Scab-resistant Apple Cultivars Research Articles

Comparative study of five scab resistant apple cultivars

Vegetative and reproductive characteristics of five resistant apple cultivars budded on ‘М9-Т337’ rootstock were compared in the intensive orchard, planted at the density of 2380 trees per hectare (3.5 × 1.2 m) in the period 2017-2023. Trees were formed as tall spindle, under an insecticidal net against hail. Trees were grown under drip irrigation and sod-mulch system was applied. The cultivars FUJIONpbr and ENTERPRISE demonstrate greater trunk-cross section area, higher trees and greater crown volume to the tested cultivars. The smallest trees were noted in Cultivar GEMINI*. The lowest yield per unit area was obtained on cultivar FUJIONpbr. There was no significant difference among other cultivars. Despite of generally good characteristics the cultivar GEMINI* has relatively small fruits. Keywords: apple, vigor, productivity, fruit weight, yield

Effect of postharvest treatments on physiological disorders of ‘Galant’: a new scab resistant apple cultivar

Effect of postharvest treatments on physiological disorders of ‘Galant’: a new scab resistant apple cultivar

Marker-assisted selection in the development of advanced apple-tree forms and donors combining scab resistance with increased fruit storability

Background. Cultivation of scab-resistant apple cultivars with better fruit storability increases the economic efficiency and environmental friendliness of horticulture. Hence, the development of such cultivars is an important task in modern apple-tree breeding.Materials and methods. A set of 646 hybrid plants obtained in six cross combinations (Renet Simirenko/Modi, Renet Simirenko/Smeralda, Renet Simirenko/Renoir, Renet Simirenko/Fujion, Renoir/Granny Smith, and Modi/Granny Smith) was studied. Their scab resistance was assessed under natural infection pressure for two years using a quantitative scale. The Rvi6 gene was identified using the PCR analysis with the primer pair VfC1+VfC. The Md-ACS1 gene alleles were detected with a known SCAR DNA marker. The chi-square test was applied for statistical confirmation of the data.Results. Based on the DNA marker analysis, 328 plants carrying the dominant allele of the Rvi6 gene were identified. The results of the phenotypic resistance assessment confirmed the correspondence of the resistant phenotype / dominant allele of the gene for most plants. Molecular genetics analysis of the Md-ACS1 gene disclosed its allelic combinations. A total of 190, 322, and 126 plants carrying allelic variants of Md-ACS1-2/2, Md-ACS1-1/2, and Md-ACS1-1/1, respectively, were identified. Among the plants with the dominant allele of the scab resistance Rvi6 gene, 92 plant forms were identified with Md-ACS1-2/2, and 143 heterozygous ones (Md-ACS1-1/2), also valuable for breeders.Conclusion. A wide range of apple breeding forms carrying valuable alleles of the Rvi6 and Md-ACS1 genes were selected. Hybrid forms with target alleles of both genes responsible for important agronomic traits would contribute to the intensification of breeding efforts aimed at producing scab-resistant apple cultivars with increased fruit storability. They can also be used for breeding purposes as complex donors.

An apparent breakdown of Vf resistance occurring in an apple orchard in Bistrita area


 Scab resistance through the Rvi6 gene was largely used in Romanian breeding programs including those from Fruit Research & Development Station (FRDS) Bistrita. The aim of the study was to verify the efficacy of the resistance due to the Vf gene under the current conditions in the Bistrita area. Three scab resistant apple cultivars bred at FRDS Bistrita were monitored in the field, in comparison with the Rvi6 ‘Florina’ and ‘Prima’ cvs., and the sensitive ‘Idared’ and ‘Golden Delicious’ cvs. Molecular markers (AM-19, U1₄₀₀ and AL07) were used in PCR to check the presence of the Rvi6 gene in the genome of the three Romanian varieties. During the years 2019-2021, scab lesions appeared on all the resistant cultivars studied. PCR results showed the presence of Rvi6 gene on ‘Bistritean’, ‘Salva’, ‘Aura’, ‘Prima’ and ‘Florina’ genoms. The results suggest a possible breakdown of the resistance given by the Rvi6 gene in the current ecological conditions in this area. Scab symptoms occurring on cultivars that have the Rvi6 gene could lead to the hypothesis that different scab races are now present in our area or that some genetic variations occurred on the existing races so that they overcome Rvi6 gene.

Comparison and Intercorrelation of Extraction Methods for Polyphenol Content and Antioxidant Capacity of Scab-Resistant Apple Cultivars

Polyphenols with antioxidant compounds represent an important group of bioactive substances in apple production. The objectives of this study were firstly to measure four parameters of antioxidant capacity (AC) and polyphenol content (AC-FRAP (Ferric Reducing Ability of Plasma), AC-DPPH (2,2-diphenyl-1-picrylhydrol), AC-TEAC (Trolox Equivalent Antioxidant Capacity) and total polyphenol content (TPC)) of four scab-resistant apple cultivars (‘Fujion’, ‘Gaia’, ‘Isaaq’ and ‘Smeralda’) using six extraction methods (water control, pectinase, two approaches using ethanol (EtOH-1 and EtOH-2), methanol (MetOH) and methanol + acetone (MetOH + Acetone), and secondly to provide intercorrelations between antioxidant and polyphenol contents of the four resistant apple cultivars under the six extraction methods. Analysis of variance on the four parameters showed a significant (p = 0.05) effect for extraction methods and cultivars. TPC showed the highest values among the four parameters in all extraction methods and cultivars compared to the other three measurements. The pectinase extraction method showed the highest TPC values for the four cultivars. The EtOH-2 extraction method showed the lowest AC-FRAP value for all cultivars. The EtOH-2 extraction method showed the highest AC-DPPH values, whereas the control method showed the lowest values for the four cultivars. The AC-TEAC values were generally the lowest, ranging between 10.8 and 40.5 mg TE 100 g−1 dry matter, and they showed various effects on extraction methods and cultivars. Correlation and regression analyses of 36 pair-variables showed that two pair-variables (TPC vs. AC-FRAP and AC-TEAC vs. AC-DPPH) were significant for all of the six extraction methods and for all cultivars. In conclusion, the extraction method using pectinase enzyme provided the most stable yield of polyphenol content from apple flesh, as confirmed by the examination of four scab-resistant apple cultivars.

FRUIT PHYSICO-CHEMICAL QUALITY PARAMETERS OF NEW INTRODUCED APPLE CULTIVARS

The apple fruit is the second most frequently consumed, after bananas and some quality characteristics like size, gloss, color, and aroma influenced directly the flesh consumption. In this study, the external (weight, size, skin colour) and internal (firmness, total soluble solids, acidity, pH) fruit quality attributes were measured experimentally before the storage, using well defined techniques. 'Corelita', 'Coreal', 'Corealor', 'Coredova', 'Corejuno', 'Coretard', 'Coreagat', 'Coreor' and 'Coreprim' cultivars were registered, in the last 15 years, by Practical Scientific Institute of Horticulture and Food Technologies Chișinău, Republic of Moldova, as scab resistant varieties. The orchard trial was established at the Research Institute for Fruit Growing Pitesti, Romania in the spring 2014 on MM106 rootstock, at the spacing of 3.5 x 2 m and fruit samples were analyzed in 2019, 2020 and 2021 seasons. All studied cultivars were harvested before 'Florina' cv., used as control. Fruit weight was quite variable among genotypes, between 115.15 g at 'Coreal' cv. and 212.41 g at 'Corejuno', and most of the cultivars had smaller fruits than 'Florina' cv. Firmness and total soluble solids varied from 70.5 to 82.61 N and 12.77 to 16.77%Brix. The Hunter color values L, a, b, were found to be in the range of 46.12 to 56.76, - 6.46 to 14, 13.75 to 23.72, respectively. The data about the external and internal fruit quality of new Moldavian scab resistant apple cultivars are useful for growers, in order to introduce in the new orchards only cultivars with high quality fruits.

How Do Consumers Perceive Sensory Attributes of Apple?

Pomological characteristics and consumer acceptability of four scab-resistant apple cultivars (‘Topaz’, ‘Florina’, ‘Goldstar’ and ‘Golden Orange’) and standard commercial cultivar ‘Golden Delicious’ were investigated. Consumer acceptability consisted of rating fruit samples on Likert scales measuring appearance, flavour, size, sweetness, acidity, crispiness, juiciness, skin texture and general impression. Consumers better evaluated the cultivar ‘Topaz’ sensory characteristics of flavour, juiciness, taste and general impression than other evaluated scab-resistant apple cultivars and the cultivar ‘Golden Delicious’. ‘Golden Delicious’ got good grades for appearance, size and sweetness. ‘Topaz’ also had the best pomological characteristic related to measured fruit firmness, contents of soluble solids and organic acids. It can be concluded that only the cultivar ‘Topaz’ among the scab-resistant apple cultivars achieved a good consumer assessment.

Colletotrichum fioriniae and Colletotrichum godetiae Causing Postharvest Bitter Rot of Apple in South Tyrol (Northern Italy).

South Tyrol (northern Italy) harbors one of the largest interconnected apple farming areas in Europe, contributing approximately 10% to the apple production of the European Union. Despite the availability of sophisticated storage facilities, postharvest diseases occur, one of which is bitter rot of apple. In Europe, this postharvest disease is mainly caused by the Colletotrichum acutatum species complex. This study aimed to characterize the Colletotrichum spp. isolated from decayed apple fruit collected in 2018 and 2019 in South Tyrol. The characterization of Colletotrichum spp. was accomplished based on multilocus DNA sequences of four different genomic regions-actin (ACT), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), histone H3 (HIS3), and the internal transcribed spacer (ITS) region-as well as morphological and pathogenicity assessment. A phylogenetic analysis based on multilocus DNA sequences showed that the isolates obtained from apples with symptoms of bitter rot belonged to the species Colletotrichum godetiae and Colletotrichum fioriniae, which are part of the Colletotrichum acutatum species complex. A third species isolated from apples belonging to the same species complex, Colletotrichum salicis, was described in this area. Moreover, the Colletotrichum isolates found in this study proved to be virulent on Cripps Pink, Golden Delicious, and Roho 3615/Evelina. To the best of our knowledge, C. godetiae and C. fioriniae have so far never been mentioned as postharvest pathogens of apple in Italy, although the reanalysis of samples collected in the past indicates that these pathogens have been occurring in Italy for at least a decade. So far, bitter rot seems to play a minor role as a postharvest disease in South Tyrol, but it was disproportionately represented on a few scab-resistant apple cultivars, which are increasingly planted in organically managed orchards. Considering that the expansion of organic apple production and the conversion to new potentially Colletotrichum-susceptible cultivars will continue, the present study represents an important contribution toward a better understanding of bitter rot in this geographic area.[Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.

Volatile profiles of 47 monovarietal cloudy apple juices from commercial, old, red-fleshed and scab-resistant apple cultivars

This study provides cultivar-specific metabolic fingerprints of volatile organic compounds in the headspace of cloudy apple juices. Cloudy juices from 47 “true to type” apple cultivars grown under identical agricultural and climatic conditions in South Tyrol, Italy, have been analysed through headspace solid-phase microextraction gas chromatography coupled with high-resolution time-of-flight mass spectrometry (HS–SPME/GC–HRTOF–MS), yielding cultivar-specific volatile organic compound (VOC) profiles. Apple cultivars included 10 old cultivars with local relevance, 18 commercial cultivars, dominating the current international market, 10 scab-resistant and 9 red-fleshed ones. The 28 most abundant VOCs were found in the whole dataset, indicating a remarkable chemodiversity within juices. The main discriminant metabolites were butyl acetate; pentyl acetate; 2-methylbutyl acetate; pentan-1-ol; hexan-1-ol; n-hexanal and (E)-2-hexenal. A principal component analysis (PCA) and a hierarchical cluster analysis (HCA) have not identified a clear separation of the analysed cultivar classes. Nevertheless, a series of scab-resistant and red-fleshed cultivars with VOC profiles similar to established commercial cultivars were identified; these data could help substituting current cultivars with more sustainable ones. On a more general basis, our study supports a knowledge-driven selection of apple cultivars for specific consumer preferences and helps appreciating the biodiversity of apples across old local and more recent (scab-resistant and red-fleshed) cultivars.

Scab Resistant Apple Cultivars for Juice Production

Abstract The purpose of this experiment was a selection of scab resistant apple cultivars suitable for juice production. Special attention was paid to cloudy juices. During three successive seasons, apple cultivars were processed into juices using laboratory method of juice extraction. Considering the possibility of both clear and cloudy juice production, apples were pressed with and without mash enzymation. The parameters investigated were: pressing yield, titratable acidity, soluble solids, juice density, and juices’ sensory characteristics. Average values indicate that all the cultivars fulfilled the requirements of the Code of Practice of the European Fruit Juice Association concerning investigated chemical components, however, in single years, there were some deviations that should be taken into consideration offering single cultivar juices. Considering a low yield of juice without mash enzymation (below 70%), cultivars ‘Renora’ and ‘Retina’ are not recommended for cloudy juice production. Sensory quality of juices, irrespectively if cloudy or clear, depended mostly on taste acceptability and in fact on soluble solids to acidity ratio. Juices with the ratio above 17 were usually scored higher concerning the taste than those with lower values. An example of exception was ‘Free Redstar’ which is highly astringent. Considering the efficiency of pressing and soluble solids content several investigated cultivars were highly suitable for concentrated apple juice production. Especially valuable may be considered ‘Regine’, ‘Rebella’, ‘Sawa’, and ‘Topaz’ and can be recommended for planting in industrial orchards, which became of special interest in recent years.

Tissue age, orchard location and disease management influence the composition of fungal and bacterial communities present on the bark of apple trees.

Plants host microbial communities that can be affected by environmental conditions and agronomic practices. Despite the role of bark as a reservoir of plant pathogens and beneficial microorganisms, no information is available on the effects of disease management on the taxonomic composition of the bark-associated communities of apple trees. We assessed the impact of disease management strategies on fungal and bacterial communities on the bark of a scab-resistant apple cultivar in two orchard locations and for two consecutive seasons. The amplicon sequencing revealed that bark age and orchard location strongly affected fungal and bacterial diversity. Microbiota dissimilarity between orchards evolved during the growing season and showed specific temporal series for fungal and bacterial populations in old and young bark. Disease management did not induce global changes in the microbial populations across locations and seasons, but specifically affected the abundance of some taxa according to bark age, orchard location and sampling time. Therefore, the disease management applied to scab-resistant cultivars, which is based on a limited use of fungicides, partially changed the taxonomic composition of bark-associated fungal and bacterial communities, suggesting the need for a more accurate risk assessment regarding possible pathogen outbreaks.

Bio-chemical properties and susceptibility to fire blight (Erwinia amylovora Burrill) of scab-resistant apple cultivars (Malus domestica Borkh.)

Abstract The focus of our research was to evaluate different apples cultivars in terms of their biological properties and bioactive compounds content, and determine the levels of their resistance (or susceptibility) to fire blight. The properties of 10 scab-resistant apple cultivars were examined on the Žiča monastery estate (West Serbia) during the period from 2011 to 2015. The biological and chemical properties such as firmness, maturity stage, total soluble solids, total acids, total and reducing sugars, ascorbic acid content and surface blush of apple fruits were monitored. Various phenolic compounds in the tested samples were tentatively identified by LC-MS analyses. A study of generative properties included: number of flower buds, fruit mass and width, crop load, yield efficiency and yield. During the period of blooming and intensive shoot growth, artificial inoculations were carried out. For each cultivar, a fire blight score was determined by dividing the average length of necrotic tissue by the average total shoot length. In the study period, the cultivars ‘GoldRush’ (41.1 t ha−1) and ‘Florina’ (35.9 t ha−1) produced the highest yields, and the cultivars ‘Discovery’ (19.0 t ha−1) and Selection 25/63 (15.1 t ha−1) the lowest. The cultivar ‘William’s Pride’ produced the largest fruits, with an average fruit mass of 206.8 g. The earliest harvest period was recorded for the cultivar ‘Discovery’ (end of July), and the latest for the cultivar ‘GoldRush’ (beginning of October). The cultivar ‘Enterprise’ had the highest value of total phenols (432.2 mg 100 g −1 FW), while the cultivar ‘Topaz’ had the highest value of total flavanols (145.2 mg 100 g−1 FW). The highest degree of susceptibility to fire blight was found in Selection 25/63, and the greatest resistance was manifested by the cultivar ‘GoldRush’. In the five-year study period, the cultivars ‘GoldRush’, ‘Rewena’ and ‘Enterprise’ exhibited better bio-chemical properties and higher levels of resistance to fire blight than the remaining cultivars.

Molecular cloning and functional analysis of a biphenyl phytoalexin-specific O-methyltransferase from apple cell suspension cultures

This manuscript describes the cloning and functional characterization of a biphenyl phytoalexin biosynthetic gene, 3,5-dihydroxybiphenyl O-methyltransferase from elicitor-treated cell cultures of scab resistant apple cultivar 'Florina'. Apples belong to the subtribe Malinae of the Rosaceae family. Biphenyls and dibenzofurans are the specialized phytoalexins of Malinae, of which aucuparin is the most widely distributed biphenyl. The precursor of aucuparin, 3,5-dihydroxybiphenyl, is a benzoate-derived polyketide, which is formed by the sequential condensation of three molecules of malonyl-CoA and one molecule of benzoyl-CoA in a reaction catalyzed by biphenyl synthase (BIS). This 3,5-dihydroxybiphenyl then undergoes sequential 5-O-methylation, 4-hydroxylation, and finally 3-O-methylation to form aucuparin. A cDNA encoding O-methyltransferase (OMT) was isolated and functionally characterized from the cell cultures of scab-resistant apple cultivar 'Florina' (Malus domestica cultivar 'Florina'; MdOMT) after treatment with elicitor prepared from the apple scab causing fungus Venturia inaequalis. MdOMT catalyzed the regiospecific O-methylation of 3,5-dihydroxybiphenyl at the 5-position to form 3-hydroxy-5-methoxybiphenyl. The enzyme showed absolute substrate preference for 3,5-dihydroxybiphenyl. The elicitor-treated apple cell cultures showed transient increases in the MdOMT (GenBank ID MF740747) and MdBIS3 (GenBank ID JQ390523) transcript levels followed by the accumulation of biphenyls (aucuparin and noraucuparin) and dibenzofuran (eriobofuran) phytoalexins. MdOMT fused with N- and C-terminal yellow fluorescent protein showed cytoplasmic localization in the epidermis of Nicotiana benthamiana leaves. In scab inoculated greenhouse-grown 'Florina' plants, the expression of MdOMT was transiently induced in the stem followed by the accumulation of biphenyl phytoalexins.

Generation of advanced fire blight-resistant apple (Malus\u2009\xd7\u2009domestica) selections of the fifth generation within 7\xa0years of applying the early flowering approach

Main conclusionThe approach presented here can be applied to reduce the time needed to introduce traits from wild apples into null segregant advanced selections by one-fourth.Interesting traits like resistances to pathogens are often found within the wild apple gene pool. However, the long juvenile phase of apple seedlings hampers the rapid introduction of these traits into new cultivars. The rapid crop cycle breeding approach used in this paper is based on the overexpression of the birch (Betula pendula) MADS4 transcription factor in apple. Using the early flowering line T1190 and ‘Evereste’ as source of the fire blight resistance (Fb_E locus), we successfully established 18 advanced selections of the fifth generation in the greenhouse within 7 years. Fifteen individuals showed the habitus expected of a regular apple seedling, while three showed very short internodes. The null segregants possessing a regular habitus maintained the high level of fire blight resistance typical for ‘Evereste’. Using SSR markers, we estimated the percentage of genetic drag from ‘Evereste’ still associated with Fb_E on linkage group 12 (LG12). Eight out of the 18 selections had only 4% of ‘Evereste’ genome left. Since genotypes carrying the apple scab resistance gene Rvi6 and the fire blight resistance QTL Fb_F7 were used as parents in the course of the experiments, these resistances were also identified in some of the null segregants. One seedling is particularly interesting as, beside Fb_E, it also carries Fb_F7 heterozygously and Rvi6 homozygously. If null segregants obtained using this method will be considered as not genetically modified in Europe, as is already the case in the USA, this genotype could be a very promising parent for breeding new fire blight and scab-resistant apple cultivars in European apple breeding programs.

Artificial spur extinction to regulate crop load and fruit quality of ‘Kalei’ apple

'Kalei' is a new scab-resistant apple cultivar released by the Department of Agriculture, Fisheries and Forestry, Queensland. It is a large apple (average weight 200 g) and trees are highly productive. Crop load management is important as overthinning and/or under-thinning can reduce yield and fruit quality. Artificial Spur Extinction (ASE) is a crop load management tool to regulate floral bud type and density just prior to the onset of spring budbreak. The impact of ASE on the productivity and quality of 'Kalei' was studied across three seasons at Applethorpe, Queensland, with trees on MM.106 and M.26 rootstocks trained as a Vertical Axis (2500 trees ha-1). ASE was compared with conventional (Conv) crop load management (no bud removal, and hand thinning seven to eight weeks after full bloom). In the ASE treatments, axillary buds borne on one-year old shoots were removed, whilst spur buds, and terminal buds of one-year old shoots (≥2.5 cm) were set to a predetermined bud density. ASE increased the proportion of terminal buds borne on shoots, compared with Conv management. ASE consistently improved fruit set, with fewer flower buds failing to set fruit and a higher proportion of flower buds setting 2 or 3 fruit. In 2012 and 2013, the mean fruit weight of 'Kalei' apples was greater with ASE than Conv management. By removing competing sinks early in the season using ASE, remaining fruitlets are given the space and resources to attain fruit size potential. No increase in yield was observed with ASE in both seasons. ASE increased 'Kalei' red blush coverage in 2013, but had no impact on flesh firmness, total soluble solids or dry matter content in 2012 or 2013.

AN INVESTIGATION OF CHILLING REQUIREMENT OF SOME SCAB RESISTANT APPLE CULTIVARS IN PO VALLEY

In order to improve the quality of fresh produce, in terms of food security, reduction of pesticide usage, preserving the environment and health of farmers, many scab resistant apple cultivars were released from several institutions, mainly located in temperate zones during the last years. The cultivation of temperate fruit trees in tropical and subtropical areas, where scab is one of the main diseases, could benefit from introduction of these cultivars, for the reasons cited above. Unfortunately, the indication of chilling requirements has been often missed in the pomology characteristics of the cultivars, although blossom and harvesting times are indicated. In order to provide more information on this matter some scab resistant apple cultivars planted in 2002 were tested. During the winter season 30 one-year-old twigs and 30 shoots with spurs were taken from the trees every week and kept with their bases in water and in a growth chamber for 20 days at 21°C. Apical and lateral buds that grew were both counted and evaluated as to percentage of the total and as to bud development stage. Temperatures during the winters were recorded and both the Richardson and Dynamic Model formulae were tested. The onset of bud break and the end of rest in the one-year-old shoots and in the spurs were assessed by means of the ratio between the chilling units (CU), the chill portions (CP), and by the above mentioned indexes, applying two parameters (% bud break or burst and bud development stage). Significant regressions were observed between the indexes and CU and CP. Throughout the years the prediction of end of the rest was generally lightly better when Dynamic Model was used. The two different buds varied in length of endo-dormancy within cultivars; this can modify the value of their chilling requirement. In the Po Valley the evaluation of the chilling requirement of some apple cultivars resistant to scab showed that low and mid-low cultivars are available and could be grown in tropical and subtropical zones.

Estimation Of Productive Value Of Czech Origin Scab-Resistant Apple Cultivars On Different Rootstocks

Abstract Apple cultivars resistant to scab are suitable for the conventional and organic cultivation. Rootstocks impact on the growth of trees, yield and fruit quality of scab-resistant cultivars were examined in the experiment conducted at Fruit Experimental Station - Samotwór near Wrocław, during the years 1998-2008. In the spring of 1998, the trees of five Czech origin scab-resistant apple cultivars ‘Rosana’, ‘Rubinola’, ‘Rajka’, ‘Goldstar’ and ‘Topaz’ each on M.9, P2, P60, P16 and P22 rootstocks were planted at a spacing of 3.5 × 1.2 m (2380 trees per hectare). The results of 11-year-long studies showed that ‘Rubinola’ and ‘Rajka’ were characterised by the strongest vigour, while ‘Rosana’ grew much weaker. Significant differences in the cumulative yield were not observed between cultivars, but rootstocks influenced cropping instantly. Trees on rootstock P60 had biggest cross-section area and canopy volume, and the highest cumulative yield. Fruit weight was highest from trees on M9 and P60. ‘Topaz’ and ‘Rosana’ formed significantly lightest fruits and ‘Goldstar’ the heaviest. Trees on the super-dwarfing P22 rootstock grew and yielded very weakly and produced very small fruits. The greatest susceptibility to powdery mildew (Podosphaera leucotricha) was observed in ‘Topaz’ and ‘Rajka’. ‘Rubinola’ has the best potential for organic cultivation, especially on dwarfing rootstocks.

Apple-Tree Resistance to Abiotic Factors in Winter

Data on the reaction of apple cultivars to unfavorable autumn-winter conditions were analysed and summarised. New scab resistant apple cultivars (gene Vf) obtained from the hybridisation of local adapted varieties with a donor of scab immunity also displayed hardiness to unfavourable winter conditions. As a result of artificial freezing, the cultivars resistant to spring frost (-3.5 oC) during flowering were identified. The mechanism of adaptation to unfavourable winter conditions, and the possibility of preliminary prediction of winter hardiness according to some indicators of the physiological state of tissues in wintering trees were found. In all apple cultivars, increase of the concentrations of sucrose, anthocyanin and cyanidin was noted during the autumn-winter period, but in winter-hardy cultivars this process was more intensive; the amount of cyanidin in the bark of shoots was 6-8 times higher in comparison with non-winter-hardy cultivars. Higher water loss in non-winter-hardy cultivars was observed under conditions of extreme temperatures, which can lead to significant freezing and sunburns late in winter. In winter-hardy cultivars, peroxidase activity decreased in winter, while in the non-winter-hardy cultivars it remains high, due to incomplete hardening of tissues.

Apple cultivars resistant to scab (Venturia inaequalis (Cke.) Aderh.) Part II. Winterhardiness of apple cultivars

The severe winter which occurred in Poland in 1986-1987 damaged the most part of scab resistant apple cultivars and selected apple hybrids. Cold hardiness studied in 1987 and 1988 showed significant differences in degree of frost injury on stem, branches, twigs and buds of apple trees. Two scab-resistance cultivars, namely Florina and Sir Prize, as well as two check culuvars, Idared and Golden Delicious, were killed by frost. Strong damages were noted in cultivars: Prima, Primula, and Priam. Lower susceptibility showed: Jonafree, Gavin, Liberty Sister and three hybrids selected from crosses of Bankroft with scab-resistant Primula. Relatively frost resistant was Novamac and three hybrids of U-breeding line: U-1101 and U-50, originated from crosses of polish culrivar Fantazja (McIntosh x Linda) with Primula, Highest resistance to frost showed cultivars: Freedom. Liberty. new polish cultivar Witos (Fantazja x Primula) and three hybrids: U-337, U-237 and U-1098. During the 1987 and 1988 seasons severe infection of apple trees by numerous fungi was noted. Twelve species of isolated fungi were identified as pathogens of apple trees bark and wood.

Field susceptibility of 13 scab-resistant apple cultivars to apple powdery mildew [Podosphaera leucotricha (Ell. et Ev.) Salmon

Field susceptibility of 13 scab-resistant apple cultivars to apple powdery mildew was evaluated in 1983-1986. Four groups of susceptibility were distinguished. None of the 13 tested scab-resistant apple trees exhibited complete field immunity to apple powdery mildew. Two cultivars, 'Prima' and 'Primula', were practically resistant. 'Liberty' and two numbered selections, NY-140-9 and NY-158-2, belonged to the group of lower susceptibility. Moderate susceptibility was shown by: 'Novamac', 'Freedom', 'Gavin', 'Prima' and 'Florina'. The group of apple trees most susceptible to <i>Podosphaera leucotricha</i> included: 'Macfree', 'Priscilla' and 'Nova Easygro'. It is not necessary to use chemical sprays to control powdery mildew on 'Prima' and 'Primula'. A reduced spraying program may be recommended only under high disease pressure on less susceptible apple cultivars. A regular spray schedule is needed on moderately susceptible apple trees, but improved chemical control is necessary on the most susceptible ones.