Introduction
Walnut (Juglans regia L.) is one of the most valuable nut crops in Iran, playing a important role in human nutrition and the prevention of chronic diseases due to its high content of unsaturated fatty acids. It is one of the oldest and most valuable edible nuts in temperate regions worldwide, cultivated in Iran for thousands of years. However, the significant variability caused by seed propagation and the inconsistency in kernel quality limit Iran's competitiveness in global markets. Therefore, identifying superior genotypes with high oil quality and desirable fatty acid profiles is an essential prerequisite for breeding programs. Walnut genotypes exhibit significant variation in fatty acid composition, with some genotypes possessing higher oleic acid content. Walnuts are a rich source of unsaturated fatty acids, and studies have shown that their fatty acid profile is influenced by genetic, climatic, and management factors.

Materials and Methods
This research was conducted during 2022-2023 in orchards located in Abiz city, in the northeast of South Khorasan province. Walnut genotypes were labeled from 1 to 61 and evaluated for 12 different quantitative and qualitative traits related to the fruit and kernel. Following a comprehensive assessment of morphological and phenological traits, 11 genotypes were selected as superior and were evaluated for their kernel fatty acid composition at the Biorefining Laboratory, Faculty of Science, Ferdowsi University of Mashhad. To determine oil percentage via the Soxhlet method, several walnuts from each sample were cracked, shelled, and ground. Fatty acid profiles were determined using Gas Chromatography with a Flame Ionization Detector (GC-FID). Separation of fatty acid components was achieved using multiple temperature gradients, and the fatty acid profile was identified by comparing sample peaks with those of a standard fatty acid mixture.
Results and Discussion
The evaluation of pomological traits revealed considerable diversity among the examined walnut samples. The highest dry fruit weight including the woody shell (17.3 g) and the lowest (11.9 g) were recorded for genotypes C5 and C2, respectively, with an overall mean of 13.40 g across all genotypes. The highest dry kernel weight (8.9 g) and the lowest (4.6 g) were observed in genotypes C5 and B6, respectively, with an overall mean of 6.29 g for all genotypes. The results indicated varying amounts of fatty acids in the kernels. The lowest palmitic acid content (5.6%) was found in genotype G6, while the highest (6.88%) was in G7, with an average of 6.33% across all samples. Stearic acid values were lower overall, averaging 3.10%, but showed greater diversity compared to palmitic acid. Oleic acid content in the kernels ranged from 12.45% to 34.15%, with an overall mean of 20.95% and a coefficient of variation of 29.59%. The mean linoleic acid and linolenic acid contents were estimated at 57.86% and 11.75%, respectively. Linoleic acid values ranged from 43.16% to 64.29%, while linolenic acid content ranged from 9.13% to 13.88%. Estimation of saturated and unsaturated fatty acids confirmed that walnut kernels contain high levels of unsaturated fatty acids. The mean saturated fatty acid content was 9.44%, while the mean unsaturated fatty acid content was 90.56%. Total oil content ranged from 65% to 71%, with a mean of 69%. Correlation analysis among fatty acids revealed a significant positive correlation between linoleic acid and total oil content (r = 0.82). Total oil content showed a positive correlation with unsaturated fatty acids and a negative correlation with saturated fatty acids. Factor analysis extracted three principal factors, which together accounted for 95.61% of the total variance among genotypes. The first factor, which included certain saturated and unsaturated fatty acids along with total oil content, was the most important, explaining 40.21% of the total variance alone.
Conclusion
The availability of plant genetic resources and the evaluation of various tools for the effective utilization of germplasm are essential for any breeding program. Breeding and developing walnut cultivars with larger fruit size, higher kernel ratio, lighter kernel color, high oil content, and high unsaturated fatty acids are of particular importance, and there is significant demand for such walnut varieties. In this study, genotypes C5, E6, G7, and B5 were ultimately identified as having desirable kernel and oil traits, making them suitable for cultivation or for developing new cultivars in walnut breeding programs.