Apple Genotypes Research Articles

Insights into Stable Apple Genotypes for Fruit Yield in Himachal Pradesh: An Assessment Using Parametric and Non-parametric Stability Measures

Insights into Stable Apple Genotypes for Fruit Yield in Himachal Pradesh: An Assessment Using Parametric and Non-parametric Stability Measures

The Biological and Genetic Mechanisms of Fruit Drop in Apple Tree (Malus × domestica Borkh.)

The apple tree (Malus × domestica Borkh.) belongs to the Rosaceae. Due to its adaptability and tolerance to different soil and climatic conditions, it is cultivated worldwide for fresh consumption. The priorities of apple growers are high-quality fruits and stable yield for high production. About 90 to 95 percent of fruits should fall or be eliminated from apple trees to avoid overcropping and poor-quality fruits. Apple trees engage in a complex biological process known as yield self-regulation, which is influenced by several internal and external factors. Apple buds develop in different stages along the branches, and they can potentially give rise to new shoots, leaves, flowers, or fruit clusters. The apple genotype determines how many buds will develop into fruit-bearing structures and the capacity for yield self-regulation. Plant hormones such as ethylene, cytokinins, auxins, and gibberellins play a crucial role in regulating the fruit set, growth, and development, and the balance of these hormones influences the flowering intensity, fruit size, and fruit number on the apple tree. Apple growers often interfere in the self-regulation process by manually thinning fruit clusters. Different thinning methods, such as by hand, mechanical thinning, or applying chemical substances, are used for flower and fruit thinning. The most profitable in commercial orchards is the use of chemicals for elimination, but more environmentally sustainable solutions are required due to the European Green Deal. This review focuses on the biological factors and genetic mechanisms in apple yield self-regulation for a better understanding of the regulatory mechanism of fruitlet abscission for future breeding programs targeted at self-regulating yield apple varieties.

Whole-genome resequencing identifies candidate genes and allelic variation in the MdNADP-ME promoter that regulate fruit malate and fructose contents in apple

Soluble sugar and organic acids are key determinants of fruit organoleptic quality and directly affect the commodity value and economic returns of fruit crops. We performed whole-genome sequencing of the apple varieties Gala and Xiahongrou, along with their F1 hybrids, to construct a high-density bin map. Our quantitative genetic analysis pinpointed 53 quantitative trait loci (QTLs) related to 11 sugar and acid traits. We identified a candidate gene, MdNADP-ME, responsible for malate degradation, in a stable QTL on linkage group 15. Sequence analysis revealed an A/C SNP in the promoter region (MEp-799) that influences binding of the MdMYB2 transcription factor, thereby affecting MdNADP-ME expression. In our study of various apple genotypes, this SNP has been demonstrated to be linked to malate and fructose levels. We also developed a dCAPS marker associated with fruit fructose content. These results substantiate the role of MdNADP-ME in maintaining the equilibrium between sugar and acid contents in apple fruits.

Optimization of Rhizobium rhizogenes-mediated transformation, regeneration and characterization of Malus domesticaBorkh. Ri lines

This study explored the establishment and optimization of Ri (root inducing) technology for apple breeding, using the bacterium Rhizobium rhizogenes to obtain Ri lines with compact shoots and stronger root systems. The transformation and shoot regeneration for Malus domestica cultivars was studied in detail. Various R. rhizogenes strains, scion and rootstock genotypes, explant types, wounding methods and explant orientations were tested for hairy root induction. Most of the 16 tested strains, especially those with plasmid type III, induced hairy roots in the rootstock genotype ‘M26’. Although apple genotypes differed in response, in most of them roots were successfully induced using strains ATCC 15834, LMG 63 and LMG 150, with leaf blades outperforming petioles as explants. Wounding by scratching or sonication further improved transformation efficiency, as did placing leaf blades with their abaxial side upward on root induction medium. The majority (94%) of roots formed in one transformation experiment were tested PCR-positive for at least one T-DNA gene. Shoot regeneration experiments investigated salt concentrations, gelling agents, cytokinin types, concentrations, and a resting period on hormone-free medium. Shoot regeneration was highly genotype-dependent varying between 0 and 83%, whereas only minor, non-significant effects were observed for the treatments tested. Copy numbers of T-DNA genes were estimated using digital PCR for the first time in apple Ri lines. In the greenhouse, two Ri lines showed compact shoots and shorter leaves, but no enhanced root system. The improved protocol provides a valuable tool for breeders and scientists to obtain and further use Ri lines.

Eco-physiological behaviors of some apple genotypes (Malus x domestica Borkh.) in the hot-and-dry climate of an inner area of Southern Italy

The Italian internal areas are distant from the main trade flows and service centers, but have important environmental and cultural resources. The Italian “National Strategy for Inner Areas” represents a novel policy aimed at contrast the abandon of these territories by supporting multiple activities aimed at stimulating economic development and promoting territorial cohesion. The condition of marginality offers the chance to pursue economic development according to the principles of sustainability. These internal areas are often distinguished by a purely rural vocation. Genotypes of fruit crops traditionally grown in inland areas cope often with difficult climatic conditions and low-input farming techniques, showing generally a good tolerance to abiotic tresses. Exploring their eco-physiological behaviors in response to the agri-environmental context is useful for identifying crops capable of stimulating the recovery and expansion of a sustainable agriculture system in inland areas. The present work reports some results of a research conducted on three traditional local apple genotypes grown in an internal hot-arid summer area of Southern Italy, evaluating their water status and the intensity of leaf gas exchange compared to those of a well-known “standard” cultivar, in a hot, dry summer period. The local genotypes tested in this case study proved to be more eco-physiologically performing. The experiment allowed to estimate their probable relative eco-physiological advantages compared to the “standard” apple genotype taken as reference.

The genetic basis of apple shape and size unraveled by digital phenotyping.

Great diversity of shape, size, and skin color is observed among the fruits of different apple genotypes. These traits are critical for consumers and therefore interesting targets for breeding new apple varieties. However, they are difficult to phenotype and their genetic basis, especially for fruit shape and ground color, is largely unknown. We used the FruitPhenoBox to digitally phenotype 525 genotypes of the apple reference population (apple REFPOP) genotyped for 303,148 single nucleotide polymorphism (SNP) markers. From the apple images, 573 highly heritable features describing fruit shape and size as well as 17 highly heritable features for fruit skin color were extracted to explore genotype-phenotype relationships. Out of these features, seven principal components (PCs) and 16 features with the Pearson's correlation r < 0.75 (selected features) were chosen to carry out genome-wide association studies (GWAS) for fruit shape and size. Four PCs and eight selected features were used in GWAS for fruit skin color. In total, 69 SNPs scattered over all 17 apple chromosomes were significantly associated with round, conical, cylindrical, or symmetric fruit shapes and fruit size. Novel associations with major effect on round or conical fruit shapes and fruit size were identified on chromosomes 1 and 2. Additionally, 16 SNPs associated with PCs and selected features related to red overcolor as well as green and yellow ground color were found on eight chromosomes. The identified associations can be used to advance marker-assisted selection in apple fruit breeding to systematically select for desired fruit appearance.

Identification of aroma compounds responsible for apple flavor via palatability score prediction in tree-based regression models

Apple flavor has been linked to the composition of aroma compounds; however, the impact of varying concentrations of aroma compounds remains poorly understood. While sensory evaluation is commonly used to analyze food palatability, assessing the effect of concentration of all aroma compounds poses challenges. This study screened 174 apple genotypes for significant aroma compounds using regression models, Gas chromatography–mass spectroscopy analysis, and sensory palatability scores. Two models viz. Random Forest and XGBoost were employed to predict palatability scores, surpassing the limitations of correlation analysis. Shapley's additive explanatory value analysis identified 5-hexenol, ethyl 2-methyl butyrate, 2-methylbutyl acetate, (E,E)-α-farnesene, and (Z)-3-hexenol as key aroma compounds. In a sensory evaluation validating the effect of aroma compound concentration, the variation in (E,E)-α-farnesene concentration negatively affected sensory palatability scores. This study demonstrated a novel approach for identifying aroma compounds that impact apple flavor, providing valuable insights to enhance apple quality and palatability.

Growth performance of cleft grafted velvet apple (Diospyros discolor Willd.)

Velvet apple is usually propagated through seeds but seeded plants do not maintain its true-to-type quality. The present work was undertaken to study the fate of cleft grafting of five selected velvet apple genotypes during 2018 - 2019 at the Germplasm Center, Patuakhali Science and Technology University. The pot experiment was conducted in RCBD with two factors as scions and Days after Grafting (DAG) consisting of 10 replications of the scions. Scions from five promising mother plants were considered as treatments (Dumki-Dd-S1, Dumki-Dd-S2, Dumki-Dd-S3, Dumki-Dd-S4 and Mirzaganj-Dd-S5) and were cleft grafted on seedling rootstock of Dumki-Dd-R1. At 84 DAG, significant differences were observed among the scion treatments regarding the studied growth parameters. The days required to bud break varied significantly which ranged from 14 days (Dumki-Dd-S4) to 18 days (Mirzagonj-Dd-S5). The maximum length (54.30 cm) and diameter (2.00 cm) of rootstock were recorded in Mirzagonj-Dd-S5 at 84 DAG. However, maximum scion length (22.20 cm) and scion diameter (0.70 cm) were noted in Dumki-Dd-S1at 84DAG. The highest graft heights of Dumki-Dd-S2 (71.20 cm) and Mirzaganj-Dd-S5(71.50 cm) were statistically similar at84 DAG. Graft success was highest in Mirzagonj-Dd-S5(60.00%) followed by Dumki-Dd-S4 (40.00%) at 84 DAG. The maximum number of sprouted shoots (2.10) was counted in Dumki-Dd-S1, however, the highest length and diameter of sprouted shoot (7.1 cm and 0.66 cm, respectively) and maximum number of leaf (7.40 per graft) were found in Mirzaganj-Dd-S5during the study period. It could be concluded that, Mirzaganj-Dd-S5 and Dumki-Dd-R1showed the best stionic relationship for multiplication of velvet apple by cleft grafting. South Asian J. Agric., Vol. 9, No.1&amp;2, 2022-‘23: 1-10

Quantitative Trait Locus Mapping for Fire Blight Resistance in an F2 Population of Malus fusca MAL0045 Uncovers Novel Resistance Loci.

Several fire blight resistance loci in Malus genotypes map on different linkage groups (LGs) representing chromosomes of the domesticated apple. Prior genetics studies primarily focused on F1 populations. A strong resistance quantitative trait locus (QTL) explained up to 66% of phenotypic variance in an F1 progeny derived from crossing the highly resistant wild apple genotype Malus fusca MAL0045 and the highly susceptible apple cultivar 'Idared', which was previously mapped on LG10 (Mfu10) of MAL0045. Strains of the causative bacterial pathogen Erwinia amylovora, notably those that show a single nucleotide polymorphism in the avrRpt2EA effector protein sequence at position 156 (e.g., Ea3049), are more virulent and overcome some known fire blight resistance donors and their QTLs. However, MAL0045 is resistant to Ea3049 and Mfu10 is not overcome, but most of the F1 progeny were highly susceptible to this strain. This phenomenon led to the assumption that other putative resistance factors not segregating in the F1 progeny might be present in the genome of MAL0045. Here, we crossed F1 progeny together to obtain 135 F2 individuals. Facilitated by genotyping-by-sequencing and phenotypic assessments, we identified and mapped two novel resistance QTLs in these F2 individuals on LGs 4 and 15, which were not identified in the F1. To our knowledge, these are the first resistance QTLs mapped in F2 progeny in Malus. In addition, we report that neither MAL0045 nor Mfu10 is broken down by a highly aggressive U.S. strain, LA635, after analyses in the original F1 individuals. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Sequence Analysis of nrDNA ITS Region in Paşa and Şah Apple (Malus × domestica) Genotypes

In this study, phylogenetic analysis of Şah and Paşa apple genotypes was performed using nrDNA ITS sequences. After the plant leaves were brought to the laboratory, gDNAs were obtained by genomic DNA isolation method. PCR amplification was performed using primers ITS4 and ITS5A. ITS sequences of some apple and Rosaceae species were retrieved from NCBI, bioinformatics analyzes were made with Bioedit 7.2.3, Finch TV 1.4.0 and MEGA 6.0 programs and phylogenetic trees were constructed. In the study, ITS sequence length of the Paşa apple genotype was 656 bp, and the ITS sequence length of the Şah apple genotype was 649 bp. Only in the maximum likelihood phylogenetic tree constructed using sequences of apple genotypes, Paşa and Şah apple genotypes appeared in the same clade as Malus domestica cultivar="Casciana'' and Malus domestica cultivar="Rotella''. In the phylogenetic tree generated including other species belonging to the Rosaceae family; apple genotypes Pyrus, Cotoneaster, Crataegus, Sorbus, Eriobotrya and Prunus were detected in a same clade. Overall results clearly suggested that the ITS sequences were both suitable for differentiation between the selected genera and were compatible with previous phylogenetic studies.

Exploring Wild and Local Fruits as Sources of Promising Biocontrol Agents against Alternaria spp. in Apples

Biological control agents (BCAs) are a promising option for managing postharvest diseases. Their environmentally friendly nature makes them valuable for sustainable and eco-friendly postharvest disease management. This study evaluated the antagonistic potential of epiphytic yeasts isolated from a local apple genotype known as “Niğde Elması” and a range of wild fruits: rosehip, hawthorn, and wild pear. There were 375 yeast isolates obtained and screened in vitro and in vivo. Initially selected were 32 isolates able to inhibit the growth of Alternaria alternata mycelia in the in vitro experiments and identified using molecular methods as candidate BCAs. These isolates were identified as Aureobasidium pullulans using sequence analysis of the internal transcribed spacer (ITS) and the translation elongation factor EF-1α gene (EF1α). Based on two rounds of in vivo screening, four isolates were subsequently selected for their capability to control the infection of apple fruits under high inoculum pressure. Finally, their volatile and non-volatile antimicrobial activity was tested against Alternaria spp. These findings showed how wild fruits and a local apple genotype could represent a promising source for new BCA isolation. However, further studies are needed to reveal the mechanisms of action of these putative BCAs for application during the postharvest processing and storage of apples.

Diversity, Genetic Structure and Relationship with Chilling Requirements of Local Varieties of Apple (Malus spp.) in the Centre for the Conservation of Agricultural Biodiversity of Tenerife (Canary Islands, Spain)

Sixty-seven apple tree accessions from the Centre for the Conservation of Agricultural Biodiversity of Tenerife (CCBAT) were molecularly characterised for the first time with 13 simple sequence repeats (SSRs). Additionally, previously studied genotypes from the Canary Islands (Tenerife, La Palma and Gran Canaria), Galicia, Asturias and commercial reference varieties were studied to identify possible synonymies and genetic structures, in order to improve the conservation of this genus in the germplasm bank. Thirty-three different genotypes were found in the new accessions analysed (51% clonality): sixteen of them (48%) exclusive to Tenerife, with no genetic coincidence with previous studies, making a total of thirty-three genotypes unique to Tenerife and sixty-five in the whole of the Canary Islands. The analysis of the population structure grouped the apple genotypes into two reconstructed panmictic populations (RPPs), one formed by local varieties or traditional ones (‘Peros’), RPP1, from all the regions studied, and the other formed by local and commercial varieties, RPP2. The RPP1 genotypes identified in Tenerife seem to show better adaptation to low chill, with a positive and significant correlation (0.388, p &lt; 0.01), highlighting the importance of local varieties and the need for their conservation. This is the first study reporting significant correlation between genetic structure and chilling requirements.

Using High-Density SNP Array to Investigate Genetic Relationships and Structure of Apple Germplasm in Bosnia and Herzegovina

Apple accessions, currently maintained within the two main ex situ collections in Bosnia and Herzegovina (B&amp;H), have previously been genotyped using microsatellite markers. The obtained molecular data provided insight into mislabeled accessions and redundancies, as well as the overall genetic structure of the germplasm. The available dataset enabled the creation of a core collection consisting of 52 accessions. The reliability and usefulness of microsatellites has made this low-density marker system a norm in studies on apple germplasm. However, the increased access to medium- and high-density SNP arrays, developed specifically for apples, has opened new avenues of research into apple genetic resources. In this study, 45 apple genotypes consisting of 33 diploid core collection accessions from B&amp;H and 12 international reference cultivars were genotyped using an Axiom® Apple 480 K SNP array in order to examine their genetic relationships, population structure and diversity, as well as to compare the obtained results with those calculated on previously reported SSR profiles. The SNPs displayed a better ability to differentiate apple accessions based on their origin, as well as to cluster them according to their pedigree. Calculating identity by descent revealed 16 pairings with first-degree relationships and uncovered the introgression of ‘Delicious’ and ‘Golden Delicious’ into the core collection.

Combinatorial approach based on conventional and molecular methods for identification of scab resistance genes in apple germplasm of Jammu and Kashmir, India

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.

Evaluating the Classification of Freeze-Dried Slices and Cubes of Red-Fleshed Apple Genotypes Using Image Textures, Color Parameters, and Machine Learning

Dried red-fleshed apples are considered a promising high-quality product from the functional foods category. The objective of this study was to compare the flesh features of freeze-dried red-fleshed apples belonging to the ‘Alex Red’, ‘Trinity’, ‘314’, and ‘602’ genotypes and indicate which parameters and shapes of dried samples are the most useful to distinguish apple genotypes. Apple samples were at the stage of harvest maturity. The average fruit weight, starch index, internal ethylene concentration, flesh firmness, total soluble sugar content, and titratable acidity were determined. One hundred apple slices with a thickness of 4 mm and one hundred cubes with dimensions of 1.5 cm × 1.5 cm × 1.5 cm of each genotype were subjected to freeze-drying. For each apple sample (slice or cube), 2172 image texture parameters were extracted from images in 12 color channels, and color parameters L*, a*, and b* were determined. The classification models were developed based on a set of selected image textures and a set of combined selected image textures and color parameters of freeze-dried apple slices and cubes using various traditional machine-learning algorithms. Models built based on selected textures of slice images in 11 selected color channels correctly classified freeze-dried red-fleshed apple genotypes with an overall accuracy reaching 90.25% and mean absolute error of 0.0545; by adding selected color parameters (L*, b*) to models, an increase in the overall accuracy to 91.25% and a decrease in the mean absolute error to 0.0486 were observed. The classification of apple cube images using models including selected texture parameters from images in 11 selected color channels was characterized by an overall accuracy of up to 74.74%; adding color parameters (L*, a*, b*) to models resulted in an increase in the overall accuracy to 80.50%. The greatest mixing of cases was observed between ‘Alex Red’ and ‘Trinity’ as well as ‘314’ and ‘602’ apple slices and cubes. The developed models can be used in practice to distinguish freeze-dried red-fleshed apples in a non-destructive and objective manner. It can avoid mixing samples belonging to different genotypes with different chemical properties. Further studies can focus on using deep learning in addition to traditional machine learning to build models to distinguish dried red-fleshed apple samples. Moreover, other drying techniques can be applied, and image texture parameters and color features can be used to predict the changes in flesh structure and estimate the chemical properties of dried samples.

Allelic variation of MdMYB123 controls malic acid content by regulating MdMa1 and MdMa11 expression in apple.

Acidity is a key determinant of fruit organoleptic quality. Here, a candidate gene for fruit acidity, designated MdMYB123, was identified from a comparative transcriptome study of two Ma1Ma1 apple (Malus domestica) varieties, "Qinguan (QG)" and "Honeycrisp (HC)" with different malic acid content. Sequence analysis identified an A→T SNP, which was located in the last exon, resulting in a truncating mutation, designated mdmyb123. This SNP was significantly associated with fruit malic acid content, accounting for 9.5% of the observed phenotypic variation in apple germplasm. Differential MdMYB123- and mdmyb123-mediated regulation of malic acid accumulation was observed in transgenic apple calli, fruits, and plantlets. Two genes, MdMa1 and MdMa11, were up- and down-regulated in transgenic apple plantlets overexpressing MdMYB123 and mdmyb123, respectively. MdMYB123 could directly bind to the promoter of MdMa1 and MdMa11, and induce their expression. In contrast, mdmyb123 could directly bind to the promoters of MdMa1 and MdMa11, but with no transcriptional activation of both genes. In addition, gene expression analysis in 20 different apple genotypes based on SNP locus from "QG" × "HC" hybrid population confirmed a correlation between A/T SNP with expression levels of MdMa1 and MdMa11. Our finding provides valuable functional validation of MdMYB123 and its role in the transcriptional regulation of both MdMa1 and MdMa11, and apple fruit malic acid accumulation.

Identification of Self Incompatibility (S) Alleles in Turkish Apple Gene Sources using Allele-specific PCR

Self-incompatibility (SI) is a genetic mechanism in many flowering plants by which generative reproduction is prevented. The self-incompatibility caused by the genetic functions of the cell is controlled by genes called S genes or self-incompatibility genes. Self-incompatibility results in decreased pollination and ultimately yield loss. In apple (Malus domestica L.), self-incompatibility is controlled by multi-allelic S-locus. Approaches in the S-glycoprotein profiles and allele-specific PCR methods using the gene profiles and S-glycoprotein profiles for determination of the incompatibility levels are of great importance. In current study, the self-incompatibility status of 192 apple genotypes (such as, Amasya, Hüryemez, Şah elması, Tokat, Demir elması etc.) obtained from the National Collection of Atatürk Horticultural Central Research Institute, Yalova, Turkey, has been determined. For this purpose, genotype-specific allele status and compatibility levels were screened via PCR (Polymerase Chain Reaction) using 4 different S-alleles (Sd, Sf, S26 and S9). 181 genotypes containing at least 1 S-allele were identified as ‘Partially Incompatible’ and 12 genotypes involving 4 S-alleles were assigned ‘Totally Incompatible’. No S-alleles were observed in 2 genotypes (Pancarlık and Hüryemez) which exhibited ‘Compatibility’ status.

Progress in apple breeding for resistance to fire blight

The paper presents the most important issues concerning the breeding of apple trees resistant to fire blight, which creates great op­portunities to increase the efficiency of apple fruit production without the use of other protection methods, including the chemical treatment. The phenotypic assessment of susceptibility of apple genotypes to the disease is based on observations on the occurrence of symptoms in field and/or closed facilities, e.g. in the greenhouse. Molecular biology methods, including identification of resistance mark­ers, and biotechnology are valuable tools to accelerate the breeding process. Breeding programs conducted in various research centers around the world use wild species of the genus Malus and commercial cultivars of apple. Apple rootstocks with very high resistance to fire blight (USA) and a number of scab-resistant cultivars, also showing high resistance to the disease (Germany, Switzerland) have already been bred. In recent years cultivar Early Szampion and clone No. 69 (J-2003-05) have been bred in Poland. Both genotypes are characterized by a very high resistance, and produce attractive tasty fruit. They have the prospect of being used in breeding programs and commercial plantings.

Assessment of different custard apple genotypes for yield and quality parameters

Assessment of different custard apple genotypes for yield and quality parameters

Screening of Venturia inaequalis virulence and resistance of Malus genotypes to apple scab using in vitro methodology

Abstract 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.