Genome size and ploidy level among wild and cultivated <Emphasis Type="Italic">Prunus</Emphasis> taxa in Slovakia

2C DNA content and ploidy level variation of Prunus spinosa and closely related taxa together with Prunus domestica L. and Prunus insititia L. was studied in Slovakia. The aim of the study was to define genome sizes and find differences between closely related taxa within Prunus spinosa sensu lato mentioned in previous works. According to our results, investigated taxa can be divided into three groups according to ploidy level: Prunus spinosa, Prunus dasyphylla, Prunus ×fruticans, Prunus ×dominii and Prunus ×schurii are tetraploids, Prunus ×fechtneri is pentaploid, and P. domestica and P. insititia are hexaploids. Genome size differences within tetraploid taxa were relatively small (Prunus spinosa: 1.40?±?0.02, P. ×domini: 1.44?±?0.01, P. ×fruticans: 1.48?±?0.02, P. ×schurii: 1.44?±?0.02), but statistically significant. Although further research is needed, it seems that the concept of several taxa as product of hybridization between P. spinosa and cultivated plum species has been supported by our study.     

Simple Sequence Repeat and S-Locus Genotyping to Assist the Genetic Characterization and Breeding of Polyploid Prunus Species,P. spinosa and P. domestica subsp. insititia

Polyploid Prunus spinosa (2n?=?4?×) and P. domestica subsp. insititia (2n?=?6?×) represent enormous genetic potential in Central Europe, which can be exploited in breeding programs. In Hungary, 16 cultivar candidates and a recognized cultivar ‘Zempléni’ were selected from wild-growing populations including ten P. spinosa, four P. domestica subsp. insititia and three P. spinosa?×?P. domestica hybrids (2n?=?5?×) were also created. Genotyping in eleven simple sequence repeat (SSR) loci and the multiallelic S-locus was used to characterize genetic variability and achieve a reliable identification of tested accessions. Nine SSR loci proved to be polymorphic and eight of those were highly informative (PIC values ? 0.7). A total of 129 SSR alleles were identified, which means 14.3 average allele number per locus and all accessions but two clones could be discriminated based on unique SSR fingerprints. A total of 23 S-RNase alleles were identified and the complete and partial S-genotype was determined for 10 and 7 accessions, respectively. The DNA sequence was determined for a total of 17 fragments representing 11 S-RNase alleles. ‘Zempléni’ was confirmed to be self-compatible carrying at least one non-functional S-RNase allele (S_J). Our results indicate that the S-allele pools of wild-growing P. spinosa and P. domestica subsp. insititia are overlapping in Hungary. Phylogenetic and principal component analyses confirmed the high level of diversity and genetic differentiation present within the analysed accessions and indicated putative ancestor–descendant relationships. Our data confirm that S-locus genotyping is suitable for diversity studies in polyploid Prunus species but non-related accessions sharing common S-alleles may distort phylogenetic inferences.

     

Simple Sequence Repeat and <Emphasis Type="Italic">S</Emphasis>-locus Genotyping to Explore Genetic Variability in Polyploid <Emphasis Type="Italic">Prunus spinosa</Emphasis> and <Emphasis Type="Italic">P. insititia</Emphasis>

Polyploid Prunus spinosa (2n = 4×) and P. insititia (2n = 6×) represent enormous genetic potential in Central Europe, which can be exploited in breeding programmes. In Hungary, 17 cultivar candidates were selected from wild-growing populations including 10 P. spinosa, 4 P. insititia and three P. spinosa × P. domestica hybrids (2n = 5×). Their taxonomic classification was based on their phenotypic characteristics. Six simple sequence repeats (SSRs) and the multiallelic S-locus genotyping were used to characterize genetic variability and reliable identification of the tested accessions. A total of 98 SSR alleles were identified, which presents 19.5 average allele number per locus, and each of the 17 genotypes could be discriminated based on unique SSR fingerprints. A total of 23 S-RNase alleles were identified. The complete and partial S-genotype was determined for 8 and 9 accessions, respectively. The identification of a cross-incompatible pair of cultivar candidates and several semi-compatible combinations help maximize fruit set in commercial orchards. Our results indicate that the S-allele pools of wild-growing P. spinosa and P. insititia are overlapping in Hungary. A phylogenetic and principal component analysis confirmed the high level of diversity and genetic differentiation present within the analysed genotypes and helped clarify doubtful taxonomic identities. Our data confirm that S-locus genotyping is suitable for diversity studies in polyploid Prunus species. The analysed accessions represent huge genetic potential that can be exploited in commercial cultivation.     

Characterization of the ribosomal DNA units in two related Prunus species (P. Cerasifera and P. Spinosa)

Summary The genetic relationships between two Prunus species, involved in rootstock breeding, were examined at the level of the ribosomal RNA genes. Twenty clones of P. cerasifera, a diploid species, and 12 clones of P. spinosa, a tetraploid wild species, were studied. The use of three heterologous ribosomal DNA probes covering different regions of the ribosomal tandem repeats enabled us to construct restriction maps for EcoRI and BamHI. We identified two unit types (unit I and unit II) in P. cerasifera. In P. spinosa, P. cerasifera units were present in addition to a third ribosomal unit type (unit III). These results appeared to confirm previous cytological studies (Salesses 1973) indicating that one of the genomes in P.spinosa has homology with the one from P. cerasifera.     

Epidemiological and molecular study on ‘Candidatus Phytoplasma prunorum’ in Austria and Hungary

The epidemiology of ‘Candidatus Phytoplasma prunorum’ was studied in Austria and Hungary from 2014 to 2018. Testing of root samples showed average infections rates of 61 and 40% of the Austrian Prunus spinosa and Prunus domestica spp. insititia samples, respectively. In Hungary, on average 21% of the P. spinosa and 13% of the feral Prunus cerasifera samples were infected. The pathogen was found in 18 out of 19 apricot orchards and PCR positive Cacopsylla pruni were observed at 11 out of 17 sampling locations in both countries. In cage experiments with C. pruni remigrants successful pathogen transmission to Prunus armeniaca, P. domestica and P. spinosa seedlings in budding and foliated developmental stages was recorded, an inoculation access period of 4 hr was sufficient for transmission. A field experiment with ungrafted apricot seedlings planted in 2012 and 2014 indicated a prominent role of the insect vectors for disease spread. In 2017, 40 and 28% of the trees planted in 2012 and 2014, respectively, were infected. Molecular characterisation based on the genes aceF and imp allowed the discrimination between 10 phytoplasma types in apricots. Around 70% of the phytoplasma types in apricots were also common in P. spinosa, in P. domestica spp. insititia and in remigrant C. pruni pointing to a possible pathogen exchange by insects between wild and cultivated Prunus spp. For disease control, vector management over the entire flight period of the remigrants seems necessary; when selecting active compounds, the short inoculation access period of not more than 4 hr should be considered.     

First finds of <Emphasis Type="Italic">Prunus domestica</Emphasis> L. in Italy from the Phoenician and Punic periods (6th–2nd centuries <Emphasis Type="SmallCaps">bc</Emphasis>)

During the archaeological excavations in the Phoenician and Punic settlement of Santa Giusta (Oristano, Sardinia, Italy), dating back to the 6th–2nd centuries bc, several Prunus fruitstones (endocarps) inside amphorae were recovered. The exceptional state of preservation of the waterlogged remains allowed morphometric measurements to be done by image analysis and statistical comparisons made with modern cultivated and wild Prunus samples collected in Sardinia. Digital images of modern and archaeological Prunus fruitstones were acquired with a flatbed scanner and analysed by applying image analysis techniques to measure 26 morphometric features. By applying stepwise linear discriminant analysis, a morphometric comparison was made between the archaeological fruitstones of Prunus and the modern ones collected in Sardinia. These analyses allowed identification of 53 archaeological fruitstones as P. spinosa and 11 as P. domestica. Moreover, the archaeological samples of P. spinosa showed morphometric similarities in 92.5% of the cases with the modern P. spinosa samples currently growing near the Phoenician and Punic site. Likewise, the archaeological fruitstones identified as P. domestica showed similarities with the modern variety of P. domestica called Sanguigna di Bosa which is currently cultivated near the village of Bosa. Currently, these findings represent the first evidence of P. domestica in Italy during the Phoenician and Punic periods.     

Structural analysis of chloroplast DNA in Prunus (Rosaceae): evolution, genetic diversity and unequal mutations

In order to understand the evolutionary aspects of the chloroplast DNA (cpDNA) structures in Rosaceous plants, a physical map of peach (Prunus persica cv. Hakuhou) cpDNA was constructed. Fourteen lambda phage clones which covered the entire sequence of the peach cpDNA were digested by restriction enzymes (SalI, XhoI, BamHI, SacI, and PstI) used singly or in combination. The molecular size of peach cpDNA was estimated to be about 152 kb. The gene order and contents were revealed to be equivalent to those of standard type of angiosperms by the localization of 31 genes on the physical map. Eighteen accessions from 14 Prunus species (P. persica, P. mira, P. davidiana, P. cerasis, P. cerasifera, P. domestica, P. insititia, P. spinosa, P. salicina, P. maritima, P. armeniaca, P. mume, P. tomentosa, P. zippeliana, and P. salicifolia) and one interspecific hybrid were used for the structural analysis of cpDNAs. Seventeen mutations (16 recognition site changes and one length mutation) were found in the cpDNA of these 18 accessions by RFLP analysis allowing a classification into 11 genome types. Although the base substitution rate in the recognition site (100p = 0.72) of cpDNA in Prunus was similar to that of other plants, i.e., Triticum–Aegilops, Brassica, and Pisum, it differed from Pyrus (100p = 0.15) in Rosaceae. Seven mutations including one length mutation were densely located within a region of about 9.1 kb which includes psbA and atpA in the left border of a large single-copy region of Prunus cpDNAs. The length mutation was detected only in P. persica and consisted of a 277 bp deletion which occurred in a spacer region between the trnS and trnG genes within the 9.1 kb region. Additional fragment length mutations (insertion/deletion), which were not detected by RFLP analysis, were revealed by PCR and sequence analyses in P. zippeliana and P. salicifolia. All of these length mutations occurred within the 9.1 kb region between psbA and atpA. This region could be an intra-molecular recombinational hotspot in Prunus species.     

Effect of meta-Topolin on micropropagation and adventitious shoot regeneration in Prunus rootstocks

The effect of meta-Topolin (mT), an aromatic natural cytokinin, on micropropagation and adventitious shoot regeneration was evaluated on Prunus rootstocks, Torinel (Prunus domestica L.) and Ferdor (Prunus insititia  ×  domestica). In vitro shoots were grown for three subcultures on a multiplication medium containing 2.1, 4.2 or 6.3 μM of mT or 2.1 µM N ⁶-benzyladenine (BA). Then, apical leaves were excised and transferred on a medium supplied with BA, thidiazuron (TDZ) or zeatin for adventitious regeneration. Shoots multiplied on 2.1 μM mT or BA, were also induced to root with α-naphthalene acetic acid and acclimatized. meta-Topolin did not improve shoot proliferation, respect to BA, however, positively influences growth and quality of shoots. Ferdor from mT showed higher rooting percentage (92 %), root number and length, respect to the control, while a similar response was observed in Torinel with both cytokinins. Acclimatisation was higher than 90 % for both genotypes and, after 5 months, the highest length of roots was found in plants from mT. Adventitious regeneration was obtained only in leaves from shoots previously grown on mT. The highest regeneration responses, 65 and 42 %, respectively for Ferdor and Torinel, were obtained in the regeneration medium supplied with TDZ.     

Improving micropropagation: effect of Azospirillum brasilense Sp245 on acclimatization of rootstocks of fruit tree

Abstract

The effect of Azospirillum brasilense Sp245 on the micropropagation of three fruit rootstocks: Mr.S 2/5 plum (Prunus cerasifera×P. spinosa), GF 677 hybrid (Prunus persica×P. amigdalus), and MM 106 apple (Northen Spy×M1) was assessed. Rooted shoots were treated with 3×10⁷ of Sp245 cells during transplantation from in vitro cultures to the acclimatization phase. After 60 days, growth parameters were positively affected by Sp245 inoculum. In the case of Mr.S 2/5, an increase in rootstock stem length and node number by 37% and 42%, respectively, compared to the control was noted. In the case of GF 677, the bacterial inoculum increased stem length and node number by up to the 75% and 65%, respectively, compared to the control. The inoculum did not exert on MM 106 for both parameters suggesting that the effects of Sp245 could depend on a specific clone-microbe association. In all cases, however, a higher vigor, consistent with a wider leaf area, was present in the inoculated plantlets demonstrating that the use of Azospirillum can significantly contribute to optimize plant performance during the phase of adaptation of plants to post-vitrum conditions.     

Excised rootstock roots cultured in vitro

Root cultures have been established successfully for the Prunus rootstocks Adafuel and Adarcias (Prunus×amygdalopersica), A843 (P. armeniaca), Mariana 2624 (P. cerasifera×munsoniana) and Myrobalan 605AD (P. cerasifera), and for the apple rootstock Jork 9 (Malus×domestica). High percentages of root tips grew during the first 15 days and then decreased. Root growth was affected by culture conditions and the composition of the culture medium. Liquid medium was preferable as increasing agar concentrations reduced root growth. Darkness, instead of a 16-h photoperiod, was beneficial for Adafuel, but not the other genotypes. Sucrose at 3% was better than higher concentrations. Full Murashige and Skoog salts sustained better root growth than dilutions to 1/2 or 1/4. The addition of various organic supplements such as coconut water, casein hydrolysate or malt extract did not improve root growth, and sucrose was the best carbon source tested. Data presented here support the notion that excised root culture is an efficient experimental model to study the response to various factors, since controlled variations in the culture medium, such as those studied here, had a very noticeable effect on root length. Received: 4 June 1997 / Revision received: 3 February 1998 / Accepted: 1 March 1998     

Genetic relatedness and genetic diversity of ornamental mei (Prunus mume Sieb. et Zucc.) as analysed by AFLP markers

The genetic diversity and genetic relatedness of mei (Prunus mume; 2n = 16) were studied using amplified fragment length polymorphism (AFLP) markers. Eight EcoRI–PstI AFLP primer combinations were applied to 121 distinct genotypes of mei cultivars and related species. A total of 508 AFLP product bands were produced, of which 382 were polymorphic. The unweighted pair group method with arithmetic averages analysis was carried out based on these AFLP markers. From this analysis, “Qugeng Mei,” “Yan Mei,” “Chaodou Mei,” and mei cultivars were seen to share the same P. mume genetic stem. The AFLP data were able to clearly discriminate P. mume from other species in the genus Prunus, with P. armeniaca aligning as its closest related species. Two major groups and nine subgroups of mei flower were identified, and there was a strong coincidence of these AFLP-based groupings with the respective morphological characters of the accessions. The genetic diversity of mei accessions was greatest in the Yunnan Province and decreased toward Eastern China and Japan, so supporting the hypothesis that the southwest of China represents the genetic diversity center of the species.     

The Stamen Patterns of Cultivated Plums

Stamen numbers were counted from flowers of cultivated plumvarieties (P. domestica), seedling clones from crosses betweenvarieties, and six other Prunus species. Varieties have a widerrange of stamen number than the presumed parental species, P.spinosa and P. cerasifera, and extend from 15.3 to 33.0 stamens. Counts on varietal and seedling clones indicate genetical controlof stamen pattern; clones have uniform patterns, but differfrom one another. Annual climatic variations affect stamen number,with varieties reacting differently. There are relationshipsbetween stamen numbers and some economic characters. Stamenpatterns may be helpful as an additional diagnostic characterand for the identification of bud-sports.     

Estimation of genetic diversity in some Iranian wild Prunus subgenus Cerasus accessions using inter-simple sequence repeat (ISSR) markers

As Iran is one of the main origins of Prunus germplasm. In this study, ISSR markers were used for genetic diversity evaluation of 39 accessions of subgenus Cerasus belonging to six species i.e. Prunus avium L., Prunus cerasus L., Prunus mahaleb L., Prunus incana Pall., Prunus microcarpa Boiss., and Prunus brachypetala Boiss.. With 12 ISSR primers, 151 polymorphic bands were detected with polymorphism ratio range of 81.8%–100%. The lowest similarity (0.04) was found between P. avium and P. microcarpa genotypes and the mean of similarity between all genotypes was 0.28. Cluster analysis separated improved cultivars from wild accessions. Improved cherry cultivars and rootstocks were placed closer to the P. avium than the other species. The principal coordinate analysis (PCoA) supported the cluster analysis results. The wild accessions were separated according to their species and collection sites. ISSR markers are useful techniques for genetic diversity evaluation in Prunus subgenus Cerasus.     

Construction of genetic linkage maps and QTL mapping for X-disease resistance in tetraploid chokecherry (Prunus virginiana L.) using SSR and AFLP markers

Chokecherry (Prunus virginiana L.) (2n = 4x = 32) is a unique Prunus species for both genetics and disease resistance research due to its tetraploid nature and known variations in X-disease resistance. X-disease is a destructive disease of stone fruit trees, causing yield loss and poor fruit quality. However, genetic and genomic information on chokecherry is limited. In this study, simple sequence repeat (SSR) and amplified fragment length polymorphism (AFLP) markers were used to construct genetic linkage maps and to identify quantitative trait loci (QTLs) associated with X-disease resistance in chokecherry. A segregating population (101 progenies) was developed by crossing an X-disease-resistant chokecherry line (RC) with a susceptible chokecherry line (SC). A total of 498 DNA markers (257 SSR and 241 AFLP markers) were mapped on the two genetic maps of the two parental lines (RC and SC). The map of RC contains 302 markers assigned to 14 linkage groups covering 2,089 cM of the genome. The map of SC has 259 markers assigned to 16 linkage groups covering 1,562.4 cM of the genome. The average distance between two markers was 6.9 cM for the RC map and 6.0 cM for the SC map. One QTL located on linkage group 15 on the map of SC was found to be associated with X-disease resistance. Genetic linkage maps and the identified QTL linked to X-disease resistance will further facilitate genetic research and breeding of X-disease resistance in chokecherry and other Prunus species.     

Genetic relationships among Pistacia species using AFLP markers

This study addresses the phylogenetic relationship between Pistacia species by amplified fragment length polymorphism (AFLP). The plant materials of this study consisted of a total of 44 accessions belonging to P. vera, P. eurycarpa, P. khinjuk, all subspecies of P. atlantica (atlantica, mutica, kurdica and cabulica), three unknown genotypes and three accessions, proposed to be hybrid from P. eurycarpa × P. atlantica. The accessions were from Iran, Turkey, USA and Syria. Six AFLP primer combinations produced a total of 475 fragments, with average of 79.16 fragments per primer pair, of which, 336 bands were polymorphic. Unweighted pair group method based on arithmetic average (UPGMA) analysis was performed on jaccard’s similarity coefficient matrix and also average similarity of each species. According to the results, two main clusters were developed and P. vera, P. eurycarpa, P. atlantica (subsp. atlantica, kurdica, mutica, cabulica) and the hybrid genotypes located in the first main cluster. P. khinjuk accessions from Iran and USA localized in second main cluster. The hybrid accessions located between eurycarpa and atlantica species and their hybrid nature between these two species were confirmed. One of the unknown accessions clustered with the hybrid ones and the two other were grouped closely with P. Khinjuk. According to this study, the closest species to P. vera was Eurycarpa group, followed by P. atlantica. UPGMA analysis separated P. atlantica subsp. mutica and cabulica from P. atlantica and P. eurycarpa. Subspecies mutica and cabulica were two closest genotypes; hence, P. atlantica subsp. mutica could be classified as a distinct species as P. mutica and the cabulica as a subspecies of P. mutica. This study revealed that P. eurycarpa is synonym for P. atlantica subsp. kurdica and should be considered distinct from P. atlantica; however, P. atlantica showed a closer genetic similarity to P. eurycarpa than the other species.     

Genetic dissection of resistance to root-knot nematodes Meloidogyne spp. in plum, peach, almond, and apricot from various segregating interspecific Prunus progenies

Sources of resistance in Prunus spp. exhibit different spectra to the root-knot nematodes (RKN) Meloidogyne incognita, Meloidogyne javanica and Meloidogyne floridensis. In this Prunus genus, two dominant genes, Ma with a complete spectrum from the heterozygous Myrobalan plums P.2175 and P.2980 (section Euprunus; subgenus Prunophora) and RMia with a more restricted spectrum from the peaches Nemared and Shalil (subgenus Amygdalus), have been identified. This study characterizes the resistance spectra of interspecific crosses involving (1) previous Myrobalan and peach sources, (2) two Alnem almonds (subgenus Amygdalus) resistant to M. javanica, and (3) the apricot A.3923, representing a species considered RKN-resistant (section Armeniaca; Prunophora). For both latter species, genetic data could be obtained through F1 crosses with genetically characterized Myrobalans that conferred their rooting ability for clonal multiplication of the hybrids and permitted their simultaneous evaluation to the three RKN. Crosses involving either Ma or RMia or both generated the expected resistance spectra. Nemared confirmed the species-specific resistance to M. incognita conferred by RMia. This rootstock, also previously considered resistant to M. javanica, was susceptible to the M. javanica isolate used, what illustrates an isolate-specific resistance to this species. Alnem accessions were shown homozygous resistant to M. javanica. In the progeny P.2980 × A.3923, Ma markers allowed to distinguish resistant individuals carrying that gene from resistant individuals lacking it. Distribution of non-Ma individuals in this cross suggested, in the apricot parent, (1) the absence of a major gene allelic to Ma and (2) the presence of a non RKN specific polygenic resistance.     

High-resolution mapping and chromosome landing at the root-knot nematode resistance locus Ma from Myrobalan plum using a large-insert BAC DNA library

The Ma gene for root-knot nematode (RKN) resistance from Myrobalan plum (Prunus cerasifera L.) confers a complete-spectrum and a heat-stable resistance to Meloidogyne spp., conversely to Mi-1 from tomato, which has a more restricted spectrum and a reduced efficiency at high temperature. This gene was identified from a perennial self-incompatible near-wild rootstock species and lies in cosegregation with the SCAR marker SCAFLP2 on the Prunus linkage group 7 in a 2.3 cM interval between the SCAR SCAL19 and SSR pchgms6 markers. We initiated a map-based cloning of Ma and report here the strategy that rapidly led to fine mapping and direct chromosome landing at the locus. Three pairs of bulks, totaling 90 individuals from half-sibling progenies derived from the Ma-heterozygous resistant accession P.2175, were constructed using mapping data, and saturation of the Ma region was performed by bulked segregant analysis (BSA) of 320 AFLP primer pair combinations. The closest three AFLP markers were transformed into codominant SCARs or CAPS designated SCAFLP3, SCAFLP4 and SCAFLP5. By completing the mapping population up to 1,332 offspring from P.2175, Ma and SCAFLP2 were mapped in a 0.8 cM interval between SCAFLP3 and SCAFLP4. A large-insert bacterial artificial chromosome (BAC) DNA library of P.2175, totaling 30,720 clones with a mean insert size of 145 kb and a 14–15× Prunus haploid genome coverage was constructed and used to land on the Ma spanning interval with few BAC clones. As P.2175 is heterozygous for the gene, we constructed the resistant and susceptible physical contigs by PCR screening of the library with codominant markers. Additional microsatellite markers were then designed from BAC subcloning or BAC end sequencing. In the resistant contig, a single 280 kb BAC clone was shown to carry the Ma gene; this BAC contains two flanking markers on each side of the gene as well as two cosegregating markers. These results should allow future cloning of the Ma gene in this perennial species.     

Genomic clues to the parental origin of the wild flowering cherry <Emphasis Type="Italic">Prunus yedoensis</Emphasis> var. <Emphasis Type="Italic">nudiflora</Emphasis> (Rosaceae)

Prunus yedoensis Matsumura is one of the popular ornamental flowering cherry trees native to northeastern Asia, and its wild populations have only been found on Jeju Island, Korea. Previous studies suggested that wild P. yedoensis (P. yedoensis var. nudiflora) is a hybrid species; however, there is no solid evidence on its exact parental origin and genomic organization. In this study, we developed a total of 38 nuclear gene-based DNA markers that can be universally amplifiable in the Prunus species using 586 Prunus Conserved Orthologous Gene Set (Prunus COS). Using the Prunus COS markers, we investigated the genetic structure of wild P. yedoensis populations and evaluated the putative parental species of wild P. yedoensis. Population structure and phylogenetic analysis of 73 wild P. yedoensis accessions and 54 accessions of other Prunus species revealed that the wild P. yedoensis on Jeju Island is a natural homoploid hybrid. Sequence-level comparison of Prunus COS markers between species suggested that wild P. yedoensis might originate from a cross between maternal P. pendula f. ascendens and paternal P. jamasakura. Moreover, approximately 81% of the wild P. yedoensis accessions examined were likely F1 hybrids, whereas the remaining 19% were backcross hybrids resulting from additional asymmetric introgression of parental genotypes. These findings suggest that complex hybridization of the Prunus species on Jeju Island can produce a range of variable hybrid offspring. Overall, this study makes a significant contribution to address issues of the origin, nomenclature, and genetic relationship of ornamental P. yedoensis.     

Phylogenetic relationships of cultivated Prunus species from an analysis of chloroplast DNA variation

Chloroplast DNA (cpDNA) restriction-site mutations in seven cultivated Prunus species were compared to establish the phylogenetic relationships among them. Mutations were detected in 3.2-kb and 2.1-kb amplified regions of variable cpDNA, cut with 21 and 10 restriction endonucleases, respectively, to reveal polymorphisms. Parsimony and cluster analyses were performed. The species pairs P. persica-P. dulcis, P. domestica-P. salicina, and P.cerasus-P. fruticosa were completely monophyletic. All of the species were grouped with conventional subgenus classifications. The subgenus Cerasus was the most diverged. Cerasus ancestors separated from the remainder of Prunus relatively early in the development of the genus. P. persica-P. dulcis, P. domestica-P. salicina and P. armeniaca formed a second monophyletic group. Prunophora species were less diverged than Amygdalus species. The results also suggest that the rate of mutation in Cerasus spp. chloroplast genomes is significantly greater than for the other subgenera sampled.     

Hybridization success is largely limited to homoploid <Emphasis Type="Italic">Prunus</Emphasis> hybrids: a multidisciplinary approach

Prunus fruticosa is a rare shrub occurring in Eurasian thermophilous forest-steppe alliances. The species frequently hybridizes with cultivated Prunus species in Europe (allochthonous tetraploid P. cerasus and partly indigenous diploid P. avium). Propidium iodide flow cytometry, distance-based morphometrics, elliptic Fourier analysis and embryology were employed to evaluate the extent of hybridization in six Slovak populations. Flow cytometric analyses revealed three ploidy levels: diploid (P. avium), triploid (P. × mohacsyana) and tetraploid (P. fruticosa, P. × eminens and P. cerasus). In addition, P. fruticosa and P. cerasus, at the tetraploid level, were found to differ in absolute genome size. An embryological evaluation suggested the existence of a triploid block in P. × mohacsyana and significant potential for hybridization among tetraploid taxa (indicated also by a continuous distribution of genome size data and further mirrored by morphometrics). Although hybrids significantly differ in ploidy level and embryological characteristics, they are almost indistinguishable using morphological characters. Hybridization with P. cerasus thus turns out to be a significant threat to wild populations of P. fruticosa compared to the relatively weak influence of P. avium.