assessment of phenotypic variation of malus orientalis in the north caucasus region

RESEARCH ARTICLE

Assessment of phenotypic variation of Malus orientalisin the North Caucasus region

Monika Hofer • Henryk Flachowsky • Magda-Viola Hanke •

Valentin Semenov • Anna Slavas • Irina Bandurko •

Artem Sorokin • Sergej Alexanian

Received: 16 May 2012 / Accepted: 6 November 2012 / Published online: 18 November 2012

� Springer Science+Business Media Dordrecht 2012

Abstract Malus orientalis Uglitzk. is the predomi-

nant Malus species of the Caucasian forests distributed

in the north of Anatolia, Armenia, Russia as well as in

Iran. It is considered as one of the probable minor

ancestors of domestic apples. Although M. orientalis

has a lower diversity of fruit quality, other valuable

traits such as later blooming, adaptation to a wider

array of habitats, and capacity for longer storage of the

apples should be taken into account for improving the

genetic makeup of the domestic apple. A joint

expedition of scientists of the Julius Kuhn-Institute

from Germany and the Nikolaj I. Vavilov Research

Institute of Plant Industry from Russia was performed

into the North Caucasus region during August/Sep-

tember 2011. Altogether 101 M. orientalis accessions

were collected from eight sites at the North Caucasus.

Twenty-six traits such as size, color, shape, flavor and

firmness of fruit and tree habit were used for

phenotypic evaluation of the accessions. A high

phenotypic diversity within the collected material of

M. orientalis was indicated. Accessions characterized

by suitable fruit traits like bigger size, larger cover

color, less bitterness and better firmness as well as

more sweetness and better flavor were found. How-

ever, small-sized flavorless fruits were also detected.

Tree habit varied widely from upright to weeping.

Subsequently, a comprehensive phenotypic and

genetic evaluation of M. orientalis increases the

knowledge of diversity, may provide new resources

of agronomically important traits for breeding pur-

poses, and gives support to determine accessions for a

core collection.

Keywords Apple � Caucasus Mountains �Evaluation � Genetic diversity � Malus orientalis

Introduction

The genus Malus Mill. comprises 25–47 species,

depending upon the rank given to several taxa and the

acceptance of putative hybrids. Malus classifications

differ primarily in the taxonomic level at which

infrageneric groupings of species are recognized.

Rehder (1920, 1927, 1949) proposed a classification

system which is nowadays well accepted. Newer

reports divided the genus Malus in six (Forsline et al.

2003) or even in seven sections (Qian et al. 2006). In

China, the centre of origin of the genus Malus, about

Scientific transliteration of Cyrillic into Latin was according to

GOST 7.79-2002 and ISO 9:1995.

M. Hofer (&) � H. Flachowsky � M.-V. Hanke

Julius Kuhn-Institute, Federal Research Centre

for Cultivated Plants, Institute for Breeding Research

on Horticultural and Fruit Crops, Pillnitzer Platz 3a,

01326 Dresden, Germany

e-mail: [email protected]

V. Semenov � A. Slavas � I. Bandurko �A. Sorokin � S. Alexanian

Nikolaj I. Vavilov Research Institute of Plant Industry,

Saint Petersburg, Russia

123

Genet Resour Crop Evol (2013) 60:1463–1477

DOI 10.1007/s10722-012-9935-2

80 % of species are indigenous and among them, eight

newly described species were recently recognized

(Zhou 1999). Most of the species intercross, and since

self-incompatibility is common, seeds are mostly

interspecific or intercultivar hybrids. Some taxa for-

merly listed as species are now classified as cultivated

species because they are not known in the wild

(Forsline et al. 2003). Malus is very diverse in

morphology in nature and the species represent a

complicated system of ecotypes, forms and varieties

(Li 1996).

Five gene centers are described for the genus Malus

(Zhukovsky 1965): The East-Asiatic, Middle-Asiatic,

Caucasian, European and the North American gene

center. Vavilov (1930) characterized the Caucasian

centre as ‘‘vast wood consisting solely of the wild

progenitors of fruit trees’’. Burmistrov (1995) speci-

fied the Caucasus as ‘‘one of the world’s richest

centres of diversity of wild fruit species: over 260

species of 37 genera occur in Caucasian forests’’.

Vavilov (1930) mentioned three different Malus

species under the 80 Linnaean species and genera of

wild fruit trees and shrubs found on the main slopes of

the Caucasus: Malus communis Desf. (a) glabra Koch

(=M. sylvestris Mill.), (b) tomentosa Koch, and

(c) pumila Koch (=M. paradisiaca Med.). The

predominant Malus species of the Caucasian centre

was first described by Uglitzkikh as Malus orientalis

(Uzencuk 1939). In Langenfelds (1991) M. orientalis

was described in two subspecies, ssp. orientalis (var.

orientalis and var. montana) and ssp. turkmenorum.

Forsline et al. (2003) summarized the data for the

Section Malus and described one series Sieversinae

Langenf. with three primary species: M. sieversii

(Ledeb.) Roem., M. orientalis and M. sylvestris (L.)

Mill. For M. orientalis two additional subspecies,

subsp. montana (Uglitzk.) Likh. and subsp. turkmeno-

rum (Juz.) Langenf., were differentiated.

Malus orientalis is distributed in the Caucasus, the

south of Russia, the north of Anatolia, Armenia, the

east of Georgia, in Turkey, the mountainous belt in the

northern part of Iran (Rechinger 1963; Vartapetyan

and Akhvlediani 1990; Buttner 2001; Khoshbakht and

Hammer 2006; Volk et al. 2009) as well as in the west,

east and centre of Iran (Rechinger 1963; Browicz et al.

1969). M. orientalis is notable for the dense pubes-

cence of the hypanthium, pedicels and young shoots

(Zhukovsky 1965). Due to the rather wide distribution

this species is highly polymorphous and a high

variability of vegetative and fruit characters can be

found (Fischer and Schmidt 1938; Buttner 2001).

Fruits of four to six centimeters are described as relicts

of former civilizations (Langenfelds 1991). Local

cultivars originating from M. orientalis are cultivated

in several regions of the Caucasus (Langenfelds 1991;

Forsline et al. 2003; Schmidt 2006). Wild trees are also

harvested from local areas. The fruits are used mainly

for stewing, processing to juice and other beverages,

jelly, syrup, jam, wine and vinegar or dried (Buttner

2001). Seedlings are used as rootstocks in addition to

rootstocks specifically developed for apples (Forsline

et al. 2003; Ercisli et al. 2004). A special consideration

is the observed use of these plants in folk medicine to

remedy illness (Khoshbakht and Hammer 2006).

The cultivated apple (Malus 9 domestica Borkh.)

is not a simple taxonomic group. Currently, the most

widely accepted theory, based mainly on morpholog-

ical and molecular evidence, points to Malus sieversii

as the most likely main maternal wild ancestor of

domestic apples (Harris et al. 2002; Robinson et al.

2001), and M. orientalis as one of the probable minor

ancestors (Hokanson et al. 1997; Gharghani et al.

2009). Close genetic relationship is also demonstrated

by determining the genomic DNA sequences (Mat-

sumoto et al. 2010; Velasco et al. 2010). Although the

true origin of cultivated apples is still very conten-

tious, it is important to note that apple cultivation

moved westward very early in history and spread north

along the various branches of the Silk trade route

(Ponomarenko 1987). Comparative genetic studies

using Iranian apple cultivars and landraces, old West

European apple cultivars, and accessions of wild

Malus species revealed a closer genetic relationship

between M. sieversii, M. orientalis and Iranian apples,

than to the old West European cultivars and to other

wild species (Gharghani et al. 2009). This may be

because of later hybridization of apple germplasm

exported to the West with other species, in particular

M. sylvestris. This later introduction of Malus sylves-

tris into the pedigree of domesticated varieties

presumably contributed to the dilution of the contri-

bution of M. sieversii and M. orientalis into

M. 9 domestica (Coart et al. 2006). Another expla-

nation could be the greater geographical distance

between the Western group of domesticated cultivars,

M. sieversii and M. orientalis compared to the distance

of M. sieversii and M. orientalis from the Iranian

group of landraces (Gharghani et al. 2010).

1464 Genet Resour Crop Evol (2013) 60:1463–1477

123

Malus orientalis was described by a lower diversity of

fruit quality, but due to the high variability in populations

M. orientalis could have contributed to the domestica-

tion of apple by introgression of some traits (Buttner

2001). Other valuable traits such as later blooming,

adaptation to a wider array of habitats, and capacity for

longer storage of the apples should be considered

important to the genetic makeup of the domestic apple

(Forsline et al. 2003). Zhukovsky (1965) highlighted the

late ripening and good transportability of fruits, high

sugar content, but also the low winter-hardiness.

A joint German-Russian expedition to the North

Caucasus region in Russia was conducted to system-

atically collect M. orientalis from eight collection

sites (Hanke et al. 2012). Seeds were collected from

101 maternal tree sources to provide wild germplasm

for inclusion into the Fruit Genebank of the Institute

for Breeding Research on Horticultural and Fruit

Crops Dresden, Germany as well as into the genebank

of the Nikolaj I. Vavilov Research Institute of Plant

Industry Sankt Petersburg, Russia. The present study

aimed on the assessment of phenotypic variation of

M. orientalis in the North Caucasus region which was

not comprehensively described before. Therefore, the

collected material was evaluated using twenty-six

morphological traits.

Materials and methods

Plant material

101 accessions of M. orientalis were collected from

eight collection sites in the North Caucasus, Russia, in

2011 (Hanke et al. 2012; Table 1). According to the

taxonomical literature (Ponomarenko 1975; Langen-

felds 1991) it was expected to find M. orientalis ssp.

orientalis var. orientalis (M. orientalis according to

Forsline et al. 2003). The route of the collecting

mission passed along the western slopes of the Greater

Caucasus Range in the Belaa, Hakodz, Psebe and

Kurdzips valleys (Majkop district of the Republic of

Adygea and Tuapsinskij district of the Krasnodar

province) around 1,500 km (Fig. 1). The position of

each tree was recorded with a hand-held Global

Positioning System (eTrex Legend C, Garmin, USA).

For each accession the latitude, the longitude and the

elevation were recorded.

The main area for collection was from 44�100Nlatitude and to 40�260E longitude. The individual trees

selected for seed collection were grown between 67

and 1,033 m elevation (Table 2). The fruits were

selected at random from trees at the collection sites.

Depending on the crop load and accessibility two to 20

fruits per tree were collected, with the intent of 10

samples per location. For each accession photo

documentation was prepared for the tree and the fruit.

Parameters studied

In total, twenty-six morphological and phenotypic

traits were evaluated for each tree (Table 3). The

evaluation included data on ten of the descriptors

established by UPOV (1995) and 16 descriptors

selected by the project partners for their value for

identification. These 26 descriptors consisted of four

morphological descriptors of the tree and 22 of the

fruit.

Table 1 Site description for M. orientalis collection regions in the North Caucasus

No. area Site name Latitude Longitude Elevation (m) Annual

precipitation (mm)

Annual

temperature (�C)

1 Dagestanskaa 44�170–180N 40�000E 460–711 824 10.5

2 Novosvobodnaa 44�190–210N 40�240–260E 490–656 762 8.2

3 Timirazeva 44�220–260N 40�050–120E 294–651 839 11.3

4 Sauman 44�130–170N 39�180–280E 242–315 1120 10.8

5 Psebe 44�100–170N 38�540–39�030E 67–74 985 12.3

6 Goracij Kluc 44�270–350N 38�040–540E 88–338 858 10.5

7 Kutais 44�260–330N 39�150–40�000E 207–377 863 8.5

8 Kamennomostskij 44�090–340N 40�040–120E 459–1,033 738 9

Genet Resour Crop Evol (2013) 60:1463–1477 1465

123

Data analysis

Statistical analyses were performed using SAS 9.3.

Frequencies of each class were calculated for the

nominal and ordinal parameters. Quantitative mea-

surements were made for various traits of the acces-

sions to enable numerical analysis of the data (means

and standard deviations). For Gaussian distributed

interval scaled traits, differences among the collecting

sites were tested by one-way analysis of variance

(ANOVA). Duncan’s Multiple Range Test was used to

determine the significant differences. Quantitative

traits not Gaussian distributed were scored in addition

to the measurement to represent the frequency distri-

bution more clearly in dependence of the collection

site. Spearmans’s correlation coefficients were deter-

mined. Principal component analysis (PCA) (Hillig

and Iezzoni 1988; Iezzoni and Pritts 1991) was used to

reveal the patterns of morphological variation within

the collected material. PCA was performed using the

PRINCOMP procedure of the SAS Statistical Package

9.3.

Results

Distribution of M. orientalis in the collection sites

at the North Caucasus

Material was collected from various growth-condition

types: 55 % from M. orientalis accessions growing at

the roadside, 7 % in small tree groups, 33 % at the

forest border, and only 6 % in the middle of the forest.

The natural renewal of apple trees was observed as

vegetative renewal by root-sucker propagation; young

Fig. 1 Schematic

illustration of collection

sites of the expedition to

Adygea and Krasnodar

region acc. to Hanke et al.

(2012)

Table 2 Data for the interval-scaled descriptors used for the

evaluation of 101 M. orientalis accessions collected in the

North Caucasus

Variable Mean Std

Dev

Minimum Maximum

Elevation (m) 415.80 223.83 67.00 1,033.00

Stem number 2.21 1.41 1.00 7.00

Tree height (m) 8.31 3.46 3.00 20.00

Stem

circumference

(cm)

56.05 41.65 7.00 240.00

Seeds/fruit 6.40 1.70 1.77 9.64

Sterile seeds (%) 6.42 8.47 0.00 59.79

Fruit height (mm) 27.07 5.66 14.50 44.22

Fruit diameter

(mm)

31.69 6.40 15.90 49.90

Ratio height/

diameter

0.86 0.07 0.74 1.17


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Table 3 List of the descriptors used in this study

Descriptor Described in

UPOV (1995)

TG/14/8

Qualitative traits Quantitative traits

Tree

Stem number Counted

Height Assessed in m

Stem perimeter Assessed in cm at a

height of app.

50 cm

Habit UPOV 3 Fastigiate (1), upright (3), spreading (5), drooping (7),

weeping (9)

External fruit

Ground color UPOV 34 Yellow (1), whitish yellow (2), green yellow (3),

green (4), whitish green (5)

Cover color UPOV 36, mod. Absent (1), orange (2), rose (3), red (4), purple (5),

brown (6)

Amount of cover color UPOV 35 Absent (1), very low (2), under 25 % (3), between 25

and 50 % (5), between 50 and 75 % (7), over 75 % (9)

Shape UPOV 20 Globose (1), globose conical (2), broad globose conical (3),

flat (4), flat globose (5), conical (6), narrow conical (7),

truncate conical (8), ellipsoid (9), ellipsoid conical (10),

oblong (11), oblong conical (12)

Shape uniformity Uniform (0), variable (1)

Star shape in the top

view

Absent (0), present (1)

Number of seeds Counted

Percentage of sterile

seeds

Estimated

morphologically,

and counted

Depth of stalk cavity UPOV 30 Shallow (3), medium (5), deep (7)

Width of stalk cavity UPOV 31 Narrow (3), medium (5), broad (7)

Depth of calyx UPOV 26 Convex (1), shallow (2), sunken (3)

Amount of russet Absent (1), medium (5), very high (9)

Length of the stalk in

relation to the fruit

height

Shorter (1), the same size (2) longer (3)

Height Average, measured

in mm

Diameter Average, measured

in mm

Ratio height/diameter UPOV 18 Average, measured

in mm

Assessment of of sooty

blotch and flyspeck

diseases

Disease-free (0), some infection (1), strong infection (2)

Internal fruit

Bitterness Absent (1), medium (5), very high (9)

Firmness of fruit flesh UPOV 43 Soft (3), medium (5), firm (7)

Juiciness Low (3), medium (5), high (7)


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daughter trees emerged directly from the parent tree

and by adventitious root regeneration. A generative

renewal by seed was also common. Seedlings of

various fruit trees (M.orientalis, Pyrus caucasica,

Prunus species) of various ages were found, especially

in large forest glades remaining from Soviet agricul-

tural production lots. The apple trees selected for seed

collection were grown at elevations between 67 and

1,033 m (Table 2).

Phenotype of wild M. orientalis trees

The phenotype of wild M. orientalis trees is described

in Tables 2 and 4. The tree height varied to the seven-

fold, and the stem circumference to the 34-fold. The

quantitative traits stem perimeter and tree height, not

Gaussian distributed, were scored in addition to the

measurement to represent the frequency distribution

more clearly in dependence of the collection site.

Fifty-six M. orientalis accessions showed a stem

circumference of around 49 cm. Altogether 75 % of

the trees obtained a height between 4 and 11 m. The

frequency of small-sized trees with a small stem

circumference was higher in the collection areas V and

VII. The tree height was positively correlated to the

stem circumference (r = 0.68; data not shown). The

portion of trees with a drooping and a weeping habit

was higher at the collection sites VI and VIII. The stem

structure included one-, two- and three to five–

stemmed and bushy trees with seven stems. A single

stem was found in 43 % of the accessions. There was

no variation between collection sites regarding the

number of stems per tree (data not shown).

Phenotypic variation of the M. orientalis fruits

In 87 % of the trees fruits were bearing five and more

seeds. Generally mean seed number ranged from 1.8 to

9.6 (Table 2). The percentage of sterile seeds revealed

a dramatic difference from none to up to 60 %. In

77 % of the seed lots of M. orientalis accessions at

least 0 to 10 % of sterile seeds were found. Using a

one-way analysis of variance (ANOVA) no significant

differences for seed sterility between the collection

sites were recorded (data not shown). The extreme

maximum values may be explained by some outliers.

The fruit height of the accessions as well as the fruit

diameter varied up to three-times (Table 2). The fruit

size parameters were related to the collection sites

(Fig. 2). Site VI is characterized by significant larger

fruits of the accessions compared to the fruits of the

accessions at site III, IV, V, VII and VIII. The averages

for each collecting site ranged from 27.8 mm diameter

at site VIII to 37.8 mm at site VI. We found an average

height/width ratio of 0.86 which reflects a flat globose

fruit shape (Table 2). Fruit height of the accessions

and fruit diameter were strong positively correlated

(r = 0.94; Table 6). The flat globose shape appeared

in 65 %, the flat shape in 14 %, the globose shape in

11 %, and the broad globose conical shape in 4 % of

the accessions (Fig. 3). All elongated forms, conical,

ellipsoid, oblong and oblong conical, appeared very

seldom, and represented a height/diameter ratio more

than 1.

Three important parameters describing the colora-

tion of fruits are summarized in Table 5. The ground

color showed a distribution over all scores, like

yellow, whitish yellow, green yellow, green, green

whitish. Minor variations were revealed between the

areas. Only at site IV yellow was the predominant

ground color of the accessions. At all other sites green

and whitish green coloration dominated. In 67 % of

the M. orientalis accessions a cover color was not

shown up. In some cases a rose (21 %) and a red

(11 %) cover color dominated nearly independent of

the collecting site. In contrast, the amount of fruits of

the accessions possessing cover color was different

between sites. While sites I, III, IV, V, VII and VIII

Table 3 continued

Descriptor Described in

UPOV (1995)

TG/14/8

Qualitative traits Quantitative traits

Relation of sweetness/

acidity

Very sweet (1), sweetish (3), balanced (5), acidulated

(7), very acid (9)

Flavor Absent (1), poor (3), slight (5), strong (7)


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were characterised by colored fruits between 17 and

38 %, site II showed 57 % of colored fruits. At site VI

50 % of fruits were colored and the coloration

dispersed over 75 % of the skin (Table 5).

Seven further parameters describing the external

fruit are demonstrated partly in Fig. 3 and should be

described in general. The uniformity of the shape was

as high as 65 % in the M. orientalis accessions.

Mixtures of fruit shapes appeared in 35 % of the

accessions, especially elongated, conical, ellipsoid,

oblong and oblong conical forms (data not shown).

The star shape in the top view (Fig. 3E, F, G), likewise

in the old apple cultivar ‘Api Etoile’, was discovered

as a specific feature in 17 accessions. Except at sites I

and VII, the star shape was found at all sites. At site III

and site VIII star shape was found in 39 % and 31 % of

the accessions, respectively. For 97 % of the acces-

sions the length of the stalk (pedicel) was shorter

compared to the fruit height, only four accessions

showed the same length (Fig. 3C, D). No stalks longer

than the fruit were found. In M. orientalis, 64 % of the

accessions had a deep stalk cavity (Fig. 3C) while

36 % had a medium cavity, only one accession had a

shallow fruit stalk end. The width of the stalk cavity

was distributed as 72 % medium (Fig. 3C), 19 %

broad (Fig. 3F), and only in 10 % of the accessions as

narrow. Across all accessions, 54 % of the fruits had a

shallow depth of calyx (Fig. 3E, G), 42 % a sunken,

Table 4 Variation of the three traits describing the tree phenotype—stem circumference, tree height and tree habit—in M. orientalisaccessions found in the North Caucasus

Stem perimetera Area site

1 2 3 4 5 6 7 8

1 0–49 cm 50 35.71 55.56 53.33 100 83.33 88.24 25

3 50–99 cm 33.33 28.57 33.33 20 0 16.67 5.88 43.75

5 100–149 cm 0 28.57 11.11 26.67 0 0 5.88 25

7 150–199 cm 0 0 0 0 0 0 0 6.25

9 Over 200 cm 16.67 7.14 0 0 0 0 0 0

Tree heighta Area site

1 2 3 4 5 6 7 8

1 1–3.5 m 0 0 0 0 40 0 11.76 0

3 4–7.5 m 16.67 28.57 47.06 42.86 60 25 76.47 31.25

5 8–11.5 m 16.67 42.86 23.53 42.86 0 62.5 11.76 43.75

7 12–11.5 m 50 21.43 29.41 14.29 0 12.5 0 25

9 Over 16 m 16.67 7.14 0 0 0 0 0 0

Tree habit Area site

5 2 3 4 5 6 7 8

1 0 0 0 21.43 0 0 0 0

3 Upright 33.33 21.43 38.89 14.29 50 0 23.53 0

4 66.67 28.57 11.11 35.71 16.67 0 0 0

5 Spreading 0 14.29 16.67 28.57 33.33 14.29 35.29 6.25

6 0 35.71 5.56 0 0 14.29 17.65 12.5

7 Drooping 0 0 27.78 0 0 42.86 23.53 81.25

9 Weeping 0 0 0 0 0 28.57 0 0

The tables represent the percentage data in dependence of the collection area sites. The italicized data are the highest percentages for

the area sitea The quantitative traits stem perimeter and tree height, not Gaussian distributed, were scored in addition to the measurement to

represent the frequency distribution in dependence of the collection site


123

and only 10 % a convex calyx (Fig. 3B). A distinctive

character for many fruits was crowning at the calyx

end, like in old apple cultivars belonging to the

‘Calville’ group (Fig. 3H). The amount of russet

reached the maximum score of 5 (medium russet) in

5 % of the accessions. Russetting was not detected in

21 %, and a very low amount in 69 % of the

accessions (data not shown).

In addition to the morphological fruit characteris-

tics, five traits characterizing the quality of the fruit,

like firmness, juiciness, bitterness, relation of sweet-

ness to acidity, and flavor were evaluated. A medium

score was dominated for fruit firmness (54 % of the

accessions; data not shown). However, 33 % were

firm, and only 12 % were soft. The juiciness of the

fruit flesh was mainly scored as medium (in 67 % of

accessions), four accessions had a high juiciness for

the fruits, and 28 were bearing rather dry fruits. There

were no distinctive differences between collection

sites for this trait. In M. orientalis 33 % of the

accessions were characterized by fruits without bitter

substances, and nearly the same amount of accession

(27 %) were bearing very bitter fruits (Fig. 4). The

highest proportion of all accessions had fruits that

tasted balanced (60 %; score 5 and 6), followed by

acidulated and very acid tasty fruits (32 %; score 7 and

9). The scores of the other taste variations were more

or less evenly distributed, with only 3 % very sweet

and sweetish. No distinctive differences were

observed for the amount of bitter substances and for

the ratio sweetness to acidity between most of the sites

(Fig. 4). Fruits of accessions harvested at site VI were

up to 50 % without bitterness, and the maximum score

was medium. No flavor was determined in 64 % of the

accessions and poor flavor was observed in 31 % of

the accessions (data not shown).

According to the analysis of Spearmans’s correla-

tion coefficients realized for the external and internal

fruit traits no strong correlations were found (Table 6).

Less strong correlations were found between the fruit

height and diameter to the amount of cover color

(r = 0.5 and 0.54, respectively). Further less strong

correlations were detected between fruit height and

flavor as well as between diameter and flavor

(r = 0.37 and 0.41). In tendency bigger fruits had

more cover color and flavor. In contrast, smaller fruits

were more bitter (r = -0.42 and r = -0.45, respec-

tively). The amount of flavor and bitterness was highly

negatively correlated (r = -0.72). Based on the high

amount of bitterness in fruits of individual trees it was

sometimes questionable if flavor was really complete

absent or not perceptible.

The disease evaluation of fruits concerning sooty

blotch and flyspeck revealed only 11 disease-free

accessions in M. orientalis, 11 % showed some

infections and most were heavily infected (data not

shown).

Principal component analysis (PCA)

Using PCA after Measure of sampling adequacy

(MSA) for all 26 tree and fruit traits, only 17 variables

Fig. 2 Variation in fruit height and diameter between the M. orientalis accessions collected in the North Caucasus in dependence on

the area site. Differences between area sites are indicated by Duncan’s multiple-range test at P \ 0.05


123

having MSA higher 0.4 were considered. The first five

principal components (PC) of the accession data

accounted for 62 % of the total variance among

accessions with Eigen-values [1 (data not shown).

The first three PC’s account for 46 % of the variability

observed (Table 7). The most important variables

integrated by PC1 were only fruit descriptors, in order

of their importance, fruit diameter and height, flavor,

amount of cover color, cover color, sweetness to

acidity, firmness and bitterness. PC2 accounted for

11 % of the variability observed and was correlated

with the two tree descriptors height and stem

Fig. 3 Variation in the fruit features of M. orientalis in the North Caucasus: fruit color; ground and over color; fruit shape—A globose;

flat globose; flat; B broad globose conical; C, D variation in length of stalk; E–G star shape in the top view; H crowning at calyx end


123

circumference. PC3 integrated traits related to tree

habit and additional morphological fruit descriptors,

as depth of stalk, star shape, and depth of calyx basin.

Discussion

Malus orientalis is likely a progenitor of domestic

apples that has yet to be included in breeding programs

(Volk et al. 2009). A joint German-Russian plant

expedition was realized to the North Caucasus region

in Russia with the aim to represent as most as possible

of the genetic diversity of M. orientalis in international

gene bank collections. Altogether 101 accessions of

M. orientalis were collected from eight collection

sites. The phenotypic variation of M. orientalis in the

North Caucasus region was comprehensively

described (Table 3). By the reason that phenotypic

variation of M. orientalis in the North Caucasus region

was not published in detail before, the data should be

compared to the published evaluation results of M.

sieversii (Dzhangaliev 2003), another apple wild

species and proposed progenitor of the domesticated

apple.

The collection area varied from densely forested to

dry, open regions that were sparsely populated with

M. orientalis trees. The ecologic-topographic scheme

of growth-condition types found for M. orientalis

corresponded to those of M. sieversii described by

Dzhangaliev (2003). They ranged from moist growth

conditions, to the semi-moist type along the slopes, to

dry growth conditions. There was a dramatic difference

Table 5 Variation of three qualitative traits describing the

coloration of fruit—ground color, cover color, and of the

amount of color—in M. orientalis accessions found in the

North Caucasus (scores acc. to the method details): The tables

represent the percentage data in dependence of the collection

area sites

Ground color Area site

1 2 3 4 5 6 7 8

1 Yellow 0 0 16.67 33.33 16.67 12.5 16.67 6.25

2 Whitish yellow 16.67 7.14 16.67 26.67 50 25 27.78 6.25

3 Green yellow 16.67 14.29 16.67 6.67 0 12.5 11.11 0

4 Green 66.67 28.57 22.22 26.67 0 12.5 27.78 62.5

5 Whitish green 0 50 27.78 6.67 33.33 37.5 16.67 25

Cover color Area site

1 2 3 4 5 6 7 8

1 Absent 83.33 42.86 72.22 86.67 66.67 50 61.11 68.75

2 Orange 0 0 5.56 0 0 0 0 0

3 Rose 0 42.86 11.11 6.67 33.33 12.5 33.33 18.75

4 Red 16.67 14.29 11.11 6.67 0 25 5.56 12.5

5 Purple 0 0 0 0 0 0 0 0

6 Brown 0 0 0 0 0 12.5 0 0

Amount of cover color Area site

1 2 3 4 5 6 7 8

1 Absent 83.33 42.86 72.22 86.67 66.67 50 61.11 75

2 Very low 0 0 0 0 0 0 11.11 0

3 Under 25 % 0 28.57 16.67 6.67 16.67 0 11.11 18.75

4 25–50 % 0 14.28 0 6.67 16.67 12.5 5.56 6.25

5 50–75 % 0 14.29 5.56 0 0 12.5 0 0

6 Over 75 % 16.67 0 5.56 0 0 25 11.11 0

The italicized data are the highest percentages for the area site


123

between the minimum and maximum values of quan-

titative parameters, like in tree height and stem

circumference (Table 2). No variation for the number

of stems per tree was observed between the different

collection sites. This is in contrast to Dzhangaliev

(2003), who described an increase of bushy-stemmed

habit for M. sieversii, especially at altitudes over

1,500 m.

The variation of external and internal fruit charac-

ters is of great importance to access the diversity of M.

orientalis in the North Caucasus. Comparing the data

presented here (Figs. 2, 3) with data obtained for

M. sieversii (Forsline 2000; Luby et al. 2001), smaller

fruits were recorded for M.orientalis, and only the

larger ones reached comparable sizes. Fruit size of

M. sieversii from different regions in Kazakhstan was

described as diverse but some fruits were as large as

commercial apples. The same large diversity in fruit

size was described in offspring of M. sieversii

originating from expeditions by USDA-ARS to

Kazakhstan (Hofer 2008). No comparable data in liter-

ature are available for the variability in M. orientalis,

Fig. 4 Variation of the content of bitterness (A) and of the relation of sweetness and acidity (B) in M. orientalis fruits collected in the

North Caucasus (scores acc. to the method details)

Table 6 Correlation coefficients among fruit descriptors studied in M. orientalis accessions collected in the North Caucasus (only

variabes considered in the table demonstrated at least once values [0.4 = bold)

Amount of

cover color

Cover

color

Depth of

stalk

Fruit height

(mm)

Fruit

diameter

(mm)

Bitterness Firmness Sweetness/

acidity

Flavor

Amount of

cover color

1.00

Cover color 0.96 1.00

Depth of stalk 0.12 0.11 1.00

Fruit height

(mm)

0.50 0.48 0.37 1.00

Fruit diameter

(mm)

0.54 0.50 0.40 0.94 1.00

Bitterness -0.17 -0.20 -0.34 -0.42 -0.45 1.00

Firmness -0.09 -0.06 -0.13 -0.24 -0.26 0.30 1.00

Sweetness/

acidity

-0.15 -0.12 -0.09 -0.26 -0.27 0.26 0.41 1.00

Flavor 0.29 0.28 0.29 0.37 0.41 -0.72 -0.40 -0.30 1.00

Correlations significant at P = 0.05 bold


123

except a few reports describing a small number of

trees. Aldwinckle et al. (2002) reported about seed-

lings from different populations of M. orientalis trees

from Russian Caucasus with approximately 30 mm

fruit size. Ercisli et al. (2004) mentioned in a review of

fruit germplasm resources of Turkey M. orientalis

fruits with roughly 2.5 cm diameters. In addition to the

size a big difference between M. orientalis and

M. sieversii belongs to the red coloration of fruits.

The percentage of colored fruits in M. orientalis

reached 17 % to 38 % depending on the collecting site

(Table 5). M. sieversii fruits collected from random

populations in Kazakhstan showed a higher percent-

age of accessions with red color; depending from the

area site between 36 and 83 % (Forsline et al. 2003). In

addition to fruit size and coloration the length of the

stalk is also an important descriptor for morphological

studies. The high percentage of M. orientalis acces-

sions with stalks shorter than the fruit height is quite

different from the offspring of M. sieversii collected

by USDA-ARS during expeditions to Kazakhstan.

16 % of the M. sieversii seedlings had fruits where

stalks and fruits had the same length whereas 4 % had

even longer stalks (Hofer 2008).

In addition to the morphological fruit characteris-

tics, five traits characterizing the fruit quality are

interesting regarding the diversity and future utiliza-

tion of the genotypes. Compared to M. sieversii

(Forsline et al. 2003), in M. orientalis a lower

percentage of soft fruits was obtained. This is

supported by the results published by Hofer (2008)

who evaluated seedlings of M. sieversii originated

from the expeditions of the USDA-ARS scientists to

Kazakhstan. Dzhangaliev (2003) devised a system of

fruit classification according to flavor types in order to

determine the processing value of wild fruit crops and

possible utilization. According to these studies the

percentage of M. sieversii accessions in Kazakhstan

having a bitter taste was much lower than presented

here for M. orientalis. The results obtained on

M. sieversii seedlings evaluated by Hofer (2008)

revealed an average of 53 % of seedlings without fruit

bitterness (Hofer 2008). In the present study only

33 % of the accessions evaluated produced fruits

without bitter substances (Fig. 4). According to the

analysis of Spearmans’s correlation coefficients no

strong correlations were found between fruit descrip-

tors studied (Table 6). Several traits showed a less

strong correlation, which has to be verified by the

offspring of the 101 maternal trees in the future.

New sources of disease resistance are of great

importance for utilization in future breeding programs.

They are not only of interest to broaden the genetic

diversity, but also for breeding of new apple cultivars

with improved disease resistance for a more con-

sumer- and eco-friendly fruit production. In this

respect selected accessions of M. orientalis are of

particular interest. During the expedition a total of 11

trees were found which were free of symptoms of

sooty blotch (caused by a complex of Peltaster

fructicola, Geastrumia polystigmatus, Leptodontium

elatus) and flyspeck (caused by Zygophiala jamaic-

ensis). Sooty blotch and flyspeck are surface blemish

diseases of apple which become more and more

important in Europe. Based on the reduction of

pesticides which can be applied to apple an increase

in infestation is expected. The introduction of resis-

tance to sooty blotch and flyspeck from M. orientalis

to the cultivated apple could be a possible solution to

Table 7 Eigenvalues, accumulated variance and correlations

between original variables and the first three PCs representing

variability of M. orientalis accessions collected in the North

Caucasus

Descriptors PC1 PC2 PC3

Fruit diameter 0.86 0.18 -0.04

Fruit height 0.83 0.17 0.00

Flavor 0.72 -0.06 -0.03

Amount of cover color 0.67 0.31 0.48

Cover color 0.60 0.30 0.55

Sweetness/acidity -0.45 0.44 0.06

Firmness -0.56 0.26 0.27

Bitterness -0.68 0.14 0.07

Tree height -0.13 0.70 -0.40

Stem circumference -0.30 0.67 -0.19

Depth of stalk 0.44 0.16 -0.52

Ground color -0.21 0.20 -0.04

Star shape -0.18 0.02 0.39

Juiciness 0.05 0.04 -0.28

Tree habit -0.17 0.39 0.45

Resistance -0.11 -0.31 -0.18

Depth of calyx basin 0.26 0.32 -0.47

Eigen value 4.22 1.89 1.76

Accumulated variance (%) 24.85 36.01 46.4

PCA was realized after measure of sampling adequacy for all

26 tree and fruit traits, only 17 variables having MSA higher

0.4 were considered


123

overcome this problem. The importance of M. orien-

talis for future breeding activities was also underlined

by other authors. Ponomarenko (1992) described wild

accessions of M. orientalis with resistance to apple

scab (Venturia inaequalis) and powdery mildew

(Podosphaera leucotricha). Investigations on M. ori-

entalis seedlings from different plant explorations

revealed individuals with resistance to fire blight

(Erwinia amylovora), apple scab and cedar-apple rust

(Gymnosporangium juniper-virginianae; Volk et al.

2008, 2009).

PCA showed that the eight external and internal

fruit parameters and two parameters describing the

tree growth contributed the two first main components,

confirming 36 % of the total variance (Table 7).

Pereira-Lorenzo et al. (2003) observed that in

M. 9 domestica apple germplasm size of fruit, color

of skin and acidity, sweetness at harvest time, and

attractiveness contributed the main source of variabil-

ity. The first two principle components accounted for

23 % of the analyzed 408 accessions demonstrated a

comparable variation in a M. 9 domestica collection.

Based on the results obtained the component scores for

the accessions were evaluated. Extreme values of the

components revealed first clusters. However, no clear

clustering structure is revealed in dependence on the

collection site. A large diversity was observed. More

relationships could be described if using genetic

markers. Dzhangaliev (2003) described for M. siever-

sii in Kazakhstan that ‘‘the number of trees with

clearly differentiated, distinctive properties is great

such that each apple tree can be described as an

independent form differing from neighboring ones.

For instance, trees in one location have various small,

large and middle sizes of fruit, fruits with yellow or red

clor, high-stemmed and low bushed with different

branch structure’’. The same observations could be

supported for M. orientalis in the North Caucasus.

Subsequently, the collected material will be eval-

uated by the participating partners regarding sources

of agronomically important traits, in order to provide

new resources for breeding and for the establishment

of core collections. In such core collections large

numbers of accessions are represented by a subset of

significantly fewer individuals to represent the genetic

diversity of populations and allow for efficient

collection strategies (Brown 1989; van Hintum et al.

2000; Volk et al. 2005; Wiedow 2006). In addition to

tests for resistance to apple scab, powdery mildew, and

fire blight, studies on genetic diversity of the collected

material using a standardized set of SSR-markers

(suggested by the European Cooperative Programme

for Plant Genetic Resources) and a comprehensive

phenotypic evaluation (comparable Tables 4, 5;

Fig. 4) of the offspring will be performed in future.

It is expected that such a detailed analysis will give us

a more detailed insight into population genetics and

biodiversity between and within the collection sites.

The standardized marker set should be used to

elucidate genetic relationships among M. orientalis

and other Malus species, and locally cultivated apple

varieties. The marker data which will be obtained on

M. orientalis can then be easily compared with data

obtained in other studies. These studies will also allow

a more clear differentiation between true-to-type

M. orientalis genotypes and putative hybrids between

M. orientalis and M. 9 domestica. Hybridization events

between both Malus species could not be excluded in

the North Caucasus region because the collecting sites

were sometimes closely located to villages.

Conclusion

The current plant expedition to the North Caucasus

targeted wild M. orientalis with the goal of enhanced

germplasm representation in Russian and German

gene banks. First statements were made about the

phenotypic variation based on the comprehensive

evaluation of 101 accessions of M. orientalis collected

from eight collection sites in the North Caucasus

region. A high phenotypic diversity within the

collected material of M. orientalis was indicated.

However, further studies could reveal a clustering

structure in dependence on the collection site increas-

ing the number of accessions during future expedtions.

Acknowledgments The authors wish to express their sincere

thank to the Federal Ministry of Nutrition, Agriculture and

Consumer Protection (BMELV), Germany for the financial

support of this expedition. We deeply acknowledge people and

friends we met in the North Caucasus for their great hospitality

and friendliness.

References

Aldwinckle HS, Gustafson HL, Forsline PL, Bhaskara Reddy

MV (2002) Fire blight resistance of Malus species from


123

Sichuan (China), Russian Caucasus, Turkey, and Germany.

Acta Hortic 590:369–372

Browicz K, Frohner S, Gilli A, Nordborg G, Riedl H, Schiman-

Czeika H, Schonbeck-Temesy E, Vassilczenko T (1969)

Rosaceae I. In: Rechinger KK (ed) Flora Iranica. Aka-

demische Druck- und Verlagsanstalt, Graz, pp 1–217

Brown AHD (1989) Core collections. A practical approach to

genetic resources management. Genome 31:818–824

Burmistrov L (1995) New Crops and Wild Fruits and Nuts.

URL: http://www.newcrops.uq.edu.au/acotanc/papers/

burmist2.htm (Stand: 30 Jan 2012)

Buttner R (2001) Rosaceae. In: Hanelt P, IPK (eds) Mansfeld’s

encyclopedia of agricultural and horticultural crops.

Springer, Berlin, pp 417–532

Coart E, van Glabeke S, De Loose M, Larsen AS, Roldan-Ruiz I

(2006) Chloroplast diversity in the genus Malus: new

insights into the relationship between the european wild

apple (Malus sylvestris (L.) Mill. and the domesticated

apple (Malus domestica Borkh.). Mol Ecol 15:2171–2182

Dzhangaliev A (2003) The wild apple tree of Kazakhstan. In:

Janick J, Forsline PhL, Dickson EE, Thompson M, Way

RD (eds) Horticultural reviews wild apple and fruit trees of

Central Asia, vol 29. Wiley, New York, pp 63–303

Ercisli S, Esitken A, Orhan E, Ozdemir O (2004) Rootstocks

used for temperate fruit trees in Turkey: an overview.

Scientific works of the Lithuanian Institute of Horticulture

and Lithuanian University of Agriculture 25:27–33

Fischer A, Schmidt M (1938) Wilde Kern- und Steinobstarten,

ihre Heimat und ihre Bedeutung fur die Entstehung der

Kultursorten und die Zuchtung. Der Zuchter 10:157–167

Forsline PL (2000) Procedures for collection, conservation,

evaluation and documentation of Malus germplasm. Acta

Hort 522:223–234

Forsline PL, Aldwinckle HS, Dickson EE, Luby JJ, Hokanson

SC (2003) Collection, maintenance, characterization, and

utilization of wild apples of central Asia. In: Janick J,

Forsline PL, Dickson EE, Thompson M, Way RD (eds)

Horticultural reviews wild apple and fruit trees of Central

Asia, vol 29. Wiley, New York, pp 1–61

Gharghani A, Zamani Z, Talaie A, Oraguzie NC, Fatahi R,

Hajnajari H, Wiedow C, Gardiner SE (2009) Genetic

identity and relationships of Iranian apple (Ma-lus 9 domestica Borkh.) cultivars and landraces, wild

Malus species and representative old apple cultivars based

on simple sequence repeat (SSR) marker analysis. Genet

Resour Crop Evol 56:829–842

Gharghani A, Zamani Z, Talaie A, Fatahi R, Hajnajari H, Or-

aguzie NC, Wiedow C, Gardiner SE (2010) The role of Iran

(Persia) in apple (Malus 9 domestica Borkh.) domestica-

tion, evolution and migration via the Silk Trade Route.

Acta Hort 859:229–236

Hanke MV, Flachowsky H, Hofer M, Semenov V, Slavas A,

Bandurko I, Sorokin A, Alexanian S (2012) Collecting

fruit genetic resources in the North Caucasus region.

J Kulturpflanzen 64:126–136

Harris SA, Robinson JP, Juniper BE (2002) Genetic clues to the

origin of the apple. Trends Genet 18:426–430

Hillig KW, Iezzoni AF (1988) Multivariate analysis of sour cherry

germplasm collection. J Am Soc Hort Sci 113:928–934

Hofer M (2008) Characterization of phenotypic diversity in

offsprings of Malus sieversii (Ledeb.) Roem. In: First

symposium on horticulturae in Europe, Vienna, Austria,

17–20 February, Abstract, p 253

Hokanson SC, McFerson JR, Forsline PhL, Lamboy WF, Luby

JJ, Djangaliev AD, Aldwinckle HS (1997) Collecting and

managing wild Malus germplasm in its center of diversity.

HortScience 32:173–176

Iezzoni AF, Pritts MP (1991) Applications of principal com-

ponent analysis to horticultural research. HortScience

26:334–338

Khoshbakht K, Hammer K (2006) Savadkouh (Iran)—an evo-

lutionary centre for fruit trees and shrubs. Genet Resour

Crop Evol 53:641–651

Langenfelds V (1991) Apple-trees—morphological evolution,

phylogeny, geography, systematics., University of Latvia,

Riga

Li Y (1996) A critical review of the species and the taxonomy of

Malus Mill. in the world. J Fruit Sci 13:63–81

Luby J, Forsline OL, Aldwinckle H, Bus V, Geibel M (2001) Silk

road apples—collection, evaluation, and utilization of Malussieversii from Central Asia. HortScience 36:225–231

Matsumoto S, Yamada K, Shratake K, Okada K, Abe K (2010)

Structural and functional analyses of two new S-RNase

alleles, Ssi5 and Sad5, in apple. J Hortic Sci Biotechnol

85:131–136

Pereira-Lorenzo S, Ramos-Cabrer AM, Ascasibar-Errasti J

(2003) Analysis of apple germplasm in Northwestern

Spain. J Am Soc Hort Sci 128:67–84

Ponomarenko VV (1975) Materials to the knowledge of apple-

trees of the Caucasus. Botaniceskij Zurnal 60:53–68 (in

Russian)

Ponomarenko VV (1987) History of Malus domestica Borkh.

Origin and evolution. Bot J USSR 176:10–18 (in Russian)

Ponomarenko VV (1992) Malus orientalis Uglitz. as a source of

resitance to diseases. Res Bull All Russ Inst Plant Indust

227:41–46 (in Russian)

Qian GZ, Liu LF, Tang GG (2006) A new section in Malus(Rosaceae) from China. Annales Botanici Fennici 43:68–73

Rechinger KH (1963–2001) Flora Iranica. Akademische Druck-

und Verlagsanstalt, Graz

Rehder A (1920) New species, varieties and combinations.

J Arnold Arboretum 2:47–58

Rehder A (1927) Manual of the cultivated trees and shrubs.

Macmillan, New York

Rehder A (1949) Bibliography of cultivated trees and shrubs.

The Arnold Arboretum of Harvard University, Jamaica

Plain

Robinson JP, Harris SA, Juniper BE (2001) Taxonomy of the

genus Malus Mill. (Rosaceae) with emphasis on the culti-

vated apple, Malus domestica Borkh. Plant Syst Evol

226:35–58

Schmidt PA (2006) Baume und Straucher Kaukasiens. Mitt

Dtsch Dendrol Ges 91:21–56

UPOV (1995) Guidelines for the conduct of tests for distinct-

ness, uniformity and stability (apple). TG/14/8, 1995

Uzencuk SW (1939) Home Malus Mill. Flora SSSR 9:492 (in

Russian)

van Hintum TJL, Brown AHD, Spillane C, Hodgkin T (2000)

Core collections of plant genetic resources. IPGRI Tech-

nical Bulletin, 2000, No. 3

Vartapetyan VV, Akhvlediani SN (1990) Study of polymor-

phism in Malus orientalis Uglietzk. in western and eastern


123

http://www.newcrops.uq.edu.au/acotanc/papers/burmist2.htm

http://www.newcrops.uq.edu.au/acotanc/papers/burmist2.htm

Georgia. Soobshcheniya Akademii Nauk Gruzinskoi SSR

137(2):373–376

Vavilov NI (1930) Wild progenitors of the fruit trees of

Turkestan and the Caucasus and the problem of the origin

of fruit trees. In: Rep. Proc. 9th Intl. Hort Congr.,

pp 271–286

Velasco R, Zharkikh A, Affourtit J, Dhingra A, Cestaro A,

Kalyanaraman A, Fontana P, Bhatnagar SK, Troggio M,

Pruss D, Salvi S, Pindo M, Baldi P, Castelletti S, Cavaiuolo

M, Coppola G, Costa F, Cova V, Dal Ri A, Goremykin V,

Komjanc M, Longhi S, Magnago P, Malacarne G, Malnoy

M, Micheletti D, Moretto M, Perazzolli M, Si-Ammour A,

Vezzulli S, Zini E, Eldredge G, Fitzgerald LM, Gutin N,

Lanchbury J, Macalma T, Mitchell JT, Reid J, Wardell B,

Kodira C, Chen Z, Desany B, Niazi F, Palmer M, Koepke

T, Jiwan D, Schaeffer S, Krishnan V, Wu C, Chu VT, King

ST, Vick J, Tao Q, Mraz A, Stormo A, Stormo K, Bogden

R, Ederle D, Stella A, Vecchietti A, Kater MM, Masiero S,

Lasserre P, Lespinasse Y, Allan AC, Bus V, Chagne D,

Crowhurst RN, Gleave AP, Lavezzo E, Fawcett JA, Proost

S, Rouze P, Sterck L, Toppo S, Lazzari B, Hellens RP,

Durel C-E, Gutin A, Bumgarner RE, Gardiner SE, Skolnick

M, Egholm M, Van de Peer Y, Salamini F, Viola R (2010)

The genome of the domesticated apple (Malus 9 domes-tica Borkh.). Nat Genet 42:833–839

Volk GM, Richards CM, Reiley AA, Henk AD, Forsline PL,

Aldwinckle HS (2005) Ex situ conservation of vegetatively

propagated species: development of a seed-based core

collection for Malus sieversii. J Am Soc Hort Sci

130:203–210

Volk GM, Richards CM, Reiley AA, Henk AD, Forsline PL,

Aldwinckle HS (2008) Genetic diversity and disease

resistance of wild Malus orientalis from Turkey and

Southern Russia. J Am Soc Hort Sci 133:383–389

Volk GM, Richards CM, Henk AD, Reiley AA, Reeves PA,

Forsline PL, Aldwinckle HS (2009) Capturing the diversity

of wild Malus orientalis from Georgia, Armenia, Russia

and Turkey. J Am Soc Hort Sci 134:453–459

Wiedow C (2006) Characterization of phenotypic and molecular

diversity in offsprings of Malus sieversii (Ledeb.) Roem.

As basis for a core collection of apple genetic resources.

Thesis, Martin-Luther-Universitat Halle-Wittenberg

Zhou ZQ (1999) The apple genetic resources in China: the wild

species and their distributions, informative characteristics

and utilization. Genet Resour Crop Evol 46:599–609

Zhukovsky PM (1965) Main gene centres of cultivated plants

and their wild relatives within the territory of the U.S.S.R.

Euphytica 14:177–188


123

assessment of phenotypic variation of malus orientalis in the north caucasus region

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