Evaluation of Genetic Diversity of Some Persian Walnut (Juglans regia L.) Genotypes of South Khorasan Using Morphological Characteristics

Document Type : Research Paper

Authors

1 Former M.Sc. Student, Department of Horticultural Sciences, Faculty of Agriculture, Ilam University, Ilam, Iran.

2 Associate Professor, Department of Horticultural Sciences, Faculty of Agriculture, Ilam University, Ilam, Iran.

3 Associate Professor in Department of Plant Production and Genetic (Biotechnology), Faculty of Agriculture, Jahrom University, Jahrom, Iran.

10.22092/spj.2026.371547.1456

Abstract

Persian walnut is one of the most important dried fruit products in Iran. In this research, the genetic diversity of 61 walnut genotypes was evaluated based on 30 quantitative and qualitative traits related to leaf, fruit, and tree traits. The results revealed high genetic diversity among the studied genotypes, with the highest coefficients of variation related to the traits of fruit split, leaf shape, fruit shape, number of fruits per branch, wooden shell color, kernel size, and kernel color. The lowest and highest dry in-shell fruit weight, ranged from 11.9 to 17.3 grams, and were recorded for genotypes C2 and C5, respectively. The mean value of this trait for all genotypes was 13.40 grams. Furthermore, the highest and lowest dry kernel weights were 8.9 and 4.6 grams, and were recorded for genotypes C5 and B6, respectively. The overall mean of all genotypes, was 6.29 grams. The highest dry kernel weight (8.9 grams) and the lowest (4.6 grams) belonged to genotypes C5 and B6, respectively. The overall mean of all genotypes was 6.29 grams. Cluster analysis of genotypes based on all morphological traits indicated two main groups at a distance of 165, each of which was subdivided into subgroups with closer kinship. The results of principal component analysis showed that the first two components explained nearly 76.80% of the total variance. The first component, which was mostly related to quantitative fruit traits, explained approximately 37.95% of the total variance. The results of this reseach showed that genotypes C5, E6, G7, and B5 possessed desirable kernel and fruit traits and could be used for establishment commercial walnut orchards as well as the development of new cultivars in walnut breeding programs.
 
Keywords: Walnut, coefficient of variation, principal component analysis, kernel weight, kernel color.
 
Introduction
The evaluation of genetic diversity of native pant populations is an important aspect for the management and utilization of plant germplasm, and plays a significant role in the survival and adaptation of species (Vahdati et al., 2019). Despite the high production of walnuts in Iran, the international trade of this valuable horticultural product has not been very successful. The main reason can be attributed to the variation of the fruit characteritics produced due to sexual propagation (Vahdati et al., 2019). Significant variation exists in the native walnut populations of Iran due to its high level of heterozygosity, dichogamy, cross-pollination, and consequently, sexual propagation (Ebrahimi et al., 2015). This genetic diversity provides an excellent opportunity for the identification of genotypes with desirable and valuable traits. A large number of walnut trees with diverse genetic backgrounds exist in the orchards of Abiz city in Qaenat region in northeast of South Khorasan provinc, in Iran, and the identification of suitable genotypes and the evaluation of kinship among them can be effective in walnut breeding programs. The aim of this research was to evaluate the selected walnut genotypes from Abiz city and identify the superior genotypes for further studies.
 
Materials and Methods
This research was conducted in 2022 and 2023 in the walnut orchards of Abiz city, located in the northeast of South Khorasan province. To identify superior and promising walnut genotypes, 61 genotypes were evaluated for 30 different quantitative and qualitative traits related to the tree, leaf, fruit, and kernel. In this study, fruits were randomly collected from various parts of the walnut trees at the ripe stage. Fifteen fruits from each genotype were evaluated. The fruit weight (weight of the fruit with green husk and dry fruit weight) and their kernel weight were measured using a digital balance (Model: BPSIID, Sartorius Company, Germany) with an accuracy of 0.01 grams. Subsequently, traits related to each genotypes, such as fruit width and length, were measured using a digital caliper (Model: EGL-111-111, Guanglu Company, Japan). Other qualitative traits of the fruit and tree, including kernel color, fruit split, tree growth vigor, tree growth habit, tree branching, etc., were assessed for each accession using the available descriptor for this plant.
 
Results and Discussion
The results indicated that the highest coefficients of variation were related to the traits of shell split, leaf shape, fruit shape, number of fruits per branch, shell color, kernel size, and kernel color, while the lowest coefficients of variation were obtained for fruit length, leaf length, dry fruit weight with wooden shell, fresh fruit weight with green husk, and leaf falling date. Furthermore, traits such as kernel removal ease, hard shell thickness, and type of fruit bearing exhibited high variation. The highest dry kernel weight (8.9 grams) and the lowest (4.6 grams) belonged to accession C5 and B6, respectively. The average for all genotypes was 6.29 grams. Shamlu et al., (2018) evaluated 102 seedling walnut genotypes, the average dry fruit weight ranged from 6.1 to 19.79 grams and kernel weight varied from 2.9 to 9.4 grams.
 The results of the present study revealed considerable genetic diversity among the 61 studied walnut genotypes in the Abiz city, particularly for traits related to fruit and kernel such as fruit weight, kernel weight, fruit shape, kernel color, and shell split. Such diversity could be attributed to sexual reproduction system, high heterozygosity, and ecological conditions (Vahdati et al., 2019). Significant positive correlation coefficients were observed among many studied traits. Cluster analysis based on morphological traits divided the walnut genotypes into two main groups, indicating heterogeneous population structure and high breeding potential of this germplasm.
Principal component analysis showed that the first eight components accounted for nearly 76.80% of total variance, with quantitative fruit traits including fruit weight, kernel weight, and kernel size loading highly on the first component, and demonstrated their importance as key discriminators among evaluated genotypes. In the present study, a substantial proportion of the total variance was explained by limited number of componnets, indicating that genetic diversity is concentrated in specific traits such as fruit weight, kernel weight, and phenological characteristics. Farrokhi Toolir and Soleimani (2024) evaluated 35 walnut genotypes based on 21 morphological and pomological traits, three first principal components accounted for approximately 58.9% of the total variance. The findings of the present research suggest that quantitative traits of fruit and the timing of growth stages accounted for the greatest contribution genetic variation among the evaluated walnut genotypes, and can be effectively utilized as selection criteria in walnut breeding programs.
 
References
Ebrahimi, A., Khadivi-Khub, A., Nosrati, Z. and Karimi, R. 2015. Identification of superior walnut (Juglans regia) genotypes with late leafing and high kernel quality in Iran. Scientia Horticulturae, 193, pp.195-201. DOI: 10.1016/j.scienta.2015.06.049
Farrokhi Toolir, J. and Soleimani, A. 2024. Evaluation of local walnut genotypes from Farrokhi Toolir, J. and Soleimani, A. 2024. Evaluation of local walnut genotypes from Kerman province using morphological and pomological traits. Seed and Plant, 40, pp.97-125 (in Persian). DOI: 10.22092/spj.2025.368013.1394
Shamlu, F., Rezaei, M., Lawson, S., Ebrahimi, A., Biabani, A. and Khan-Ahmadi, A. 2018. Genetic diversity of superior Persian walnut genotypes in Azadshahr, Iran. Physiology and Molecular Biology of Plants, 24, pp.939–949. DOI: 10.1007/s12298-018-0573-9
Vahdati, K., Arab, M.M., Sarikhani, S., Sadat-Hosseini, M., Leslie, C.A. and Brown, P.J. 2019. Advances in Persian walnut (Juglans regia L.) breeding strategies. Pp. 401–472. In: Al-Khayri, J., Jain, S. and Johnson, D. (eds.), Advances in Plant Breeding Strategies: Nut and Beverage Crops, 4. Springer, Cham. DOI: 10.1007/978-3-030-23112-5_11

Keywords

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Seed and Plant Journal
Volume 41, Issue 1
April 2025
Pages 47-23

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