Introduction

Iran comprises a land area of 1.64 million km2. It lies in the northern part of the temperate zone, between latitudes 25°03′ to 39°47′N and longitudes 44°14′ to 63°20′E. It is bordered on the north by Armenia, Azerbaijan, Turkmenistan, and the Caspian Sea (the Caucasus mountains, Middle Asian natural regions), on the east by Afghanistan and Pakistan, on the south by the Persian Gulf and the Gulf of Oman, and on the west by Iraq and Turkey (Anatolian and Mesopotamian regions). The existence of high mountains (esoecially the Elborz range) in the north, the Zagros range in the west and southwest, and the eastern mountains which surround the Iranian plateau, provides Iran with rugged mountains and spectacular terrains (Abolghasemi 2011) (Fig. 1). The height of some of the mountains exceeds 5000 m. There are wide plains including low coastal lands (the Caspian Sea, 26 m below sea level) both in the north and south of the country (Firuz 1974). Most of Iran is located in the Palaearctic region considered to be the centre of origin of many crop genetic resources of the world, including many original land races of commercially valuable crop species. The Iranian vascular plant flora comprises approximately 8000 species, with about 20% being endemic, based on the published and forthcoming volumes of Flora Iranica (Rechinger 1963–2001).

Fig. 1
figure 1

The map of Iran with the main mountain ranges, plains, counties and locations bordering neighboring countries

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Prunus spp. (Rosaceae) comprises over 200 species of deciduous and evergreen trees and shrubs with several members that are economically important fruit and nut crops (Chin et al. 2014). The most recent classification of Rosaceae proposed by Potter et al. (2007) grouped Prunus as the only genus in the tribe Amygdaleae within an expanded subfamily Spiraeoideae. The most widely accepted infrageneric classification of Prunus by Rehder (1940) consists of five subgenera: Amygdalus, Prunus, Cerasus, Laurocerasus, and Padus: The subgenus Amygdalus, to which diploid peaches and nectarins (P. persica Batsch) and diploid almonds (P. dulcis (Mill.) D. A. Webb.) belong, and the subgenus Prunus, which includes section Prunophora comprises diploid Japanese plums (P. salicina L.) and hexaploid European plums (P. × domestica L.) and section Armeniaca containing diploid apricots (P. armeniaca L.), and the subgenus Cerasus comprising diploid sweet cherry (P. avium L.) and tetraploid sour cherry (P. cerasus L.). Recently, Shi et al. (2013) divided Prunus L. into three subgenera: Prunus (consist of almond, peaches, apricoat and plums which have been classified into the different sections), Cerasus (including cherries), and Padus.

Iran is amongst the countries in the world widely known to produce tree fruits belonging to the Prunus spp. Major achievements in identification, collection and breeding of fruit crops in the genus Prunus in Iran have been recorded by higher education and research institutes in Iran including the horticultural research stations in Sahand (in the East Azerbaijan province), Shahrood (in Semnan province), Karaj–Kamalshahr (in Alborz province), Mashhad (Khorasn-e Razavi province) and Tehran university (in the department of horticultural sciences). Many members of the genus Prunus are widely cultivated for fruit and as ornamental trees. The fruit is commonly regarded as the stone fruit. In botany, the stone fruit (or drupe) is an indehiscent fruit in which an outer fleshy part (exocarp or skin and mesocarp or flesh) surrounds a shell (the pit, stone) of a hardened endocarp with a seed (kernel) inside (Khoshkhui et al. 2004). However, the almond is different from other stone fruits and is cultivated as a nut crop. The edible portion is the seed while the almond fruit is a drupe and not a true nut.

Almond

Almond, P. dulcis (Mill.) D. A. Webb. [syn. P. amygdalus (L.) Batsch] (Fig. 2) is an economically important nut crop in warm temperate regions. Almond species are deciduous trees (low or tall) or shrubs (with various heights) that grow in semi-arid places, stepps and as a belt along margins of xerophytic forests (e.g. the Quercus forests of the Zagros mountain) (Attar et al. 2009). They also grow on rocky mountains or limestone slopes (Browicz and Zohary 1996) at elevations ranging from ca 500 m above sea level in the southern mountains of Iran in the Bushehr province to 3800 m above sea level on the Taftan mountain in the Sistan–Baluchistan province in southeast Iran (Attar et al. 2009). P. dulcis, the cultivated almond is thought to have originated in the arid mountainous regions of Central Asia (Gradziel et al. 2001). Several species are also found in these mountainous areas, from the Tian Shan Mountains of western China, through Afghanistan, Kurdistan, and Turkestan and into Iran and Iraq (Gradziel 2011). Also, P. fenzliana Fritsch, P. bucharica (Korsh) B. Fedtsch. and P. argentea Lam., from these regions are described as wild species most closely related to almonds and may be the ancestral species of the modern cultivated almond (Gradziel et al. 2001, 2011). The exact origin of almonds has been difficult to ascertain and several hypotheses have been advanced concerning the origin. Evreinoff (1958) first suggested that the cultivated almond originated by hybridization among P. fenzliana Fritsch and probably P. bucharica (Korsh) B. Fedtsch. and P. kuramica (Korsh) Kitam. This theory has been supported by molecular data based on nuclear and chloroplast DNA markers, morphological and habitat studies in Prunus species (Ladizinsky 1999). Simple sequence repeat (SSR) marker analysis (Zeinalabedini et al. 2010) suggested that P. fenzliana Fritsch could be the most plausible progenitor of the cultivated almonds. Furthermore, as the almond moved toward the mediterranean region, new hybridizations might have occurred, especially with the wild mediterranean species, P. webbii (Spach) Vierh. (Socias i Company 1990), resulting in some of the almond populations found along the northern border of the mediterranean sea, from Greece and the Balkans to Spain and Portugal. However, according to Fernández i Martí et al. (2015) there could be a disconnection between almond and the related wild species despite the gene flow from wild relatives into almond. So further research is needed to test the hypothesis on the origin of cultivated almonds thought to have arisen as a result of natural hybridizations of wild species.

Fig. 2
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Flower and fruit of almond [P. dulcis (Mill.) D. A. Webb.]

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Although almond is one of the most important perennial nut crops in the arid and semi-arid regions of Iran, almond production in Iran is based on locally adapted clones, with minimum to no inputs, and managed traditionally (Sorkheh et al. 2009a). Iran with 41, 261 ha of harvestable area and 87, 281 t in production, ranked number 5 in the world in almond production after USA, Australia, Spain and Morocco in 2013 (FAOSTAT 2016). About 72% of almond production (rainfed and irrigated orchards) occurs in Fars, Chaharmahal–Bakhtiari, Khorasan, Isfahan and Kerman provinces (Ministry of Agriculture 2014). In Iran, almond is called “Badam”.

Wild and domesticated genetic resources

Many wild almond species including 20 wild species (Mozaffarian 2005) and six inter-specific hybrids have been reported in Iran (Khatamsaz 1992) indicating that Iran is within the centre of origin of almonds. Most of these species are found in Azarbayjan, Chaharmahal–Bakhtiari, Kerman and Fars provinces (Rahemi 2001). Seventeen (11 wild species and 6 inter-specific hybrids) of these are endemic to Iran including P. glauca (Browicz) A. E. Murray, P. runemarkii Eisenman (Amygdalus reticulata Runem. et Khat.), P. haussknechtii (Bornm.) C. K. Schneid., P. elaeagnifolia Spach, P. wendelboi (Freitag) Eisenman, P. eburnea Spach, P. pabotii (Browicz) Eisenman, P. kurdistanica (Attar, Maroofi et Vafadar) Eisenman, P. orazii (Maroofi, Attar et Vafadar) Eisenman, P. lycioides var. horrida (Spach) C. K. Schneid., P. spinosissima (Bunge) Franch. var. urumiensis Bornm., P. × keredjensis Browicz, P. × iranshahrii (Khat.) Eisenman, P. × mozaffarianii (Khat.) Eisenman, P. × yasujensis (Khat.) Eisenman, P. × podperae (Woron.) Náb., and P. × kamiaranensis (Khat. et Assadi) Eisenman (Table 1) (Khatamsaz 1992; Mozaffarian 2005; Attar et al. 2009; Eisenman 2015).

Table 1 Tree and fruit characteristics and distribution of almond species in Iran.
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Almonds have been cultivated from seeds for centuries in Iran. The existence of a large number of trees grown from seed under various ecological conditions provides an invaluable source for varietal selections. The most important indigenous cultivars include ‘Mamaei’, ‘Rabi’, ‘Sefid’, ‘Monagha’, ‘Sangi’, ‘Dobahre’ and ‘Tajeri’. These are typically early flowering, however, due to late spring frost, the flowers are often destroyed. So, breeding for cold hardiness and late flowering has often been an objective in almond breeding programs.

Evaluation and use of genetic resources

Almond breeding in Iran was started by Chaichi in 1969 at the Sahand Horticulture Research Station in East Azarbayjan province. Following the evaluation of foreign cultivars and locally selected genotypes, a crossing program was initiated to develop late blooming cultivars resulting in the release of three cultivars including ‘Azar’, ‘Shekofeh’ and ‘Harir’ (Chaichi and Eskandari 1999). In addition, ‘Sahand’ was introduced from the selection program including local cultivars (Chaichi 1999). In 2009–2010, new superior genotypes including ‘Eskandari’ and ‘Araz’ at the Sahand research station (Eskandari and Majidazar 2009) and ‘Saba’ and ‘Aidin’ at the Karaj research station were introduced from new cross programs. These cultivars are all late blooming (Table 2). In addition, 4000 progenies from 20 cross combinationss involving self-compatible cultivars and late blooming cultivars have been developed in order to obtain late blooming and self-compatible cultivars with high quality. These crosses have been under evaluation in Karaj, Sahand and Shahrekord research stations (Imani 2015).

Table 2 Phenological and pomological characteristics of indigenous almond cultivars of Iran
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Iran is extremely rich in wild almond species. Sorkheh et al. (2009b) reported that all the species are self-incompatible with bitter or slightly bitter seeds. These wild species provide an enlarged pool of available germplasm which possess desired characteristics including late bloom [P. carduchorum (Bornm.) Meikle, P. elaeagnifolia Spach, P. kotschyi (Boiss. et Hohen.) Meikle, P. glauca Browicz or P. scoparia (Spach) C. K. Schneid.], early maturity [P. spinosissima (Bunge) Franch. var. urumiensis Bornm.], compact growth habit [P. fenzliana Fritsch, P. orientalis (Mill.) Koehne or P. scoparia (Spach) C. K. Schneid.], resistance to drought (wild almond species with very small leaves especially in the Spartioides section including P. scoparia), salinity, adaption to low winter temperatures and reduced insect infestation and fungal attack. However, species in the Spartioides section with hard shells and well-sealed sutures have not been sufficiently exploited (Sorkheh et al. 2009b; Gradziel and Martínez-Gómez 2002; Gharaghani and Eshghi 2015; Baninasab and Rahemi 2007). On the other hand, the germplasm of wild species in Iran is not a useful source for selection of larger nut and kernel size with the possible exception of P. korshinskyi Hand-Mazz. and P. communis L. However, for local production, some of the wild accessions possessed relatively large kernel weight that were similar or exceeded the kernel weights of local commercial cultivars (Sorkheh et al. 2009b).

Using wild almond species as rootstock in Iran date back to about 300 years (Madani et al. 2006). The seedlings of P. scoparia (Spach) C. K. Schneid., growing wild in Iran have been used by growers in very arid conditions for top-working almond cultivars (Gentry 1956). More than 5000 ha of almond cultivars grafted on wild rootstocks have been reported in Fars, Kerman, Boushehr and Hormozgan provinces. Prunus scoparia (Spach) C. K. Schneid., is one of the main species that have been used as a rootstock for almond in non-irrigated conditions (Rahemi and Yadollahi 2006). In addition, P. scoparia (Spach) C. K. Schneid., P. elaeagnifolia Spach, and P. eburnea Spach, naturally distributed in many regions of Iran, have been used in arid and semi-arid areas to control soil erosion and as water sheds (Madam et al. 2011) and their products are used locally. For example, the kernel of P. scoparia (Spach) C. K. Schneid., is used as an edible nut after de-bittering and roasting (Gholami et al. 2010; Gharaghani and Eshghi 2015). In Iranian traditional folk medicine, the kernel oil of P. scoparia has been used to treat cancer (especially of the bladder, breast, mouth, spleen, and uterus), asthma, kidney stone, spasm, bronchitis and heart disease (Gharaghani and Eshghi 2015). Prunus elaeagnifolia Spach, is also used as a rootstock for plum (Gholami et al. 2010).

In recent years, many studies have been conducted to unravel the morphological and molecular diversity of Iranian genotypes, cultivars and wild species of almond. Molecular markers such as amplified fragment length polymorphism (AFLPs) (Sorkheh et al. 2007, 2009a; Zeinalabedini et al. 2014), SSRs (Shiran et al. 2007; Fathi et al. 2008a; Sorkheh et al. 2009a; Zeinalabedini et al. 2010, 2014; Kadkhodaei et al. 2011; Zamani et al. 2009a; Rahemi et al. 2012; Mehdigholi et al. 2013; Rasouli et al. 2014a), and random amplified polymorphic DNAs (RAPDs) (Shiran et al. 2007; Sorkheh et al. 2009a; Nikoumanesh et al. 2011; Rasouli et al. 2012), have been used in addition to cytogenetical analysis (Rasouli et al. 2014b; Yousefzadeh et al. 2010) and morphological analysis (Fathi et al. 2008a; Sorkheh et al. 2009b; Kadkhodaei et al. 2011; Zamani et al. 2009a; Rahemi et al. 2011; Ardjmand et al. 2014). As a whole, the results of these studies demonstrate considerable genetic diversity in the Iranian almond germplasm both at morphological and molecular levels indicating a rich and valuable gene pool for almond rootstock improvement. Also, molecular markers (especially SSR markers) could be successfully used to determine the genetic diversity among Iranian almond landraces/cultivars and to also identify informative markers for improving traits in breeding programs. In addition, based on molecular dendrograms, groupings of different almond cultivars have been identified based on geographic origin and some morphological traits.

Considerable genetic variation exists in nut traits within and between populations of P. scoparia (six populations from different regions of Fars province and one population from the Chaharmahal–Bakhtiari province), P. dulcis, P. eburnea, and P. elaeagnifolia (Rahimi Dvin et al. 2016; Ansari and Gharaghani 2016). They showed that cluster analysis divided wild populations into four sub clusters based on geographic proximity and species. Also, Khadivi-Khub and Anjam (2014) studied morphological characterization (21variables of tree, leaf and fruit traits along with flowering and ripening date) of 150 wild accessions of P. scoparia species from four regions of Iran including Estahban, Arak, Sardasht and Mehalat. They reported that all the characteristics examined showed a high degree of variation although this was pronounced for secondary shoot number, leaf area and shape, growth habit, fruit exocarp color, nut shape, pubescence on fruit, canopy size and trunk diameter (Khadivi-Khub and Anjam 2014). As a whole, the phenotypic variability in Iranian wild P. scoparia species is very high, suggesting an extensive genetic diversity of genetic resources available for use in the almond cultivar and rootstock development programs. The wide adaptation of this species highlights its potential as genetic resource for breeding for resistance to abiotic and biotic stresses such as drought and spring frost.

Cytological studies of four wild almond species including P. elaeagnifolia Spach, P. erioclada Bornm., P. eburnea Spach, and P. scoparia separated them into 2A (P. elaeagnifolia Spach and P. erioclada Bornm.) and 2B (P. eburnea Spach and P. scoparia Spach) karyotypic symmetry classes (Yousefzadeh et al. 2010). Shiran et al. (2007) grouped almond cultivars with accessions of P. dulcis indicating a very close relationship, whereas, P. orientalis and P. scoparia clustered together and separately from the rest of P. dulcis. Zeinalabedini et al. (2010) showed that P. fenzliana had the closest genetic relationship with cultivated almonds, suggesting that P. fenzliana may be the most plausible progenitor of cultivated almonds. Zeinalabedini et al. (2008) and Sorkheh et al. (2009b) suggested that the presence of undesirable fruit and kernel traits such as self-incompatibility, bitter kernel taste and small fruit size limits the use of wild almond species for transferring useful properties into cultivated almonds and concluded that wild Prunus species are less useful in almond cultivar improvement. In contrast, Nikoumanesh et al. (2011) reported that the wild plant materials used in the previous studies above provide valuable sources for rootstock genetic improvement programs in arid and semi-arid regions.

Fertilization is essential for almond commercial production although most almond cultivars are self-incompatible (Socias i Company 1990). Self-incompatibility in almond is gametophytic and controlled by a single S-locus with multiple codominant alleles (Dicenta and Garcia 1993). The identity of S-alleles is important for designing crosses and choosing parents for breeding self-compatible cultivars which are suitable for monoculture orchards with reduced need for honeybee pollinators (Batlle et al. 1997). Many studies have been carried out to identify incompatibility alleles of Iranian almond cultivars and wild species mainly based on polymerase chain reaction (PCR) (Valizadeh and Ershadi 2009; Rahemi et al. 2010; Sheikh-Alian et al. 2010; Mousavi et al. 2011; Momenpour et al. 2011; Zeinalabedini et al. 2012; Hafizi et al. 2013; Rahemi et al. 2013; Mousavi et al. 2014). Results showed that Iranian almond cultivars are valuable sources of new almond self-incompatibility and self-compatibility alleles and good agronomic traits, all of which are of interest in almond breeding and conservation programs. Mousavi et al. (2014) studied the diversity of self-incompatibility alleles in Iranian cultivars and introduced 8 new alleles (S 36–S 43) including ‘Tejari’ (S 36), ‘Holouei’ (S 37), ‘Sefid’ (S 38), ‘Yazd-17’ (S 39 and S 40), ‘Mashhad 40’ (S 41), ‘G-R-16’ (S 42) and ‘Mamaei’ (S 43). They also reported that one of the alleles (S 40) was similar to S 5 which was identified previously in an accession of the wild species, P. webbii (Spach) Vierh. This finding points to the existence of a common ancestor with other Prunus species and also suggests a possible introgression from P. webbii (Spach) Vierh., a primary ancestor in almond evolution. Similarly, Hafizi et al. (2013) identified 6 new S-RNase alleles (S 45–S 50) in local cultivars including ‘Sher badam’ (S 45), ‘Haji badam’ (S 46), ‘Mamaei’ (S 47), ‘Sefied’ (S 48), ‘Shekofeh’ (S 49) and ‘Shahrodi-1’ (S 50). They also showed that some cultivars like ‘Azar’ (S 24 S na), ‘Shekofeh’ (S49S?) and ‘Shahrodi-1’ (S50S?) displaying one non-functional S-RNase would be of interest in almond breeding programs as resources for new almond self-compatibility alleles. Based on the above-mentioned results it appears that the cultivars with new S alleles may be useful as suitable parents in almond breeding programs to ensure the success of controlled crosses.

Initial assessments of tolerance of some native cultivars, genotypes and wild species of almond to abiotic stresses have been conducted under in vitro or in vivo conditions. Further studies undertaken to validate the performance of highly tolerant cultivars identified in previous research showed variations in response to water stress presumably due to the rich genetic resources of wild almonds in Iran. This suggests the possibility of using them in breeding programs. It may appear that P. scoparia Spach (Madam et al. 2011; Gholami et al. 2010), P. eburnea Spach (Zokaee-Khosroshahi et al. 2014), P. arabica (Oliv.) Meikle, P. glauca Browicz and P. scoparia Spach (in the Spartioides section) (Sorkheh et al. 2011a), and the local cultivar ‘Sefid’ (Yadollahi et al. 2011) could be useful under drought conditions. Among the Iranian cultivars, ‘Shekofeh’ (grafted on ‘GF677’, will tolerate salinity of 7.3 ds/m and partly salinity of 9.8 ds/m) (Momenpour et al. 2015), ‘Araz’ and ‘Eskandar’ (Bybordi 2013) have been identified as salinity tolerant at a base concentration of nutritional elements and their ratios. On the other hand, ‘Sahand’ (grafted on ‘GF677’) is believed to be the most sensitive to salinity stress (Momenpour et al. 2015). The effect of temperature (between 5 and 50 °C, at 5 °C intervals) on pollen germination and pollen tube growth of native Iranian almonds species was studied (Sorkheh et al. 2011b) under in vitro conditions to identify differences in the tolerance of pollen to temperature variations. The species in the section Lycioides (P. lycioides (Spach) C. K. Schneid., P. reuteri Boiss. et Buhse) and P. communis L. were the most heat-tolerant species, those in the section Euamygdalus (P. elaeagnifolia Spach, P. orientalis (Mill.) Koehne) were intermediate, while those in the section Spartioidies (P. arabica (Oliv.) Meikle, P. glauca Browicz, P. scoparia Spach) were the most heat-susceptible.

Cherry

In Iran, sweet cherry (P. avium L.), sour cherry (P. cerasus L.) and mahaleb (P. mahaleb L.) (Fig. 3) are called Gilas, Albaloo and mahleb, respectively. Based on the latest available statistics of FAOSTAT (2016), Iran with 200,000 t production and 29, 000 ha of harvestable area is the 3rd largest producer of sweet cherry in the world after Turkey and USA. Also, Iran with 106,972 t production from 12,000 ha of harvestable area ranks 6th in the world in sour cherry production. The major commercial cherry orchards in Iran are in Tehran, Alborz, Khorassan-Reazavi, Isfahan, Ghazvin and West Azerbayjan provinces (Ministry of Agriculture 2014). The two main species, sweet and sour cherries, are reported to have originated from an area between the Black and Caspian seas including Asia Minor, Iran, Iraq, and Syria, from where they spread gradually to other areas due to human and animal migration (Zamani et al. 2012). The mahaleb cherry is native to Mediterranean, Southeast Europe and West Asia, although it is sometimes also found in Central Europe (Buman 1977).

Fig. 3
figure 3

a Flower and fruit of sweet cherry (P. avium L.), and b sour cherry (P. cerasus L.)

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Wild and domesticated genetic resources

Iran represents a significant source of germplasm for different fruit species in the Cerasus subgenus including 13 species of which P. chorassanica (Pojark.) A. E. Murray, P. microcarpa (Boiss.) C. A. Mey. subsp. diffusa (Browicz) Schneid. (Sabeti 1997; Khatamsaz 1992), P. yazdiana Mozaff. (Mozaffarian 2005) and P. paradoxa Dehshiri et Mozaff. (Dehshiri et al. 2012) are endemic to Iran (Table 3). The Most important native cultivars of sweet cherry in Iran are ‘Siah Mashhad’, ‘Tak daneh’, ‘Siah Shabestar’, ‘Zarde Daneshkadeh’, ‘Soraty Lavasan’, ‘Ghermeze Rezaeyeh’, ‘Haj Yousefy’, ‘Pishrase Mashhad’ (early season), ‘Dovomras Mashhad’, ‘Siah Ghazvin’ and two new cultivars, ‘Sefide 90’ and ‘Zarde 90’ (released in 2011). All genetic resources of sweet cherry in Iran are self-incompatible and mid-season excluding ‘Sefide 90’ which is self-compatible and late-season with high production (i.e., 20% more production). ‘Sefid-90’ was released in Karaj research station and has many useful traits including dwarfing, suitability for processing (canned industry, jam, etc.), ease of transportation, waste reduction and resistance to fungal diseases (Seed and plant improvement institute 2016). Also, 14 years of research (from 1998 to 2012) at the Khorasan-e Razavi agricultural and natural resource research center and Karaj horticultural research station resulted in the introduction of a new cultivar ‘Adli’ from the selection program of local germplasm from Khorasan province. ‘Adli’ is very early cultivar (a week earlier than foreign early cultivar ‘Blamarka’) and is resistant to fruit twining and cracking, and has marketable fruit with big size (Khorasan-Razavi Agricultural and Natural Resources Research Center 2016). Wild genotypes and local cultivars are likely gene sources to achieve breeding objectives such as resistance to pests and diseases, suitability for table and processing, extending the market season, and developing new resistant and dwarfing rootstocks. Therefore, it is necessary to characterize and preserve these genotypes and cultivars (Demirsoy and Demirsoy 2004). The first published work on collection of cherry germplasm including 39 indigenous and imported cultivars was by Gohar Khai (1987). This collection was reclaimed at 1998 by adding 70 genotypes and imported cultivars (Abdollahi et al. 2010). Also, Khorasan germplam including 50 genotypes and local cultivars was collected and reclaimed by Ganji Moghadam which resulted in the protection of the mutants of the local cultivar ‘Siah mashhad’ (Ghanji Moghadam 2004). In the case of sour cherry germplam, Bouzari et al. (2009a) collected more than 250 genotypes and 5 important species from 12 provinces in Iran. Today, there are 160 accessions of sweet cherry and 180 accessions of sour cherry at the Kamal-shahr station in Karaj and other affiliated provincial stations (Abdollahi et al. 2010).

Table 3 Tree and fruit characteristics and distribution of cherry species in Iran.
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Evaluation and use of genetic resources

In Iran, sweet cherry is valuable due to its edible fruit (with good taste), short ripening period, and eraly blooming in the spring (Ganji Moghadam et al. 2013). Sour cherry is also cultivated for its sharp taste and juicy fruits, mostly for industrial preserves. Sour cherry is also used as rootstock for sweet cherry. Other types of use for sour cherry specific to Iran include; ‘Albaloo Akhteh’ (a de-pited, semi-dried and salted form of sour cherry which is used in special dishes) and ‘Chay Albaloo’ (sour cherry fruit tea common in Ardebil and other parts of Iran). Sour cherry is also used for cooking, and in making jams and syrups in Iran.

Some species in the Cerasus subgenus are used for landscaping, and also as rootstocks for sweet and sour cherries. In addition, these species are used in breeding programs for developing new commercial cultivars as well as dwarfing and resistant rootstocks (Iezzoni 2008). For example, Mahaleb cherry (P. mahaleb L.) is tolerant to lime-induced iron chlorosis and zinc deficiency and is currently used as sweet cherry rootstock in light and calcareous soils, as well as, in arid climates in Iran (Ganji Moghadam and Khalighi 2007). P. microcarpa (Boiss.) C. A. Mey., P. brachypetala (Boiss.) Walp., P. pseudoprostrata (Pojark.) Rech.f., and P. incana (Pall.) Batsch are shrubs with mostly recumbent habit. P. mahaleb L. and P. cerasus L. have spreading to erect habit and medium-sized trees, while most P. avium L. genotypes have large erect trees. These species may be useful as gene sources for cherry breeding programs (Shahi-Gharahlar et al. 2010). Breeding goals for sweet and sour cherries are dependent on many factors such as environment, biotic factors, and economic conditions, although the main breeding targets are high yield, resistance to diseases, suitability for mechanical harvesting and processing, precocity, tolerance to frost and freeze damage, self-compatible pollination, round pits, firm, large, and good shipping-quality fruit with resistance to cracking and pitting, early to late ripening, reduced double fruiting, dwarfing rootstocks adapted to different soils, and low suckering (Iezzoni 2008; Shahi-Gharahlar et al. 2010; Zamani et al. 2012).

Genetic variation in Iranian Cerasus subgenus species and genotypes has been studied based on molecular markers including RAPDs (Khadivi-Khub et al. 2008; Zamani et al. 2009b; Zamani et al. 2009c; Zamani et al. 2012; Homayouni et al. 2012; Gharooni et al. 2012), SSRs (Najafzadeh et al. 2013a; Khadivi-Khub et al. 2014; Farsad and Esna-Ashari 2016), inter simple sequence repeat (ISSR) (Najafzadeh et al. 2013b), sequence-related amplified polymorphism (SRAP) (Abedian et al. 2012), protein markers (Bouzari et al. 2006) and morphological markers (Ganji-Moghadam et al. 2006; Ganji Moghadam and Khalighi 2006; Khadivi-Khub et al. 2008; Shahi-Gharahlar et al. 2010; Zamani et al. 2012; Homayouni et al. 2012; Gharooni et al. 2012; Ganji Moghadam et al. 2013; Farsad and Esna-Ashari 2016) or pomological characteristics (Ahmadi Moghadam et al. 2012; Najafzadeh et al. 2014). Results showed considerable genetic diversity at both morphological and molecular levels, indicating that there is a pool of valuable plant material for future cherry scion and rootstock breeding programs. Conclusions from ongoing studies suggest that a combination of molecular and morphological data provides the best data for identifying informative markers. Similarly, all molecular marker platforms can be successfully used to dissect genetic diversity among Iranian cherry landraces/cultivars and identify informative markers for the breeding of important traits. Studies have also shown that divergence among accessions occurred via genetic diversity of species and genotypes in the Cerasus subgenus according to genetic base and origins. These divergent genotypes should provide useful resources for breeders interested in improving sweet and sour cherry cultivars and rootstocks for special traits. Moreover, Khadivi-Khub et al. (2008) and Zamani et al. (2009b) showed that RAPD markers can be successfully used to study incompatibility for sweet cherry pollination. Results by Khadivi-Khub et al. (2014) study confirmed that nuclear SSR (nuSSR) marker data can be used for taxonomic purposes in the Prunus (subgenus Cerasus). The authors also reported that Chloroplast SSR (cpSSR) markers clearly differentiated between P. avium and P. cerasus and also confirmed that the chloroplast genome of P. cerasus L. was not derived from P. avium L. This provides support for the assertion that P. avium L. is not the maternal parent of P. cerasus L. The authors also observed some cases of similarity between nuSSR and cpSSR data sets. For example, both subspecies of P. microcarpa (Boiss.) C. A. Mey. showed similarity to P. avium L. In addition, P. brachypetala (Boiss.) Walp., P. incana (Pall.) Batsch, P. pseudoprostrata (Pojark.) Rech.f. and P. yazdiana Mozaff. showed interspecific similarity with each other and were placed in the same cluster. Also, this was true in the case of P. mahaleb L. that was separated from other species based on the two data sets. In contrast, P. avium L. and P. cerasus L. showed high interspecific similarity using nuSSR data but not with cpSSR data (Khadivi-Khub et al. 2014).

Homayouni et al. (2012) studied Iranian sour cherry genotypes from 10 provinces using morphological and molecular markers (RAPD) and reported that sour cherry has more genetic diversity in the north west of Iran (in the west of Azerbayjan province) indicating more genetic distance by moving toward the center of diversity.

Shahi-Gharahlar et al. (2010) evaluated 74 accessions of the Cerasus subgenus in Iran based on vegetative characters and reported that genotypes of P. microcarpa (Boiss.) C. A. Mey., P. pseudoprostrata (Pojark.) Rech.f. and P. brachypetala (Boiss.) Walp., produced shrubs of short stature with recumbent vegetative habits, low leaf area and high pubescence on the leaf upper and lower surface. These species may appear suitable for breeding, especially for developing dwarfing rootstocks with resistance to drought and cold tolerance. Also, cluster analysis (Ward method) based on seven factors classified the genotypes into two main groups (Microcerasus and Eucerasus). Tri-plot analysis using three factors also confirmed the location of genotypes and differentiated the species from each other.

According to vegetative traits, Ganji Moghadam and Khalighi (2007) classified different mahaleb (P. mahaleb L.) genotypes (17 autochthonous populations of mahaleb) into several groups. The authors showed that mahaleb genotypes had a lot of variation in vigor. Also, autochthonous Kurdistan-1 (K-1) and Khorasan-7 (KH-7) populations had the lowest and highest heights, width and crown volume, respectively.

Evaluation of pomological and morphological variation in some selected sour cherry genotypes showed that Iranian sour cherry genotypes were superior in terms of properties such as high vigor, yield, fruit weight, total soluble solids (TSS), high firmness, total acidity (TA), panel test results and redness than foreign cultivars (Najafzadeh et al. 2014).

Self-icompatibility in sweet cherry (P. avium L.) is one of the main challenges in commercial cherry orchards in Iran and many other countries, and plays an important role in yield reduction. Most cherry cultivars need a pollinizer cultivar to encourage pollination (Tehrani and Browns 1992). In addition to self-incompatibility, cherry cultivars also show incompatibility toward each other (cross incompatibility). Therefore, identification of compatible and incompatible groups is of great importance for the establishment of cherry orchards (Roger 1986).

The development of self-compatible cultivars has become a primary goal of many breeders. With a few exceptions, self-compatible genotypes usually guarantee steady and higher yields, as well as ease of adaptation to a wider range of environmental conditions, than self-incompatible genotypes (Stanys et al. 2008). They can also be used as universal pollinators when planted with the latter genotypes (Sansavini and Lugli 2005). With the exception of ‘Sefid-90’, all Iranian sweet cherry cultivars are self-incompatible. Self and cross-(in) compatibility in Iranian cultivars of sweet cherry have traditionally been determined by monitoring the fruit set percentage under field conditions (Arzani et al. 1992; Ganji Moghadam et al. 2009; Rasouli et al. 2010; Ahmadi Moghadam et al. 2012; Imani et al. 2013), and by observation of pollen-tube growth in the pistil using fluorescence microscopy (Asghari, 2003; Mahmoudi et al. 2007; Rasouli and Arzani 2010; Imani et al. 2013). Modern methods of identification of S-alleles in local cultivars of sweet cherry have also been investigated based on Allele-Specific PCR amplification (Hasani Moghadam 2006; Ershadi and Moghadam 2009). Other studies based on RAPD markers have shown that the grouping of some cultivars was correlated with the incompatibility system of pollination of sweet cherry (Khadivi-Khub et al. 2008; Zamani et al. 2009c). The S-genotypes of 25 Iranian and foreign sweet cherry cultivars were studied using classical PCR (Ershadi and Moghadam 2009) and the results showed that only S 3, S 4, and S 14 alleles were detected in Iranian sweet cherry cultivars. S 3S4 was the most frequent cross incompatibility group (CIG) observed in 36% of Iranian sweet cherry cultivars. Moreover, one new CIG was proposed with S 4 S 14 genotype including ‘Sorati hamadan’, ‘Binam’, and ‘Siah gazvin’ cultivars.

Plant tissue culture is an important tool in both basic and applied studies as well as in commercial application. In Iran, the use of in vitro propagation of some cherry and mahaleb dwarf genotypes has been reported (Izadpanah 2001; Amiri 2007; Ganji Moghadam 2011; Daneshvar Hosseini et al. 2011). Amiri (2007) reported micrografting with the homoplastic apex graft (shoot-tip), with apical bud scion length greater than 6 mm having a good potential for mass propagation of disease-free sweet cherry. Also, the findings of Daneshvar Hosseini et al. (2011) showed that mahaleb rootstock can be propagated using an in vitro method. It appears that Murashig and Skoog (MS) media including 6-benzylaminopurine (BAP), indole-3-butyric acid (IBA) growth regulators may be the most suitable for micro propagation.

The diseases that breeders mostly emphasize include brown rot (Monilinia laxa), cilindrosporiosis (Blumeriella jaapii), root-crown rot (Phytophthora spp.), and bacteria canker (Pseudomonas syringae). Twenty-one selected Iranian and seven introduced cultivars of sweet/sour/duke cherries were examined for resistance to bacterial canker (Farhadfar et al. 2016). Under field conditions ‘Siyah-daneshkadeh’ (sweet cherry cultivar) was rated as the most susceptible while ‘Albaloo-meshkinshahr’ (sour cherry cultivar) was collectively rated as the most resistant cultivar. Also, ‘Siyah-mashhad’ and ‘Haj Yousefi’ (sweet cherry cultivars) and the duke cherry cultivar, ‘Albaloogilas-daneshkadeh’, were ranked as intermediate in resistance. In conclusion, cherry cultivars vary in susceptibility to P. syringae pv. syringae, therefore, resistance or susceptibility to bacterial canker should be taken into consideration during orchard establishment/renewal.

Peach

Peach, P. persica (L.) Batsch (Fig. 4) grown throughout the warmer temperate regions of both the Northern and Southern hemispheres is thought to have originated in China, but was later introduced into Persia (Salunkhe and Desai 1984). Peach, which at one time was called “Persian apple”, quickly spread from here to Europe (Lurie and Crisosto 2005). Their seed is enclosed in a hard, stone-like endocarp. Peach and nectarine are called ‘Huloo’ and ‘Shalil’, respectively in Iran. According to the latest available statistics of FAOSTAT (2016), Iran with 514,986 t production from 21,463 ha of harvested area is the 7th largest peach and nectarine producer in the world after China, Italy, Spain, USA, Greece and Turkey. Peach and nectarine are produced in different parts of Iran but Alborz and Mazandaran provinces are the main producers of these valuable fruits (Ministry of agriculture 2014). Peaches are cultivated commercially in Iran with the fruit being consumed fresh, canned, dried and processed into jelly, jam and juices. Double-flowering forms of peaches are cultivated as ornamentals.

Fig. 4
figure 4

Flowers and fruits of a peach (P. persica var. vulgaris Maxim.), and b nectarine (P. persica var. nectarina Maxim.)

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Wild and domesticated genetic resources

Peaches and nectarines are mainly self-fertile and naturally self-pollinating fruit species with very low genetic variability. This species has been cultivated since ancient times in Iran but has changed greatly recently with many forms, including P. persica f. atropurpurea Schneid. (with pink flowers), P. persica f. alba Schneid. (with white flowers), P. persica f. duplex Rehd. (with very dense double and pink flowers), P. persica f. camelliaefolia Dippel. (with very dense double and dark red flowers), P. persica f. albo-plena Schneid. (with double row and white flowers), P. persica f. rubro-plena Schneid. (with double row and red flowers), P. persica f. magnifica Schneid. (with double row and light red flowers), P. persica f. dianthiflora (Vanh.) Dipp. (with almost double row and pink flowers), P. persica f. versicolor (Vanh.) Voss (with almost double row, red or white and streaky flowers), P. persica f. pyramidalis Dippel. (with a thin pyramided vegetative form), P. persica f. pendula Dipp. (with overhanging branches), and P. davidiana (Carr.) Franch. (trees up to 10 m, with glaborous twigs and round yellowish fruits) (Mozaffarian 2005). Three varieties can be recognized taxonomically based on fruit morphology. The common peach (P. persica var. vulgaris Maxim.) has rounded and hairy fruits 5–7 cm in diameter. The nectarines (P. persica var. nectarina Maxim.) have rounded fruits that lack pubescence on the skin, which is controlled by a single locus (Lill et al. 1989). Also, nectarine cells have smaller intercellular spaces than peaches and are, therefore, denser. The flat peach [P. persica var. platycarpa Bailey (syn: P. persica var. compressa Bean.)] has flat fruits and a small pit (Mozaffarian 2005).

On the basis of separation of the stone from the flesh, peaches and nectarines can be divided into two groups: freestone peach (P. persica f. aganopersica (Reichb.) Voss): pit relatively free from the flesh and clingstone peach (P. persica f. scleropersica (Reichb.) Voss): pit adheres to flesh (Mozaffarian 2005).

Today, most cultivated peachs and nectarines in Iran are improved or imported cultivars. Local cultivars also exist. Local famous cultivars include ‘Sorkh-Sefide Mashhad’, ‘Ghermeze Mashhad’, ‘Huloo Sefid-Zard’, ‘Anjiri-e Maleki’ (a flat cultivar) ‘Anjiri-e Tabestaneh’ (a flat cultivar), ‘Haj kazemi’, ‘Makhmali’ and ‘Shalile Shams’ (nectarine) Also, there is a specific type of peach in Iran which is called ‘shaftaloo’ with glaborous fruits that are small in size (fruits are smaller than those of nectarines) and green to cream in color.

Evaluation and use of genetic resources

There are some reports on the evaluation of genetic resources of local peach germplasm in Iran. Studies on peach and nectarine genotypes of East Azerbayjan (at Sahand research station), Ardabil (at Meshkin shahr research station) and Alborz (at Karaj research station) provinces resulted in the collection and identification of some superior genotypes (Fathi et al. 2008b; Imani 2009). Genetic diversity analysis of 123 peach genotypes from Khorasan province based on morphological markers (Raji et al. 2011) based on cluster analysis categorized the genotypes into 4 main groups based on fruit properties including size, flesh and peel color, rate of pubescence and fruit acidity. Fruit acidity, in particular, had a significant impact on genetic diversity.

Chilling injury of vegetative and generative buds, bark and wood during fall and winter seasons are among the main limiting factors for productivity of peaches and nectarines. Selecting and expanding cultivars for more yield and quality without considering frost resistance is practically not possible. Investigations into frost susceptibility of some peach and nectarine cultivars showed that ‘Mashhad Sorkh-sefid’ and ‘Mashhad Ghermez’ cultivars (both native cultivars to Iran), had the most resistant reproductive buds (Aryanpooya et al. 2009; Shojaee et al. 2012). Studies on stigma receptivity in local peach cultivars (‘Makhmali’, ‘Anjiri-e-tabestane’, ‘Anjiri-e maleki’, ‘Haj-kazemi’ and ‘Zoodras’) using fluorescence microscopy for examination of in vitro germination and pollen-tube growth in the pistil, showed that all cultivars are self-compatible and male-fertile (Fakhimrezaei and Hajilou 2013).

Plums

Plum, P. × domestica L. (Fig. 5) is one of the most commercially important fruit species in Iran. Plums are temperate zone fruits, but are widely grown throughout the world, from the cold climate of Siberia to the sub-tropical conditions of the Mediterranean region (Son 2010). Plums represent a diverse group of fruits that include European, Asian, and American species, but the principal economically important plum species are Prunus × domestica L. and P. salicina Lindl. The cultivated European plum, P. × domestica L. is a hexaploid (2 n = 6, x = 42) that probably originated as a hybrid between P. cerasifera Ehrh. (diploid) and P. spinosa L. (tetraploid) (Hummer and Janick 2009). P. × domestica seems to have originated in southern Europe or western Asia around the Caucasus Mountains and the Caspian Sea, but is widespread in the Balkans and in mediterranean countries (Ramming and Cociu 1990). According to the latest available statistics of FAOSTAT (2016), Iran with 305, 262 t of production from 11,702 ha of harvestable area is the 6th largest plum and sloe producer in the world after China, Serbia, Romania, Chile, and Turkey in 2013. In Iran, the major plum and sloe production occurs in Khorasn, Alborz, Fars and Tehran provinces (Ministry of agriculture 2014). In Persian language, plum and sloe are called ‘Aloo’ and ‘Aloocheh’, respectively. Also, in the north of Iran several local names are used for sloe including ‘Shal Holoo’, ‘Khooli’, ‘Hali’, and ‘Nisoogh’. Special types of plums are specific to Iran such as greengage (Goje Sabz), consumed when it is unripe as early season fruit. Different types of prunes (dried plum) are used as special dishes such as Persian prune stew (Khoresh-e Aloo). Also, in Iran, a tart fruit roll (Lavashak-e Aloo torsh) is made with sour plums and served as a favorite dessert especially for kids.

Fig. 5
figure 5

Flowers and fruits of a European plum (P. × domestica L.), and b Japanese plum (P. salicina L.)

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Wild and domesticated genetic resources

P. × domestica L., P. spinosa L., P. divaricata Ledeb., P. cerasifera Ehrh., P. × bilireina Andre., and P. × dasycarpa Ehrh. are the most important species and hybrids in Iran (Table 4). There are two alternative names for cherry plum including P. divaricata Ledeb. and P. cerasifera Ehrh. (Büttner 2001). The latter name is often used for cultivated forms, which are also referred to as myrobalan plums (Wöhrmann et al. 2011). There are about 75 cultivars of plum and prune native to Iran. Native Prunus species exist in diverse climates ranging from sub-arctic regions to dry deserts where they are subjected to high and low temperatures, high and low moisture conditions, and variable soil conditions. The most important local cultivars are ‘Bokhara’, ‘Siah-e Karaj’, ‘Zard-e Arak’, ‘Shamsaei’, ‘Mirzaei’, and ‘Sadie Uremia’ (‘Goje Sadie Uremia’) (Khoshkhui et al. 2004). Also, there are different types of prune (dried plum) in Iran, but ‘Bokhara’, ‘Baraghan’, ‘Shoghani’ and ‘Torghabe’ are the most common ones. The first attempt to revive genetic resources of plum and sloe was begun by researchers including Gohar Khai (1983), Attar (1989), Dabir-Eshrafi and Gohar Khai (1992). This resulted in the establishment of the first collection consisting of 40 genotypes and local cultivars in research stations at Karaj and Khorasan and in 2009 this collection was upgraded to 60 cultivars (Abdollahi et al. 2010).

Table 4 Tree and fruit characteristics and distribution of plum species in Iran (Adapted from Khatamsaz 1992; Mozaffarian, 2005)
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Evaluation and use of genetic resources

The wild cherry plum, P. cerasifera Ehrh. subsp. divaricata (Ledeb.) C. K. Schneid. (P. divaricata Ledeb.) is used as a rootstock for grafting P. × domestica cultivars and certainly has some potential for further domestication, to provide economic and livelihood benefits for subsistence farmers (Wöhrmann et al. 2011). Fruits are mainly collected from the forest. They are edible and used in several local foods (Khoshbakht and Hammer 2006). Individual wild cherry plum trees (P. divaricata Ledeb.) have been semi-cultivated for edible fruits, especially in home gardens along the Caspian coast (Khoshbakht et al. 2007). The fresh fruits are part of the diet of the local people, and are either eaten raw or used to prepare a local tart candy called ‘‘Lavashak’’ (Wöhrmann et al. 2011). Khoshbakht et al. (2007) reported that there are significant variation in pomological characteristics (such as fruit dimensions, fruit mass, flesh mass, nut mass, shell mass and kernel mass) between wild and semi-cultivated populations of this species (P. divaricata Ledeb.) in the southern part of the Caspian Sea. The cultivated form of cherry plum, P. cerasifera Ehrh., is an agriculturally important species, and is distinguished from other plums based on its drought tolerance, high resistance to root-knot nematodes and the suitability as a rootstock (Wöhrmann et al. 2011; Dirlewanger et al. 2004). The blackthorn, P. spinosa, is planted for soil stabilization and also as a hedge row for wind protection. The bitter fruits are used to make jellies, conserves and syrups and for various uses in folk medicine. The flowers are used as a blood cleaner and the leaves have been dried and used as a substitute for tea. Moreover, dyes have been obtained from the fruits, leaves and bark (Khoshbakht and Hammer 2006). While plums are mostly consumed as a fresh or processed fruit, the prune-type plums produce a well-known product called prunes or dried plums. Prunes have long been a healthy product promoting digestive regularity among seniors, although the industry has developed moist types as a snack food (Hummer and Janick 2009). Among local genotypes, ‘Tanasgol’, a natural hybrid between apricot and plum (apricot prune) which is late blooming can be useful in breeding programs as a parent for producing late bloom genotypes (Aran et al. 2011). Moreover, using this ‘Tanasgol’ as an inter stock for ‘Shahroodi’ apricot, ‘Baraghan’ plum and ‘Ghermeze Majlesi’ plum cultivars can result in lower vegetative growth (Mir-Abdolbaghi 2010). In recent years, the genetic diversity of plum and sloe germplasm has been evaluated in Iran based on molecular markers including RAPDs (Aran et al. 2011; Darabifard et al. 2012), SSRs (Etehadpoor et al. 2012a, b; Wöhrmann et al. 2011) and expressed sequence tag-SSR (EST-SSR) (Wöhrmann et al. 2011), morphological characteristics (Khoshbakht et al. 2007; Sedaghathoor et al. 2009; Jalili et al. 2011; Ganji Moghadam et al. 2011; Darabifard et al. 2012).

Wöhrmann et al. (2011) examined genetic variation in wild populations of cherry plum (P. divaricata Ledeb.) sampled along the Iranian coast of the aspian sea (in northern Iran) using genomic SSR and EST-SSR markers developed in peach (P. persica (L.) Batsch) and Japanese plum (P. salicina Lindl.). Their results indicated high levels of genetic diversity and a lack of genetic differentiation of P. divaricata in northern Iran, suggesting that the natural populations of cherry plum in the Caspian forests are close to Hardy–Weinberg equilibrium and have not yet experienced measurable genetic drift. They also reported that the focus for in situ conservation should be on populations with the highest level of genetic diversity, such as the populations from Kashafi, Hashtpar, Asalem and Babol areas. The highly diverse P. divaricata populations could well turn out to be a valuable gene donor to increase variation in cultivated Prunus species by cross-breeding.

A study of genetic variation in 72 plum genotypes using RAPD markers showed relatively high genetic diversity among the genotypes (Aran et al. 2011). Cluster analysis based on the Jaccard’s similarity coefficients and the unweighted pair-group method with arithmetic mean (UPGMA) at a similarity level of 0.58, divided the genotypes into 13 sub-clusters with ‘Tanasgol’ (natural hybrid between apricot and plum) being separated individually from other genotypes at a distance of 0.29. Aran et al. (2011) identified informative markers with the highest regression coefficient (r2) as tree height, growth habit, leaf color and leaf width.

To study the genotypic diversity of prune and plum, 18 quantitative and qualitative characteristics of 38 genotypes were evaluated based on the International Board for Plant Genetic Resources (IBPGR) descriptors (Jalili et al. 2011). Variance analysis showed that most of the characteristics evaluated, were significantly different, in the genotypes indicating high variation. Cluster analysis (Ward method) divided genotypes into four main groups. These groups mainly differed in fruit and stone shape, self-compatibility and stone adherence to the flesh and had an effective role in cluster organizing (Jalili et al. 2011).

An important factor for successful plum cultivation is the knowledge of the cultivar’s degree of self-compatibility. Diploid plum species such as P. salicina Lindl. and P. cerasifera Ehrh. are mostly self-incompatible, while fertility of the hexaploid European plum (P. × domestica L.) cultivars vary between self-compatibility, partial self-compatibility and self-incompatibility (Szabó 2003). There are also some male sterile plum cultivars (e.g. ‘Crvena Ranka’, ‘Tuleu Gras’, and ‘Tuleu Timpuriu’). From production practice and breeding point of view, self-compatible cultivars are of the highest value, because when growing partially self-compatible, self-incompatible and self-sterile cultivars, it is necessary to provide adequate pollinizers (Nikolić and Milatović 2010). In this regard, the S-RNase genotypes of 34 plum genotypes from different areas in Iran, five commercial cultivars and a Mirobolan cultivar (making a total of 40 genotypes) were determined by PCR amplification of the S-RNase gene using degenerate primers (Etehadpoor et al. 2012b). Results suggested that PCR can be a rapid and effective method for identifying S genotypes in local plums. According to the results Sc, 621 bp and Si alleles had the highest frequencies (30, 17.5 and 12.5 percent respectively) while Sc had highest frequency in Iranian plums (17.1%) in Velian of Karaj population.

Apricot

According to the famous Russian Botanist Vavilov, there are three important regions where apricots, Prunus armeniaca L. (Fig. 6) originated, including the Chinese center (China and Tibet), the Central Asian center (from Tien-Shan to Kashmir) and the Near-Eastern (Irano–Caucasian) center (Iran, Caucasus, Turkey) (Yilmaz and Gurcan 2012). The Near-Eastern center could be a secondary gene center because of cultivated varieties and the absence of wild apricot forms according to Bailey and Hough (1975). The cultivars of eco-geographical groups in the Central Asian and Irano–Caucasian centers including Turkey and Iran show the richest phenotypic variability, while the European group including cultivars grown in North America, Australia and South Africa exhibit the least diversity (Halasz et al. 2010). Iran is very important for apricot production and has a long history of apricot cultivation as well as rich apricot germplasm (Raji et al. 2014). In 2013, Iran with 457,308 tonnes of production from 58,726 ha of cropping area is the 2nd largest apricot producer in the world after Turkey (FAOSTAT 2016). Most apricot production in Iran is located in the Semnan, Tehran, Yazd, Kerman and Fars provinces. However, the West Azerbayjan province with 10,461 ha has the largest harvestable area among the provinces in Iran (Ministry of agriculture 2014).

Fig. 6
figure 6

Flowers and fruits of apricot (P. armeniaca L.)

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Apricot has an important place in human nutrition. The fruit of apricot is not only consumed fresh but can also be used to produce dried apricot, frozen apricot, jam, jelly, marmalade, pulp, juice, nectar, extrusion products, etc. Moreover, apricot kernels are used for the production of oils, Benzaldehyde, cosmetics, active carbon, and aroma perfume (Yildiz 1994). Apricot is rich in minerals such as potassium, and vitamins such as β-carotene which is the pioneer substance in minerals necessary for epithelia tissues covering our bodies and organs, eye-health, bone and teeth development and working of endocrine glands (Hacisefrogullari et al. 2006). In Iran, apricot is called ‘Zardaloo’, and dried apricot is known as ‘Gheysii’ among the ordinary people.

Wild and domesticated genetic resources

Iranian apricot germplasm is placed mainly into the Irano–Caucasian group. The secondary gene center of apricot, the Irano–Caucasian group, is generally self-incompatible, but on the contrary, they produce large fruits and bloom earlier than the apricots of Central Asia and require lower chilling hours (Yilmaz and Gurcan 2012).

P. armeniaca L. (apricot): Trees are up to 15 m in height, with spherical canopy, gray–brown bark, glaborous and glossy twigs, The fruit is a drupe, 2.5–5 cm in diameter, from yellow to orange, often tinged red on the side mostly exposed to the sun, glaborous or velvety with very short pubescence. This species is cultivated in many parts of Iran. The Iranian apricot germplasm is quite a genetically rich population. In the past, most apricot trees in Iran have been propagated by seed, so there were numerous cultivars and strains resulting from that (Arzani et al. 2005). The identification and classification of apricot cultivars belonging to this species is complicated due to numerous duplicates and/or synonyms (Nejatian 2003). Probably, several cultivars are indicated by the same name (homonyms), or the same cultivar is known by different names (synonyms) in either the same or different environments (Arzani et al. 2005). Most important local cultivars include ‘Shahroodi’, ‘Jahangiri’, ‘Nasiri’, ‘Noori’, ‘Shekarpareh’, ‘Ziamaleki’, ’Ordobad’, ‘Nakhjavan’, ‘Mirzaei’, ‘Shams’, ‘Tabarzeh’, ‘Ghorban-e-Maragheh’, ‘Gheysii’. ‘Noori-Dirras’ is a cultivar tolerant to late spring frost (Raji et al. 2014).

P. mandshurica Koehne (Manchurian apricot): Small trees up to 5 m in height, with spreading branches, round yellow fruit, 2.5 cm in diameter, small stone with a dull edge, planted in the National Botanical Garden of Iran (Mozaffarian 2005).

P. dasycarpa Ehrh. (Purple apricot or apricot plum): Small deciduous trees up to 6 m high, with purplish, glaborous twigs, with most trees producing no fruit. When they do bear fruit, the fruits are round, 3 cm in diameter, dark purple in color, with a waxy layer and minutely downy. This species arose from a cross between P. armeniaca × P. cerasifera. They are mostly planted in the north of Iran in Tehran province and at the National Botanical Garden of Iran (Mozaffarian 2005). ‘Tanasgol’ leaves are similar to apricot, but its fruit is similar to plum. The fruit taste is tart and is a late blooming cultivar. These characteristics make ‘Tanasgol’ a cultivar of interest as a parent in breeding programs to transfer the late flowering trait. The characteristics of P. × dacycarpa Ehrh., are very similar to ‘Tanasgol’, although more studies are required to understand the relationship between them (Raji et al. 2014).

Evaluation and use of genetic resources

Germplasm collection and characterization is an early essential stage to initiate a breeding program for diversity. In this regard, collection and conservation of 170 accessions of the genetic resources of apricot from Semnan (Shahrood), Khorasan, Tehran, west Azerbayjan, Kurdistan, Ghazvin and other regions is noteworthy (Mostafavi 1991; Mansourfar 1994; Bouzari et al. 2009b; Dejampour 2009; Rahnemoon 2010; Abdollahi et al. 2010).

Different types of marker systems including morphological, molecular, and biochemical have been used for genetic analysis of apricot germplasm. Among the DNA markers, RAPDs (Jannatizadeh et al. 2011 and Mohammadzadeh et al. 2013), flurescent-AFLP (Majidian et al. 2011) and SSRs (Najafi et al. 2012; Raji et al. 2014) are the most frequently used for assessment of genetic variability and relationships among Iranian apricot cultivars. These studies demonstrate that the Iranian apricot germplasm provide a high level of genetic diversity. It appears that the Prunus SSR loci are highly conserved and can be used in apricot-breeding programs to maximize genetic variability which will be useful in generating new cultivars (Raji et al. 2014). According to Majidian et al. (2011), the flurescent-AFLP markers classified apricot genotypes into six groups corresponding to their origin and geographical distribution. In comparison to traditional AFLP markers, the fluorescent-AFLP markers appear more efficient in the understanding of genetic diversity and population structure in apricots and may be useful in other Prunus fruit tree species as well.

Evaluation of Iranian apricot germplasm shows potential for selecting apricot accessions according to their ripening season, fruit size, and TSS/TA ratio (Jannatizadeh et al. 2011; Raji et al. 2014).

Similar to other Prunus species, apricots show gametophytic self-incompatibility controlled by a single locus with multiple genes, S-haplotypes (De Nettancourt 2001). The Irano–Caucasian group is usually self-incompatible whereas, the Europan apricots are mostly self-compatible (Yilmaz and Gurcan 2012). Iranian apricots have been shown to be mainly self-incompatible based on self-pollen tube growth observations under fluorescence microscopy, pollen germination in vitro, pistil and ovary length and diameter, fruit set after self-pollination under field conditions, PCR and sequencing approaches (Nejatian and Arzani 2004; Nejatian and Ebadi 2006; Hajilou et al. 2006a; Nekonam et al. 2011; Gharebeikloo et al. 2013; Molaie et al. 2014). Also, the existence of cross-incompatibility between some Iranian apricot cultivars has been documented by Hajilou et al. (2006a) and Molaie et al. (2014). According to Hajilou et al. (2006a), the cultivars, ‘Ghorban-e-Marageh’ and ‘Ghermez-e-Shahroodi’ were self-compatible and, interestingly, shared a PCR band with all Spanish self-compatible apricot cultivars examined to date. Also, research has shown that the S-genotypes in the progenies from ‘Goldrich’ × ‘Pepito’ cross were detected as ScS1 and ScS2 in 6 and 3 seedlings, respectively. Furthermore, self-compatible progenies were determined when self-compatible cultivars were inter-crossed or with self-incompatible cultivars (Hajilou et al. 2006b).

Despite an increase in production in the 50 years, world production of apricot is actually low due to limited capabilities of adaptation to different environments, limited number of varieties, self-incompatibility, frost damage, and susceptibility to Sharka and Monilinia (Sclerotinia laxa Aderh et. Ruhl.) (Yilmaz and Gurcan 2012). Apricot cultivation in different parts of Iran is still very traditional and in most years, late spring frost (February and March) usually damages flowers and reduce yield. Early flowering and the use of late frost susceptible cultivars in orchards are the most important issues and the main priorities of apricot breeding programs in Iran to develop cultivars resistant to late spring frost. However, no frost resistant cultivar has been released to date due to lack of genotypes exhibiting resistance to late spring frost in the wild apricots and germplasm collections. Although, breeding programs for selecting or producing resistant genotypes are being developed especially, at the Sahand horticultural research station and some other research stations. Razavi et al. (2011) reported that peach and apricot have close chilling requirements, although the heat requirement of apricot cultivars was lower than that of peach cultivars. The lower heat requirement observed in apricot cultivars indicates the risk of growing this cultivar in cold areas, because flowering happens too early than in peach and low temperatures can induce a loss of yield by early spring frosts. Evaluation of super-cooling temperatures in flowers of apricot cultivars ‘Noori-Dirras’ and ‘Nasiri’ showed that the lowest super-cooling temperature was −6.1 °C recorded at the full bloom stage in ʽNori-Dirrasʼ suggesting that this cultivar is tolerant to late spring frost (Jannatizadeh et al. 2014). The results of 21 years of study in order to select spring frost resistant apricot germplasm (evaluating more than 120 genotypes) by Javaherdeh (2009) at the Shahrood research station in Semnan province clustered 110 genotypes into a very susceptible group while only two cultivars ‘Jahangiri’ and ‘Khieba-e-bastam’ were placed in a very resistant group. In addition, ‘Noori-Dirras’ and ‘Noori-Zoodras’, ‘Ghorban-e-Maraghe’ and ‘Stiut-e-Maraghe’ were found in the resistant group.

In 2011, four new cultivars including ‘Ordobad-90’, ‘Nasiri-90’, ‘Maraghe-90’ and ‘Aibatan’ from the Irano–Caucasian group were released from selection programs of local cultivars with superior fruit quality that are suitable for both processing as dried fruit as well as for table fruit consumption at the Sahand research station (Seed and plant improvement institute 2016). In 2014, a very promising dwarf rootstock SJ/M has been released from the Sahand research station which decreased the canopy volume of apricots by up to 50% (East Azerbayjan Research and Education Center for Agriculture and Natural Resources 2016). This rootstock is a cross between native and foreign apricot germplasm.

Conservation of genetic resources of stone fruits in Iran

The survival of most natural habitats for plant genetic resources is being threatened by urbanization, industrialization, road construction, fires, drought, pollution, indiscriminate use of herbicides and pesticides, overgrazing, etc. It behooves germplasm exploration scientists to collect these wild genetic resources for conservation in gene banks. In addition, evaluation, characterization and enlargement of the germplasm diversity represented in ex situ and in situ collections are important to plant breeders for crop improvement and to multiple stakeholders for efficient use and effective management of plant genetic resources. The genetic resources of stone fruits in Iran are mainly conserved in ex situ collections in research stations across the country especially at Sahand, Kamalshahr, Shahrood and Mashhad horticultural research stations. The protected area ‘Mian Jangal’ in Fars province is the only in situ collection in Iran for wild almond species such as P. scoparia, P. erioclada and P. lycioides. The morphological, molecular, biochemical characterization of stone fruit accessions enhance the value and potential utilization of the germplasm, thus making it available at the international level. Introduction of new cultivars either through breeding or selection programs, improved propagation techniques and use of biotechnology are contributing to the replacement of local cultivars and land races by new commercial cultivars.

Conclusion

There is a large diversity of genetic resources of stone fruits including commercial cultivars, landraces and wild species in Iran. This diversity encompasses almost all key morphological and pomological traits, as well as, resistance/tolerance to biotic and abiotic stresses. Some accessions have potential to be utilized directly as new scion or rootstock cultivars, while many could be utilized indirectly through breeding programs as parents to develop new superior cultivars with novel traits. However, the survival of most natural habitats for these genetic resources is being threatened by urbanization, industrialization, road construction, arson and fires, drought, indiscriminate use of agricultural practices, overgrazing, etc. The research centers including those belonging to Iranian Institute for Horticultural Research as well as important public universities have done a lot of research on evaluation, identification, conservation and characterization of the genetic resources of stone fruits. Nonetheless, the approaches need to be modernized to cope with current and future challenges. Besides, comprehensive and efficient in situ conservation programs in natural habitats for the genetic resources, new genetic resources must be explored, exploited and included in existing collections through tissue culture and traditional propagation techniques. The emphasis of collection efforts should be on wild types, especially, in sites that are in danger of deterioration. Although some breeding activities are taking place, these efforts are scattered and need to be harmonized among different sectors including the academia, and the ministry of agriculture and private sectors.