Genetic Structure of a Worldwide Germplasm Collection of Prunus armeniaca L. Reveals Three Major Diffusion Routes for Varieties Coming From the Species' Center of Origin

Multi-environment GWAS uncovers markers associated to biotic stress response and genotype-by-environment interactions in stone fruit trees

While breeding for improved immunity is essential to achieve sustainable fruit production, it also requires to account for genotype-by-environment interactions (G × E), which still represent a major challenge. To tackle this issue, we conducted a comprehensive study to identify genetic markers with main and environment-specific effects on pest and disease response in peach (Prunus persica) and apricot (Prunus armeniaca). Leveraging multienvironment trials (MET), we assessed the genetic architecture of resistance and tolerance to seven major pests and diseases through visual scoring of symptoms in naturally infected core collections, repeated within and between years and sites. We applied a series of genome-wide association models (GWAS) to both maximum of symptom severity and kinetic disease progression. These analyses lead to the identification of environment-shared quantitative trait loci (QTLs), environment-specific QTLs, and interactive QTLs with antagonist or differential effects across environments. We mapped 60 high-confidence QTLs encompassing a total of 87 candidate genes involved in both basal and host-specific responses, mostly consisting of the Leucine-Rich Repeat Containing Receptors (LRR-CRs) gene family. The most promising disease resistance candidate genes were found for peach leaf curl on LG4 and for apricot and peach rust on LG2 and LG4. These findings underscore the critical role of G × E in shaping the phenotypic response to biotic pressure, especially for blossom blight. Last, models including dominance effects revealed 123 specific QTLs, emphasizing the significance of non-additive genetic effects, therefore warranting further investigation. These insights will support the development of marker-assisted selection to improve the immunity of Prunus varieties in diverse environmental conditions.

Efficient Plant Regeneration and Transient Genetic Transformation System of Prunus xueluoensis via an Agrobacterium-Mediated Method

Prunus xueluoensis, a unique Prunus germplasm resource native to China, exhibits significant ornamental value due to its short juvenile phase, early flowering period, abundant flowers, and elegant tree form. However, the lack of an efficient regeneration and genetic transformation system has hindered its genetic improvement and wider application. In this study, we focused on optimizing the tissue culture conditions for P. xueluoensis and establishing an Agrobacterium-mediated transient genetic transformation system. We first determined the optimal medium compositions for different stages of tissue culture, including seed germination, callus induction, adventitious bud differentiation, and rooting. For seed germination, the optimal medium was MS supplemented with 200 mg/L GA3 and 4 mg/L 6-BA. For callus induction, the best medium was MS containing 2.00 mg/L 6-BA, 1.00 mg/L NAA, and 200 mg/L VC. Adventitious bud differentiation was favored on MS medium with 1.00 mg/L 6-BA, 0.10 mg/L NAA, and 200 mg/L VC, while rooting was optimal on 3/4 MS medium supplemented with 0.50 mg/L NAA. Subsequently, we established an Agrobacterium-mediated transient genetic transformation system using stem segments of P. xueluoensis as explants. Through orthogonal experiments, we identified the optimal conditions for genetic transformation as pre-cultivation for 2 days, an Agrobacterium concentration of OD600 = 0.6, an infection time of 30 min, and co-cultivation for 3 days. Under these conditions, the transient genetic transformation efficiency reached 10.42%, as confirmed by PCR and GFP fluorescence detection. This study provides a reliable transient genetic transformation system for P. xueluoensis, facilitating further functional gene analysis and genetic improvement of this valuable ornamental species.

Structural analyses of apricot pectin polysaccharides

Apricot pectin polysaccharides' fine structure was performed using HPSEC, HPAEC-PAD, GC-MS, NMR and FTIR spectroscopies. Purified pectin fraction (F1AP) was composed of D-galacturonic acid, L-rhamnose, D-arabinose and D-galactose, Mw ∼ 1588 kDa. F1AP was eluted by water and with 0.2 M NaCl from DEAE Sepharose fraction resulting in two distinct fractions, F1AP1 and F1AP6, with different structures, molecular weights, and conformations, providing insights into their structural diversity. F1AP1 neutral properties were related to its association with protein. F1AP1 had a backbone of (1 → 4)-linked-D-galacturonic acid and (1 → 2)-linked-L-rhamnopyranosyl residues branched with arabinogalactan including multiple glycosidic linkages of T-α-Araf, 3-α-Araf, 5-α-Araf, T-α-Arap, 2-α-Arap, t-Galp, 2-Galp, 3-Galp, 4-Galp, 6-Galp, 2,4-Galp, 3,4-Galp, 3,6-Galp and 4,6-Galp side chains, having methyl and acetylated groups, and a high molecular weight (1945 kDa). The Mark-Houwink exponent was 0.276, indicating a compact spherical conformation. While the other F1AP6 fraction consists predominately of less methylated HG regions of pectin polysaccharides. The molar mass of this fraction was 117.5 kDa, which adopted a stiffer and random coil conformation. This knowledge allows us to evaluate how the balance of chemical structure and physical properties of the two pectin domains may manifest itself in the isolated structure of apricot pectin and its applications.

Genetic analyses and dispersal patterns unveil the Amazonian origin of guava domestication

Guava (Psidium guajava L.) is a semi-domesticated fruit tree of moderate importance in the Neotropics, utilized for millennia due to its nutritional and medicinal benefits, but its origin of domestication remains unknown. In this study, we examine genetic diversity and population structure in 215 plants from 11 countries in Mesoamerica, the Andes, and Amazonia using 25 nuclear microsatellite loci to propose an origin of domestication. Genetic analyses reveal one gene pool in Mesoamerica (Mexico) and four in South America (Brazilian Amazonia, Peruvian Amazonia and Andes, and Colombia), indicating greater differentiation among localities, possibly due to isolation between guava populations, particularly in the Amazonian and Andean regions. Moreover, Mesoamerican populations show high genetic diversity, with moderate genetic structure due to gene flow from northern South American populations. Dispersal scenarios suggest that Brazilian Amazonia is the probable origin of guava domestication, spreading from there to the Peruvian Andes, northern South America, Central America, and Mexico. These findings present the first evidence of guava domestication in the Americas, contributing to a deeper understanding of its evolutionary history.

Sequencing and Phylogenetic Analysis of the Chloroplast Genome of Three Apricot Species

The production and quality of apricots in China is currently limited by the availability of germplasm resource characterizations, including identification at the species and cultivar level. To help address this issue, the complete chloroplast genomes of Prunus armeniaca L., P. sibirica L. and kernel consumption apricot were sequenced, characterized, and phylogenetically analyzed. The three chloroplast (cp) genomes ranged from 157,951 to 158,224 bp, and 131 genes were identified, including 86 protein-coding genes, 37 rRNAs, and 8 tRNAs. The GC content ranged from 36.70% to 36.75%. Of the 170 repetitive sequences detected, 42 were shared by all three species, and 53-57 simple sequence repeats were detected with AT base preferences. Comparative genomic analysis revealed high similarity in overall structure and gene content as well as seven variation hotspot regions, including psbA-trnK-UUU, rpoC1-rpoB, rpl32-trnL-UAG, trnK-rps16, ndhG-ndhI, ccsA-ndhD, and ndhF-trnL. Phylogenetic analysis showed that the three apricot species clustered into one group, and the genetic relationship between P. armeniaca and kernel consumption apricot was the closest. The results of this study provide a theoretical basis for further research on the genetic diversity of apricots and the development and utilization of molecular markers for the genetic engineering and breeding of apricots.

Genetic diversity and conservation of Siberian apricot (Prunus sibirica L.) based on microsatellite markers

Siberian apricot (Prunus sibirica L.) is a woody tree species of ecological, economic, and social importance. To evaluate the genetic diversity, differentiation, and structure of P. sibirica, we analyzed 176 individuals from 10 natural populations using 14 microsatellite markers. These markers generated 194 alleles in total. The mean number of alleles (13.8571) was higher than the mean number of effective alleles (6.4822). The average expected heterozygosity (0.8292) was higher than the average observed heterozygosity (0.3178). Shannon information index and polymorphism information content were separately 2.0610 and 0.8093, demonstrating the rich genetic diversity of P. sibirica. Analysis of molecular variance revealed that 85% of the genetic variation occurred within populations, with only 15% among them. The genetic differentiation coefficient and gene flow were separately 0.151 and 1.401, indicating a high degree of genetic differentiation. Clustering results showed that a genetic distance coefficient of 0.6 divided the 10 natural populations into two subgroups (subgroups A and B). STRUCTURE and principal coordinate analysis divided the 176 individuals into two subgroups (clusters 1 and 2). Mantel tests revealed that genetic distance was correlated with geographical distance and elevation differences. These findings can contribute to the effective conservation and management of P. sibirica resources.

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.

Biodiversity Evaluation and Preservation of Italian Stone Fruit Germplasm (Peach and Apricot) in Southern Italy

The Prunus genus encompasses a group of economically important and closely related crops, sharing an essentially common genome and, thereby, a high level of conserved and transferable microsatellite (SSR) loci. In Southern Italy, many of the local and/or neglected varieties are abandoned and at risk of extinction due to the high degree of urbanization and agricultural intensification, despite their value as genetic resources for crop improvement. This research aimed to genetically and morphologically characterize the traditional apricot (P. armenica) and peach (P. persica) germplasms collected in old family orchards. Most of the official descriptor categories were scored, thus revealing a rather high level of phenotypic variation in both collections. Genetic data allowed the discovery of diversity masked by morphological traits. Genotyping in 15 and 18 SSRs, eight of which were transferable across both species, showed an average polymorphic informativeness (PIC) of 0.44 and 0.59 for apricot and peach, respectively, and a total of 70 and 144 alleles. A reliable identification of each genotype was achieved, and the presence of possible mislabeling and/or erroneous denominations was solved. These results are encouraging for the valorization of the still poorly explored Italian Prunus germplasm, with significant economic consequences for bioresource conservation and management.

Genetic diversity analysis of apricots from Dagestan using SSR markers

Background. This publication presents the results of a study into the genetic structure of apricot genotypes from Dagestan using the SSR genotyping technique. The importance of the study is seen in the still underexplored gene pool of Dagestani apricot at the genetic level. With this in view, an assessment of the Dagestani apricot genetic diversity, followed by an analysis of its genetic structure, is of theoretical and practical interest.

Materials and methods. The study included 27 apricot genotypes of Dagestani origin: 9 advanced contemporary cultivars and hybrids, 15 seed selections and landraces, and 3 wild forms. Eight SSR markers were used for the genetic diversity analysis: H1-3, A1-91, H2-79, H1-26-2, H2-16, A1-17, RPPG1-032, and RPPG3-026.

Results. The UPGMA and NJ dendrogram construction techniques revealed the genetic similarity among the Dagestani apricots, confirmed by a low level of cluster significance. The tendency towards setting apart the genotypes of hybrid origin (obtained from free pollination of introduced cultivars) from the locally selected cultivars was observed by comparing the results of Bayesian analysis and the K-means approach using the Structure and Statistica software. Such isolation is partial, being obviously affected by constant integration of new apricot genotypes into the local gene pool and its enrichment with new alleles at the genetic level.

Conclusion. The contemporary assortment of apricots in Dagestan was formed on the basis of both the local autochthonous gene pool and Central Asian and European cultivars introduced into this area. The obtained data will enrich the knowledge about the genetic diversity of apricots in Dagestan and serve as the platform for further studies into the florigenetic links of the North Caucasus with other regions. 

Properties of Biochar Derived from Tea Waste as an Alternative Fuel and Its Effect on Phytotoxicity of Seed Germination for Soil Applications

Tea waste as a potential biofuel and bio fertilizer was analyzed. Samples were collected from various tea species and torrefied to five different temperatures. All samples were analyzed for their proximal composition and calorific value. From the results, stoichiometric properties were calculated. A phytotoxicity test was performed, and the germination index was measured. Tea waste torrefied at 350 °C may be suitable biofuel reaching the calorific value of 25-27 MJ kg^-1, but with quite a high share of ash, up to 10%, which makes its use technically challenging and may lead to operating issues in a combustion chamber. The same biochar may be a suitable fertilizer for increasing the germination index, therefore, applicable to the soil. The non-torrefied sample and the sample treated at 250 °C are not suitable as fertilizers for being toxic. The total phenolic content in waste black tea was reduced from 41.26 to 0.21 mg g^-1, depending on the torrefaction temperature. The total flavonoid content was also reduced from 60.49 to 0.5 mg g^-1. The total antioxidant activity in the non-torrefied sample was 144 mg g^-1, and after torrefaction at 550 °C, it was 0.82 mg g^-1. The results showed that black tea waste residues have the potential for further use, for example, in agriculture as a soil amendment or as a potential biofuel.

Breeding and genetics of disease resistance in temperate fruit trees: challenges and new opportunities

Climate change, large monocultures of disease-susceptible cultivars, overuse of pesticides, and the emergence of new pathogens or pathogenic strains causing economic losses are all major threats to our environment, health, food, and nutritional supply. Temperate tree fruit crops belonging to the Rosaceae family are the most economically important and widely grown fruit crops. These long-lived crops are under attack from many different pathogens, incurring major economic losses. Multiple chemical sprays to control various diseases annually is a common practice, resulting in significant input costs, as well as environmental and health concerns. Breeding for disease resistance has been undertaken primarily in pome fruit crops (apples and pears) for a few fungal and bacterial diseases, and to a lesser extent in some stone fruit crops. These breeding efforts have taken multiple decades due to the biological constraints and complex genetics of these tree fruit crops. Over the past couple of decades, major advances have been made in genetic and physical mapping, genomics, biotechnology, genome sequencing, and phenomics, along with accumulation of large germplasm collections in repositories. These valuable resources offer opportunities to make significant advances in greatly reducing the time needed to either develop new cultivars or modify existing economic cultivars for enhanced resistance to multiple diseases. This review will cover current knowledge, challenges, and opportunities in breeding for disease resistance in temperate tree fruit crops.

Genetic dissection of fruit maturity date in apricot (P. armeniaca L.) through a Single Primer Enrichment Technology (SPET) approach

Background

Single primer enrichment technology (SPET) is an emerging and increasingly popular solution for high-throughput targeted genotyping in plants. Although SPET requires a priori identification of polymorphisms for probe design, this technology has potentially higher reproducibility and transferability compared to other reduced representation sequencing (RRS) approaches, also enabling the discovery of closely linked polymorphisms surrounding the target one.

Results

The potential for SPET application in fruit trees was evaluated by developing a 25K target SNPs assay to genotype a panel of apricot accessions and progenies. A total of 32,492 polymorphic sites were genotyped in 128 accessions (including 8,188 accessory non-target SNPs) with extremely low levels of missing data and a significant correlation of allelic frequencies compared to whole-genome sequencing data used for array design. Assay performance was further validated by estimating genotyping errors in two biparental progenies, resulting in an overall 1.8% rate. SPET genotyping data were used to infer population structure and to dissect the architecture of fruit maturity date (MD), a quantitative reproductive phenological trait of great agronomical interest in apricot species. Depending on the year, GWAS revealed loci associated to MD on several chromosomes. The QTLs on chromosomes 1 and 4 (the latter explaining most of the phenotypic variability in the panel) were the most consistent over years and were further confirmed by linkage mapping in two segregating progenies.

Conclusions

Besides the utility for marker assisted selection and for paving the way to in-depth studies to clarify the molecular bases of MD trait variation in apricot, the results provide an overview of the performance and reliability of SPET for fruit tree genetics.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08901-1.

Self-Incompatibility in Apricot: Identifying Pollination Requirements to Optimize Fruit Production

In recent years, an important renewal of apricot cultivars is taking place worldwide, with the introduction of many new releases. Self-incompatible genotypes tolerant to the sharka disease caused by the plum pox virus (PPV), which can severely reduce fruit production and quality, are being used as parents in most breeding programs. As a result, the self-incompatibility trait present in most of those accessions can be transmitted to the offspring, leading to the release of new self-incompatible cultivars. This situation can considerably affect apricot management, since pollination requirements were traditionally not considered in this crop and information is lacking for many cultivars. Thus, the objective of this work was to determine the pollination requirements of a group of new apricot cultivars by molecular identification of the S-alleles through PCR amplification of RNase and SFB regions with different primer combinations. The S-genotype of 66 apricot cultivars is reported, 41 for the first time. Forty-nine cultivars were considered self-compatible and 12 self-incompatible, which were allocated in their corresponding incompatibility groups. Additionally, the available information was reviewed and added to the new results obtained, resulting in a compilation of the pollination requirements of 235 apricot cultivars. This information will allow an efficient selection of parents in apricot breeding programs, the proper design of new orchards, and the identification and solution of production problems associated with a lack of fruit set in established orchards. The diversity at the S-locus observed in the cultivars developed in breeding programs indicates a possible genetic bottleneck due to the use of a reduced number of parents.

Home gardens of Central Asia: Reservoirs of diversity of fruit and nut tree species

Central Asia is an important center of origin for many globally valued fruit and nut tree species. Forest degradation and deforestation are cause for concern for the conservation of these valuable species, now confined to small remnant populations. Home gardens have the important function of sustaining household food consumption and income generation, and can potentially play a critical role in conserving diversity of fruit and nut trees. These systems have been very poorly documented in the scientific literature. This study contributes to filling this gap by describing the diversity of fruit and nut trees in home gardens of Kyrgyzstan, Uzbekistan, and Tajikistan, examining their dynamic flow of planting material and its sources, understanding their future prospects, and looking at significant differences between the three countries. Home gardens show a similar portfolio of the most abundant tree species (apple, apricot, walnut, pear, and plum). Although the diversity of tree species and varieties recorded is significant, small population sizes can limit future possibilities for this diversity to thrive, given the pressure on natural stands and on habitats where the preferred species are found. Furthermore, the selection of species and varieties to be planted in home gardens is increasingly influenced by market opportunities and availability of exotic material. Some of the most abundant tree species recorded are represented largely by exotic varieties (apple, pear), while others (e.g., apricot, walnut, plum) are still mainly characterized by traditional local varieties that are not formally registered. Home gardens continue to play a critical role in rural livelihoods and in national economies, and many rural inhabitants still aspire to maintain them. Thus, home gardens should be integrated in national research and extension systems and closely linked to national conservation efforts. Changes and possible declines in the diversity they host, their health status, and resilience should be carefully monitored.

Genetic diversity of Prunus armeniaca L. var. ansu Maxim. germplasm revealed by simple sequence repeat (SSR) markers

The genetic diversity and genetic structure of P. armeniaca var. ansu were analyzed based on SSR markers. The aim was to provide scientific basis for conservation, efficient utilization, molecular marker assisted breeding and improved variety selection of P. armeniaca var. ansu germplasm resources. The results showed that the level of genetic diversity within the population was high. Among the 30 SSR markers, the mean number of observed alleles was 11.433, the mean number of effective alleles was 4.433, the mean of Shannon information index was 1.670, and the mean of polymorphic information content was 0.670. Among the eight provenances, Tuanjie Township, Xinyuan County, Xinjiang had the highest genetic diversity. The observed alleles, effective alleles, Shannon information index and Nei’s gene diversity index among provenances were higher than those within provenances. Based on Bayesian mathematical modeling and UPGMA cluster analysis, 86 P. armeniaca var. ansu accessions were divided into three subpopulations and four groups, which reflected individual differences in provenances. Subpopulations classified by Bayesian mathematical modeling and groups classified by UPGMA cluster analysis were significantly correlated with geographical provenance (Sig<0.01) and the provenances significantly impacted classification of groups. The provenances played an important role in classification of groups. The genetic distance between Tuanjie Township of Xinyuan County and Alemale Township of Xinyuan County was the smallest, while the genetic relationship between them was the closest and the degree of genetic differentiation was small.

Simple Sequence Repeat (SSR)-Based Genetic Diversity in Interspecific Plumcot-Type (Prunus salicina × Prunus armeniaca) Hybrids

The main objective of many fruit-breeding programs around the world is the release of new cultivars from interspecific hybridizations between species of the Prunus genus. Plum × apricot (Prunus salicina Lindl. × Prunus armeniaca L.) are the most widespread interspecific hybrids, which include plumcots, pluots, and apriums. In this work, 115 accessions of interspecific hybrids from different origins and 27 reference genotypes of apricot and other diploid plum species were analyzed using eight simple sequence repeat (SSR) markers to assess the population structure and current genetic diversity. A total of 149 alleles were obtained, with an average of 19 alleles per locus. The overall polymorphic information content (PIC) mean value of SSR markers was 0.81, indicating a high degree of polymorphism of the SSR. The genetic analysis revealed 141 unique genotypes and two synonyms. The unweighted pair group method with arithmetic averages (UPGMA) dendrogram and the population structure with five groups inferred through the discriminant analysis of principal components (DAPC) revealed a clear genetic differentiation between apricot genotypes and the rest of the accessions since the interspecific hybrids clustered with the Japanese plum genotypes. Repeated backcrosses between interspecific hybrids with plum genotypes could be the cause of the higher genetic proximity of the hybrids with respect to plum than with apricot genotypes. This corresponds to the fruit morphology and agronomic behavior observed in most interspecific hybrids, which also resemble plums more than apricots.

Nearly Complete Genome Sequence of Cherry Virus A, Isolated from Prunus armeniaca in Jammu and Kashmir, India

A nearly complete genome sequence of cherry virus A (CVA), isolated from the Prunus armeniaca plant, is presented in this publication. The genome is 7,380 bases in length and is divided into two open reading frames, with a 54-nucleotide (nt) 5′ noncoding region (NCR) and a 297-nt 3′ NCR.

Elucidating Genetic Diversity in Apricot (Prunus armeniaca L.) Cultivated in the North-Western Himalayan Provinces of India Using SSR Markers

Apricot (Prunus armeniaca L.) is an important temperate fruit crop worldwide. The availability of wild apricot germplasm and its characterization through genomic studies can guide us towards its conservation, increasing productivity and nutritional composition. Therefore, in this study, we carried out the genomic characterization of 50 phenotypically variable accessions by using SSR markers in the erstwhile States of Jammu and Kashmir to reveal genetic variability among accessions and their genetic associations. The genetic parameter results revealed that the number of alleles per locus (Na) ranged from 1 to 6 with a mean Na value of 3.89 and the mean effective number of alleles (Ne) per locus 1.882 with a range of 1.22 to 2. Similarly, the polymorphic information content (PIC) values ranged from 0.464 to 0.104. The observed heterozygosity (Ho) (0.547) was found to have higher than expected heterozygosity (He) (0.453) with average heterozygosity of 0.4483. The dendrogram clustered genotypes into three main clades based on their pedigree. The population structure revealed IV sub-populations with all admixtures except the III sub-population, which was mainly formed of exotic cultivars. The average expected heterozygosity (He) and population differentiation within four sub-populations was 1.78 and 0.04, respectively, and explained 95.0% of the total genetic variance in the population. The results revealed that the SSR marker studies could easily decrypt the genetic variability present within the germplasm, which may form the base for the establishment of good gene banks by reducing redundancy of germplasm, selection of parents for any breeding program.

Frequent germplasm exchanges drive the high genetic diversity of Chinese-cultivated common apricot germplasm

The genetic diversity of germplasm is critical for exploring genetic and phenotypic resources and has important implications for crop-breeding sustainability and improvement. However, little is known about the factors that shape and maintain genetic diversity. Here, we assembled a high-quality chromosome-level reference of the Chinese common apricot 'Yinxiangbai', and we resequenced 180 apricot accessions that cover four major ecogeographical groups in China and other accessions from occidental countries. We concluded that Chinese-cultivated common apricot germplasms possessed much higher genetic diversity than those cultivated in Western countries. We also detected seven migration events among different apricot groups, where 27% of the genome was identified as being introgressed. Remarkably, we demonstrated that these introgressed regions drove the current high level of germplasm diversity in Chinese-cultivated common apricots by introducing different genes related to distinct phenotypes from different cultivated groups. Our results highlight the consideration that introgressed regions may provide an important reservoir of genetic resources that can be used to sustain modern breeding programs.

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.

Casein/Apricot Filler in the Production of Flame-Retardant Polyurethane Composites

Polyurethane (PUR) composites reinforced with 1, 2, and 5 wt.% of apricot filler modified with casein were synthesized in the following study. The impact of 1, 2, and 5 wt.% of casein/apricot filler on the cellular structure and physico-mechanical performances of reinforced PUR composites were determined. It was found that the incorporation of 1 and 2 wt.% of casein/apricot filler resulted in the production of PUR composites with improved selected physical, thermal, and mechanical properties, while the addition of 5 wt.% of casein/apricot filler led to some deterioration of their physico-mechanical performance. The best results were obtained for PUR composites reinforced with 2 wt.% of casein/apricot filler. Those composites were characterized by a uniform structure and a high content of closed cells. Compared with the reference foam, the incorporation of 2 wt.% of casein/apricot filler resulted in improvement in compressive strength, flexural strength, impact strength, and dynamic mechanical properties-such as glass transition temperature and storage modulus. Most importantly, PUR composites showed better fire resistance and thermal stability due to the good thermal performance of casein. The main aim of this article is to determine the influence of the natural combination of the apricot filler and casein on the mechanical properties and flammability of the obtained composites.

Genetic Diversity of Phyllanthus emblica From Two Different Climate Type Areas

Phyllanthus emblica L. is a well-known medicinal and edible plant species. Various medicinal compounds in the fruit make it an important medicinal and promising economic material. The plant is widely distributed in Southwestern and Southern China. However, due to massive deforestation and land reclamation as well as deterioration of its natural habitat in recent years, the wild resources of this species have been sharply reduced, and it is rare to see large-scale wild P. emblica forests so far. In order to effectively protect and rationally utilize this species, we investigated the genetic diversity, genetic structure, and population dynamics of 260 individuals from 10 populations of P. emblica sampled from the dry climate area in Yunnan and wet climate area in Guangxi using 20 polymorphic EST-SSR markers. We found high genetic diversity at the species level (He = 0.796) and within populations (He = 0.792), but low genetic differentiation among populations (F _ST = 0.084). In addition, most genetic variation existed within populations (92.44%) compared with variation among the populations (7.56%). Meanwhile, the NJ tree, STRUCTURE, and hierarchical analysis suggested that the sampled individuals were clustered into two distinct genetic groups. In contrast, the genetic diversity of the dry climate group (He = 0.786, Na = 11.790, I = 1.962) was higher than that of the wet climate group (He = 0.673, Na = 9.060, I = 1.555), which might be attributed to the combined effects of altitude, precipitation, and geographic distance. Interestingly, only altitude and precipitation had significant pure effects on the genetic diversity, and the former was slightly stronger. In addition, DIYABC analysis suggested the effective population size of P. emblica might have contracted in the beginning of the Last Glacial Maximum. These genetic features provided vital information for the conservation and sustainable development of genetic resources of P. emblica, and they also provided new insights and guidelines for ecological restoration and economic development in dry-hot valleys of Yunnan and karst areas in Guangxi.