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Apple scab, a fungal disease caused by Venturia inaequalis , leads to losses in both yield and fruit quality of apples (Malus domestica Borkh.). Most commercial apple cultivars, including those containing the well-characterized Rvi6- scab-resistance locus on linkage group (LG) 1, are susceptible to scab. HcrVf2 and HcrVf1 are considered the main paralogs of the Rvi6 locus. The major apple scab-resistance loci Vhc1 in "Honeycrisp" and Rvi17 in "Antonovka," were identified in close proximity to HcrVf2. In this study, we used long-read sequencing and in silico gene sequence characterization to identify candidate resistance genes homologous to HcrVf2 and HcrVf1 in Honeycrisp and Antonovka. Previously published chromosome-scale phased assembly of Honeycrisp and a newly assembled phased genome of Antonovka 172670-B were used to identify HcrVf2 and HcrVf1 homologs spanning Vhc1 and Rvi17 loci. In combination with 8 available Malus assemblies, 43 and 46 DNA sequences highly homologous to HcrVf2 and HcrVf1 , respectively, were identified on LG 1 and 6, with identity and coverage ranging between 87–95 and 81–95%, respectively. Among these homologs, 2 candidate genes in Antonovka and Honeycrisp haplome A are located in close physical proximity to the scab-resistance marker Ch-Vf1 on LG 1. They showed the highest identity and coverage (95%) of HcrVf2 and only minor changes in the protein motifs. They were identical by state between each other, but not with HcrVf2. This study offers novel genomic resources and insights into the Vhc1 and Rvi17 loci on LG 1 and identifies candidate genes for further resistance characterization. [ABSTRACT FROM AUTHOR]

The apple (Malus x domestica) scab (Venturia inaequalis) resistance genes Rvi4 and Rvi15 were mapped to a similar region on the top of linkage group 2 and both resistance genes elicit the same type of resistance reaction, i.e., a hypersensitive response; hence, it is suspected that the two genes may be the same. As the two resistance genes Rvi4 and Rvi15 are currently used in apple breeding, it is important to clarify whether the two resistance genes are the same or not. Several approaches were used to make this determination. First, the pedigree of the genotype GMAL 2473, the source of Rvi15, was reconstructed. GMAL 2473 was found to be an F1 of ‘Russian seedling’, the genotype, which is known to also be the source of Rvi4. Next, it was further demonstrated that ‘Regia’, a cultivar known to carry Rvi4 (and Rvi2), carries the same gene (Vr2-C), which was demonstrated to be the gene inducing Rvi15 resistance. Finally, it was shown that transgenic lines carrying Vr2-C are compatible with race 4 apple scab isolates. Taken all together, these results defnitively demonstrate that Rvi4 and Rvi15 are the same resistance gene. For future studies, we suggest referring to this resistance with the frst name that was assigned to this gene, namely Rvi4. [ABSTRACT FROM AUTHOR]

The European Green Deal demands a system-wide rethinking of Europe's approach to food production, with ambitious targets that could result in repercussions for consumers across the globe if tools for adaptation are not supported. Integrated pest management is a holistic approach to plant health that is centered around varieties with improved biotic resistances. New genomic techniques ease the development of varieties with durable biotic resistances through the stacking of resistance genes. Varieties with durable biotic resistances enable a system-wide rethinking of disease control, which can result in sizable reductions of pesticide use without affecting yields. While environmental benefits, due to the reduction in pesticide use, are to be expected from the adoption of the here reviewed cisgenic varieties, economic benefits are likely conditional on consumers' acceptance of the technology. Significant shares of harvests are lost to pests and diseases, therefore, minimizing these losses could solve part of the supply constraints to feed the world. Cisgenesis is defined as the insertion of genetic material into a recipient organism from a donor that is sexually compatible. Here, we review (i) conventional plant breeding, (ii) cisgenesis, (iii) current pesticide-based disease management, (iv) potential economic implications of cultivating cisgenic crops with durable disease resistances, and (v) potential environmental implications of cultivating such crops; focusing mostly on potatoes, but also apples, with resistances to Phytophthora infestans and Venturia inaequalis, respectively. Adopting cisgenic varieties could provide benefits to farmers and to the environment through lower pesticide use, thus contributing to the European Green Deal target. [ABSTRACT FROM AUTHOR]

Apple scab instigated by Venturia inaequalis impels remarkable losses to apple fruit production. In an effort to comprehend the key mechanisms of evolutionary potential defining V. inaequalis population, 132 isolates of V. inaequalis from five commercial apple orchards were collected and assayed using 14 microsatellite markers. The average diversity was observed within the individuals of populations based on the Shannon-Wieners index (I) and observed heterozygosity (Ho) was average but considerably lower than expected heterozygosity (He). The genetic differentiation based on FST values was revealed as an average measure of divergence between populations and had varying proportions of gene flow and migration among themselves. Analysis of Molecular Variance (AMOVA) revealed that variance (94%) was dispersed across individuals with a significant (6%) variation between populations from different regions. To examine host specialization within the V. inaequalis population, the assignment approach based on K-means of clustering (an unsupervised machine learning approach), revealed that the clustering method supported three clusters at (K = 3) and three major clusters were also observed in Principle Component Analysis (PCA). Additionally, Nei's genetic distance values, pairwise estimates of genetic differentiation, dendrogram using the neighbor-joining and PCoA revealed the random distribution of V. Inaequalis isolates that depicted a high proportion of genotypic diversity within populations and population genetic structure. [ABSTRACT FROM AUTHOR]

Apple scab instigated by Venturia inaequalis impels remarkable losses to apple fruit production. In an effort to comprehend the key mechanisms of evolutionary potential defining V. inaequalis population, 132 isolates of V. inaequalis from five commercial apple orchards were collected and assayed using 14 microsatellite markers. The average diversity was observed within the individuals of populations based on the Shannon-Wieners index (I) and observed heterozygosity (Ho) was average but considerably lower than expected heterozygosity (He). The genetic differentiation based on FST values was revealed as an average measure of divergence between populations and had varying proportions of gene flow and migration among themselves. Analysis of Molecular Variance (AMOVA) revealed that variance (94%) was dispersed across individuals with a significant (6%) variation between populations from different regions. To examine host specialization within the V. inaequalis population, the assignment approach based on K-means of clustering (an unsupervised machine learning approach), revealed that the clustering method supported three clusters at (K = 3) and three major clusters were also observed in Principle Component Analysis (PCA). Additionally, Nei's genetic distance values, pairwise estimates of genetic differentiation, dendrogram using the neighbor-joining and PCoA revealed the random distribution of V. Inaequalis isolates that depicted a high proportion of genotypic diversity within populations and population genetic structure. [ABSTRACT FROM AUTHOR]

Apple scab caused by Venturia inaequalis is the most threatening plant disease in Aomori Prefecture, which receives heavy snowfall. Here, we collected 169 monoconidial isolates of V. inaequalis from Tsugaru (6 orchards) and Nanbu regions (3 orchards) in Aomori Prefecture, Japan, and analyzed their genetic diversity and population structure using 15 microsatellite markers. One hundred and six alleles were detected, ranging from 3 to 17 alleles per locus. Genetic diversity analysis showed high variability from 0.35 to 0.85. One hundred and sixty-six haplotypes were detected, suggesting that genetic recombination occurred at a high frequency. In a principal coordinate analysis, V. inaequalis isolates from the Tsugaru and Nanbu regions showed partial overlap and no distinct clusters. In a structure analysis, the optimal population number (K) was estimated to be 2. One of the estimated populations consisted of 83% Nanbu isolates and the other of 71% Tsugaru isolates, supporting the occurrence of geographically defined populations. Pairwise genetic differentiation between orchards showed a wide range within the Tsugaru population, whereas the lowest values were observed between the Tsugaru and Nanbu orchards. This result suggests a link between geographic distance and gene flow, suggesting long-distance movement between populations via nursery plants. This report using microsatellite markers is the first analysis of the population genetics of V. inaequalis in Aomori. [ABSTRACT FROM AUTHOR]

Apple and pear scab are foliar pathogens of apple and pear trees. Unmanaged, yield and aesthetic losses can be severe. The risk of resistance associated with over-reliance on fungicides means novel pathogen management methods and products are increasingly required. Chitin and chitosan are widely recognised as induced resistance (IR) agents that trigger plant defence responses that in turn enhance plant resilience to pathogen ingress. A container and field trial was conducted using apple (Malus sylvestris) and pear (Pyrus communis 'Conference') respectively to assess the efficacy of a range of liquid and granular chitin/chitosan-based IR agents and fertilisers against apple and pear scab. A synthetic fungicide (penconazole) spray program used within the UK for apple and pear scab control was included for comparison. Application of chitin/chitosan IR agents at concentrations above 1% caused phytotoxicity. Limited efficacy as scab protectants was also demonstrated when chitin/chitosan IR agents were applied at concentrations of 0.25%. However, chitin IR agents when applied at 0.5% and 1% and chitosan IR agents at 1% demonstrated efficacy as scab protectants and resulted in an increased leaf chlorophyll content, increased fruit yield, and reduced leaf scab severity when compared against the watered control. Only one of three chitin/chitosan fertilisers evaluated demonstrated efficacy as scab protectants (liquid chitosan). A synthetic fungicide penconazole spray program provided the greatest protection against apple and pear scab in the container trials. However, under field conditions the degree of scab control following application of chitin and chitosan at 1% and the chitosan containing fertiliser liquid chitosan was statistically comparable to fungicide treated trees. Results suggest application of an appropriate chitin/chitosan IR agent(s) and fertiliser offers a useful addition to existing methods of apple and pear scab management under field and container conditions. [ABSTRACT FROM AUTHOR]

Background: Scab, caused by the biotrophic fungus Venturia inaequalis, is the most economically important disease of apples worldwide. During infection, V. inaequalis occupies the subcuticular environment, where it secretes virulence factors, termed effectors, to promote host colonization. Consistent with other plant-pathogenic fungi, many of these effectors are expected to be non-enzymatic proteins, some of which can be recognized by corresponding host resistance proteins to activate plant defences, thus acting as avirulence determinants. To develop durable control strategies against scab, a better understanding of the roles that these effector proteins play in promoting subcuticular growth by V. inaequalis, as well as in activating, suppressing, or circumventing resistance protein-mediated defences in apple, is required. Results: We generated the first comprehensive RNA-seq transcriptome of V. inaequalis during colonization of apple. Analysis of this transcriptome revealed five temporal waves of gene expression that peaked during early, mid, or mid-late infection. While the number of genes encoding secreted, non-enzymatic proteinaceous effector candidates (ECs) varied in each wave, most belonged to waves that peaked in expression during mid-late infection. Spectral clustering based on sequence similarity determined that the majority of ECs belonged to expanded protein families. To gain insights into function, the tertiary structures of ECs were predicted using AlphaFold2. Strikingly, despite an absence of sequence similarity, many ECs were predicted to have structural similarity to avirulence proteins from other plant-pathogenic fungi, including members of the MAX, LARS, ToxA and FOLD effector families. In addition, several other ECs, including an EC family with sequence similarity to the AvrLm6 avirulence effector from Leptosphaeria maculans, were predicted to adopt a KP6-like fold. Thus, proteins with a KP6-like fold represent another structural family of effectors shared among plant-pathogenic fungi. Conclusions: Our study reveals the transcriptomic profile underpinning subcuticular growth by V. inaequalis and provides an enriched list of ECs that can be investigated for roles in virulence and avirulence. Furthermore, our study supports the idea that numerous sequence-unrelated effectors across plant-pathogenic fungi share common structural folds. In doing so, our study gives weight to the hypothesis that many fungal effectors evolved from ancestral genes through duplication, followed by sequence diversification, to produce sequence-unrelated but structurally similar proteins. [ABSTRACT FROM AUTHOR]

In vitro antifungal tests with one of the most popular medical substance in the world – L – ascorbic acid, widely known as vitamin C, were conducted with three of the most spread plant pathogens in Bulgaria: Monilia frucigena, Alternaria solani and Venturia inaequalis in order to evaluate the direct antifungal action of the acid used in agriculture as ISR promoter (phytovaccine). The expression of pesticide action of ISR promoters is not unusual unlike the vaccines for the animals and humans. Conducted tests shows the strong antifungal activity of L – ascorbic acid towards mycelium and conidiospores of Alternaria solani and Venturia inaequalis and a very weak antifungal action towards Monilia frucigena which means that vitamin C can be used as a direct fungicide agent and phytovaccine in the pest management simultaneously. The substance has excellent water solubility which make is very appropriate for formulation as a plant protection product. [ABSTRACT FROM AUTHOR]

Modern reviews of challenges related to deep learning application in agriculture mention restricted access to open datasets with high-resolution natural images taken in field conditions. Therefore, artificial intelligence solutions trained on these datasets containing low-resolution images and disease symptoms in the advanced stage are not suitable for early detection of plant diseases. The study aims to train a convolutional neural network for apple scab detection in an early stage of disease development. In this study a dataset was collected and used to develop a convolutional neural network based on the sliding-window method. The convolutional neural network was trained using the transfer-learning approach and MobileNetV2 architecture tuned on for embedded devices. The quality analysis in laboratory conditions showed the following accuracy results: F1 score 0.96 and Cohen's kappa 0.94; and the occlusion maps — correct classification features. [ABSTRACT FROM AUTHOR]

To control apple scab caused by Venturia inaequalis, fungicides inhibiting the growth of fungal pathogens during the initial stages of infection are important management tools. From 2019 to 2021, bioassays to evaluate the curative effects of fungicides typically used to control apple scab revealed that iminoctadine triacetate, inpyrfluxam, pydiflumetofen, ipflufenoquin, fluopyram, fluxapyroxad, and cyprodinil exerted curative effects against V. inaequalis. Overall, iminoctadine triacetate, inpyrfluxam, and pydiflumetofen were particularly effective. Control of primary infection is important for the management of scab. Therefore, these curative fungicides should be applied during the period from half-inch green to fruit set. [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]

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]

This paper reports the interception of Venturia inaequalis, a pathogen of quarantine significance in apple consignments imported to India. During 2018-2020, apple shipments from eighteen countries representing six continents were imported through Chennai port. Shipments from seven countries representing five continents were intercepted with quarantine fungal pathogens Venturia inaequalis and Monilinia fructicola. The intercepted shipments were issued Deportation Orders as per the provisions of Plant Quarantine (Regulation of Import into India) Order, 2003. The non-compliances were notified to the trading partners on each interception as per the IPPC guidelines. [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]

This research aimed to study the leaf micromorphological and biochemical features of columnar apple cultivars that are immune and moderately resistant to Venturia inaequalis, the causal agent of scab disease, during 2017-19 at the Federal Horticultural Research Center for Breeding, Agrotechnology, and Nursery, Moscow, Russia. Results revealed that the immune cultivars showed a higher level of adaptability to the fungus V. inaequalis than the moderately resistant cultivars. The large number of leaf trichomes on the abaxial leaf surface that confer protection was characteristic of the immune cultivars. The immune columnar apple cultivars had 6% fewer leaf stomata than the moderately resistant ones. The stomata of the immune cultivars were placed high in the leaf surface, were surrounded by chords and folds, and had high cuticular peristomatal rings that provided additional protection by preventing pathogen entry. Inclusions with parallelogram and rounded-star shapes were found in the cross-section cut of the central leaf midrib of the immune cultivars. By contrast, the inclusions were mostly rounded-star-shaped in moderately resistant cultivars. Analysis through electronic microscopy with energy dispersion spectrometry revealed that the Ca and K contents in the parallelogram-shaped inclusions were 3 and 2 times higher than those in the rounded-star-shaped inclusions, respectively. In terms of ash composition, the P, Mg, and Ca contents in the leaves of immune columnar apple cultivars were 1.5, 1.5, and 1.6 times higher than those in the leaves of moderately resistant cultivars. The ultrafine surface study was more reasonable than other methods for identifying the phytopathogen resistance of fruit trees. The use of modern instrumental analytical methods for the complex evaluation of fruit crop leaves to reveal adaptations to biotic factors is meaningful for breeding use. [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]

Apple and pear scab are foliar diseases of ornamental and fruiting apple and pear trees. Unmanaged, yield and aesthetic losses can be severe. Overreliance on synthetic fungicides means novel means of disease management are required. Field trials were conducted using apple (Malus cv. Crown Gold) and pear (Pyrus communis 'Williams Bon Chrétien') to assess the efficacy of a range of commercially available inducing resistance (IR) agents (harpin protein, potassium phosphite, salicylic acid derivative, and chitosan) as root drenches against both scab diseases. A synthetic fungicide (penconazole) spray program used within the UK for apple and pear scab control was included for comparison. Each IR agent was applied four times, (i) before the visible appearance of scab (April through June, i.e., preventatively) or (ii) after symptoms of scab were visibly observed (June through August, i.e., curatively). Limited efficacy as scab protectants was demonstrated when IR agents were applied curatively. Likewise, limited efficacy was recorded when IR agents were applied once or twice as a preventative measure. However, when IR agents were applied as root drenches greater or equal to three times, efficacy as scab protectants was confirmed (increased leaf chlorophyll content, increased fruit yield, reduced leaf and fruit scab severity). A synthetic fungicide penconazole spray program provided the greatest protection against apple and pear scab in all trials when sprayed preventatively rather than curatively. Results suggest application of at least three root drenches from April through June with an appropriate IR agent provides a useful addition to existing methods of apple and pear scab management under field conditions. [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]

Summary: Apple (Malus sp.) and other genera belonging to the sub‐tribe Malinae of the Rosaceae family produce unique benzoic acid‐derived biphenyl phytoalexins. Cell cultures of Malus domestica cv. 'Golden Delicious' accumulate two biphenyl phytoalexins, aucuparin and noraucuparin, in response to the addition of a Venturia inaequalis elicitor (VIE). In this study, we isolated and expressed a cinnamate‐CoA ligase (CNL)‐encoding sequence from VIE‐treated cell cultures of cv. 'Golden Delicious' (M. domestica CNL; MdCNL). MdCNL catalyses the conversion of cinnamic acid into cinnamoyl‐CoA, which is subsequently converted to biphenyls. MdCNL failed to accept benzoic acid as a substrate. When scab‐resistant (cv. 'Shireen') and moderately scab‐susceptible (cv. 'Golden Delicious') apple cultivars were challenged with the V. inaequalis scab fungus, an increase in MdCNL transcript levels was observed in internodal regions. The increase in MdCNL transcript levels could conceivably correlate with the pattern of accumulation of biphenyls. The C‐terminal signal in the MdCNL protein directed its N‐terminal reporter fusion to peroxisomes in Nicotiana benthamiana leaves. Thus, this report records the cloning and characterisation of a cinnamoyl‐CoA‐forming enzyme from apple via a series of in vivo and in vitro studies. Defining the key step of phytoalexin formation in apple provides a biotechnological tool for engineering elite cultivars with improved resistance. Significance Statement: Apple scab is a serious apple disease. The scab resistance mechanism in apple is poorly understood. This report records the cloning and characterisation of a cinnamoyl‐CoA‐forming enzyme from apple via a series of in vivo and in vitro studies. Defining the key step of phytoalexin formation in apple provides a biotechnological tool for engineering elite cultivars with improved scab resistance. [ABSTRACT FROM AUTHOR]

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]

Apple scab is one of the most commercially significant apple diseases, caused by the ascomycete fungus Venturia inaequalis. In gene-for-gene (R-Avr) interactions, a subset of effectors known as avirulence (Avr) gene products can be identified by the host, resulting in the activation of the host defence response. Several important scab resistance (R) genes have been identified in apple cultivars and wild relatives; however, little is known about interacting Avr genes from V. inaequalis. Major Avr genes such as AvrRvi1 , AvrRvi2 , and AvrRvi5 have been extensively studied in this fungus. A few complicated interactions involving AvrRvi2 AvrRvi8 and AvrRvi9 have also been discovered. Several Avr analogues have been predicted from this fungus using comparative genomics techniques. Therefore, the aim of this study is to characterize several Avr genes in V. inaequalis to better understand host-pathogen interactions in this pathological system. This review provides an up-to-date understanding of the large number of Avr genes identified to date in V. inaequalis. • Apple scab caused by Venturia inaequalis is economically most important disease of apple. • Several major Avr-R interactions has been reported in V. inaequalis- apple pathosystem. • Avr genes like AvrRvi1, AvrRvi2 and AvrRvi5 have been characterized in detail. • Some SSP like Avr of other dangerous fungi have also been identified in V. inaequalis. • Various extended Avr gene families from V. inaequalis have also been reported using comparative genomics. [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]

Apple scab (Venturia inaequalis) (AS) and frogeye leaf spot or black rot (Botryosphaeria obtusa) (FLS or BR) are two diseases of apples that affect developing foliage and fruit during summer and cause significant losses in the field and during storage. In this 3-year study (2014–2016), salicylic acid (2-hydroxybenzoic acid) or its analogue (Benzothidiazole or Actigard®) were applied to field-established apple 'Honeycrisp' at the tight cluster stage of flower bud development and at late pink bloom as either trunk injection or foliar sprays and to 'Cortland' (injection only). AS and FLS leaf infections were assessed 1, 2, and 3 weeks after the second treatment while infections on fruit were assessed at harvest. Main treatment effects were significant (P = 0.05) and both salicylic acid and Actigard® showed less infections on foliage due to AS in 2014 and 2016, and only salicylic acid showed less BR infections on fruit in both years. The cultivar effects were also significant, showing consistently less AS infections on the foliage and fruit of 'Honeycrisp', and less FLS infections on 'Cortland' foliage. Injection and spray treatments of salicylic acid and Actigard® showed no differences in infections by AS and FLS or BR on foliage or fruit. The method of application × treatment interactions were only significant in 2014; both salicylic acid and Actigard®-treated 'Cortland' trees showed less FLS infections on foliage and less BR infections on fruit, and only salicylic acid-treated 'Honeycrisp' trees showed less percentage of AS and BR infected fruit. In 2015, both salicylic acid and Actigard® treatments showed less infections of FLS on foliage and lower BR-infected fruit on 'Cortland'. In 2016, both these treatments reduced incidence of AS and FLS on 'Cortland' foliage, and only salicylic acid reduced AS infections on 'Honeycrisp' foliage. Further studies are needed to integrate salicylic acid or Actigard® treatments into an apple foliar disease management program with registered fungicides. [ABSTRACT FROM AUTHOR]

Apple scab, Venturia inaequalis (Cooke) G. Winter, results in numerous fungicide applications in the Sais region of Morocco. We conducted the study to determine the susceptibility of cultivars through field survey and to evaluate the sensitivity of V. inaequalis to three fungicides using both in vitro and in vivo methods. We surveyed 100 apple orchards and collected two samples. Disease survey showed that the cultivars were highly susceptible to apple scab (grand mean of leaf scab: Golden Delicious, 40.31%; Starking Delicious, 20.45%; and Gala, 18.92%). Results underlined no significant differences between isolates in term of inhibition rate of mycelial growth and averaged disease severity. However, both treatment and concentration were statistically significant. EC50 values ranged from 2.33 μg/ml to 7.40 μg/ml and resistance factor (RF) values of 0.55, 1.02 and 1.79 were obtained for difenoconazole, trifloxystrobin and thiophanate-methyl, respectively. In vivo tests at a concentration of 10 μg/ml on the isolate ViIF using a curative method showed a high efficacy of trifloxystrobin (96.38%), and low efficacy of thiophanate-methyl (29.65%) and difenoconazole (24.62%). V. inaequalis was most sensitive to trifloxystrobin followed by difenoconazole and thiophanate-methyl, respectively. From this work, it was recommended testing more isolates and contact fungicides in order to develop a baseline sensitivity of the pathogen population against commonly used fungicides to treat the disease, as continued usage over time and the introduction of new fungal races may result in a decrease in fungicide efficacy. [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]

Management of scab through resistant varieties represents a cost effective and eco-friendly alternative to chemical control. The accurate identification of resistant genotypes is carried out both at phenotypic as well as genotypic levels and most of the previous studies on resistance screening have been carried out using only one of these strategies. We used a combination of conventional and molecular marker based approaches for screening of 75 apple genotypes, in Kashmir region of India, to get more reliable results. We identified 17 genotypes carrying major scab resistance genes Rvi2, Rvi6, Rvi8 and Rvi11 with genotypes like Shalimar 2nd, Liberty and Sangerwan Delicious carrying multiple scab resistance genes, a finding that bypasses the use of tedious and time consuming procedure of gene pyramiding and could save researchers invaluable resources and time. We also identified two genotypes of Indigenous Ambri cultivars carrying Rvi11 scab resistance gene, a finding that may play an important role for revival and commercialization of Ambri cultivars which is considered as native of Kashmir valley of Jammu and Kashmir but are under serious threat from other commercially viable cultivars. Earlier scales used for resistance screening lack a separate category for identification of quantitative resistance. We introduce a separate class for genotypes carrying quantitative resistance because we believe it can be very important for disease management especially when present alongside a major scab resistance gene. We also conclude that genetic background in which a scab resistance gene is embedded is the major factor for the phenotypic response it shows upon inoculation with the pathogen. • We used a combination of inoculation and molecular methods to screen 75 apple genotypes and identified 17 genotypes carrying scab resistance genes Rvi6, Rvi11 and Rvi2/Rvi8. • We also introduce a separate class to the scale used for scab assessment, besides we conclude that genetic background contributes significantly to the phenotypic response a scab resistance gene shows upon inoculation of host plant with the pathogen. • We also identified resistance in traditional Ambri apple cultivars of the region which could be vital for the revival of these varieties. [ABSTRACT FROM AUTHOR]

Summary: Apple scab caused by Venturia inaequalis is the most destructive disease of apple worldwide. In this study, genetic diversity of 101 V. inaequalis isolates from cultivated apples and ornamental crabapples in Pennsylvania (PA, USA) was characterized using 14 microsatellite markers. A total of 157 alleles ranging from 5 (Vitg9/99) to 26 (Vica10/154) per locus were detected. Regardless of the host of origin, isolates were grouped into five clusters, which were largely supported by STRUCTURE and principal coordinate analysis. Cluster analyses based on genetic distances and population structure analysis suggest very small differentiation (PhiPT ranging from 0.016 to 0.103, depending on the population comparison) between apple and crabapple isolates of V. inaequalis. Pairwise comparisons among populations from different locations showed very low differentiation, and POPGENE analysis indicated frequent migration of alleles (Nm = 1.47). In pathogenicity tests using a detached leaf assay, isolates of V. inaequalis from crabapple caused characteristic scab symptoms on apple and were highly virulent. Results of the study indicate that scab lesions in crabapple trees in close vicinity to apple orchards could serve as reservoirs for spread of the pathogen. Movement of inoculum among locations and between hosts may be responsible for the limited population structure observed. Understanding the population structure of V. inaequalis isolates is significant for apple scab management as crabapples are often used as pollinizers and rootstock in apple orchards, and as ornamental trees. [ABSTRACT FROM AUTHOR]

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]

Salicylic acid (SA) is known to trigger a number of plant defense responses upon pathogen attack. It is well known that apple ( Malus domestica ) plants respond to pathogen invasion by synthesizing SA, but its biosynthesis is not well understood. In this study, we report salicylaldehyde synthase (SAS) activity from Venturia inaequalis elicitor (VIE)-treated cell suspension cultures of apple ( Malus domestica ‘Florina’). SAS catalyzes non-oxidative C 2 -side chain cleavage of 2 -coumaric acid to form salicylaldehyde (SALD) in the presence of a reducing agent such as cysteine. The side chain cleavage mechanism was found to be very similar to that of salicylaldehyde synthase activity from tobacco and 4-hydroxybenzaldehyde synthase activity from Vanilla planifolia and Daucus carota . A basal SAS activity was observed in the non-elicited cell cultures, and a 7-fold increase in SAS activity was observed upon elicitation. In parallel to SAS activity, the level of total SA accumulation increased by 5.6-fold after elicitation compared to the untreated control cells. Elicitor treatment further resulted in an 8.7-fold increase in the activity of the phenylalanine ammonia-lyase (PAL) enzyme that preceded the peak of SAS activity and total SA accumulation, suggesting the involvement of the phenylpropanoid pathway in SA metabolism. The preferred substrate for SAS was 2 -coumaric acid ( K m = 0.35 mM), with cysteine being the preferred reducing agent. In addition, a 1.8-fold enhancement in the SA content and 0.7-fold enhancement in the SALD content was observed when elicited cell cultures were fed with 2-coumaric acid. These observations suggest the involvement of SAS in SALD biosynthesis. [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]

"AMALIA" is an apple variety obtained by clonal selection at SC FRUCTEX BACAU SRL, homologated in 2018 by Prof. Engineer Rati Ioan Viorel, PhD. "AMALIA" has been assigned by the reporting authority (ISTIS) the reference number 05076. This variety is present in the Fructex Bacau orchard and collection, being one of the varieties demanded by farmers due to its qualities. The tree is medium in size, cone-like shaped, with short, medium and long fruit branches. It is a selffertilizing variety. The fruit is large, weighing between 190-200g, dark red in colour; the pulp displays great firmness and medium juice content, and pleasant taste. It has significant harvesting yield, achieving constantly 25-30 t/ha. Qualities: It presents resistance to Apple scab (Venturia inaequalis) and good resistance to powdery mildew (Podosphaera leucotricha); the capacity of yield self-regulation enables constant crops every year. [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]

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]

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]

Background: Fungal plant pathogens belonging to the genus Venturia cause damaging scab diseases of members of the Rosaceae. In terms of economic impact, the most important of these are V. inaequalis, which infects apple, and V. pirina, which is a pathogen of European pear. Given that Venturia fungi colonise the sub-cuticular space without penetrating plant cells, it is assumed that effectors that contribute to virulence and determination of host range will be secreted into this plant-pathogen interface. Thus the predicted secretomes of a range of isolates of Venturia with distinct host-ranges were interrogated to reveal putative proteins involved in virulence and pathogenicity. Results: Genomes of Venturia pirina (one European pear scab isolate) and Venturia inaequalis (three apple scab, and one loquat scab, isolates) were sequenced and the predicted secretomes of each isolate identified. RNA-Seq was conducted on the apple-specific V. inaequalis isolate Vi1 (in vitro and infected apple leaves) to highlight virulence and pathogenicity components of the secretome. Genes encoding over 600 small secreted proteins (candidate effectors) were identified, most of which are novel to Venturia, with expansion of putative effector families a feature of the genus. Numerous genes with similarity to Leptosphaeria maculans AvrLm6 and the Verticillium spp. Ave1 were identified. Candidates for avirulence effectors with cognate resistance genes involved in race-cultivar specificity were identified, as were putative proteins involved in host-species determination. Candidate effectors were found, on average, to be in regions of relatively low gene-density and in closer proximity to repeats (e.g. transposable elements), compared with core eukaryotic genes. Conclusions: Comparative secretomics has revealed candidate effectors from Venturia fungal plant pathogens that attack pome fruit. Effectors that are putative determinants of host range were identified; both those that may be involved in race-cultivar and host-species specificity. Since many of the effector candidates are in close proximity to repetitive sequences this may point to a possible mechanism for the effector gene family expansion observed and a route to diversification via transposition and repeat-induced point mutation. [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]

This study was conducted in an experimental ecological orchard in central Poland in 2011-2013. The experiment assessed the variation in damage to the fruit of ten apple cultivars by the codling moth Cydia pomonella (L.) under an organic system of apple cultivation. The cultivars were divided into two groups according to their susceptibility to apple scab Venturia inaequalis (Cooke) Wint. The first group of apple trees (A) consisted of cultivars resistant to scab (Enterprise, Gold Milenium, Rajka, Rewena, and Topaz), while the second group (B) consisted of cultivars with reduced susceptibility to scab (Delbard Jubile, Ligolina, Pinova, Piros, and Szampion). All of the trees of the evaluated cultivars were protected against the codling moth by applying treatments containing the codling moth granulosis virus (CpGV). Codling moth adults were monitored using pheromone traps during the study period. Each year, an assessment of fruit damage was made for all apple cultivars. The 3-year average percentage of damaged fruit for group A ranged from 1.0% (Gold Milenium) to 4.1% (Topaz), and in group B from 1.3% (Piros) to 3.3% (Pinova). Overall, the highest percentage of damaged fruit was recorded in 2013. [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]

Quantitative plant resistance affects the aggressiveness of pathogens and is usually considered more durable than qualitative resistance. However, the efficiency of a quantitative resistance based on an isolate-specific Quantitative Trait Locus (QTL) is expected to decrease over time due to the selection of isolates with a high level of aggressiveness on resistant plants. To test this hypothesis, we surveyed scab incidence over an eight-year period in an orchard planted with susceptible and quantitatively resistant apple genotypes. We sampled 79 Venturia inaequalis isolates from this orchard at three dates and we tested their level of aggressiveness under controlled conditions. Isolates sampled on resistant genotypes triggered higher lesion density and exhibited a higher sporulation rate on apple carrying the resistance allele of the QTL T1 compared to isolates sampled on susceptible genotypes. Due to this ability to select aggressive isolates, we expected the QTL T1 to be non-durable. However, our results showed that the quantitative resistance based on the QTL T1 remained efficient in orchard over an eight-year period, with only a slow decrease in efficiency and no detectable increase of the aggressiveness of fungal isolates over time. We conclude that knowledge on the specificity of a QTL is not sufficient to evaluate its durability. Deciphering molecular mechanisms associated with resistance QTLs, genetic determinants of aggressiveness and putative trade-offs within pathogen populations is needed to help in understanding the erosion processes. [ABSTRACT FROM AUTHOR]

The population genetic structure of 278 Venturia inaequalis isolates, collected from different apple cultivars of eighteen different provinces in Iran, was investigated using 22 polymorphic microsatellite markers. Analysis of molecular variation, Bayesian clustering and Nei's genetic distance analyses based on 88 microsatellite alleles indicated substantial levels of gene flow among the collection sites. Ninety three percent of the variation was observed among the individuals within the populations and only 7% variation was observed among the populations. Structure analysis grouped the isolates into two populations. Maximum number of pathogen genotypes (44) was observed in the North of Iran that grows various different apple cultivars. Investigation on the variation of the pathogen on different cultivars in the North of Iran suggested a significant differentiation of the pathogen populations between wild apple and commercial cultivars. During sampling, varying ranges of scab infection were observed on various apple cultivars in forests, monoculture and mix orchards. Wild type apple (Malus orientalis) along the Caspian Sea Coast had the most infection in comparison with the Iranian endemic and commercial cultivars. Based on the genetic analysis and host tracking scenario of the pathogen, it was presumed that Iran could potentially be the center of origin of V. inaequalis, which requires further detailed studies with isolates collected from different parts of central Asia and world for confirmation. [ABSTRACT FROM AUTHOR]

The ascomycete Venturia inaequalis causes annual epidemics of apple scab worldwide. Scab development is reduced in mixed cultivar orchards compared with monocultures. In order to use mixtures in commercial production, how the population of scab changes in a mixed orchard needs to be understood, together with how likely a super race, with virulence factors overcoming multiple resistance factors in the mixed orchard, is to emerge and become dominant. This study used simple sequence repeat ( SSR) markers to investigate the temporal change of scab populations in two mixed cultivar orchards in the UK to infer the likelihood of emergence of a scab super race. There were no significant differences between the populations at the two sampling times (6 or 7 years apart) in either of the two mixed orchards. In one of the orchards, apple scab populations on different cultivars were significantly different and the differences did not diminish over time. These results suggest that it is not inevitable that a super race of V. inaequalis will become dominant during the lifetime of a commercial apple orchard. [ABSTRACT FROM AUTHOR]

In vitro experiments indicated that boric acid, monopotassium phosphate, sodium metabisulfite and synthetic fungicide fluopyram + tebuconazole were effective in inhibiting conidia germination and germ-tube elongation of Venturia inaequalis. Monopotassium phosphate even at the highest concentration used in the study reduced conidia germination and germ-tube elongation of V. inaequalis by 22.1% and 28.8%, respectively; however, the difference between two compounds at lower concentrations except 0.05% (for conidia germination) and 0.1% (for germ-tube elongation) of boric acid was statistically significant (P ≤ 0.05). Complete inhibition was achieved by 0.01% sodium metabisulfite, 0.035% fluopyram + tebuconazole and 0.2% boric acid. Two orchard trials were conducted on the highly susceptible cv. Mutsu to apple scab to ascertain the efficacy of 0.2% boric acid, 0.5% monopotassium phosphate, 0.5% sodium metabisulfite and 0.035% fluopyram + tebuconazole for the control of apple scab. In both 2013 and 2014, except for the applications of monopotassium phosphate and sodium metabisulfite, the applications of boric acid and fluopyram + tebuconazole to trees at 10-day intervals significantly reduced disease incidence and severity on leaves and fruit compared to the water-treated control. In both years, the efficacy of boric acid and fluopyram + tebuconazole treatments was similar in reducing both disease incidence and severity on leaves and fruit in all monthly assessments from July to September. All treatments were neither phytotoxic to leaves and fruit nor did they adversely affect quality parameters of harvested fruit. These results show that boric acid treatment may be applied as an alternative chemical for the control of apple scab. [ABSTRACT FROM AUTHOR]

The succinate dehydrogenase inhibiting (SDHI) fungicides are a class of single-site fungicides that are increasingly important in the management of Venturia inaequalis. In this study, the baseline sensitivity of V. inaequalis to penthiopyrad, fluopyram, and benzovindiflupyr was investigated. In all, 35 to 70 isolates with no prior exposure to single-site fungicides were used to determine the effective concentration at which growth was inhibited by 50% (EC50). Mean EC50 values for the conidial germ tube growth stage for penthiopyrad, fluopyram, and benzovindiflupyr were 0.086, 0.176, and 0.0016 μg ml-1, respectively. Linear correlation analysis revealed a significant and positive correlation between fluopyram and penthiopyrad (P ⩽ 0.0001, r = 0.66) and fluopyram and benzovindiflupyr (P = 0.0014, r = 0.52). Baseline sensitivities of V. inaequalis during the mycelial growth stage were also determined for fluopyram and benzovindiflupyr. EC50 values were higher for fluopyram and benzovindiflupyr during this stage compared with the conidial germ tube growth stage, with means of 0.043 and 2.02 μg ml-1, respectively. In addition, the sdhB gene was characterized for three isolates of V. inaequalis collected from a research, baseline, and commercial orchard population. No common mutation sites associated with SDHI resistance in other phytopathogenic fungi were discovered in these isolates or isolates that were recovered following field applications of SDHI fungicides. The results of this study suggest that SDHI fungicides have a high level of activity during the conidial germ tube elongation stage in V. inaequalis and provide a basis for phenotypic and genotypic monitoring of shifts toward resistance of V. inaequalis populations to the SDHI fungicide class. [ABSTRACT FROM AUTHOR]

In pathogens, introgressions through secondary contacts between divergent populations from agricultural and nonagricultural disease reservoirs are expected to have crucial evolutionary and epidemiological implications. Despite the importance of this question for disease management, experimental demonstrations of these implications remain scarce., Recently, we identified a virulent population of the apple scab pathogen Venturia inaequalis that migrated from nonagricultural hosts to European domestic apple orchards. Here, we investigated the occurrence of gene flow between agricultural and nonagricultural populations sampled in two orchards, and thereafter its consequences on the pathogenicity of hybrids., Population genetic structure and demographic inferences based on the genotypes of 104 strains revealed a high amount of gene flow between the two populations in one orchard. In this site, mating between populations was made possible by the presence of a common host. Our results revealed an invasion of the virulent trait in the agricultural population; a main direction of introgression in hybrids from the agricultural to nonagricultural genetic backgrounds; and a population of hybrids with transgressive traits., We demonstrate a secondary contact with gene flow between divergent populations of pathogens. Our findings highlight evolutionary and epidemiological changes in pathogens and have concrete implications for sustainable disease management. [ABSTRACT FROM AUTHOR]