Genetic Diversity and Population Structure in Walnut Species

Walnut species (genus Juglans) exhibit considerable genetic diversity shaped by a long history of natural migration, glacial refugia and human-mediated dispersal. Native to temperate regions of Asia, Europe and North America, common walnut (Juglans regia) and its relatives display high levels of allelic variation within populations and moderate differentiation among them. Molecular studies have revealed that within-population diversity often exceeds inter-population divergence, reflecting extensive pollen and seed flow as well as centuries of cultivation and trade along historic routes. Population structure analyses identify geographic clusters corresponding to centres of origin, post-glacial recolonisation pathways and modern breeding germplasm. Advances in genotyping—from simple sequence repeat markers to high-density single nucleotide polymorphism arrays and whole-genome resequencing—now enable fine-scale resolution of demographic history, kinship and adaptive loci. Understanding genetic diversity and structure in walnuts is crucial for conserving threatened landraces, optimising breeding programmes and securing resilient forestry and nut-production systems under changing climatic conditions.

Research from Nature Portfolio

One notable study applied a 700K single nucleotide polymorphism array to a panel of Persian walnut genotypes from eight Iranian provinces. Genome-wide analyses revealed four principal genetic clusters aligned with geography, moderate population differentiation and low relatedness among accessions. The high-resolution SNP data enabled genome-wide association mapping to identify multiple loci linked to key nut and kernel quality traits. These findings provide a genomic framework for marker-assisted selection and the conservation of under-represented Iranian walnut germplasm.

Genetic Diversity and Population Structure in Walnut Species publication trend

The graph below shows the total number of articles in genetic diversity and population structure in walnut species across all publications each year (not limited to Nature Index journals).

Technical terms

Simple sequence repeat (SSR): A short, tandemly repeated DNA motif used as a molecular marker to assess genetic variation.

Single nucleotide polymorphism (SNP): A single base-pair change in the genome that serves as a high-resolution marker for diversity and association mapping.

Fixation index (FST): A measure of genetic differentiation among populations, ranging from zero (no divergence) to one (complete separation).

Gene flow (Nm): The movement of alleles between populations via pollen or seed dispersal, influencing genetic cohesion.

Genome-wide association study (GWAS): An analytical approach that correlates genetic variants across the genome with phenotypic traits in a population.

References

1. Molecular Characterization of Local Walnut (Juglans regia) Genotypes in the North-East Parnon Mountain Region of Greece. International Journal of Molecular Sciences (2023).
2. Unravelling the genetic diversity and population structure of common walnut in the Iranian Plateau. BMC Plant Biology (2023).
3. A Multiplex PCR System of Novel Microsatellite Loci for Population Genetic Application in Walnuts. Plants (2023).
4. Genome-wide patterns of population structure and association mapping of nut-related traits in Persian walnut populations from Iran using the Axiom J. regia 700K SNP array. Scientific Reports (2019).