Genetic Diversity and Structure of Persian Walnut (Juglans regia L.) in Pakistan: Implications for Conservation (original) (raw)
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Unravelling the genetic diversity and population structure of Persian walnut in the Iranian Plateau
Research Square (Research Square), 2022
Background: Common walnut (Juglans regia L.) has a long cultivation history, given its highly valuable wood and rich nutritious nuts. The Iranian Plateau has been considered one of the last glaciation refugia and a center of origin and domestication for the common walnut. However, a prerequisite to conserve or utilize the genetic resources of J. regia in the Plateau is a comprehensive evaluation of the genetic diversity that is conspicuously lacking. In this regard, we used 31 polymorphic simple sequence repeat (SSR) markers to delineate the genetic variation and population structure of 508 J. regia individuals among 27 populations from the Iranian Plateau. Results: The SSR markers expressed a relatively high level of genetic diversity (H O = 0.438, and H E = 0.437). Genetic differentiation among the populations was moderate (F ST = 0.124), and genetic variation within the populations (79%) signi cantly surpassed among populations (21%). The gene ow (N m = 1.79) may have remarkably in uenced the population genetic structure of J. regia, which can be attributed to anthropological activities and wind dispersal of pollen. The STRUCTURE analysis divided the 27 populations into two main clusters. A comparison of the neighbor-joining (NJ) and Principal coordinate analysis (PCoA) dendrograms and the Bayesian STRUCTURE analysis revealed the general agreement between the population subdivisions and the genetic relationships among the populations. However, a few geographically close populations dispersed into different clusters. Further, the low genetic diversity of the SMR and TKR populations necessitates urgent in situ conservation; additionally, we recommend the indispensable preservation of the RGR and AKR populations. Conclusion: These results re ected consistent high geographical a nity of the accession across the Plateau. Our ndings suggest that gene ow is a driving factor in uencing the genetic structure of J. regia populations, whereas ecological and geological variables did not act as a strong barrier. Moreover, the data reported herein provide new insights into the population structure of J. regia germplasm, which will help conserve genetic resources for the future improving walnut breeding programs' e ciency. Background Genetic diversity has been constantly found to be essential for adapting the population to environmental changes (1). Genetic diversity analysis of plants' germplasm can expand our knowledge of evolution and genetic variability determinants giving profound insights into plant conservation (1-3). Juglans L. belongs to the Juglandaceae family, which includes ca. 21 deciduous tree species (4); It's a widespread genus ranging from North and South America, the West Indies, and Southeast Europe to East Asia (4-6). Juglans regia L., also called common walnut, English walnut, or Persian walnut (hereafter refer as common walnut), is monoecious and heterodichogamous with 2n=2x=32 (7). The species is cultivated across the temperate and tropical regions of the world for its timber and excellent edible nuts (8,9). High genetic variation has been reported among walnut populations worldwide, and seed Author details
Pakistan Journal of Agricultural Sciences, 2015
RAPD based estimation of genetic diversity in walnut genotypes growing in Malakund division, Pakistan, was made by collecting nut samples of 226 walnut genotypes from four walnut growing districts of Malakand division. On the basis of various qualitative traits, 18 superior walnut genotypes were selected along with two exotic varieties. Every single band was considered as a single locus/allele for all the genetic analyses. The 18 indigenous genotypes showed various levels of genetic polymorphism for the loci detected by using primers GLA-05 and GLA-10. The loci were scored as present (1) and absent (0). Bivariate 1-0 data matrix was used to estimate genetic distances (GD) and for construction of Phylogenetic tree based on cluster analysis. Maximum genetic distance (100%) was observed between Payne and Sw-58 and Payne and Serr, closely followed by 94% dissimilarity between Payne and Dr-67. Based on the data presented as dendrogram, the walnut genotypes were classified in to four major groups. The maximum numbers (13) of genotypes fall in group-I. Sw-58 was the only genotypes in group-IV and the most distinct from others. Classification of wild genotypes will help in breeding as well as vegetative propagation of walnut trees.
Tree Genetics & Genomes, 2016
Persian walnut (Juglans regia L.) is the world's most widely grown nut crop, but large-scale assessments and comparisons of the genetic diversity of the crop are notably lacking. To guide the conservation and utilization of Persian walnut genetic resources, genotypes (n = 189) from 25 different regions in 14 countries on three continents were sampled to investigate their genetic relationships and diversity using ten microsatellite (SSR) loci. The SSRs amplified from 3 to 25 alleles per locus, with a mean value of 11.5 alleles per locus. The mean values of observed and expected heterozygosity were 0.62 and 0.73, respectively. Based on Nei's genetic identity, accessions from Bratislava (Slovakia) and Antalya (Turkey) showed the lowest similarity (0.36), while accessions from Algeria and Tunisia as well as accessions from Debrecen (Hungary) and Trnava (Slovakia) had the highest similarity (0.97). Two populations from Iran (Alborz and Ardabil) had the highest number of private alleles (7 and 5), but they were quite different as they also had the lowest genetic identity when compared to the remaining populations as well as to each other. Although overall differentiation among regions was relatively low (F ST = 0.07), cluster analysis grouped accessions generally but not completely according to geography. STRUCTURE software confirmed these results and divided the accessions into two main groups, separating accessions collected from Europe and North Africa from those from Greece and the Near East. Results indicate the presence of a likely center of diversity for Persian walnut in Eastern and Southeastern Europe. They also provide information that can be used to devise conservation actions. Notably, the genetic diversity of threatened populations from two regions in Iran should be conserved.
Landscape genetics of Persian walnut (Juglans regia L.) across its Asian range
Tree Genetics & Genomes, 2014
Persian walnut (Juglans regia L) is an economically important species cultivated worldwide for its wood and nuts. Despite the increasing interest in the development of conservation strategies for walnut germplasm, an accurate and full-scale overview of wild genetic resources of J. regia has not been conducted because natural populations are located in regions of Asia historically difficult to access. In this study, we estimated the genetic diversity and spatial genetic structure of 39 autochthonous Persian walnut populations sampled across its Asian range using 14 neutral microsatellite markers. A landscape genetic overlay approach was applied to detect the areas of current reservoirs of walnut genetic diversity in the Asian range and to evaluate the role of landscape in shaping walnut genetic diversity since the Last Glacial Maximum. Although Persian walnut has been highly manipulated by humans over the last 2,000 years, we determined that patches of high genetic diversity still exist in the Caucasus and mountains of Central Asia where J. regia might have survived after Pleistocene glaciations. We detected a clear separation of Persian walnut into four main genetic clusters centered in (1) western Kyrgyzstan, (2) western and south-central Asia, (3) east-central Uzbekistan, and (4) Xinjiang and Shandong provinces (China). Overlay of maps showed a coincidence between groups of walnut populations and potential barriers to gene flow such as the Hindu Kush, Pamir, Tien Shan, and Himalaya mountains and the Karakum, Kyzyl Kum, and Taklamakan deserts. This study claimed the relevance of the preservation of walnut genetic resources in the Asian range.
Unravelling the genetic diversity and population structure of common walnut in the Iranian Plateau
BMC Plant Biology, 2023
Background Common walnut (Juglans regia L.) has a long cultivation history, given its highly valuable wood and rich nutritious nuts. The Iranian Plateau has been considered as one of the last glaciation refugia and a centre of origin and domestication for the common walnut. However, a prerequisite to conserve or utilize the genetic resources of J. regia in the plateau is a comprehensive evaluation of the genetic diversity that is conspicuously lacking. In this regard, we used 31 polymorphic simple sequence repeat (SSR) markers to delineate the genetic variation and population structure of 508 J. regia individuals among 27 populations from the Iranian Plateau. Results The SSR markers expressed a high level of genetic diversity (H O = 0.438, and H E = 0.437). Genetic differentiation among the populations was moderate (F ST = 0.124), and genetic variation within the populations (79%) significantly surpassed among populations (21%). The gene flow (N m = 1.840) may have remarkably influenced the population genetic structure of J. regia, which can be attributed to anthropological activities and wind dispersal of pollen. The STRU CTU RE analysis divided the 27 populations into two main clusters. Comparing the neighbor-joining and principal coordinate analysis dendrograms and the Bayesian STRU CTU RE analysis revealed the general agreement between the population subdivisions and the genetic relationships among the populations. However, a few geographically close populations dispersed into different clusters. Further, the low genetic diversity of the Sulaymaniyah (SMR) population of Iraq necessitates urgent conservation by propagation and seedling management or tissue culture methods; additionally, we recommend the indispensable preservation of the Gonabad (RGR) and Arak (AKR) populations in Iran. Conclusions These results reflected consistent high geographical affinity of the accession across the plateau. Our findings suggest that gene flow is a driving factor influencing the genetic structure of J. regia populations, whereas ecological and geological variables did not act as strong barriers. Moreover, the data reported herein provide new insights into the population structure of J. regia germplasm, which will help conserve genetic resources for the future, hence improving walnut breeding programs' efficiency.
Plant Systematics and Evolution, 2014
Iran is reported to be a center of diversity for Juglans regia and wild walnut trees are found in virtually every corner of the country. Thus Iran is considered a rich natural pool of walnut germplasm for developing improved genotypes. Kerman province is the most important Iranian province for walnut culture and has the largest walnut plantations in Iran. Genetic structure and gene flow were analyzed in six walnut populations of this province using 17 microsatellite loci. The number of alleles per locus ranged from 4 to 11, with a total of 147 alleles and 5.16 effective alleles per locus. The polymorphism information content for the loci ranged from 0.56 to 0.82. The expected heterozygosity (H e) for the populations ranged from 0.65 to 0.87. There were differences between populations regarding the number of effective alleles and Shannon's information index (I). In all populations, observed heterozygosity (H o) was lower than expected, but diversity within the populations was high (I = 1.5) and many of the private alleles were present at relatively high frequency. The average F st value was 0.08. The level of gene flow based on F st was high (N m = 3.01), which meant that the high level of genetic diversity maintained within each population was less susceptible to genetic drift. The geographical proximity of the populations was not correlated with their level of genetic relatedness. These results imply the high potential of walnut populations of Kerman province for breeding programs.
Journal of Crop production and processing, 2016
Genetic resources are the most valuable national treasure of countries, being vital to identify, conserve and use them. The Persian Walnut (Juglans regiaL.), a diploid species native to the mountainous regions of Central Asia, is the major walnut species cultivated for nut production and one of the most widespread tree nut species in the world. This research was conducted in Meshkinshahr in Ardabil Province. In this study, to determine the level of genetic diversity, a total of 31 walnut genotypes were analyzed using Inter Simple Sequence Repeats(ISSR) markers. Genotypes were evaluated using 10 ISSR markers and a total of 26 polymorphic alleles were identified.The average of the observed alleles was equal to 7 in each locus. The lowest and highest RP valueswere found ISSR5and ISSR9, respectivly.Cluster analysis based on Jacard similarity coefficient matrix using WARD method classified the genotypes into three main groups.The highest genetic distance was found between genotypes AK4 and RM2, and the lowest was among genotypes MZ4 and ES1.Both clustering and PCA divide genotypes with similar geographic origins.
Scientia Horticulturae, 2017
We compared the genetic diversity of Juglans regia L. growing in the cold temperate region of the eastern U.S. with J. regia growing in the cold-temperate and Mediterranean regions of Europe. Ten microsatellite (SSR) loci were used to assess the genetic relationships among 114 total trees originating from the Midwestern USA (n = 34), Hungary (n = 30), Slovakia (n = 28), and Italy (n = 22). All SSR loci were highly polymorphic with an average of 7.4 alleles per locus. All 114 trees were confirmed to be unique genotypes. Cluster analysis using Neighbor-joining (NJ) placed genotypes according to their geographic origin. STRUCTURE software confirmed the results of the NJ analysis and produced three main groups consistent with the geographic origins of the samples. According to Nei's genetic identity, samples from Slovakia and Hungary showed the highest similarity (0.94), while samples from the USA and Hungary had the lowest similarity (0.37). The genetic diversity of J. regia from the USA and Eastern Europe was relatively high compared to Italian samples. We found little genetic similarity between J. regia sampled from the eastern USA with J. regia currently growing near the Carpathian Mountains. There was strong evidence for a bottleneck in the U.S. population, but no evidence of inbreeding.
Spatial genetic structure of common walnut (Juglans regia L.) in central Asia
Acta Horticulturae, 2018
Landscape genetics is a powerful approach that combines ecology, geography, and population genetics to quantify the effects of landscape on evolutionary processes. Juglans regia is native to southeastern Europe and west-central Asia, but its distribution was modified by human management during the last 3,000 years. Despite impressive morphological and phenological variation, an accurate overview of the genetic diversity and spatial genetic structure of Asian walnut is incomplete. Studies of the genetic structure of autochthonous populations, when combined with analyses of geographic data, can reveal how geographic barriers have shaped the distribution of walnut genetic resources. Sampled and analyzed walnut populations were geographically isolated by arid lowland, mountain slopes and highland steppes. Clustering approaches produced convergent results, dividing the samples into four main genetic clusters. Most genetic clusters were confined to particular mountain ranges, showing distinct phylogeographic structure. The spatial arrangement of genetic clusters of Eurasian walnut indicated that ancient trade routes facilitated walnut dispersal and gene flow over enormous distances. By combining genetic analysis with ethno-linguistic and historical data, we demonstrated a statistically significant association between ancient language phyla in Asia and the genetic structure of walnut. This result indicated that walnut's natural gene flow was substantially supplemented by human commerce over ancient trade routes such as the Persian Royal Road and Silk Road.