Unravelling the genetic diversity and population structure of common walnut in the Iranian Plateau

Abstract

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 (HO = 0.438, and HE = 0.437). Genetic differentiation among the populations was moderate (FST = 0.124), and genetic variation within the populations (79%) significantly surpassed among populations (21%). The gene flow (Nm = 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 STRUCTURE analysis divided the 27 populations into two main clusters. Comparing the neighbor-joining and principal coordinate analysis 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 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.

Utilizing SSR markers to examine the population structure and molecular genetic diversity of walnut (Juglans regia L.) genotypes in the Northwestern Himalayan region of Jammu and Kashmir

“…A substantial degree of genetic diversity is present in walnut trees, and significant divergence is observed in their germplasm (Shahi et al 2023). The observed genetic heterogeneity and heterozygosity among walnut genotypes are primarily attributable to plantations cultivated from seeds (Buyuksolak et al 2020).…”

A Multiplex PCR System of Novel Microsatellite Loci for Population Genetic Application in Walnuts

“…Hence, our newly reported m-PCR system is applicable for population genetic analysis. Notably, the m-PCR system developed here was successfully used in several recent studies of walnut genetic diversity [ 41 , 48 ].…”

Human‐associated genetic landscape of walnuts in the Himalaya: implications for conservation and utilization

“…It is widely cultivated throughout the temperate regions of the world for its high-quality timber, highly nutritious nuts and medicinal purposes (Lu et al, 1999). The population genetics of common walnut has therefore been well-investigated at regional, national and continental scales over the past two decades (Guney et al, 2021;Karimi et al, 2010;Pollegioni et al, 2020;Shahi Shavvon et al, 2023). Juglans sigillata (iron walnut) bears thick-shelled, edible nuts and is distributed in China, India, Myanmar, Bhutan and Nepal (Lu et al, 1999;Maity et al, 2019).…”