Nasrin Seyedi

Aleppo oak (Quercus infectoria) is among the most industrially and ecologically significant oak species, valued for its medicinal properties and considerable genetic importance. Cytogenetic analysis provides critical insight into evolutionary history, interspecific relationships, and karyotypic differentiation. This study investigated the chromosomal architecture and karyotypic diversity of five natural populations of this species in western Iran (Sardasht, Oramanat, Baneh, Paveh, and Marivan) using actively dividing root meristems and a high-resolution image-based cytogenetic system. All examined cells displayed a basic chromosome number of x = 12 and a diploid condition, and chromosome lengths ranged from 0.90 to 2.12 µm. ANOVA and mean comparisons of five chromosomal parameters (Long Arm, Short Arm and Total Length, Arm Ratio, and Centromeric Index) revealed significant interpopulation differences in chromosome length and arm dimensions. All populations shared the karyotype formula 12 m and were classified into Stebbins’ Category B, indicating a moderately symmetrical, relatively primitive cytogenetic structure. Principal component analysis reduced the dataset to two major axes explaining 99.93% of the total variance, predominantly influenced by SA and TL on PC1 and by LA, AR, and CI on PC2. Hierarchical clustering grouped the populations into three distinct lineages, with Sardasht–Oramanat–Baneh showing the greatest divergence. Biplot vector patterns further clarified trait correlations, highlighting genomic structuring and potential breeding utility.

Walnut biodiversity represents a critical genetic resource for developing climate-resilient cultivars capable of withstanding increasing drought stress under changing environmental conditions. Understanding the genetic basis of drought tolerance mechanisms is essential for sustainable nut production and conservation of valuable genetic resources. This study investigated the genetic and physiological basis of drought tolerance in walnut ( Juglans regia L.) saplings, providing crucial insights for breeding programs aimed at developing climate-resilient cultivars. A comprehensive analysis was conducted using 65 walnut samples collected from diverse geographic locations, employing SSR (simple sequence repeat) markers for genetic characterization combined with detailed morphological and physiological assessments under controlled drought stress conditions. Our findings revealed significant variability in drought stress responses among walnut saplings. Morphological and physiological traits exhibited substantial variation under drought stress, reflecting the genetic diversity present in natural populations. Population structure analysis performed using STRUCTURE software identified three distinct genetic clusters within the studied population, with varying degrees of admixture indicating complex evolutionary relationships and gene flow patterns across different populations. Some individuals showed strong affiliation to a single cluster, while others exhibited significant admixture patterns. Mixed Linear Model analysis identified significant marker-trait associations between SSR markers and drought tolerance traits. Multiple markers showed strong correlations with physiological parameters including chlorophyll content, leaf characteristics, and stress response indicators. Hierarchical clustering and phylogenetic analyses confirmed the genetic relationships among populations and revealed patterns consistent with geographic distribution and environmental adaptation. This research elucidates the genetic architecture underlying drought tolerance in walnuts and demonstrates the effectiveness of SSR markers for identifying drought-responsive genes. The identified marker-trait associations provide valuable tools for marker-assisted selection in breeding programs. Furthermore, the observed genetic diversity and its correlation with drought-related traits offer a foundation for developing more resilient walnut cultivars. These findings contribute to the conservation and utilization of walnut genetic resources while supporting the development of climate-adaptive breeding strategies for sustainable nut production under water-limited conditions.