Tree Genetics & Genomes

, 1:151

Microsatellite variability in apricots (Prunus armeniaca L.) reflects their geographic origin and breeding history

Authors

  • Fatemeh Maghuly
    • Plant Biotechnology UnitInstitute of Applied Microbiology BOKU
  • Eduviges Borroto Fernandez
    • Plant Biotechnology UnitInstitute of Applied Microbiology BOKU
  • Szabolcs Ruthner
    • Corvinus University
  • Andrzej Pedryc
    • Corvinus University
    • Plant Biotechnology UnitInstitute of Applied Microbiology BOKU
Original Paper

DOI: 10.1007/s11295-005-0018-9

Cite this article as:
Maghuly, F., Fernandez, E.B., Ruthner, S. et al. Tree Genetics & Genomes (2005) 1: 151. doi:10.1007/s11295-005-0018-9
  • 232 Views

Abstract

A collection of 133 apricot cultivars and three related species originating from different geographical regions were studied with 10 polymorphic microsatellite markers developed in apricot. Altogether, 133 alleles were identified in the set of accessions, with an average of 13.30 alleles per locus. Out of them, 32 alleles occurred only once in the investigated samples, especially in apricots originating from different eco-geographic groups or in different species. The observed heterozygosity for individual loci ranged from 0.8636 to 0.3182, with an average of 0.6281. An unweighted pair group method with arithmetic mean dendrogram based on Nei's genetic distance grouped the accessions according to their eco-geographical origin and/or their pedigree information. Central Asian cultivars have a distinct position on the dendrogram, which supports the assumption that most cultivars have an Asian ancestor. Most East European cultivars analysed cluster together, and the data even revealed a few synonyms. Results show that American cultivars have not only European germ plasm in their pedigree, but they have also been enriched with germ plasm of Asian origin. The implications of these data for the use of simple sequence repeat (SSR) markers as a tool for fingerprinting cultivars in breeders' rights protection and apricot breeding are discussed. In this paper, we demonstrate for the first time the variability of apricot SSRs in a large collection of apricot cultivars and closely related species.

Keywords

Genetic diversityCultivar characterizationGermplasm managementFruit breedingSSRs

Introduction

Apricots belong to the family Rosaceae, genus Prunus L., section Armeniaca (Lam.) Koch [38], which includes eight different species: P. ansu Maxima.; P. armeniaca L.; P. brigantiaca Vill. (Alpine apricot); P. mandshurica (Maxima.) Koehne; P. x dasycarpa Ehrh.; P. holosericea (Batal) Kost. (Tibetian apricot); P. mume (Sieb.) Sieb. et Zucc. and P. siberica L. All are interfertile diploid species with eight pairs of chromosome [35]. Apricots are grown in temperate and subtropical zones worldwide, being the third economically most important stone fruit crops after peach and plum [35]. The main apricot growing areas are China, the Irano-Caucasian region (Turkey and Iran, with 22.6% of the world production), Central Asia, Europe and North America [9], which represent different eco-geographical groups. The Central Asian group is the oldest group with the richest variation. Most of the cultivars are self-incompatible; fruits are small to medium and ripen over a long period. The Irano-Caucasian group is mostly self-incompatible, produces larger fruit than the Central Asian group and shows lower chilling requirements. The European and the North American groups are the youngest, with the lowest variation, probably originating from a few Asian ancestors [48]. Domestication of this fruit tree led to a decrease in variability in the European cultivars, which are mostly self-compatible, show lower chilling requirements and have only a short ripening time [30].

A large number of cultivars are commercialised, and the breeding industry is particularly dynamic, with new cultivars being released annually [1, 4, 8]. The high number of existing cultivars with different synonyms of important economic values requires the use of fast and reliable techniques for molecular fingerprinting. For a long period, the identification of the apricot cultivars was based on pomological, morphological and horticultural traits [21]. Molecular markers like isoenzymes [2] showed low levels of polymorphism and variability among cultivars. DNA-based markers provide a new possibility for evaluating biodiversity among plant genome [22]. Random amplification polymorphic DNAs (RAPDs) [14, 19, 46] and restriction fragment length polymorphism (RFLPs) markers were developed for apricots [7]; however, both methods have been shown to have some limitations.

Among all available markers, nuclear simple sequence repeats (SSRs or microsatellites) are a widely used class of genetic markers for population studies and genetic diversity assessment [12, 44]. The abundance of microsatellites in many plant species, codominant Mendelian inheritance, high level of polymorphism and easy detection by PCR and electrophoretic methods have made them the genetic markers of choice [31, 37].

Homologous microsatellites were recently made available from genomic DNA and appeared more polymorphic when tested on European accessions [17, 27, 29]. Cultivar identity and phylogenetic origin in apricot was confirmed using amplified fragment length polymorphisms (AFLPs) [13, 16] or peach microsatellites primers [20, 39, 47] until SSRs were isolated from apricots [27, 29].

In this paper, we present the first demonstration of genetic variability in a large collection of apricot cultivars and related species with the use of apricot SSR markers. The Hungarian apricot breeding work has yielded many new cultivars, which are now the basis of apricot production in Eastern Europe. The assessment of the relationship between Hungarian and other cultivars, which traditionally was done according to morphological and phenological traits, is important. The unambiguous identification and clarification of synonyms of Hungarian cultivars is one of the major goal of this work. The detailed genetic knowledge of SSR markers allowed not only to determine the genetic relationships among cultivar and variability analysis, but also to assess the importance of certain factors for the accurate use of SSRs in the defence of breeders' right. The results in genetic diversity allow to discuss the relation between established eco-geographic groups and to test relationships between different hybrid groups.

Material and methods

Plant material

One hundred and thirty-three apricot accessions and one sample of P. x dasycarpa, P. brigantiaca and Plumcot were chosen to represent the European, Irano-Caucasian, Central Asian and North American cultivars with different origin kept at the germ plasm collection of Corvinus University (Budapest, Hungary), BOKU University (IOG, Vienna), Laimburg (South Tyrol, Italy) and at the Consorzio Italiano Vivaisti (CIV, Ferrara, Italy) (Table 1).
Table 1

List of cultivars studied and their five main fruit traits

Cultivar

Pedigree or cultivar group according to morphological characteristics

Origin of samples

Country of origin

Fruit traits

Ripening time

Self-C

References

AIA 0–10

Seedling

Italy

Italy (WE)

Y, F, -, L, SE

Late

SC

CIV

AIA 0–28

Seedling

Italy

Italy (WE)

Y, MF, -, M, SE

Late

SC

CIV

AIA 0–68

Seedling

Italy

Italy (WE)

O, F, -, M, A

Late

SC

CIV

Albena

Silistrenska kajsija × Krasnoschokij

Hungary

Bulgaria (EE)

DO, MF, SK, M

Middle

Pedryc et al. (personal communication)

Ananasnij ciurpinskij

Hungary

Ukraine (EE)

LO,MF, SK, M, SE

Middle

SC

Pedryc et al. (personal communication)

Andornaktájai magyar kajszi

Hungarian Best

Hungary

Hungary (EE)

DO, MF, SK, -

Middle

SC

Pedryc et al. (personal communication)

Arvam aramat

Hungary

Central Asia (CA)

Pedryc et al. (personal communication)

Bachinger (two accessions)

Seedling

Austria

East Europe (EE)

LO, F, -, M, A

Middle

SC

Modl (personal communication)

Bahrt (Orangered) (two accessions)

Lasgerdi Mashhadi × NJA2

Austria

USA (NA)

DO, MF, SK, L, -

Early

SI

[25, 26] and Pedryc et al. (personal communication)

Bebeco

Chance seedling Greece

Hungary

Greece 1988 (WE)

LO, F, BK, L, T

Middle

SC

[25] and Karayiannis (personal communication)

Bergeron

Unknown seedling , Lyon , France

Hungary

France, Lyon 1920 (WE)

O, F, SK, M, T

Late

SC

[5, 25, 26]

Borjana

Hungarian Best × Erevan

Hungary

Moldavia

Pedryc et al. (personal communication)

Borsi-féle kései rózsa

"Rose" group

Hungary

Hungary (EE)

O, F, -, SM, -

Late

SC

[5]

Bronzovij

Khurmai × Krasnij Partizan

Hungary

Ukraine

O, -, SK, M, -

Middle-late

Pedryc et al. (personal communication)

Budapest

Nancy × (Hungarian Best, Kesei rózsa, Acme ?)

Hungary

Hungary 1957 (EE)

LO, F, -, L, A

Late

SC

[5]

Bukurija

Shalakh open pollinated

Hungary

Moldavia

LO, S, SK, S, -

Very early

SI

[5]

Cacansko zlato

Clone of Hungarian Best

Hungary

Serbia (EE)

-, -, -, L, -

Middle

SC

Pedryc et al. (personal communication)

Callatis

(Tarzii de Bukuresti × Ananas) × (Luizet × Umberto)

Hungary

Romania

O, MF, -, L, -

Late

SC

Pedryc et al. (personal communication)

Ceglédi arany

Ceglédi óriás × Rozsa barack C.1668

Hungary

Hungary 1994 (EE)

Y, F, -, L, T

Middle

SC

[5]

Ceglédi bíbor

Chance seedling

Hungary

Hungary 1953 (EE)

DK, S, SK, L, SE

Middle

SC

[5]

Ceglédi kedves

Ceglédi óriás × open pollinated

Hungary

Hungary 1994 (EE)

O, F, -, M, T

Middle-late

SC

[5]

Ceglédi óriás

"Giant" group

Hungary

Hungary 1953 (EE)

DO, MF, SK, L,T

Early

SI

[5]

Ceglédi piroska

Ceglédi óriás × Hungarian Best C.1789

Hungary

Hungary 1995 (EE)

O, MF, SK, M, -

Early-middle

SI

[5]

Chershonskij 1469

Clone of Hungarian Best

Hungary

Ukraine (EE)

DO, MF, SK, M, -

Middle

SC

Pedryc et al. (personal communication)

CIV Nr. 1

Seedling

Italy

Italy (WE)

CIV

Comandor (Marculesti 18/6)

Marculesti 17/52 (Luizet × Umberto) × Marculesti 43/1 (Silistra × Ananas)

Hungary

Romania, 1985

DO, MF, SK, L

Late

SC

Pedryc et al. (personal communication)

Crvena ungarska

Clone of Hungarian Best

Hungary

Macedonia (EE)

DO, F, SK, M, T

Middle

SC

Pedryc et al. (personal communication)

Darunek malahojev

Hungary

Central Asia (CA)

Pedryc et al. (personal communication)

Dionis 1482

Shalakh × Kok-pshar

Hungary

Ukraine

LO, S, -, SM, -

Very early

[39]

Dolgocsukna

Clone of Hungarian Best

Hungary

Hungary (EE)

Middle

SC

Pedryc et al. (personal communication)

Dr. Mascle

Austria

France (WE)

Modl (personal communication)

Effekt 2441

Krupnolodnij open pollinated (Hungarian Best)

Hungary

Ukraine (EE)

Y, MF, SK, L, -

Early

SC

Pedryc et al. (personal communication)

Erevan (syn.: Shalakh) (two accessions)

Local variety in Armenia

Hungary

Armenia (IC)

LO, F, SK, L, SE

Early

SC

[28, 39]

Festival

Hungary

Ukraine

Pedryc et al. (personal communication)

Goldrich

Sungold × Perfection

Austria

North America (NA)

O, F, -, L, -

Middle

SI

[25, 26]

Gönci magyar kajszi

Hybrid of Hungarian Best

Hungary

Hungary 1960 (EE)

DO, S, SK, M, SE

Middle

SC

[5]

Gulkin (four accessions)

Seedling

Pakistan

Pakistan (CA)

O, F, SK, S, SE

Early

SI?

Thompson (personal communication)

Harcot

[Geneva × Naramata) × (Morden 604) × (Phelps × Perfection)]

Hungary

Canada 1968 (NA)

DO, F, SK, M, SE

Middle

SI

[16, 25, 39]

Harmat

Seedling from open pollinated Jubilar (Jubilar is an open pollinated seedling of Shalakh)

Hungary

Irano-Caucasian (IC)

O, S, BK, M, -

Very early

SI

[39]

Hunza (three accessions)

Seedling

Pakistan

Pakistan (CA)

O, F, SK, S, SE

Early

SI?

Thompson (personal communication)

Junskij

Shalakh open pollinated

Hungary

Moldavia (IC)

Y, S, SK, SM, -

Very early

Pedryc et al. (personal communication)

Kalasek

Clone of Hungarian Best

Hungary

Czech (EE)

DO, F, SK, M, T

Middle

SC

Pedryc et al. (personal communication)

Karim-Abad (five accessions)

Seedling

Pakistan

Pakistan (CA)

O, F, SK, S, SE

Early

SI?

Thompson (personal communication)

Karola

Kloboucka × Velkoparlovicka

Hungary

Slovakia

DO, F, -, M, -

Early

SC

Pedryc et al. (personal communication)

Kech-psar 1445

Local variety in middle Asia

Hungary

Central Asia, 1930 Kostina (CA)

Y, F, SK, M, -

Very late

SI

[30]

Kecskemet late

Hungarian seedling

Austria

East Europe (EE)

LO, F, -, M, -

Late

SC

Hemmelmeyer 2003 (personal communication)

Kecskemet early

Hungarian seedling

Austria

East Europe (EE)

LO, F, -, M, A

Middle

SC

[28]

Khurmai

Hungary

Central Asia (CA)

Y-O, S, SK, M, SE

Late

SI

[28]

Kijevskij aromatij

Hungary

Ukraine

Pedryc et al. (personal communication)

Kletnice

Local clone

Hungary

Czech

LO, MF, SK,M, SE

Middle

SC

Krska et al. (personal communication)

Klosterneuburger (two accessions)

Unknown seedling (local variety in Austria)

Austria

Austria (EE)

LO, F, BK, M, SE

Early-middle

SC

[28]

Konkurencia 2442

Effect (Krupnoplodnij o.p.) × Priusadebnij rannij

Hungary

Ukraine

O, -, SK, M, -

Early

Pedryc et al. 2004 (personal communication)

Konzervnij pozdnij

Seedling of local cultivar

Hungary

Ukraine

DO, MF, SK, L, -

Late

SC

Pedryc et al. (personal communication)

Korai piros

Originated form old Hungarian variety group

Hungary

Hungary (EE)

O, S, SK, SM, -

Early

SI

[5]

Korai zamatos

Jubilar (Shalakh) open pollinated

Hungary

Irano-Caucasian (IC)

O, MF, SK, M, SE

Very early

SI

[5]

Krasnoshchokij iz Nikolajeva 1468

Hungarian Best

Hungary

Ukraine (EE)

DO, MF, SK, L, -

Middle

SC

Pedryc et al. (personal communication)

Krimskij amur

Mulla sadik × Udarnik

Hungary

Ukraine

O, F, SK, L, -

Middle-late

SC

[47] and Pedryc et al.(personal communication)

Ksna ugarska

Hybrid of Hungarian Best

Hungary

Bulgaria (EE)

DO, -, SK, S, -

Middle

SC

Pedryc et al. (personal communication)

Kuresia (KU9)

Austria

Europe, North Africa

LO, F, -, M, SE–A

Late

SC

[11]

Ligeti óriás

Hybrid of Cegledi orias, "Giant" group

Hungary

Hungary 1959 (EE)

O, MF, SK, VL, -

Middle

SI

[5]

Litoral

(Luizet × Umberto) × (Ananas × Ananas)

Hungary

Romania

Pedryc et al. (personal communication)

Luizet 343

Seedling, Lyon, France

Italy

France, 1838 (WE)

LO, F, SK, M, SE

Early

SC

[25, 28]

M2000 m (Pakistan)

Seedling

Pakistan

Pakistan (CA)

Fliri (personal communication)

Magyar kajszi C.235

Hungarian Best

Hungary

Hungary (EE)

DO, F, SK, M, T

Middle

SC

[5]

Mandulakajszi

Unknown

Hungary

Hungary (EE)

O, MF, SK, L, T

Middle-late

SC

[5]

Mari de Cenad 1419

Local variety in Romania

Hungary

Romania (EE)

O, MF, -, L, -

Middle

SC

Pedryc et al. (personal communication)

Marille Bauer

Unknown seedling

Austria

East Europe (EE)

LO, -, -, M–L, SE–A

Middle

SC

Modl (personal communication)

Marille Viessling

Unknown seedling

Austria

East Europe (EE)

LO, -, -,M–L, SE–A

Middle

SC

Modl (personal communication)

Moniqui

Hungary

Spain (WE)

Y, S, BK, VL, SE

Middle

SI

[25]

Morden-604

Scout × McClure

Hungary

Canada (NA)

Y, S, -, SM, -

Middle

SC

[39]; Pedryc et al. (personal communication)

MT 6/17(T-6, Transgenic)

Late Kecskemeter open pollinated

Austria

East Europe (EE)

Late

SC

Modl (personal communication)

MT 8/9 (T-8, Transgenic)

Late Kecskemeter open pollinated

Austria

East Europe (EE)

Late

SC

Modl (personal communication)

Murfatlar

Hungary

Romania

LO, -, -, S, -

Pedryc et al. (personal communication)

Naggyümölcsü magyar kajszi

Hungarian Best

Hungary

Hungary (EE)

DO, F, SK, M, T

Middle

SC

Pedryc et al. (personal communication)

Nahoznij zazrak

Hungary

Czech (EE)

Middle

Narjadnij

Oranshevo Krasnij × Shirazkij

Hungary

Ukraine

LO, -, BK, M, -

Middle-late

Pedryc et al. (personal communication)

P. x dasycarpa Ehrh. (black apricot)

P. cerasifera × P. armeniaca

Austria

Italy (WE)

Purple, hairy, sweet

Middle

 

Paksi magyar kajszi

Clone of Hungarian Best

Hungary

Hungary (EE)

DO, MF, SK, M, -

Middle

SC

Pedryc et al. (personal communication)

Pasinok 1464

Vinoslivij × Erevan

Hungary

Ukraine

LO, MF, SK, M, -

Early

SC

Pedryc et al. (personal communication)

Pieber Baum 13

Austria

East Europe (EE)

SC

Modl (personal communication)

Pieber Baum 15

Austria

East Europe (EE)

SC

Modl (personal communication)

Pieber Baum 17

Austria

East Europe (EE)

SC

Modl (personal communication)

Pisana ICAPI 26/5

Open pollinated

Hungary

Italy 1995 (WE)

O, MF, -, L, -

Late

SC

Pedryc et al. (personal communication)

Plumcot

P. armeniaca × P. salicinia

Hungary

USA (NA)

Medium, taste between plum and apricot, freestone fruit

May–June

SC

http://WWW.digitalseed.com/gardener/fruit/apricotplum.html

Polduj junskij

Hungary

Moldavia

Pedryc et al. (personal communication)

Polonaise

Chance seedling, France

Hungary

France (WE)

LO, F, SK, M, SE

Middle

SC

[5]

Priana

Canino × Hamidi

Italy

France

Y, S,- , SM, -

Very early

[25]

Priusadebnij

Samarkandskij rannij × Krasnoshchokij

Hungary

Ukraine

LO, S, SK, SM

Very early

SI

Pedryc et al. (personal communication)

Prunus brigantiaca Vill.

P. brigantiaca (Alpine plum)

France

France 1779 (WE)

Fruit resembles a golden cherry tomato, tastes like a plum, and botanists class it as a little apricot, sweet

SC

Jacobson 2003 (web site)

Rakovsky

Seedling from the garden of Rakovszky Genz

Hungary

Hungary 1941 (EE)

DO, -, SK, M, -

Middle

SC

[5]

Rakvice

Hungary

Czech

Pedryc et al. (personal communication)

Rana Dokucana

Hungary

East Europe (EE)

Pedryc et al. (personal communication)

Rosensteiner (two accessions)

Seedling

Austria

East Europe (EE)

LO, F, -, M, A

Middle

SC

Modl (personal communication)

Rouge de Sernhac (two accessions)

Chance seedling, Sernhac, France

Austria

France, 1973 (WE)

LO, F, BK, M, SE

Early-middle

SC

[25]

Rózsa C.1406

" Rose " group

Hungary

Hungary 1955 (EE)

O, MF, -, M, SE

Late

SC

[5]

Sabinovska

Hungarian Best

Hungary

Slovakia (EE)

SC

Pedryc et al. (personal communication)

Samarkandskij rannij

Krasznoscoskij × Majszkaja szkoroszpelka

Hungary

Uzbekistan (CA)

O, MF, SK, SM, SE

Very early

SI

[5]

San Castrese

Italy

Italy (WE)

DO, F, -,L, -

Late-middle

SC

[25]

Selena

(Luizet × Umberto) × (Ananas × Ananas)

Hungary

Romania

DO, MF, -, L, T

Late

SC

Pedryc et al. (personal communication)

Silvercot

New variety

Austria

USA (NA)

Modl (personal communication)

Sirena (Marculesti 18/4)

(Ananas × Ananas) × (Luizet × Umberto)

Hungary

Romania

-, -, -, L, -

Late

Pedryc et al. (personal communication)

Spätblühende Koch

Austria

East Europe (EE)

DO, -, -, L, SE

Middle

SC

Modl (personal communication)

Sulmona

(Luizet × Umberto) × (Ananas × Ananas)

Hungary

Romania

O, MF, -, L, -

Late

SC

Pedryc et al. (personal communication)

Szegedi mamut

Hybrid of Cegledi orias, "Giant" group

Hungary

Hungary (EE)

O, MF, SK, L, T

Early

SI

[5]

Szilisztrenka compotna

Hybrid of Hungarian Best

Hungary

Bulgaria (EE)

DO, F, SK, M, T

SC

Pedryc et al. (personal communication)

Skopszka krupna

Hybrid of Hungarian Best

Hungary

Macedonia (EE)

DO, F, SK, M, T

Middle

SC

Pedryc et al. (personal communication)

Tilton

Austria

USA 1885 (NA)

Y, F, SK, L, -

Very late

SC

[28]

Tomis

Hungary

Romania

-, -, -, EL, -

Pedryc et al. (personal communication)

Ungarische Beste

Hungarian Best

Austria

East Europe (EE)

RO, F, SK–BK, M, SE–A

Early-middle

SC

[11]

Uzsgorod

Hungary

Ukraine

Pedryc et al. (personal communication)

VAV B1

Unknown seedling

Austria

Czech (EE)

LO, F, -,M- L, SE–A

Middle

SC

Modl (personal communication)

Veecot

“Reliable” open pollinated

Hungary

Canada (NA)

RO, F, BK, SM, SE

Middle

SI

Karayiannis (personal communication)

Velikij

Hybrid

Hungary

Ukraine

Pedryc et al. (personal communication)

Velkopavlovicka (Le 1)

Clone of Hungarian Best

Hungary

Czech (EE)

DO, MF, SK, M, T

Middle

SC

Krska et al. (personal communication)

Venus 1414

(Umberto × Ananas) × (Luizet × Umberto)

Hungary

Romania 1985

O, MF, -, L, -

Late

SC

Pedryc et al. (personal communication)

Vesna

Magyar Kayszi × pollen mixture

Hungary

Slovakia (EE)

O, F, -, L, -

Early

SI

Pedryc et al. (personal communication)

Vinschger Marille (Val Venosta)

Old local variety

South Tyrol

Italy (WE)

LO, MF, SK, M, SE

Late

SC

[42]

Vnuk Partizana 2436

“Krasnij partizan” open pollinated

Hungary

Ukraine

LO, MF, SK, L, -

Middle

[39] and Pedryc et al. (personal communication)

Vognic

Hybrid

Hungary

Ukraine

Pedryc et al. (personal communication)

Voski 2425

Sateni open pollinated

Hungary

Armenia (IC)

Y, MF, -, L, -

Middle

SI

Pedryc et al. (personal communication)

Zaposdolje 2404

Hungary

Ukraine

O, ., SK, M, -

Late

SC

Pedryc et al. (personal communication)

Zard 2407

Hungary

Central Asia (CA)

Y, S, -, SM, -

Middle

SI

Pedryc et al. (personal communication)

Fruit traits: (1) colour: LO light orange, DO dark orange, Y yellow, O orange, RO red-orange; (2) consistency: F firm, S soft, MF middle firm; (3) taste of kernel: SK sweet kernel, BK bitter kernel; (4) size: EL extremely large, VL very large, L large, M medium, SM small; (5) taste of the fruit flesh: SE sweet, B bitter, A acidic, T tasty. Compatibility: SI self-incompatible, SC self-compatible. Origin: CA Central Asia, IC Irano-Caucasian, EE East Europe, WE West Europe, NA North America. CIV Consorzio Italiano Vivaisti

DNA extraction

Total genomic DNA was extracted from leaves using the DNeasy Plant Mini Kit (QIAGEN) according to the supplier's instructions.

PCR amplification and electrophoresis

Ten different primer combinations originally developed for apricot SSR loci [27, 29] and representing different regions of the apricot genome were used for amplification of DNA from different apricot cultivars (Table 2). Polymerase chain reaction (PCR) amplifications were conducted in a total volume of 25 μl using 1× PCR buffer (provided by the manufacturer, QIAGEN), 2 mM MgCl2, 0.2 mM dNTPs, 4 pmol of each primer, 0.6 units HotStarTaq polymerase (QIAGEN HotStarTaq PCR), 20–30 ng of total genomic DNA. PCR cycling conditions consisted of an initial denaturation step of 95°C for 15 min, followed by 35 cycles of 50 s at 95°C, 50 s at annealing temperature and 1 min at 72°C. A final extension step of 10 min at 72°C ended the cycle.
Table 2

Characteristics of the ten SSRs studied

Locus

Predicted length (bp)

Size range (bp)

Annealing temperature (°C)

Repeat type

Reference

SsrPaCITA7

211

186–224

60

(AG) n

[27]

ssrPaCITA10

175

142–212

58

(CT) n

[27]

ssrPaCITA19

114

98–148

60

(TC) n

[27]

ssrPaCITA23

146

112–157

56

(AC) n(AG) n

[27]

ssrPaCITA27

262

224–266

58

(TC) n(TA) n (TG) n

[27]

UDAp-407

188

118–162

58

(TC) nTT(TC) n

[29]

UDAp-410

155

116–146

58

(AG) n

[29]

UDAp-414

174

150–214

58

(AG) n

[29]

UDAp-415

156

139–143

58

(GA) n

[29]

UDAp-420

175

154–262

58

(CT) n

[29]

Fluorescently labelled microsatellite fragments were analysed on an ABI 3100 capillary sequencer. Fragment sizing was performed using the ABI Genotyper software.

Data analysis

For each of the defined loci, SSR allelic composition was determined in 136 accessions. Putative alleles were indicated in alphabetical order (A for smallest fragment, etc.). The programme POPGENE (version 1.32; [50]; http://www.ualberta.ca/~fyeh/index.htm) was used to calculate allele frequencies at each locus, number of alleles, inbreeding coefficient (FST), gene flow (Nm) estimated from the formula Nm=0.25(1/FST-1) by Nei [34]; observed (Ho) and expected (He) heterozygosity were measured as described by Levene [24] and Nei [33]. Based on the microsatellite data, genetic identity (I) and genetic distance (D) were calculated according to Nei [32, 34], and values of D were used to conduct cluster analysis with an unweighted pair group method with arithmetic mean (UPGMA) algorithm and construct a dendrogram; a further dendrogram was constructed using the programme TREEVIEW [36]. Pairwise genetic distances among the 133 apricot accessions were computed using the programme PAUP version 4.

Results

Microsatellites diversity

One hundred and thirty-three apricot accessions and three related species were analysed with ten apricot SSRs. Polymorphic bands were obtained with all primers. Alleles were clearly differentiated using the capillary electrophoresis sequencer. Locus UDAp-407 was the most polymorphic among the ten loci (22 alleles), with the highest effective number of alleles (Table 3), while locus ssrPaCITA27 was the least polymorphic (seven alleles). Altogether, 133 alleles were identified in the set of 133 apricot accessions, with an average of 13.30 alleles per locus (Table 3). The observed heterozygosity for individual loci ranged from 0.8636 in locus UDAp-410 to 0.3182 in locus ssrPaCITA 27, with an average of 0.6281 (Table 3). In all individuals, the observed heterozygosity (Ho) was clearly lower than the expected heterozygosity (He).
Table 3

Variability parameters calculated for ten SSR markers in 133 apricot cultivars

Locus

Number of putative alleles

Effective alleles per locus (Ne)

Observed heterozygosity (Ho)

Expected heterozygosity (He)

FST

Nm

SsrPaCITA7

14 (A–O)

4.2511

0.8346

0.7677

0.4544

0.3002

ssrPaCITA10

17 (A–Q)

3.4492

0.5038

0.7128

0.6453

0.1374

ssrPaCITA19

12 (A–L)

3.9001

0.7519

0.7464

0.4944

0.2556

ssrPaCITA23

11 (A–K)

4.2604

0.6031

0.7682

0.6154

0.1562

ssrPaCITA27

7 (A–G)

2.4551

0.3182

0.5949

0.7363

0.0895

UDAp-407

22 (A–Y)

6.4712

0.6917

0.8487

0.5909

0.1731

UDAp-410

12 (A–P)

4.6933

0.8636

0.7899

0.4576

0.2963

UDAp-414

14 (A–Q)

5.0867

0.4887

0.8064

0.6958

0.1093

UDAp-415

11 (A–K)

3.2244

0.6241

0.6925

0.5477

0.2065

UDAp-420

13 (A–N)

3.1568

0.6015

0.6858

0.5598

0.1966

Mean

13.30

4.0948

0.6281

0.7413

0.5768

0.1834

SD

4.00

1.1461

0.1666

0.0725

Out of the 133 different alleles detected in all individuals, 32 alleles occurred only once in the investigated samples. They were found in apricots that originated from different eco-geographic groups or in different species: Arwam aramat, Effekt, Karim Abad 8, Hunza 1 and Vesna (at locus ssrPaCITA 10); Vesna (at locus ssrPaCITA 19); Kijevskij aromatij and Harcot (at locus ssrPaCITA 23); Polduij junskij (at locus ssrPaCITA 27); Priana (at locus ssrPaCITA 7); Effekt, Erevan, Kuresia, Junskij, Poldij junskij and Priusadenbnij (at locus UDAp-407); Ananasznij ciurpinskij and Kech-psar (at Locus UDAp-415); Gulkin (at locus UDAp-410); Gulkin, Morden-604 and Pasinok (at locus UDAp-414); Cegledi kedves, Mari de Cenad and Zaposzdolij (at locus UDAp-420).

Non-amplifying (null) alleles were observed in three loci of five accessions: Zard (at locus ssrPaCITA 27), Uzsgorod and Rakovice (at locus ssrPaCITA 23) and finally early Kecskemeter (at locus UDAp-410) (data not shown).

FST values ranged from 0.4544 (ssrPaCITA 7) to 0.7363 (ssrPaCITA 27), with an average of 0.5768. The gene flow Nm estimated from FST in locus ssrPaCITA 7 was estimated at 0.3002, a value three times higher than that in locus ssrPaCITA 27 (0.0895) (Table 3).

Relationships between cultivars

To elucidate the genetic relationship among apricot cultivars, a dendrogram was produced using UPGMA analysis of pairwise genetic distances over ten SSR loci. The dendrogram divided the cultivars into two major clusters (Fig. 2). In cluster 1, there are two subclusters (1.1 and 1.2) that include most of the East European cultivars. Subcluster 1.1 includes six European cultivars and the American cultivar Goldrich. Subcluster 1.2 comprises most of the European cultivars that are divided into five East European groups, with pedigree relatedness based on morphological characteristics: 1, Magyar kaijszi hybrids (black circle); 2, Cegledi orias hybrids, (black square); 3, Luizet hybrids, crossed with Ananas or Umberto (white circle); 4, Kecskemet apricots (KCSK) and 5, Shalakh hybrids (white square) (Fig. 2 and Table 1).

The rest of the apricot cultivars originating from different eco-geographical areas were located in the remaining subclusters of cluster 1 (1.3). Cluster 2 contains only cultivars from Central Asia (14 accessions).

Genetic relationships among eco-geographical groups

Genetic distance and genetic identity among five eco-geographic groups were quantified based on allele frequencies according to Nei [32] (Table 4). The genetic identity between Central Asian and West European groups was the lowest (43%). In comparison, the East European, West European and Irano-Caucasian groups are very similar, with identity values between 79 and 81%. The UPGMA dendrogram based on genetic distances yielded two main clusters (Fig. 1), one containing the Central Asian group and the other including two subclusters. One subcluster comprises the West European and North American groups and the other comprises the Irano-Caucasian and East European groups.
Table 4

Genetic identity (above diagonal) and distance (below diagonal) according to Nei [32] between the five apricot groups and three related species

 

West European

North-American

Central Asian

Irano-Caucasian

East European

P. x dasycarpa

Plumcot

P. brigantiaca

West European

****

0.7653

0.4391

0.6606

0.7982

0.6156

0.4716

0.1572

North-American

0.2674

****

0.5092

0.6188

0.6510

0.5001

0.2936

0.0979

Central Asian

0.8231

0.6749

****

0.5712

0.4568

0.2362

0.2148

0.0967

Irano-Caucasian

0.4146

0.4800

0.5601

****

0.8239

0.3738

0.4252

0.1595

East European

0.2254

0.4292

0.7834

0.1937

****

0.4653

0.5664

0.2206

P. x dasycarpa

0.4852

0.6930

1.4430

0.9839

0.7651

****

0.2224

0.1112

Plumcot

0.7517

1.2254

1.5380

0.8552

0.5685

1.5034

****

0.2143

P. brigantiaca

1.8503

2.3240

2.3365

1.8360

1.5115

2.1965

1.5404

****

https://static-content.springer.com/image/art%3A10.1007%2Fs11295-005-0018-9/MediaObjects/11295_2005_18_Fig1_HTML.gif
Fig. 1

Dendrogram of apricot cultivars and related species by UPGMA based on Nei's genetic distance (1972)

Relation between species and cultivar groups

The relationship between the different Prunus species and P. armeniaca was analysed using Nei's genetic distance (Fig. 1). P. x dasycarpa, P. brigantiaca and Plumcot were distant from the common apricot cluster, P. brigantiaca being the most distant species. P. x dasycarpa, an apricot x P. cerasifera hybrid, was found intermediate between apricot groups and Plumcot, which is a hybrid between apricot and P. salicinia. The genetic identity between P. brigantiaca and apricot groups was generally low (Table 4), reaching 0.09% between P. brigantiaca and the Central Asian and North American groups.

Discussion

Microsatellites polymorphism

One potential advantage of microsatellites in conservation genetics is the fact that primers developed for a particular species were shown to be applicable across related taxa [6]. Heterologous peach primers were extensively used for cross-amplification in stone fruit [20, 39, 47]. It has been suggested that, usually, a greater genetic distance implies a decrease in the ability to amplify the loci and in the amount of polymorphism detected and a shortening of the length of microsatellites [20, 41]. Furthermore, the frequency of “null” alleles may increase with the degeneracy of primer used due to a greater tendency for sensitivity to mis-priming [6].

The results obtained in this study show that highly polymorphic homologous microsatellite markers could be effectively used for fingerprinting purposes in apricot. The average number of alleles per locus was 13.30, which was higher than the 4.1 detected by 19 polymorphic SSRs in 48 different genotype apricots by Hormaza [20], the 7.64 observed by Zhebentyayeva et al. [47] in 74 native apricot accessions with 14 polymorphic SSRs and the 3.1 previously observed by Romero et al. [39] in a set of 40 apricots cultivars with 16 microsatellites. In all previous studies on genetic diversity of apricot, microsatellites developed from peach were used. The higher number of alleles in our study is due to the use of ten SSRs developed in apricot and selected for their high level of polymorphism [27, 29] and due to the high number of analysed cultivars. In our study, heterozygosity observed averaged over the ten loci was 0.6281, higher than the mean value reported with peach SSRs by Romero et al. [39] and Zhebentyayeva et al. [47] in apricot (0.32 and 0.517, respectively). High allele number and heterozygosity reflect the ability of SSR marker to provide a unique genetic profile for individual genotypes.

FST values describe the proportion of variance within a species that is due to the populations' subdivision. According to Wright, FST values above 0.25 indicate very great genetic differentiation [18]. As the average of FST values were 0.5768 (Table 2), genetic differentiation is relatively high among accessions. In apricot, the high level of genetic differentiation could be explained by the mating system and by low migration rates. Most fruit trees under cultivation are derived from allogamic wild progenitors in which cross-pollination was maintained by self-incompatibility. Genetically, domestication of fruit trees means changing the reproductive biology by shifting from sexual reproduction (in the wild) to vegetative propagation (under cultivation) [48]. In Central Asia, domestication may have occurred through the natural association of wild and semi-wild forms and propagated seedlings, while in Europe, the introduction of vegetative propagation and the selection of a few superior cultivars to a certain extent reduced genetic variability. In apricot, mutations caused the breakdown of self-incompatibility, or at least rendered this system “leaky”, so that self-pollination also brings about considerable fruit set in such clones [49]. In fact, most of the Central Asian apricots cultivars are self-incompatible, while most European cultivars are self-compatible [30]. A high level of FST value indicates a low level of gene flow. Indeed, the gene flow estimated in this study was low, as described by Nm (Table 3). These findings could be attributed either to the different geographical region of accessions or to human impact.

Apricot genetic diversity and relationships among accessions

The dendrogram generated from the UPGMA cluster analysis produced several significant groups related to the pedigree and/or geographical origin of the genotypes.

Most of the European cultivars analysed belong to subcluster 1.2. Several hybrids with large fruits and sweet kernels belonging to the self-compatible Magyar kajszi or Hungarian Best group are present in Central Europe, particularly in the Pannonian region, with different designations suspected to be synonyms. In fact, we found that 15 out of 18 accessions are closely related, five of them (Albena, Andornaktajai magyar kajszi, Crvena ungarska, Gönci magyar kajszi and Nagyümölcsü magyar kajszi) could even be synonyms (Fig. 2). Three cultivars (Mari de Canad, Szilisztrenka compotna and Vesna) clustered very far from the other hybrids, which could be due to the fact that they are hybrids, but a labelling mistake also cannot be completely ruled out.
https://static-content.springer.com/image/art%3A10.1007%2Fs11295-005-0018-9/MediaObjects/11295_2005_18_Fig2_HTML.gif
Fig. 2

UPGMA dendrogram for 133 apricot cultivars based on genetic distance. Black circle, Hungarian Best hybrids; white circle, Luizet hybrids; black square, Cegledi orias hybrids; white square, Shalakh hybrids; KCSK Kecskemet

Cultivars including the hybrids of Cegledi orias are divided in two groups, one representing self-incompatible cultivars, also known as the “giant group” in Hungary, which confirm previous morphological characteristics and RAPD analysis [40], and the second self-compatible group with Cegledi kedves and Cegledi arany. This fertility trait could be the reason for the separation. The first group clustered with Cegledi bibor, which might be a hybrid or an ancestor of Cegledi orias.

The cultivars Comandor, Sirena, Litora, Selena and Sulmona were obtained from crosses of Umberto, Ananas and Luizet, and correspondingly, all of them cluster together on the dendrogram. Interestingly, the French group (Luizet) and Hungarian Best (Magyar kajszi) hybrids also cluster together. Indeed, it has been suggested that the Central European cultivar Hungarian Best occurs in the pedigree of Luizet [10, 20].

The relationship of cultivars obtained with our SSR results are supported by data obtained with AFLP markers by Geuna et al. [13], clustering Hungarian cultivars Budapest, Bergeron, Ananas, Comandor, Selena, Cegledi orias, Cegledo bibor and Magyar kajszi in one group.

The Kecskemet group contains two subclusters, the early and late Kecskemet, separated only by different ripening times (Fig. 2 and Table 1).

Hybrids of the Central Asian cultivar Shalakh appear in subcluster 1.2, together with the Hungarian cultivars. These results indicate that the Hungarian cultivars are to be considered as intermediate link in the apricot distribution from its origin in Central Asia to Europe, which has already been suggested by Faust et al. [10].

Klosterneuburger apricot is a local cultivar from Lower Austria, with suspected Hungarian origin. The discussion as to whether it is identical with Hungarian Best already begun in the last century. The fruit was classified for the first time as Hungarian Best at apricot expositions in Vienna in 1898 and Krems in 1901. However, at the apricot expositions in 1943 in Vienna and Krems, the two cultivars were separated [28]. Our data clearly demonstrate that they are two distinct cultivars.

Vinschger Marille and Annanasnij ciurpinszkij cluster together, indicating that they could have a common genetic background.

Subcluster 1.1 and 1.3 includes the West and East European and most of the North American cultivars. The presence of Harcot, Veecot, Bahrt (Orangered) and Morden-604 in subcluster 1.3 could be explained by the fact that most of the American cultivars carry European germ plasm in their pedigree. The vicinity of Irano-Caucasian accessions including Erevan, Shalakh and Khurmai supports the view that most American cultivars, besides having European germ plasm in their pedigree, have also been enriched with germ plasm of Asian origin. These results are in agreement with the hypothesis that apricot cultivars from China moved to Armenia (Central Asia) and finally were introduced to Europe by the Romans (70–60bc) through Greece and Italy [45]. Apricot probably moved to the USA through English settlers and Spanish missionaries or directly from Asia [10, 16, 30, 35,]. Hagen et al. [16] reported that the North American cultivar Veecot is genetically related to a Turkish cultivar, and Geuna et al. [13] found Veecot with other North American cultivars close to the cultivar Erevan. Our results cluster Veecot along with three other North American cultivars (Bahrt, Orangered and Kuresia), close to West European cultivars, and in the same group with Erevan.

Cluster 2 includes only Asian accessions (seedlings from Pakistan) with a high variability of different alleles. As a rule, cultivated varieties of fruit trees are maintained vegetatively by cutting, rooting of twigs, suckers or by the seed. This is in sharp contrast with their wild relatives, which reproduce from seed. Wild populations maintain themselves through sexual reproduction and, as a rule, are distinctly allogamous. Cross-pollination is brought about by self-incompatibility. Spontaneous populations manifest wide variability and maintain high levels of heterozygosity [49]. In much of Asia, evolution of the genetic basis of apricot germ plasm occurred through natural seedling and may have preserved genetic diversity, while in Europe, clonal production through grafting and vegetative propagation has been practised [16, 47].

According to Fig. 2, the clearly defined Central Asian cultivar Zard is close to the cultivar Zaposdolij, whose geographic origin we do not possess any validated information about. However, our analyses confirm the presence of Asian alleles in the cultivar Zaposdolij.

Species comparison

In comparison with the related species, the common apricots were clustered, indicating a common genetic basis. The most distant from the common apricots is P. brigantiaca (Fig. 1). It has several morphological differences from the common apricot, such as its fruit resembles a golden cherry tomato, plum taste and botanists class it as a little apricot. In addition, Takeda et al. [43] and Hagen et al. [16], using RAPD and AFLP markers, found P. brigantiaca as the most distantly related species of the common apricot cultivars. P. x dasycarpa and Plumcot, hybrids of P. armeniaca x P. cerasifera and P. armeniaca x P. salicinia, respectively, are intermediate between P. brigantiaca and other apricot species, also confirmed by Takeda et al. [43] and Hagen et al. [16].

Variation between eco-geographical groups

Traditional classifications of apricot based on physiological and morphological differences mention four major eco-geographical groups [23]. In this study, three groups were represented: the European group including West and East European and North American cultivars, the Irano-Caucasian group and the Central Asian group. The UPGMA cluster analysis of genetic distance between the groups highlighted the relationship between them. The explanation for the presence of North American group and the West European group in one cluster could be the fact that all the American cultivars carry some European germ plasm. According to literature, some North American cultivars originated from hybridization between European and Asian apricots [2, 23]. It is possible that with our nine selected North American cultivars, we have chosen some cultivars that are derived from European cultivars, which could explain the presence of this group close to the West European cultivars. The presence of the East European group with the Irano-Caucasian group in one subgroup would support the hypothesis that most of the European cultivars have originated by hybridization with genotypes from the Irano-Caucasian group [10, 23].

Molecular markers and breeding programmes

The use of molecular markers for genotyping of the accessions, the classification and management of apricot collections, germ plasm management or breeding purpose can be also tools to potentially promising paternal genotype advantageous in fruit tree species. Cultivars of most fruit tree species are maintained by vegetative propagation, and selection has operated during a limited number of generations [20].

To achieve certain breeding goals in apricot, particularly for wider ecological adaptation, disease resistance and novel fruit quality traits, the use of germ plasm from different groups and eco-geographical regions will be necessary [1, 3, 4, 8, 15].

Results from this study indicate that SSRs are excellent co-dominant markers for pedigree analysis that can be used in plant breeding programmes and to distinguish synonyms and hybrids.

Acknowledgements

Drs. A. Martinelli (CIV, Ferrara, Italy), M. Fliri (South Tyrol) and R. Zelger (Laimburg, South Tyrol) are kindly acknowledged for providing material of CIV breeding lines, seedlings of apricots from Pakistan and Vinschger Marille, respectively. The authors thank the ZAG, BOKU, Vienna, for the opportunity to use the Capillary Sequencer 3100. This work was supported financially by the projects “Pannonia” of the BMBWK and “Charakterisierung transgener Obstbäume und Untersuchungen direkter und indirekter biologischer Wechselwirkungen” of the BMBWK and the BMLFUW.

Copyright information

© Springer-Verlag 2005