Walnut Production Research Articles

A Model for Fat Content Detection in Walnuts Based on Near-Infrared Spectroscopy

Near-infrared spectroscopy (NIR) is an efficient and accurate method for fat content detection in walnuts. ‘Wen 185’ walnut is grown in large quantities in southern Xinjiang, and its fat content is an important indicator for evaluating the intrinsic quality. The excessive pursuit of yield efficiency, combined with the neglect of quality, agricultural product safety and other factors, has led to the production of poor-quality walnuts. Moreover, research on predicting walnut kernel fat content based on near-infrared spectroscopy technology is rarely reported. Therefore, a technical framework for walnut kernel detection based on near-infrared spectroscopy and the technical standards for ‘Wen 185’ are urgently needed. After first optimizing the initial spectrum data using five preprocessing methods, we established separate prediction models for walnut kernel fat content based on either a back propagation neural network or a support vector regression (SVR) algorithm. The results show that the correction set and validation set coefficients of determination of the walnut kernel fat content prediction model using the back propagation neural network algorithm were 0.86 and 0.89, respectively, with root mean square errors of 1.56 and 1.58, and an RPD value of 2.57; the coefficients of determination for the calibration and validation sets of SVR were 0.90 and 0.83, respectively, with root mean square errors of 1.76 and 1.70, respectively, and an RPD value of 1.70. Thus, near-infrared spectroscopy can be used to establish a foundation for realizing the rapid detection of walnut kernel fat content.

Soil Fertility Dynamics and Identify the Most Limiting Nutrients Affecting Walnut Productivity in Nepal

This study aimed to assess the soil nutrient status in walnut orchards of different ages in Jajarkot district, Nepal, to understand soil fertility dynamics and identify the most limiting nutrients affecting walnut productivity. The research employed a randomized complete block design (RCBD) with three treatments representing different age groups of walnut orchards (1-5 years, 6-10 years, and 11-15 years), each replicated seven times across various municipalities. The study was conducted in Jajarkot district, Karnali Province, Nepal, encompassing municipalities including Nalgad, Junichadey, and Barekot, from March to April 2023. Soil samples were collected from multiple depths (1, 2, and 3 feet) in each orchard and analyzed for pH, soil organic matter (SOM), total nitrogen, available phosphorus, and available potassium. Data analysis included descriptive statistics, one-way analysis of variance (ANOVA), and correlation analyses to explore relationships between soil parameters and orchard age. The study showed that significant variations were observed among different age groups of walnut orchards for soil pH, SOM, nitrogen, phosphorus, and potassium levels. Soil pH decreased with orchard age, while SOM, nitrogen, and phosphorus tended to increase with orchard age. Phosphorus was identified as the most limiting nutrient across all sampled soils, followed by nitrogen and potassium. Moreover, strong correlations were found between orchard age and soil N (r = 0.894, p < 0.01) and P (r = 0.776, p < 0.01), underscoring age-dependent nutrient dynamics. The study highlights the critical role of orchard age in shaping soil nutrient dynamics in walnut orchards. Older orchards exhibited higher levels of SOM, nitrogen, and phosphorus, indicating the accumulation of organic matter and nutrients over time. Phosphorus emerged as the primary limiting nutrient, essential for root growth, flowering, and fruiting in walnut trees. These findings underscore the importance of targeted fertilization strategies to optimize soil fertility and sustain long-term walnut productivity in the region.

Cooler Is Better: The Role of Temperature in the Reproductive Biology of Persian Walnut (Juglans regia L.) Studied in a Hungarian-Bred Cultivar

The aim was to determine the growth of pollen tubes throughout the transmitting tissue and the process of fertilization in open, optimal and over pollination on the 3rd, 6th and 9th day after pollination of pistillate flowers, together with apomixis. The experiment was carried out over 2 years in Lovasberény, Fejér district, Hungary, which differed in temperature conditions. The average number of pollen tubes in the locule of the ovary was significantly higher in 2017 (1.3%) than in 2019 (1%). A higher percentage of fruit set was recorded in 2017 compared to 2019. The percentage of apomictic fruits from variant of unpollination was higher in 2017 (10%) than in 2019 (3.7%). Based on these results it can be concluded that pollen tube growth and post-fertilization processes together with apomixis of cultivar ‘AK’ are better adaptable to lower temperatures. These findings may help us to move walnut production to the north or to higher altitudes, where the climate is more continental.

A General Image Super-Resolution Reconstruction Technique for Walnut Object Detection Model

Object detection models are commonly used in yield estimation processes in intelligent walnut production. The accuracy of these models in capturing walnut features largely depends on the quality of the input images. Without changing the existing image acquisition devices, this study proposes a super-resolution reconstruction module for drone-acquired walnut images, named Walnut-SR, to enhance the detailed features of walnut fruits in images, thereby improving the detection accuracy of the object detection model. In Walnut-SR, a deep feature extraction backbone network called MDAARB (multilevel depth adaptive attention residual block) is designed to capture multiscale information through multilevel channel connections. Additionally, Walnut-SR incorporates an RRDB (residual-in-residual dense block) branch, enabling the module to focus on important feature information and reconstruct images with rich details. Finally, the CBAM (convolutional block attention module) attention mechanism is integrated into the shallow feature extraction residual branch to mitigate noise in shallow features. In 2× and 4× reconstruction experiments, objective evaluation results show that the PSNR and SSIM for 2× and 4× reconstruction reached 24.66 dB and 0.8031, and 19.26 dB and 0.4991, respectively. Subjective evaluation results indicate that Walnut-SR can reconstruct images with richer detail information and clearer texture features. Comparative experimental results of the integrated Walnut-SR module show significant improvements in mAP50 and mAP50:95 for object detection models compared to detection results using the original low-resolution images.

Arbuscular mycorrhizal symbiosis with Rhizophagus irregularis DAOM197198 modifies the root transcriptome of walnut trees.

Walnut trees are cultivated and exploited worldwide for commercial timber and nut production. They are heterografted plants, with the rootstock selected to grow in different soil types and conditions and to provide the best anchorage, vigor, and resistance or tolerance to soil borne pests and diseases. However, no individual rootstock is tolerant of all factors that impact walnut production. In Europe, Juglans regia is mainly used as a rootstock. Like most terrestrial plants, walnut trees form arbuscular mycorrhizal symbioses, improving water and nutrient uptake and providing additional ecosystem services. Effects of arbuscular mycorrhizal symbiosis on root gene regulation, however, has never been assessed. We analyzed the response of one rootstock of J. regia to colonization by the arbuscular mycorrhizal fungus Rhizophagus irregularis DAOM197198. Plant growth as well as the nitrogen and phosphorus concentrations in roots and shoots were significantly increased in mycorrhizal plants versus non-colonized plants. In addition, we have shown that 1,549 genes were differentially expressed, with 832 and 717 genes up- and down-regulated, respectively. The analysis also revealed that some rootstock genes involved in plant nutrition through the mycorrhizal pathway, are regulated similarly as in other mycorrhizal woody species: Vitis vinifera and Populus trichocarpa. In addition, an enrichment analysis performed on GO and KEGG pathways revealed some regulation specific to J. regia (i.e., the juglone pathway). This analysis reinforces the role of arbuscular mycorrhizal symbiosis on root gene regulation and on the need to finely study the effects of diverse arbuscular mycorrhizal fungi on root gene regulation, but also of the scion on the functioning of an arbuscular mycorrhizal fungus in heterografted plants such as walnut tree.

Energy Use and Carbon Emissions of Walnut Production in Türkiye

Energy Use and Carbon Emissions of Walnut Production in Türkiye

Flavor release from walnut kernels in an in-vitro mastication model with decoupled oral parameters

Consumer preferences for walnut products are largely determined by the flavors released during mastication. In this study, a peeled walnut kernel (PWK) model was established with oral parameters decoupled using a Hutchings 3D model. The model explored in vitro variations using head-space solid-phase microextraction-gas chromatography-mass spectrometry and intelligent sensory techniques. The fracture strength, hardness, particle size, adhesiveness, springiness, gumminess, and chewiness were significantly reduced during mastication. We identified 61 volatile compounds and found that 2,5-dimethyl-3-ethylpyrazine is a key component, releasing predominantly baking and milky notes. Glutamic acid, alanine, arginine, and sucrose were identified as the key compounds in taste perception. The method can help establish a mastication model for nuts and facilitate breakthroughs in the development of walnut products and processing methods.

Development of Real-time PCR Method for Detection of Xanthomonas campestris pv. juglandis Causing Walnut Bacterial Blight

Walnut is one of the important economic tree species in the world. For the past few years, with the continuous expansion of walnut planting area, walnut bacterial blight caused by Xanthomonas campestrispv. juglandis has critically affected walnut production and caused economic losses. In this research, by comparing the gene sequences of X. campestrispv. juglandis and its closely related bacterial species, the 16S rDNA gene sequence was selected, and the specific primers were evaluated using PCR. Subsequently, the real-time fluorescence PCR specific detection method of X. campestrispv. juglandis was established and optimized. The specificity of real-time PCR was verified for 23 strains isolated from walnut and its surrounding soil, including eight target pathogens. The specific amplification was possible even when the cDNA template concentration was 7.0×10-5 µg/mL, hence, the detection sensitivity of the standard method is 7.0×10-5 µg/mL. The reliability of the established real-time PCR detection method in field detection was verified by the identification of target bacteria in 8 randomly collected healthy leaves and leaves of suspected walnut blight. This method laid a foundation for the early diagnosis of X. campestrispv. juglandis.

Genome-wide identification of the walnut MYC gene family and functional characterization of Xinjiang wild walnut under low-temperature stress.

Introduction: MYC transcription factors are the basic regulators of the jasmonic acid signaling pathway and play important roles in plant growth and development and the response to adverse stress. In recent years, severe winter freezing and late spring frost in the main planting area of walnut in Xinjiang have affected the growth and development of walnut, which has become a prominent problem restricting walnut production. Xinjiang wild walnut is the only remaining wild species of walnuts in China, which contains a lot of genes with excellent traits, and is important for the cultivation and breeding. Methods: In this paper, the physicochemical properties and bioinformatics of MYC transcription factor members in walnut were analyzed, and the nine MYC were screened from the transcriptome data under low temperature stress. At last, we study the subcellular localizations and the expression patterns of the nine MYC members in Xinjiang wild walnut. Results: The results revealed that 30 MYC members were identified from published walnut whole-genome data, and their evolutionary relationships with Arabidopsis and poplar were divided into six groups according to clustering analysis, among which JrMYC22 and JrMYC23 had high homology with PtrMYC2b, which is induced by jasmonic acid in response to low-temperature stress. Walnut MYC members are unevenly distributed on 12 chromosomes. The prediction of promoter cis-acting elements of walnut MYC transcription factor family members revealed that cis-acting elements related to jasmonic acid and lowtemperature stress were the ones with the greatest number of members, with 12. In addition, all nine MYC family members in Xinjiang wild walnut plants responding to low-temperature stress exhibited strong fluorescence responses in the nucleus. The expression levels of these members in response to low-temperature stress revealed that JrMYC28, JrMYC31, JrMYC33, JrMYC34, and JrMYC35 were highly expressed, and it was hypothesized that JrMYC28, JrMYC31, JrMYC33, JrMYC34, and JrMYC35 might play a key role in the response to lowtemperature stress. Discussion: The results of this study provide a theoretical basis for further research on the functional mechanisms of the MYC transcription factor family members in walnut.

Morphological and pomological assessments of seedling-originated walnut (Juglans regia L.) trees to select the promising late-leafing genotypes.

In many parts of the world, including Iran, walnut (Juglans regia L.) production is limited by late-spring frosts. Therefore, the use of late-leafing walnuts in areas with late-spring frost is the most important method to improve yield. In the present study, the phenotypic diversity of 141 seedling genotypes of walnut available in the Senejan area, Arak region, Markazi province, Iran was studied based on morphological traits to obtain superior late-leafing genotypes in the cropping seasons of 2022 and 2023. Based on the results of the analysis of variance, the studied genotypes showed a significant variation in terms of most of the studied morphological and pomological traits. Therefore, it is possible to choose genotypes for different values ​​of a trait. Kernel weight showed positive and significant correlations with leaf length (r = 0.32), leaf width (r = 0.33), petiole length (r = 0.26), terminal leaflet length (r = 0.34), terminal leaflet width (r = 0.21), nut length (r = 0.48), nut width (r = 0.73), nut weight (r = 0.83), kernel length (r = 0.64), and kernel width (r = 0.89). The 46 out of 141 studied genotypes were late-leafing and were analyzed separately. Among late-leafing genotypes, the length of the nut was in the range of 29.33-48.50mm, the width of the nut was in the range of 27.51-39.89mm, and nut weight was in the range of 8.18-16.06g. The thickness of shell was in the range of 1.11-2.60mm. Also, kernel length ranged from 21.97-34.84mm, kernel width ranged from 21.10-31.09mm, and kernel weight ranged from 3.10-7.97g. Based on important and commercial traits in walnut breeding programs, such as nut weight, kernel weight, kernel percentage, kernel color, and ease of kernel removal from nuts, 15 genotypes, including no.92, 91, 31, 38, 33, 18, 93, 3, 58, 108, 16, 70, 15, 82, and 32 were superior and could be used in walnut breeding programs in line with the introduction of new cultivars and the revival of traditional walnut orchards to commercialize them.

Impact of climatic variations in horticulture sector, Kinnaur, Himachal Pradesh, India

Climate change has an impact on the horticulture crops of Himachal Pradesh in relation to the varying climatic conditions in the Himalayan Region. The purpose of the study was to determine how frequently these differences in horticultural crops occur in the Kinnaur district of Himachal Pradesh since the horticulture industry in Himachal Pradesh greatly benefits from this district. Long-term temperature (maximum, minimum, and diurnal) and rainfall data from 1990 to 2020 were analyzed for different phenological stages (pre-flowering, flowering, and fruit setting). The findings revealed that the average maximum and diurnal temperatures were found to have increased significantly, at the rate by 0.027 °C and 0.042 °C, respectively, during the flowering stages. However, there were no appreciable changes in the variations for other phenological stages. Under trend analysis of crop yield, the productivity of Pear and Almond notably fell over the past 20 years, at -0.029 t/ha/year and -0.016 t/ha/year, respectively, whereas Walnut productivity climbed at 0.008 t/ha/year. The relationship or impact between the climate and the crop was also examined in addition to the trend analysis for crop and climatic variables. The results showed that among the three phenological stages, Apple and Apricot were highly impacted (54.4%) during pre-flowering stage, followed by Apricot, i.e., 72.6% during flowering, and Grapes (53.2%) during the fruit setting stage. In the current situation, climate fluctuations had a favorable effect on Apples, Walnuts and Grapes while having a negative effect on Apricots, Plums, Pears and Almonds.

Genome-wide identification analysis of the 4-Coumarate: CoA ligase (4CL) gene family expression profiles in Juglans regia and its wild relatives J. Mandshurica resistance and salt stress

Persian walnut (Juglans regia) and Manchurian walnut (Juglans mandshurica) belong to Juglandaceae, which are vulnerable, temperate deciduous perennial trees with high economical, ecological, and industrial values. 4-Coumarate: CoA ligase (4CL) plays an essential function in plant development, growth, and stress. Walnut production is challenged by diverse stresses, such as salinity, drought, and diseases. However, the characteristics and expression levels of 4CL gene family in Juglans species resistance and under salt stress are unknown. Here, we identified 36 Jr4CL genes and 31 Jm4CL genes, respectively. Based on phylogenetic relationship analysis, all 4CL genes were divided into three branches. WGD was the major duplication mode for 4CLs in two Juglans species. The phylogenic and collinearity analyses showed that the 4CLs were relatively conserved during evolution, but the gene structures varied widely. 4CLs promoter region contained multiply cis-acting elements related to phytohormones and stress responses. We found that Jr4CLs may be participated in the regulation of resistance to anthracnose. The expression level and some physiological of 4CLs were changed significantly after salt treatment. According to qRT-PCR results, positive regulation was found to be the main mode of regulation of 4CL genes after salt stress. Overall, J. mandshurica outperformed J. regia. Therefore, J. mandshurica can be used as a walnut rootstock to improve salt tolerance. Our results provide new understanding the potential functions of 4CL genes in stress tolerance, offer the theoretical genetic basis of walnut varieties adapted to salt stress, and provide an important reference for breeding cultivated walnuts for stress tolerance.

An exploratory analysis of the structure of tetranychid and phytoseiid assemblages in walnut orchards in California.

Spider mites were considered secondary pests of walnut production in California, under the control of phytoseiid predators. Due to increased importance as walnut pests in recent decades there is renewed interest in the structure and function of the associated phytoseiid assemblage. In this study we report the results from a 3 year survey of the tetranychid and phytoseiid assemblages in walnut orchards in the Central Valley of California. The survey was conducted to determine the range and dominance of web-spinning Tetranychus species present, to investigate the species richness and dominance of the phytoseiid species present, and to explore whether patterns of variation in the relative abundance of phytoseiid species could be explained by one or more explanatory variables. Tetranychus urticae was the dominant spider mite in all growing regions and years with T. pacificus and T. turkestani also present in orchards in the southern San Joaquin Valley. Phytoseiid species richness declined with latitude among the three walnut growing regions and of the 13 species found Amblyseius similoides, Euseius stipulatus, Galendromus occidentalis and Typhlodromus caudiglans were the most abundant and widespread species present. Mean proportional abundance significantly increased from early (mid May-July) to late (August-mid October) season and from southern to northern growing regions for Type II and IV predators, but significantly decreased from early to late season and from southern to northern growing regions for Type III predators. The mean proportional abundance of Type II predators, particularly G. occidentalis, significantly increased and that of Type III predators significantly decreased with mean Tetranychus density in individual orchards. The current survey provides a more in-depth analysis of mite assemblages in walnut orchards in California and can be used to better inform adaptive management strategies for integrated mite management in the future.

Soil Fertility Dynamics and Identify the Most Limiting Nutrients Affecting Walnut Productivity in Nepal

Soil Fertility Dynamics and Identify the Most Limiting Nutrients Affecting Walnut Productivity in Nepal

Colletotrichum species (Glomerellales, Glomerellaceae) causing walnut anthracnose in China.

Colletotrichum species can function as plant pathogens, saprobes or endophytes on a wide variety of plant hosts and are considered amongst the ten most significant genera of plant pathogens globally. China contributes almost half the walnut production in the world. However, Colletotrichum species occurring on walnut remain largely unresolved in China. To explore the Colletotrichum species found on walnut in China, 470 walnut fruit or leaf samples with anthracnose were collected from 14 main walnut-producing regions across seven provinces. A total of 165 Colletotrichum strains were isolated from these samples. The Colletotrichum isolates were identified, based on morphological characteristics and sequence analyses of ACT, CHS-1, GAPDH, ITS and TUB2. Twelve species, including 11 known Colletotrichum species (C.boninense, C.citrulli, C.fioriniae, C.fructicola, C.godetiae, C.juglandicola, C.karsti, C.mengyinense, C.pandanicola, C.peakense and C.siamense) and a novel species (C.chinensis sp. nov.) were identified. The species distribution revealed regional prevalence as follows: C.mengyinense was the most dominant species in Gansu, C.mengyinense and C.siamense in Shandong, C.chinensis in Beijing, C.pandanicola in Shaanxi and C.godetiae in Yunnan. Colletotrichumsiamense was the sole species isolated in Sichuan and Xinjiang Provinces. Koch's postulates were fulfilled, demonstrating that all 12 species cause anthracnose on walnut. This is the first report of C.boninense, C.citrulli and C.karsti as pathogens of walnut anthracnose worldwide.

Forecasting business risk in organic walnut production

Forecasting business risk in organic walnut production

Economic and Profitability Analysis of Walnut Production in Kashmir Valley, India

The Jammu and Kashmir union territory is the largest producer of walnuts in India, and this crop provides an important source of livelihood for many farmers. This study aims to measure the economic efficiency and profitability of walnut orchards and explore constraints in cultivation in the Kashmir Valley. It relies on a crosssectional database collected from 240 walnut growers in the study area during the 2018/19 production period. Results reveal that walnut cultivation is highly laborintensive as it incurs 80 percent of total production costs. The cost-benefit ratio of 1:5.35 per hectare indicates better economic prospects for the walnut industry in Kashmir Valley. The factors affecting productivity include farmyard manure, labor, chemical fertilizers, plant density, women participation, and information. The regression coefficients of production analysis, marginal value product, and marginal factor cost ratio indicate that there is ample scope for the expansion of walnut cultivation in the research area. However, walnut growers are confronted by several problems that tend to be location specific. The study calls for policy intervention concerning improved access to extension services, credit, and farmer training programs to boost walnut production in the study region.

Antimicrobial Activity and Mechanisms of Walnut Green Husk Extract.

Walnut green husks (WGHs), by-products of walnut production, are believed to possess antimicrobial properties, making them a potential alternative to antibiotics. In this study, the antibacterial activities of three extracts, derived from WGH, against Staphylococcus aureus, Bacillus subtilis, and Escherichia coli were investigated, and the antibacterial mechanisms of an anhydrous ethanol extract of WGH (WGHa) were examined. The results showed that WGHa exhibited inhibitory effects on all tested bacteria. The ultrahigh-performance liquid chromatography-tandem mass spectrometry analysis revealed that the major active compounds present in WGHa were terpenoids, phenols, and flavonoids. Treatment with WGHa resulted in the leakage of intracellular ions and alkaline phosphatase; a reduction in intracellular ATP content, ATPase activity, and nucleic acid content; as well as cellular metabolic viability. The transmission electron microscopy images showed varying degrees of cell deformation and membrane damage following WGHa treatment. The transcriptome sequencing and differentially expressed gene enrichment analyses revealed an up-regulation in pathways associated with RNA degradation, translation, protein export, and oxidative phosphorylation. Conversely, pathways involved in cell movement and localization, as well as cell wall organization and carbohydrate transport, were found to be down-regulated. These findings suggest that WGHa alters cell membrane permeability and causes damage to the cell wall. Additionally, WGHa interferes with cellular energy metabolism, compromises RNA integrity, and induces DNA replication stress, consequently inhibiting the normal growth and proliferation of bacteria. These findings unveiled the antimicrobial mechanisms of WGHa, highlighting its potential application as an antibiotic alternative.

Comparison of different drying technologies for walnut (Juglans regia L.) pellicles: Changes from phenolic composition, antioxidant activity to potential application

The analysis of the phenolic profile in the walnut pellicle (WP) and its exploitability can help to promote the valorization of the industrial waste from walnut production. Three forms of 33 monomeric phenols in WPs were quantified based on our previously established LC-MS/MS method. The levels of protocatechuic acid and 4-hydroxybenzoic acid in the WPs were the highest, exceeding 400 μg/g. Antioxidant tests revealed that all three phenolic forms of WPs were effective antioxidants (IC50: 2.12–35.05 µg/mL). The findings also revealed that drying temperature had a substantial type-dependent effect on phenolics and their antioxidant ability in WPs. KEGG enrichment analysis found that drying method has the greatest impact on WPs phenols in six metabolic pathways. Besides, 11 active substances in WPs were identified by a compound-targeted activity screening approach, indicating that WPs could be used as a natural antioxidant source in the development of medical and nutraceutical products.

Juglans regia and Carya illinoinensis: safety, chemical composition, and preference

This study aimed to investigate the global scientific production of Chilean walnuts and pecans, analyze the efficiency of hygienic-sanitary treatments, compare both nuts for chemical composition and preference, perform chemical analyses of the pecan nutshell, prepare food bars with nuts and shells, and test their acceptability. Studies were consulted in the Scopus database and then directed to bibliometric analysis. Hygienic-sanitary treatments were performed by placing the nuts in the shell in hot water, cold water with hypochlorite, hot water with hypochlorite, and microwave. The proximate composition followed the official methods, and the sensorial analysis of the nuts was performed through a bilateral paired affective test. Food bars were prepared, tested by an affective acceptability test, and analyzed for chemical composition. After refining the research, we observed more publications for the walnut and its satisfactory hygienic-sanitary treatment with hot water of mesophilic aerobic bacteria, molds, yeasts, Salmonella, Escherichia coli, and mycotoxins. Regarding the physicochemical composition, the results differed significantly except for the ether extract; the untrained tasters preferred pecans. The pecan nutshell showed expressive amounts of carbohydrates and fiber, and the food bars were accepted by the tasters.