate and continuous treatment in order to control the disease. Nowdays there are several fungicides for treatment of apple scab with different application time. The objective of this study was to identify the optimal action threshold and combining it with some treatment programs for managing the scab disease. For this reason eight treatment programs were created consisting with several fungicides and were realized in three different treatment periods within same year. This research is conducted in one experimental orchard from 2015 to 2017. The disease infection levels were checked on 2400 leaves from 98 apple trees. Based on analyzed disease index the treatment times and variants were compared with each other to results with the best combination of chemicals and application time frame for disease management. [ABSTRACT FROM AUTHOR]

For two consecutive growing seasons (2017 and 2018), three different fungicide spray programs, each with five sprays from unrelated chemical groups, were evaluated for their effectiveness against apple scab (causal agent: Venturia inaequalis) in an experimental trial in Greece. The targeted application programs consisted of five sprays with protective and systemic fungicides from unrelated chemical groups, in alternation. The applications were started at the pink bud stage (a copper-based fungicide had previously been applied at the green bud stage) and completed at the second fruit fall to arrest the primary infections by ascospores. These five-spray programs were compared to the standard farmer practice (12 sprays per season), whereas untreated plots were used as controls. The timing of the applications was based: a) on the critical growth stage of the crop, and b) on the risk analysis for infection calculated by the software Field Climate, which incorporated meteorological data from the trial site. All the five-spray programs were of very high efficacy against apple scab, showing disease severity ratings on leaves and fruits below 1.88%. In both years, in the untreated control, the disease incidence and severity on leaves ranged from 96.5% to 99.3% and from 65.2% to 75.93%, respectively. The five-spray programs showed similar efficacy to the standard 12-application program in all cases. From the results, it becomes apparent that apple scab can be controlled effectively by five targeted applications with selected fungicides at critical growth stages of the crop.

Scab caused by the fungus Venturia inaequalis (Cook) G. Winter is the most devastating disease of the apple worldwide. To control the disease most efforts have been directed toward the breeding programmes by introgression of scab resistance genes from wild apples into commercial cultivars. Although, various apple genotypes exist in Iran, no comprehensive data regarding the possible presence of scab resistance genes is available. In this research the presence of five R genes ( Rvi2 , Rvi4 , Rvi6 , Rvi8 and Rvi11 ) was assessed in 28 wild and domestic apple genotypes using 13 SCAR and SSR markers. Sequencing and blastN results confirmed the identify of Rvi2 , Rvi6 , Rvi8 and Rvi11 genes. Based on the results, wild apples had more resistance genes and among foreign and autochthonous apples, ‘Golden Delicious’, ‘Malayer-1’ and ‘Shahroud-6’ carrying at least three R genes categorized as almost tolerant cultivars. However, ‘Gala’, ‘Boshghabi-e Damavand’, ‘Manouchehri’ and ‘Golab’ had just one R gene and classified as susceptible cultivars. The most frequent scab resistance breeding programmes rely on Rvi6 gene ( HcrVf2 gene), which was also detected in this study in crabapple Malus floribunda providing a rich resource for developing resistant apple cultivars in Iran. [ABSTRACT FROM AUTHOR]

Background: Tracking newly emergent virulent populations in agroecosystems provides an opportunity to increase our understanding of the co-evolution dynamics of pathogens and their hosts. On the one hand host plants exert selective pressure on pathogen populations, thus dividing them into subpopulations of different virulence, while on the other hand they create an opportunity for secondary contact between the two divergent populations on one tree. The main objectives of the study were to explore whether the previously reported structure between two Venturia inaequalis population types, virulent or avirulent towards Malus x domestica cultivars carrying Rvi6 gene, is maintained or broken several years after the first emergence of new virulent strains in Poland, and to investigate the relationship between 'new' and 'native' populations derived from the same commercial orchards. For this purpose, we investigated the genetic structure of populations of the apple scab fungus, occurring on apple tree cultivars containing Rvi6, Rvi1 or Rvi17 resistance gene or no resistance at all, based on microsatellite data obtained from 606 strains sampled in 10 orchards composed of various host cultivars. Results: Application of genetic distance inferring and clustering methods allowed us to observe clear genetic distinctness of the populations virulent towards cultivars carrying Rvi6 gene from the Rvi6-avirulent populations and substructures within the Rvi6-group as a consequence of independent immigration events followed by rare, longdistance dispersals. We did not observe such a structuring effect of other genes determining apple scab resistance on any other populations, which in turn were genetically homogenous. However, in two orchards the cooccurrence of strains of different virulence pattern on the same trees was detected, blurring the genetic boundaries between populations. Conclusions: Among several resistance genes studied, only Rvi6 exerted selective pressure on pathogens populations: those virulent toward Rvi6 hosts show unique and clear genetic and virulence pattern. For the first time in commercial Malus x domestica orchards, we reported secondary contacts between populations virulent and avirulent toward Rvi6 hosts. These two populations, first diverged in allopatry, second came into contact and subsequently began interbreeding, in such way that they show unambiguous footprints of gene flow today. [ABSTRACT FROM AUTHOR]

Apple scab, caused by the apoplastic fungal pathogen Venturia inaequalis , is one of the most damaging apple diseases worldwide and scab resistance is still one of the most important goals in apple breeding programmes. Improving knowledge of defence systems against pathogens through the identification of resistance and defence-related genes enables the development of molecular tools that can be used for assisted-selection of elite varieties. The apple scab Rvi6 (formerly HcrVf2 ) resistance gene has been extensively used to breed resistant varieties, and several defence-related genes activated downstream have recently been identified. In this work, subtractive hybridisation was performed in order to collect cDNA differentially expressed in the resistant Rvi6 cultivar ‘Florina’ after challenge with the fungus and treatment with salicylic acid. A total of 97 unique sequences were identified, and most of them were successfully annotated and located on the apple genome in silico . The expression profiles of twelve candidate genes were analysed using quantitative real-time PCR in both incompatible and compatible Malus - V.inaequalis interactions. The responses induced by the two treatments differed significantly, suggesting that salicylic acid might be not involved in apple scab defence mechanisms. Some candidate genes are involved in well-known defence strategies against apoplastic fungal pathogens, such as the reinforcement and maintenance of cell wall integrity and fungal growth hindrance. Others are presumed to play a role in the signal transduction pathway, in a similar way to that known for other pathosystems. Finally, potential mechanisms involved in the defence response against apple scab are proposed. [ABSTRACT FROM AUTHOR]

Apple scab, caused by Venturia inaequalis, can lead to large losses of marketable fruit if left uncontrolled. The disease appears in orchards during spring as lesions on leaves. These primary lesions are caused by spores released at bud burst from overwintering sources; these spores can be sexually produced ascospores from the leaf litter or asexual conidia from mycelium in wood scab or within buds. The relative importance of conidia and ascospores as primary inoculum were investigated in an orchard in southeast England, UK. Potted trees not previously exposed to apple scab were placed next to ( c. 1 m) orchard trees to trap air-dispersed ascospores. Number and position of scab lesions were assessed on the leaves of shoots from both the potted trees (infection by airborne ascospores) and neighbouring orchard trees (infection by both ascospores and splash-dispersed, overwintered conidia). The distribution and population similarity of scab lesions were compared in the two tree types by molecular analysis and through modelling of scab incidence and count data. Molecular analysis was inconclusive. Statistical modelling of results suggested that conidia may have contributed approximately 20-50% of the primary inoculum in early spring within this orchard: incidence was estimated to be reduced by 20% on potted trees, and lesion number by 50%. These results indicate that, although conidia are still a minority contributor to primary inoculum, their contribution in this orchard is sufficient to require current management to be reviewed. This might also be true of other orchards with a similar climate. [ABSTRACT FROM AUTHOR]

The agent of apple scab disease ( Venturia inaequalis ) is the most common pathogen in apple cultivation. Its ascospores are released in spring, mainly during daylight hours and triggered by rain events. To investigate the causes of diurnal rhythm of ascospore dissemination of the apple scab fungus ascospore releases were examined continuously with spore traps in the orchard and with laboratory assays. One of the spore traps was illuminated at night with different light sources in each year during 2011–2015. The laboratory assays were performed with different light sources with varying wavelengths and intensities. In field and laboratory conditions only light including infrared radiation stimulated ascospore release, but not with light in the visible spectrum only. Artificial illumination during night was correlated with an increase of up to 46 % of ascospores released overnight in the field. We proved that infrared radiation induces V. inaequalis to release its spores. This is the first report in which spore discharge could be stimulated during night under field conditions. [ABSTRACT FROM AUTHOR]

Venturia inaequalis isolates were collected during the 2012/13 and 2013/14 seasons from the four principal apple growing regions of South Africa, Elgin (n = 114), Koue Bokkeveld (n = 126), Lower Langkloof (n = 92), and Upper Langkloof (n = 103). Sequence analysis of the ribosomal internal transcribed spacer (ITS) gene regions and genotyping with six (2012/13) and seven (2013/14) microsatellite (SSR) markers was conducted. A subset of 12 isolates from the individual ITS haplotype groups were sequenced for the translation elongation factor-1 alpha (TEF1) and the large subunit of the RNA polymerases II (RPB1) gene regions. Four haplotypes were found for ITS, whereas all isolates were identical for the TEF1 and RPB1 gene regions. The SSR markers revealed considerable variation with an average gene diversity (H) of 0.675. Multivariate analysis (discriminant analysis of principal components [DAPC]) revealed that the two Langkloof populations clustered together with the Koue Bokkeveld population. The population from the warmer winter region, Elgin, clustered separately from the rest of the populations (ΦPT = 0.076 to 0.116; P ≤ 0.05). Estimates of gene flow showed the highest migration rate from the Koue Bokkeveld, toward the Lower Langkloof (M = 151.1), and the least migration to and from the Elgin region (average M = 42.75). Occasionally, identical genotypes (clones) were detected across seasons in the Koue Bokkeveld and Elgin area, which might contribute to overwintering conidia. From this study, it is evident that South Africa most likely has V. inaequalis subpopulations linked to diverse climatic conditions of the coastal Elgin region compared with the mountainous inland regions of the Koue Bokkeveld and the Langkloof. [ABSTRACT FROM AUTHOR]

Quantitative plant resistance is supposed to be more durable than qualitative resistance for the control of plant diseases. However, it has been experimentally shown that erosion of quantitative resistance can occur. Cumulation of quantitative resistance loci ( QRLs) in the same cultivar is considered to improve the efficiency and durability of quantitative resistance, but the choice of QRLs to be combined is of crucial importance. This study investigated whether the combination of QRLs acting on different stages of pathogen development could improve the efficiency of resistance in the apple scab pathosystem. The efficiencies of three QRLs were evaluated against 10 isolates of Venturia inaequalis and the stages of pathogen development that were affected by the QRLs were defined microscopically. A gain in the efficiency of resistance was observed when QRLs were pyramided compared to when they acted alone. Thanks to the combined effects of the individual QRLs, the pyramiding of the three QRLs hindered fungal development at different stages: before the penetration of the plant cuticule, after the penetration with hypersensitivity reaction, and during the colonization and asexual reproduction. These effects were dependent on the V. inaequalis isolates. These results suggest that the gain in efficiency of resistance by pyramiding may derive from the combination of different and complementary molecular mechanisms underlying QRLs. Thus, the resistance achieved from pyramiding such a combination of QRLs should be durable. [ABSTRACT FROM AUTHOR]

Apple scab (Venturia inaequalis (Cke) Wint) is the main disease of apple trees not only in the world but also in Turkey. The disease can cause severe yield losses in all Turkish apple orchards. Genetic diversity and relatedness of apple scab (Venturia inaequalis (Cke) Wint) isolates collected from Turkey and Europe were investigated in this study through molecular markers. RAPD, ISSR, SSR and SRAP markers were used in the molecular studies. Results obtained by marker system revealed that isolates were quite separated from each other and it is appeared to exist a variation between them. Genetic relatedness between the isolates are very close to each other, and difference among the groups is not significant due to host specificity and geographical location. The groups are consisted of more number of isolates when SSR and SRAP markers are used compared with ISSR and RAPD markers. Using SSR and SRAP markers are preferable to provide more informative outcomes because of ease of use, repeatability and specificity. [ABSTRACT FROM AUTHOR]