Walnut Accessions Research Articles

Molecular Characterization of Local Walnut (Juglans regia) Genotypes in the North-East Parnon Mountain Region of Greece.

Walnut is one of the most important nuts regarding their production and consumption. The available but uncharacterized genetic resources of walnut are important for the development and breeding of local varieties. Greece holds an important number of genetically uncharacterized walnut landraces, especially within the area of Parnon, which is considered to play a significant role as an in situ gene bank, due to its unique location traits. However, the genetic characterization and further use of these resources has been insufficient, due to the absence of genetic studies. In this study, we implemented SSR molecular markers, both to genetically characterize the walnut tree genetic diversity of the Parnon area and to identify its unique genetic structure, which will form the starting material for subsequent breeding programs. Overall, high levels of genetic variation were found among the individual walnut accessions that were collected in the Parnon mountain region.

Domestication and selection footprints in Persian walnuts (Juglans regia).

Walnut (Juglans) species are economically important hardwood trees cultivated worldwide for both edible nuts and high-quality wood. Broad-scale assessments of species diversity, evolutionary history, and domestication are needed to improve walnut breeding. In this study, we sequenced 309 walnut accessions from around the world, including 55 Juglans relatives, 98 wild Persian walnuts (J. regia), 70 J. regia landraces, and 86 J. regia cultivars. The phylogenetic tree indicated that J. regia samples (section Dioscaryon) were monophyletic within Juglans. The core areas of genetic diversity of J. regia germplasm were southwestern China and southern Asia near the Qinghai-Tibet Plateau and the Himalayas, and the uplift of the Himalayas was speculated to be the main factor leading to the current population dynamics of Persian walnut. The pattern of genomic variation in terms of nucleotide diversity, linkage disequilibrium, single nucleotide polymorphisms, and insertions/deletions revealed the domestication and selection footprints in Persian walnut. Selective sweep analysis, GWAS, and expression analysis further identified two transcription factors, JrbHLH and JrMYB6, that influence the thickness of the nut diaphragm as loci under selection during domestication. Our results elucidate the domestication and selection footprints in Persian walnuts and provide a valuable resource for the genomics-assisted breeding of this important crop.

Genome-wide association analysis of 101 accessions dissects the genetic basis of shell thickness for genetic improvement in Persian walnut (Juglans regia L.)

BackgroundUnderstanding the underlying genetic mechanisms that drive phenotypic variations is essential for enhancing the efficacy of crop improvement. Persian walnut (Juglans regia L.), which is grown extensively worldwide, is an important economic tree fruit due to its horticultural, medicinal, and material value. The quality of the walnut fruit is related to the selection of traits such as thinner shells, larger filling rates, and better taste, which is very important for breeding in China. The complex quantitative fruit-related traits are influenced by a variety of physiological and environmental factors, which can vary widely between walnut genotypes.ResultsFor this study, a set of 101 Persian walnut accessions were re-sequenced, which generated a total of 906.2 Gb of Illumina sequence data with an average read depth of 13.8× for each accession. We performed the genome-wide association study (GWAS) using 10.9 Mb of high-quality single-nucleotide polymorphisms (SNPs) and 10 agronomic traits to explore the underlying genetic basis of the walnut fruit. Several candidate genes are proposed to be involved in walnut characteristics, including JrPXC1, JrWAKL8, JrGAMYB, and JrFRK1. Specifically, the JrPXC1 gene was confirmed to participate in the regulation of secondary wall cellulose thickening in the walnut shell.ConclusionIn addition to providing considerable available genetic resources for walnut trees, this study revealed the underlying genetic basis involved in important walnut agronomic traits, particularly shell thickness, as well as providing clues for the improvement of genetic breeding and domestication in other perennial economic crops.

Genetic diversity based on morphological traits and germplasm conservation of walnut in Kashmir, Pakistan

Persian walnut is an economically important nut crop of temperate regions of the world. In the present study 225 local walnut accessions from 37 sites of Azad Jammu and Kashmir were analysed for morphological traits to investigate variability and identify superior one. Nut length, nut weight, shell thickness and nut diameter varied from 20.87–47.34 mm, 6.44–17.7 g, 1.61–2.54 mm and 27.25–44.31 mm respectively. Kernel weight and percentage varied from 2.81–8.65 g and 32.53–77.34%. Data were analysed statistically using multivariate analysis such as Principal Components Analysis and Cluster Analysis. Pearson correlation coefficient among traits revealed a positively significant correlation between nut weight and nut thickness (r = 0.45987), kernel weight and nut weight (r = 0.94777), kernel% and nut thickness (r = 0.48346), shell thickness and kernel% (r = 0.21961), a negative correlation with significant differences was found between kernel weight and nut thickness (r = –0.40968), kernel% and nut length (r = –0.10844) and between kernel% and nut weight (r = –0.95209). The highest and most significant positive correlation (0.96024) was observed between kernel weight and kernel% and (r = 0.94777) between kernel weight and nut weight. A wide range of variability was observed among walnut accessions and BA2, BN2, CN3 and BN4 accessions are reported as superior and conserved for future breeding programs due to their distinct characteristics.

A genome variation map provides insights into the genetics of walnut adaptation and agronomic traits

BackgroundCommon walnut (Juglans regia L.) is one of the top four most consumed nuts in the world due to its health benefits and pleasant taste. Despite its economic importance, the evolutionary history and genetic control of its adaptation and agronomic traits remain largely unexplored.ResultsWe report a comprehensive walnut genomic variation map based on whole-genome resequencing of 815 walnut accessions. Evolutionary analyses suggest that Chinese J. regia diverged from J. sigillata with extensive hybridizations after the split of the two species. In contrast to annual crops, the genetic diversity and heterozygous deleterious mutations of Chinese common walnut trees have continued to increase during the improvement process. Selective sweep analyses identify 902 genes uniquely selected in the improved common walnut compared to its progenitor population. Five major-effect loci are identified to be involved in walnut adaptations to temperature, precipitation, and altitude. Genome-wide association studies reveal 27 genomic loci responsible for 18 important agronomic traits, among which JrFAD2 and JrANR are the potentially major-effect causative genes controlling linoleic acid content and color of the endopleura of the nut, respectively.ConclusionsThe largest genomic resource for walnuts to date has been generated and explored in this study, unveiling their evolutionary history and cracking the genetic code for agronomic traits and environmental adaptation of this economically crucial crop tree.

Phenological Differences, Genetic Diversity, and Population Structure of Genotypes Obtained from Seeds of Kaman-1 Walnut Cultivar

Walnut (Juglans regia L.) is a diploid (2n = 32), deciduous, monoecious, and generally open-pollinated tree with nuts of high nutrient content. In this study, the phenological differences, genetic diversity, and population structure of Kaman-1 and its 79 progenies obtained by open pollination were characterized by ISSR primers and some important phenological traits. As a result of the phenological observations, it was determined that the progenies differ significantly from Kaman-1. Besides, using ISSR primers, walnut genotypes were found to have genetic similarities ranging from 0.52 to 0.99. UPGMA cluster analysis showed that accessions from 2 different groups were classified, and population structure analysis confirmed this finding. Based on the results, a significant variation both phenologically and genetically was found within the walnut accessions. Also, this study confirmed that the progenies obtained from the Kaman-1 walnut cultivar have a quite wide variation and that ISSR primers and phenological traits are an important tool in determining genetic diversity.

Composite core set construction and diversity analysis of Iranian walnut germplasm using molecular markers and phenotypic traits.

Iran is a center of origin and diversity for walnuts (Juglans regia L.) with very good potential for breeding purposes. The rich germplasm available, creates an opportunity for study and selection of the diverse walnut genotypes. In this study, the population structure of 104 Persian walnut accessions was assessed using AFLP markers in combination with phenotypic variability of 17 and 18 qualitative and quantitative traits respetively. The primers E-TG/M-CAG, with high values of number of polymorphic bands, polymorphic information content, marker index and Shannon's diversity index, were the most effective in detecting genetic variation within the walnut germplasm. Multivariate analysis of variance indicated 93.98% of the genetic variability was between individuals, while 6.32% of variation was among populations. A relatively new technique, an advanced maximization strategy with a heuristic approach, was deployed to develop the core collection. Initially, three independent core collections (CC1-CC3) were created using phenotypic data and molecular markers. The three core collections (CC1-CC3) were then merged to generate a composite core collection (CC4). The mean difference percentage, variance difference percentage, variable rate of coefficient of variance percentage, coincidence rate of range percentage, Shannon's diversity index, and Nei's gene diversity were employed for comparative analysis. The CC4 with 46 accessions represented the complete range of phenotypic and genetic variability. This study is the first report describing development of a core collection in walnut using molecular marker data in combination with phenotypic values. The construction of core collection could facilitate the work for identification of genetic determinants of trait variability and aid effective utilization of diversity caused by outcrossing, in walnut breeding programs.

Diversity assessment and selection of superior Persian walnut (Juglans regia L.) trees of seedling origin from North-Western Himalayan region

North-Western Himalayan region of Jammu and Kashmir has significant Persian walnut (Juglans regia L.) trees, most of which are of seedling origin. The region have rich morphological, phenological, and carpological walnut diversity because of the large variability of native walnut, resulting from cross-pollination and seedling propagation. We studied 84 walnut accessions from this region to assess this diversity and identified trees with superior fruit traits. Studying the growth, leaf, phenological, inflorescence, and fruit characteristics show high variability. Nut weight (NW) ranged from 10.04 to 22.66 g, whereas kernel weight (KW) varied from 4.75 to 14.00 g. In this study, we recorded kernel percentage in a broader range from 30.64% to 61.78%, and shell thickness (ST) from 0.98 to 2.83 mm. The principal component analysis revealed that traits related to KW, kernel percentage, ST, NW, nut length (NL), kernel length (KL), and kernel width (KW) accounted for a large proportion of phenotypic variability. Cluster analysis divided accessions into four cluster groups. We identified three promising genotypes, such as JWSP-06, JWSG-43, and JWSD-59, after considering the important traits in a selection index. These promising genotypes will be used to the benefit of conservation research, cultivation, and breeding. Based on the observed differentiation of variation, it is concluded that the magnitude of phenotypic variation in the population under study is high, and the implication of the results will play a vital role in future walnut breeding programmes.

Major QTL with pleiotropic effects controlling time of leaf budburst and flowering-related traits in walnut (Juglans regia L.)

Breeding studies in walnut (Juglans regia L.) are usually time consuming due to the long juvenile period and therefore, this study aimed to determine markers associated with time of leaf budburst and flowering-related traits by performing a genome-wide association study (GWAS). We investigated genotypic variation and its association with time of leaf budburst and flowering-related traits in 188 walnut accessions. Phenotypic data was obtained from 13 different traits during 3 consecutive years. We used DArT-seq for genotyping with a total of 33,519 (14,761 SNP and 18,758 DArT) markers for genome-wide associations to identify marker underlying these traits. Significant correlations were determined among the 13 different traits. Linkage disequilibrium decayed very quickly in walnut in comparison with other plants. Sixteen quantitative trait loci (QTL) with major effects (R2 between 0.08 and 0.23) were found to be associated with a minimum of two phenotypic traits each. Of these QTL, QTL05 had the maximum number of associated traits (seven). Our study is GWAS for time of leaf budburst and flowering-related traits in Juglans regia L. and has a strong potential to efficiently implement the identified QTL in walnut breeding programs.

Association mapping of several nut characters in walnut (Juglansregia L.)

In the current study, significant variations were identified for seven fruit traits of the walnut accessions. The highest correlations were detected between nut height and nut width, and between nut weight and kernel weight. Most traits had a continuous normal binominal distribution. A total of 16,774 single-nucleotide polymorphism SNP markers based on diversity arrays technology were generated and after filtering the missing data, the remaining 13,611 SNP data were used for genotyping. STRUCTURE v.2.2 analysis revealed two possible scenarios K = 3 and K = 5 according to the results of ΔK computation. While K = 3 indicated that walnut cultivars were clustered into three different groups, K = 5 revealed five different groups. Results of the dendrogram tree analysis were supported by the results presented in the STRUCTURE analysis. A total of 98 association signals were detected with FDR =< 0.05 from MLM K using BLUP predictors for the seven agronomic traits. Out of these 98 associations, seven SNPs were associated with nut weight, 26 SNPs with nut length, 15 SNPs with nut height, 18 SNPs with nut width, 18 SNPs with shell thickness, 12 SNPs with kernel weight, and 2 SNPs with kernel ratio.

Association and linkage mapping to unravel genetic architecture of phenological traits and lateral bearing in Persian walnut (Juglans regia L.)

BackgroundUnravelling the genetic architecture of agronomic traits in walnut such as budbreak date and bearing habit, is crucial for climate change adaptation and yield improvement. A Genome-Wide Association Study (GWAS) using multi-locus models was conducted in a panel of 170 walnut accessions genotyped using the Axiom™ J. regia 700 K SNP array, with phenological data from 2018, 2019 and legacy data. These accessions come from the INRAE walnut germplasm collection which is the result of important prospecting work performed in many countries around the world. In parallel, an F1 progeny of 78 individuals segregating for phenology-related traits, was genotyped with the same array and phenotyped for the same traits, to construct linkage maps and perform Quantitative Trait Loci (QTLs) detection.ResultsUsing GWAS, we found strong associations of SNPs located at the beginning of chromosome 1 with both budbreak and female flowering dates. These findings were supported by QTLs detected in the same genomic region. Highly significant associated SNPs were also detected using GWAS for heterodichogamy and lateral bearing habit, both on chromosome 11. We developed a Kompetitive Allele Specific PCR (KASP) marker for budbreak date in walnut, and validated it using plant material from the Walnut Improvement Program of the University of California, Davis, demonstrating its effectiveness for marker-assisted selection in Persian walnut. We found several candidate genes involved in flowering events in walnut, including a gene related to heterodichogamy encoding a sugar catabolism enzyme and a cell division related gene linked to female flowering date.ConclusionsThis study enhances knowledge of the genetic architecture of important agronomic traits related to male and female flowering processes and lateral bearing in walnut. The new marker available for budbreak date, one of the most important traits for good fruiting, will facilitate the selection and development of new walnut cultivars suitable for specific climates.

Distinguishing Sichuan Walnut Cultivars and Examining Their Relationships with Juglans regia and J. sigillata by FISH, Early-Fruiting Gene Analysis, and SSR Analysis.

Walnuts are economically important tree species in Sichuan Province (China) that provide heathy nuts. Fluorescence in situ hybridization (FISH) and analyses of an early-fruiting gene fragment and simple sequence repeats (SSRs) were used to distinguish Sichuan walnut cultivars and examine their relationships with Juglans regia L. and Juglans sigillata Dode. Thirty-four small chromosomes were counted in four Sichuan walnut cultivars. In the four cultivars, 5S rDNA was located in the proximal regions of two chromosomes (5 and 6), while (AG3T3)3 was located at both ends of each chromosome. The existence of the signal at both chromosome ends ensured accurate chromosome counts. 5S rDNA and (AG3T3)3 were not effective in identifying Sichuan walnut cultivars. Evolutionary analysis involving 32 early-fruiting nucleotide sequences from Sichuan walnut materials were performed with the maximum likelihood method. There were a total of 602 positions. All positions with gaps and missing data were eliminated, resulting in a final dataset of 562 positions. The ML tree with the highest log likelihood (−1607.82) revealed two obvious groups: one including materials of J. regia, which fruits 1 year after grafting, and another including materials of J. sigillata, which fruits >3 years after grafting. The early-fruiting gene fragment divided 22 walnut materials (10 walnut cultivars and 12 walnut accessions) into two groups, indicating that it was somewhat effective for distinguishing Sichuan walnut cultivars. Furthermore, 22 SSR loci were revealed to identify nine walnut cultivars. Eight cultivars were exclusively discerned by one SSR locus each: Chuanzao 1 [CUJRB307 (116) or CUJRA206a (182)], Chuanzao 2 [JSI-73 (154)], Shuangzao [CUJRB103a (123), CUJRB218 (144), JSI-71 (146), or CUJRA206a (176)], Shimianju [ZMZ11 (138)], Meigupao [CUJRB218 (149), CUJRB103a (151), or CUJRA206a (190)], Muzhilinhe [CUJRB220 (136), ZMZ11 (147), CUJRC310 (156), or JSI-73 (166)], Maerkang [CUJRA124 (154), CUJRB218 (159), or CUJRA123 (182)], Yanyuanzao [CUJRA124 (150) or CUJRA206a (192)]. The Shuling cultivar was identified by the combination of ZMZ11 (148) and other SSR loci, which distinguished and excluded the Chuanzao 1 and Yanyuanzao cultivars. Our results will guide the identification and breeding of Sichuan walnut cultivars.

Biochemical characterization and antioxidant activity of walnut kernel (Juglans regia L.) of accessions from Middle and High Atlas in Morocco

Biochemical composition and antioxidant activity were determined in kernel nuts for eleven Moroccan walnut (Juglans regia L.) accessions representing its main cropping area. Total oil, carbohydrates, crude protein, energy value, crude fiber and flavonoid have varied significantly between accessions, respectively within the range values of 54.50-65.48%, 8.17-19.25%, 11.5-25.58%, 648.91-713.83 Kcal, 4.17-6.75% and 12.59-62.11mg RE 100 g-1 DM. Besides, mineral composition (mg 100 g-1) of kernel have varied also significantly among accessions and particularly for phosphorus (338.1-675.87), copper (2.08-6.67), zinc (3.39-18.63), iron (1.17-2.64), chromium (0.16-0.20), nickel (1.26-1.45) and boron (0.07-1.49). However, dry matter (96.75-98.56%), moisture (1.44-3.24%), ash (1.67-2.53%), total phenols content (1017-3739 mg GAE 100 g-1 DM), DPPH radical scavenging activity (75.02-85.96%), potassium (210.10-338.93 mg 100 g-1), magnesium (79.15-374.54 mg 100 g-1), sodium (1.17-12.63 mg 100 g-1) and manganese (0.79-1.67 mg 100 g-1) did not show significant variations between accessions. Furthermore, the results showed that Moroccan walnut constitutes an important source of nutrient elements, essentially fat, carbohydrates, protein, phosphorus and zinc, and natural antioxidants, phenolic compounds. Accordingly, consumption of all studied kernels accessions would be beneficial to health. This study showed considerable biochemical variation between the analyzed walnut accessions, which could help to select genotypes with desired traits according to their chemotypes.

Development of a core collection in Iranian walnut (Juglans regia L.) germplasm using the phenotypic diversity

Persian walnut (Juglans regia L.) is a very important nut crop with increasingly attention in the world. It was among the fruit tree species that has been propagated sexually, up to some decades ago. So, there were no or limited cultivars and the breeding works are usually new. In order to release new cultivars, a walnut improvement program started in Iran in 1980s. There was established a walnut collection, with selection of some superior genotypes from the orchards together with some introductions. As, the comprehensive characterization of germplasm is necessary in the breeding programs, in this study a collection of 104 Persian walnut accessions has been evaluated especially in order to create a core or breeding collection with reduced number of accessions and keeping maximum variability. To carry out this work, 18 walnut important traits were evaluated during 2014 and 2015 in the walnut collection of Horticultural Science Research Institute, Karaj, Iran. A wide variation was observed for several important characteristics such as leafing date (from March, 5 to April, 27), nut weight (6.60–15.33 g), kernel weight (2.67–8.21 g), and kernel percentage (35.39–71.09%). Significant correlations were observed between traits. Factor analysis showed that the six major factors affecting traits were explaining 79.9% of the total variance. The analysis, using maximization strategy through a heuristic algorithm, determined a core collection consisted of 27 accessions with similar variability respect to primary collection (mean difference percentage = 9.88% and coincidence rate of range = 95.05%). The parameters showed that this core includes 100% coverage of the primary diversity. According to result the F-test revealed no-significant differences for all traits. In this paper, for the first time, a walnut core collection was established from a primary collection. Conservation of this core collection could be more economic and better manageable for breeding purposes.

Evaluation of genetic variability among “Early Mature”Juglans regiausing microsatellite markers and morphological traits

Limiting the juvenile phase and reducing tree size are the two main challenges for breeders to improve most fruit crops. Early maturation and dwarf cultivars have been reported for many fruit species. “Early mature” and low vigor walnut genotypes were found among seedlings of Persian walnut. Nine microsatellite markers were used to evaluate genetic diversity among “Early Mature” Persian walnut accessions and provide a comparison with “normal growth” accessions. Six maturation related characteristics were also measured in “Early Mature” samples. Phenotypic traits and diversity indices showed relatively high levels of genetic diversity in “Early Mature” seedlings and indicated high differentiation between individuals. Seedling height, the most diverse phenotypic trait, has an important role in the clustering of “Early Mature” accessions. The “Early Mature” type had higher number of alleles, number of effective allele, and Shannon index compared to the “Normal Growth” group. The two types of studied walnuts had different alleles, with more than half of produced alleles specific to a specific group. “Early Mature” and “Normal Growth” walnuts had 27 and 17 private alleles, respectively. Grouping with different methods separated “Early Mature” and “Normal Growth” samples entirely. The presence of moderate to high genetic diversity in “Early Mature” walnuts and high genetic differentiation with “Normal Growth” walnuts, indicated that “Early Mature” walnuts were more diverse and distinct from “Normal Growth” samples. Moreover, our results showed SSR markers were useful for differentiating between “Early Mature” and “Normal Growth” walnuts. A number of identified loci have potential in breeding programs for identification of “Early Mature” walnuts at the germination phase.

Phenological and pomological characterization of Persian walnut to select promising trees

Iran has significant Persian walnut (Juglans regia L.) trees, most of which are seedling-grown. Due to the extensive variability of biological material, the result of cross-pollination and generative propagation prevailed about by natural dissemination or anthropogenic, Neiriz region in Iran has rich phenotypic diversity in walnut germplasm. Thus, morphological diversity of 540 walnut accessions from this region was studied and trees with promising fruits characteristics were identified. There was high variability for the measured phenological and pomological characteristics. The variance analysis detected significant differences among the studied accessions for most of characters. The coefficient of variation varied from 9.02 (nut diameter) to 104.20 % (first female flowering date). Among the accessions studied, the ranges of 3.60–20.28 g for nut weight, 1.32–10 g for kernel weight and 17.44–83.88 % for kernel percentage were observed. Positive and negative correlations were detected among different phenotypic traits. The first three factors explained 34.95 % of the total variability among the studied accessions. The accessions studied were clustered into several groups by a bi-plot and cluster analysis. The best accessions were no. 573, 506, 374, 399, 527, 101, 150, 95, 91 and 472, which had thinner shell, heavier kernel, light kernel, more lateral fruitfulness and late flowering. The most promising trees will be used to the benefit of conservation research, breeding and cultivation. Moreover, based on the observed structures of variation, it is concluded that the magnitude of morphological variation in the material studied is high and the implications of the results for plant breeding programs are discussed.

Genetic divergence in seedling trees of Persian walnut for morphological characters in Markazi province from Iran

Walnut (Juglans regia L.) is one of the most important nutritional nut crops. Iran is considered as one of the centers for diversity and cultivation of walnut in the Middle East. In this investigation, 30 morphological traits were used to evaluate genetic potential of 100 walnut accessions. Results showed considerable phenotypic diversity in the studied walnut germplasm. High correlations were found among evaluated variables, e.g., positive correlations between nut and kernel characters. Principal components analysis revealed that traits related to shell texture, shell serrations, nut length, nut width, and kernel length accounted for a large proportion of the observed variability. UPGMA cluster analysis divided accessions into five different cluster groups. These groups mainly differed in nut and kernel traits. In the present study, 26 of the 100 studied accessions were trees possessing desirable qualities of late leafing, nut weight, kernel weight, light kernel color, and kernel ratio, and are recommended for cultivation. Furthermore, high morphological variability indicated that this germplasm includes rich and valuable plant material for future walnut breeding.

Characterization of 14 Microsatellite Markers for Genetic Analysis and Cultivar Identification of Walnut

One hundred and forty-seven primer pairs originally designed to amplify microsatellites, also known as simple sequence repeats (SSR), in black walnut (Juglans nigra L.) were screened for utility in persian walnut (J. regia L.). Based on scorability and number of informative polymorphisms, the best 14 loci were selected to analyze a diverse group of 47 persian walnut accessions and one J. hindsii (Jepson) Jepson ex R.E. Sm × J. regia hybrid (Paradox) rootstock. Among the 48 accessions, there were 44 unique multi-locus profiles; the accessions with identical profiles appeared to be synonyms. The pairwise genetic distance based on proportion of shared alleles was calculated for all accessions and a UPGMA (unweighted pair group method with arithmetic mean) dendrogram constructed. The results agree well with what is known about the pedigree and/or origins of the genotypes. The SSR markers distinguished pairs of closely related cultivars and should be able to uniquely characterize all walnut cultivars with the exception of budsports. They provide a more powerful and reliable system for the molecular characterization of walnut germplasm than those previously tested. These markers have numerous applications for the walnut industry, including cultivar identification, verification of pedigrees for cultivar and rootstock breeding programs, paternity analysis, and understanding the genetic diversity of germplasm collections.

Genetic Relationships and Characterization of Persian Walnut (Juglans regia L.) Cultivars Using Restriction Fragment Length Polymorphisms (RFLPs)

RFLP markers were used to investigate genetic diversity among California walnut (Juglans regia) cultivars and germplasm collected worldwide. Sixteen of 21 RFLP markers were polymorphic in the 48 walnut accessions tested. RFLP markers were useful for identifying walnut cultivars. All genotypes were heterozygous at ≈20% of the loci for both California and worldwide germplasm. California walnut germplasm contained 60% of the worldwide allelic diversity. Cluster analysis of genetic distance between accessions and principal component analysis of allelic genotypes showed two major groups of walnut domestication. California germplasm was associated with germplasm from France, central Europe, and Iran and had less genotypic similarity with germplasm from Nepal, China, Korea, and Japan.

675 PB 157 GENETIC RELATIONSHIPS OF JUGLANS REGIA L. CULTIVARS DETERMINED FROM RFLP ANALYSIS

RFLP markers were used to study genetic diversity among California walnut (Juglans regia L.) cultivars and germplasm collected worldwide. 16 of 21 RFLP markers were polymorphic in the 48 walnut accessions tested. Seven RFLP markers permitted unique identification of all walnut cultivars. All genotypes were heterozygous at approximately 20% of the loci for both California and worldwide germplasm. California walnut germplasm contained 65% of the worldwide allelic diversity. Cluster analysis of genetic distance between accessions and principal component analysis of allelic genotypes showed two major groups of walnut domestication. California germplasm was associated with germplasm from France, Central Europe, and Iran, and had less genotypic similarity with germplasm from Nepal, China, Korea, and Japan.