Self-(in)compatibility genotypes of Moroccan apricots indicate differences and similarities in the crop history of European and North African apricot germplasm

Kodad et al. BMC Plant Biology 2013, 13:196 http://www.biomedcentral.com/1471-2229/13/196 RESEARCH ARTICLE Open Access Self-(in)compatibility genotypes of Moroccan apricots indicate differences and similarities in the crop history of European and North African apricot germplasm Ossama Kodad1*, Attila Hegedűs2, Rafel Socias i Company3 and Júlia Halász2 Abstract Background: Allelic diversity of the S-locus is attributed to the genetic relationships among genotypes and sexual reproduction strategy. In otherwise self-incompatible Prunus species, the emergence of loss-of-function in S-haplotypes has resulted in self-compatibility. This information may allow following major stages of crop history. The genetic diversity in the S-locus of local apricots (Prunus armeniaca L.) from different oasis ecosystems in Morocco and the comparison of the occurrence and frequency of S-alleles with other regions may allow testing the validity of previous theories on the origin and dissemination of North African apricots. Results: The S-genotypes of 55 Moroccan apricot accessions were determined, resulting in 37 self-compatible genotypes, from which 33 were homozygotes for self-compatibility. SC was the most frequent S-allele in this germplasm, followed by S13, S7, S11, S2, S20, S8, and S6. New approaches (CAPS or allele-specific PCR) were designed for a reliable verification of the rare or unexpected alleles. The frequency and distribution of the S-alleles differed among the oases. Some of these alleles, S8, S11, S13 and S20, were formerly detected only in the Irano Caucasian germplasm and are not present in Europe. Conclusions: Our data supports the Irano-Caucasian origin of the Moroccan apricots and their original introduction by Phoenicians and Arabs through the North African shore. North Africa seems to have preserved much higher variability of apricot as compared with Europe. The loss of genetic diversity in apricot might be explained by the occurrence of self-compatibility and the length of time that apricot has spent with this breeding system in an environment without its wild relatives, such as the Moroccan oases or Central Europe. Keywords: Apricot, Crop evolution, Genetic variability, S-alleles, Self-incompatibility Background Apricot (Prunus armeniaca L.) originated in Central Asia and was primarily domesticated in China, with a secondary centre of origin in the Middle East [1]. It is a traditional fruit crop in North Africa and its first introduction in the Maghreb is attributed to the Phoenicians more than 2500 years ago [2] due to the exchange of commercial products between the eastern and western parts of the Mediterranean basin. Evidence of its * Correspondence: 1 Département d’Arboriculture, École Nationale d’Agriculture de Meknès, BP S/40, Meknès, Morocco Full list of author information is available at the end of the article cultivation in the Maghreb can be traced back as far as to the 12th century [3]. Apricot is supposed to have been again introduced in Morocco by the Arabs [4], belonging to a homogenous Maghreb gene pool, since Algerian, Moroccan and Tunisian apricot accessions have close genetic relationships [5]. Moroccan apricot material can be divided into two categories: local genotypes propagated by seed and recently introduced cultivars propagated by grafting, mainly ‘Canino’ and ‘Del Patriarca’. The introduced cultivars are grown according to a semiintensive system, mainly in Central-South Morocco (Marrakech and its surrounding regions), whereas local genotypes are grown in oases and valleys in the South © 2013 Kodad et al.; licensee BioMed Central Ltd. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Kodad et al. BMC Plant Biology 2013, 13:196 http://www.biomedcentral.com/1471-2229/13/196 and Central-East Morocco according to the traditional system, without pruning, training and chemical treatments against pests and diseases [6]. Apricot belongs to the Rosaceae family and shows gametophytic self-incompatibility (GSI), a genetically controlled mechanism enabling styles to reject self-pollen [7]. Self-incompatibility is a mechanism of hermaphrodite plants to prevent self-fertilization and to promote outbreeding by inhibiting pollen tube growth within the third quarter of the style. Self-incompatibility in apricot is controlled by a single locus with multiple variants, called S-haplotypes [7]. The S-haplotype contains a gene encoding for a ribonuclease enzyme in the pistil, S-RNase [8], and an S-haplotype-specific F-box gene in the pollen [9,10]. The molecular basis of GSI is similar in the Solanaceae and Scrophulariaceae [11]. Much progress has been recently made in the identification of the S-genotypes in apricot. Seven S-alleles have been described in North American and Spanish apricot for self-incompatibility, labelled as S1-S7, and one for self-compatibility, identified as SC [12]. These alleles were later confirmed using a PCR approach [13]. Nine new alleles (S8-S16) were found among 27 apricot accessions from Hungary using non-equilibrium pH gradient electrofocusing (NEpHGE) and PCR [14]. Ten new putative alleles (S11-S20) were found among 16 native Chinese apricots with PCR and sequencing [15], although these alleles were not named following Halász et al. [14]. More recently, eight new S-alleles (S23-S30) have been identified and characterized in Chinese apricots using PCR and DNA sequencing [16]. The identification of S-alleles in different apricot cultivars is useful to establish cross-incompatibility groups to avoid pollination problems in the orchard and also to provide useful information for breeders to choose parental genotypes. From this information, 14 cross-incompatibility groups have been established for the North American, European and Turkish apricot cultivars [17-20]. Moreover, the determination of the S-alleles in different Turkish and Hungarian apricot accessions furnished molecular evidence supporting the historical connection between these two apricot germplasm [17]. Consequently, S-genotyping is also useful in the elucidation of crop evolution and propagation history of a given species. Self-incompatibility is a common feature among apricot cultivars of the Central Asian and Irano-Caucasian eco-geographical groups, whereas the European group is traditionally considered to be self-compatible [21]. Central Asian and Chinese apricots have been shown to be self-incompatible using self-pollen tube growth observation under fluorescence microscopy, fruit set after self-pollination under field conditions, PCR and sequencing approaches [15,16,22]. However, the presence of self-compatibility has been confirmed for the Page 2 of 11 apricot cultivars of the European and Irano-Caucasian groups [14,17,18]. Two mutatio (...truncated)