Genetic diversity of Spanish Prunus domestica L. germplasm reveals a complex genetic structure underlying

Fingerprinting of Plum (Prunus domestica) Genotypes in Lithuania Using SSR Markers

This study's aim was to evaluate the genetic diversity of European plum (Prunus domestica) cultivars and hybrids in Lithuania using SSR markers. In total, 107 plum genotypes (including 68 European plum cultivars and 39 hybrids) from the genetic resources collection of the Institute of Horticulture of the Lithuanian Research Centre for Agriculture and Forestry (LRCAF IH) were evaluated using nine microsatellite markers (SSRs) previously published and suggested by the European Cooperative Programme for Plant Genetic Resources (ECPGR). Up to six alleles per locus with each primer pair were generated for some genotypes due to the hexaploidy of plums. The number of alleles in each primer ranged from 18 to 30, with an average of 24.33. The highest number of alleles was generated with the PacA33 primer pair (30). The most informative primer, according to the PIC value, was BPPCT007. Sixty-two unique alleles (representing 39.5% of all polymorphic alleles) have been detected in the plum germplasm developed in Lithuania. According to UPGMA cluster analysis, 58 European plum genotypes were separated into eight groups without any relation to fruit color or shape. By genetic diversity (UPGMA) and structure (Bayesian) analysis, European plum hybrids were grouped into clusters according to their pedigree.

Genetic diversity and structure of Slovenian native germplasm of plum species (P. domestica L., P. cerasifera Ehrh. and P. spinosa L.)

Slovenia has particular climatic, soil, geographic and historical conditions that lead to long tradition of plum cultivation and use. In this work, a set of 11 SSR and three universal cpDNA markers, as well as flow cytometry, were used to (1) evaluate the genetic diversity of 124 accessions of the three Prunus species (P. domestica L., P. cerasifera Ehrh., and P. spinosa L.), (2) investigate the possible involvement of P. cerasifera and P. spinosa species in P. domestica origin, (3) study the genetic relationships and variability among the most typical P. domestica accessions present in Slovenia. Ten haplotypes of cpDNA were identified and clustered into three groups according to the Neighbor-Joining analysis (NJ). All 11 SSR primer pairs were polymorphic, revealing 116 unique genotypes. A total of 328 alleles were detected with an average value of 29.82 alleles per locus, showing relatively high diversity. Bayesian analysis of genetic structure was used to identify two ancestral populations in the analyses of all three species as well as in a separate set consisting of P. domestica material only. Principal Coordinate Analysis (PCoA) showed that accessions clustered largely in agreement with Bayesian analysis. Neighbor-Joining analysis grouped 71 P. domestica accessions into three clusters with many subgroups that exhibited complex arrangement. Most accessions clustered in agreement with traditional pomological groups, such as common prunes, mirabelle plums and greengages. In this study, the analyses revealed within P. domestica pool valuable local landraces, such as traditional prunes or bluish plums, which seem to be highly interesting from a genetic point of view. Moreover, complementary approaches allowed us to distinguish between the three species and to gain insights into the origin of plum. The results will be instrumental in understanding the diversity of Slovenian plum germplasm, improving the conservation process, recovering local genotypes and enriching existing collections of plant genetic resources.

Population Structure and Association Mapping for Agronomical and Biochemical Traits of a Large Spanish Apple Germplasm

A basic knowledge of linkage disequilibrium and population structure is necessary in order to determine the genetic control and identify significant associations with agronomical and phytochemical compounds in apple (Malus × domestica Borkh). In this study, 186 apple accessions (Pop1), representing both Spanish native accessions (94) and non-Spanish cultivars (92) from the EEAD-CSIC apple core collection, were assessed using 23 SSRs markers. Four populations were considered: Pop1, Pop2, Pop3, and Pop4. The initial Pop1 was divided into 150 diploid (Pop2) and 36 triploid accessions (Pop3), while for the inter-chromosomal linkage disequilibrium and the association mapping analysis, 118 phenotype diploid accessions were considered Pop4. Thus, the average number of alleles per locus and observed heterozygosity for the overall sample set (Pop1) were 15.65 and 0.75, respectively. The population structure analysis identified two subpopulations in the diploid accessions (Pop2 and Pop4) and four in the triploids (Pop3). Regarding the Pop4, the population structure with K = 2 subpopulations segregation was in agreement with the UPGMA cluster analysis according to the genetic pairwise distances. Moreover, the accessions seemed to be segregated by their origin (Spanish/non-Spanish) in the clustering analysis. One of the two subpopulations encountered was quite-exclusively formed by non-Spanish accessions (30 out of 33). Furthermore, agronomical and basic fruit quality parameters, antioxidant traits, individual sugars, and organic acids were assessed for the association mapping analysis. A high level of biodiversity was exhibited in the phenotypic characterization of Pop4, and a total of 126 significant associations were found between the 23 SSR markers and the 21 phenotypic traits evaluated. This study also identified many new marker-locus trait associations for the first time, such as in the antioxidant traits or in sugars and organic acids, which may be useful for predictions and for a better understanding of the apple genome.

Genetic Analysis of Prunus salicina L. by Random Amplified Polymorphic DNA (RAPD) and Intersimple Sequence Repeat (ISSR)

Background

Prunus salicina L. is an important fruit tree species of great economic value which is mainly distributed in the northern hemisphere.

Methods

25 samples of Prunus salicina L. were collected from 8 provinces in China, Japan, USA, and New Zealand. The genetic variations of these samples were characterized by the random amplified polymorphic DNA (RAPD) and intersimple sequence repeat (ISSR) technique, respectively, and in combination.

Results

Totally, 257 RAPD bands ranging 200∼2300 bp was found, and 81.59% of these bands were polymorphic. ISSR analysis identified 179 bands ranging 300∼2500 bp, and 87.74% of the bands were polymorphic. ISSR results showed that the similarity coefficient index between samples P10 (Maihuangli in Anhui, Chin) and P13 (Longyuanqiuli in Heilongjiang, China) was lowest, while that between samples P10 (Maihuangli in Anhui, Chin) and P15 (Baili in Japan) was highest. Combined analysis of RAPD and ISSR demonstrated that the similarity coefficient index between samples P4 (Qiepili in Ningbo, Zhejiang, China) and P13 (Longyuanqiuli in Heilongjiang, China) was lowest, while that between samples P19 (Laroda in USA) and P20 (Red heart in USA) was highest.

Conclusion

RAPD combined with ISSR analysis can be used for genetic characterization of Prunus L. species.

Molecular Characterization of Prunus Cultivars from Romania by Microsatellite Markers

In Romania, Prunus species have great economic and social importance. With the introduction of new cultivars arises the need to preserve and characterize the local Prunus germplasm. Thus, a set of 24 polymorphic SSRs were selected for the overall characterization, including 10 peach, 11 apricot and 5 nectarine cultivars. The average number of alleles per locus (Na = 1.958), in addition to overall observed (Ho = 0.299) and expected heterozygosity (He = 0.286) were lower or comparable to those reported in similar studies, probably explained by the smaller number of analyzed cultivars restricted to a smaller geographic area. Among 26 genotypes a total of 101 alleles were identified, of which 46 alleles were in peach, 55 in apricot and 40 in nectarine, respectively. Six alleles from six loci (CPPCT-030, Pchgms-003, Pchgms-004, Pchgms-010, UDP97-401, UDP98-405) were common to all taxonomic groups. The most informative loci were BPPCT-025, Pchgms-021 and UDP96-001 in peach; BPPCT-025, BPPCT-001 and UDP96-001 in nectarine; and BPPCT-002, BPPCT-025, Pchgms-004, Pchgms-020 and Pchgms-021 in apricot. Clustering and genetic similarity analysis indicated that the degree of interspecific divergence in peach and nectarine cultivars was less than that in peach and apricot. These results will be useful to prevent confusion between cultivars, to improve breeding strategies and to benefit the management of Prunus cultivars bred in Romania.

Micropropagation of Plum (Prunus domestica L.) in Bioreactors Using Photomixotrophic and Photoautotrophic Conditions

In this study, we propagated two old Galician plum varieties in liquid medium using a temporary immersion system with RITA© bioreactors. Environmental variables including culture system, light intensity, CO2 enrichment, immersion frequency and sucrose supplementation were evaluated in relation to in vitro proliferation, physiological status and ex vitro performance. Bioreactors were superior to jars for culturing shoots in photomixotrophic conditions, producing up to 2 times more shoot numbers and up to 1.7 times more shoot length (depending on the genotype) using shoot clusters. The number and quality of shoots were positively influenced by the sucrose concentration in the medium, plus by the light and gaseous environment. For individual apical sections the best response occurred with 3% sucrose, 150 µmol m−2 s−1 photosynthetic photon flux density and 2000 ppm CO2, averaging 2.5 shoots per explant, 26 mm shoot length and 240 mm2 leaf area, while with 50 µmol m−2 s−1 light and ambient CO2 (400 ppm) values decreased to 1.2 shoots per explant, 14 mm of shoot length and 160 mm2 of leaf area. Shoots cultured photoautotrophically (without sucrose) were successfully rooted and acclimated despite of showing limited growth, low photosynthetic pigments, carbohydrate, phenolic and antioxidant contents during the multiplication phase.

Unlocking Plum Genetic Potential: Where Are We At?

Plums are a large group of closely related stone fruit species and hybrids of worldwide economic importance and diffusion. This review deals with the main aspects concerning plum agrobiodiversity and its relationship with current and potential contributions offered by breeding in enhancing plum varieties. The most recent breeding achievements are revised according to updated information proceeding from relevant scientific reports and official inventories of plum genetic resources. A special emphasis has been given to the potential sources of genetic traits of interest for breeding programs as well as to the need for efficient and coordinated efforts aimed at efficaciously preserving the rich and underexploited extant plum agrobiodiversity. The specific objective of this review was to: (i) analyze and possibly evaluate the degree of biodiversity existing in the cultivated plum germplasm, (ii) examine the set of traits of prominent agronomic and pomological interest currently targeted by the breeders, and (iii) determine how and to what extent this germplasm was appropriately exploited in breeding programs or could represent concrete prospects for the future.

Chloroplastic and nuclear diversity of endemic Prunus armeniaca L. species in the oasis agroecosystems

Tunisia is characterized by the presence of specific seed-propagated apricot (Prunus armeniaca L.) material which is found in the oasis agroecosystems. In order to highlight the genetic diversity, population structure, and demographic history of this germplasm, 33 apricot accessions collected from six different oasis regions in southwestern Tunisia were genotyped using 24 microsatellite markers. A total number of 111 alleles was detected with an average of 4.62 alleles per locus. Bayesian model-based clustering analysis indicated four subdivisions within the collection sampled that corresponded mainly to the geographic origin of the material. The analysis of the 33 accessions using chloroplast markers allowed the identification of 32 haplotypes. Overall, the present study highlighted the high Tunisian apricot's diversity in the traditional oasis agroecosystems with low genetic differentiation. Understanding the structure of seed-propagated apricot collection is crucial for managing collections in regard to adaptive traits for Arid and Saharan climates as well as for identifying interesting genotypes that can be integrated into international coordinated actions of breeding programs.

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.

Recent Large-Scale Genotyping and Phenotyping of Plant Genetic Resources of Vegetatively Propagated Crops

Several recent national and international projects have focused on large-scale genotyping of plant genetic resources in vegetatively propagated crops like fruit and berries, potatoes and woody ornamentals. The primary goal is usually to identify true-to-type plant material, detect possible synonyms, and investigate genetic diversity and relatedness among accessions. A secondary goal may be to create sustainable databases that can be utilized in research and breeding for several years ahead. Commonly applied DNA markers (like microsatellite DNA and SNPs) and next-generation sequencing each have their pros and cons for these purposes. Methods for large-scale phenotyping have lagged behind, which is unfortunate since many commercially important traits (yield, growth habit, storability, and disease resistance) are difficult to score. Nevertheless, the analysis of gene action and development of robust DNA markers depends on environmentally controlled screening of very large sets of plant material. Although more time-consuming, co-operative projects with broad-scale data collection are likely to produce more reliable results. In this review, we will describe some of the approaches taken in genotyping and/or phenotyping projects concerning a wide variety of vegetatively propagated crops.

Development of novel g-SSR markers in guava (Psidium guajava L.) cv. Allahabad Safeda and their application in genetic diversity, population structure and cross species transferability studies

Dearth of genomic resources particularly, microsatellite markers in nutritionally and commercially important fruit crop, guava necessitate the development of the novel genomic SSR markers through the library enrichment techniques. Three types of 3' -biotinylated oligonucleotide probes [(CT)14, (GT)12, and (AAC)8] were used to develop microsatellite enriched libraries. A total of 153 transformed colonies were screened of which 111 positive colonies were subjected for Sanger sequencing. The clones having more than five motif repeats were selected for primer designing and a total of 38 novel genomic simple sequence repeats could be identified. The g-SSRs had the motif groups ranging from monomer to pentamer out of which dimer group occurred the most (89.47%). Out of 38 g-SSRs markers developed, 26 were found polymorphic, which showed substantial genetic diversity among the guava genotypes including wild species. The average number of alleles per locus, major allele frequency, gene diversity, expected heterozygosity and polymorphic information content of 26 SSRs were 3.46, 0.56, 0.53, 0.29 and 0.46, respectively. The rate of cross-species transferability of the developed g-SSR loci varied from 38.46 to 80.77% among the studied wild Psidium species. Generation of N-J tree based on 26 SSRs grouped the 40 guava genotypes into six clades with two out-groups, the wild guava species showed genetic distinctness from cultivated genotypes. Furthermore, population structure analysis grouped the guava genotypes into three genetic groups, which were partly supported by PCoA and N-J tree. Further, AMOVA and PCoA deciphered high genetic diversity among the present set of guava genotypes including wild species. Thus, the developed novel g-SSRs were found efficient and informative for diversity and population structure analyses of the guava genotypes. These developed novel g-SSR loci would add to the new genomic resource in guava, which may be utilized in genomic-assisted guava breeding.

Analysis of Self-Incompatibility and Genetic Diversity in Diploid and Hexaploid Plum Genotypes

During the last decade, S-genotyping has been extensively investigated in fruit tree crops such as those belonging to the Prunus genus, including plums. In plums, S-allele typing has been largely studied in diploid species but works are scarcer in polyploid species due to the complexity of the polyploid genome. This study was conducted in order to analyze the S-genotypes of 30 diploid P. salicina, 17 of them reported here for the first time, and 29 hexaploid plums (24 of P. domestica and 5 of P. insititia). PCR analysis allowed identifying nine S-alleles in the P. salicina samples allocating the 30 accessions in 16 incompatibility groups, two of them identified here for the first time. In addition, pollen tube growth was studied in self-pollinated flowers of 17 Tunisian P. salicina under the microscope. In 16 samples, including one carrying the Se allele, which has been correlated with self-compatibility, the pollen tubes were arrested in the style. Only in one cultivar ("Bedri"), the pollen tubes reached the base of the style. Twelve S-alleles were identified in the 24 P. domestica and 5 P. insititia accessions, assigning accessions in 16 S-genotypes. S-genotyping results were combined with nine SSR loci to analyze genetic diversity. Results showed a close genetic relationship between P. domestica and P. salicina and between P. domestica and P. insititia corroborating that S-locus genotyping is suitable for molecular fingerprinting in diploid and polyploid Prunus species.

Integration of expert knowledge in the definition of Swiss pear core collection

Core collections (CCs) constitute a key tool for the characterization and management of genetic resources (GR). When the institutions involved in GR preservation decide to define a CC, they frequently prefer to select accessions based not only on strictly objective criteria, but also to add others following expert knowledge considerations (popularity, prestige, role in breeding history, or presence of phenotypic features of interest). The aim of this study was to evaluate the implications of approaches that combine formal analytical procedures and expert knowledge on the efficiency of CC definition through a case study to establish a pear CC from the Swiss National Pear Inventory. The CC had to represent a maximum of the genetic diversity, not to exceed 150 accessions, and required to include a priority set (SPPS) with 86 genotypes selected based on expert knowledge. In total, nine strategies were evaluated, resulting of combining compositions of the dataset sampled, sampling sizes and methods. The CCs sampled by mixed approaches provided similar scores, irrespective of the approach considered, and obtained similar efficiency in optimizing the genetic diversity retained. Therefore, mixed approaches can be an appropriate choice for applications involving genetic conservation in tree germplasm collections.