Walnut Quality Research Articles

Influence of Soil Extractable Plant Nutrients on the Walnut Kernel Ionome in Southern Kyrgyzstan at Different Elevations

Abstract Background and Aims Climate change causes altered precipitation patterns and temperature increases, which may affect food quantity and quality. In Kyrgyzstan anticipated temperature changes are expected to influence the physiology of walnuts (Juglans regia L.) and soil properties relevant to plant nutrition, thereby impacting walnut fruit quality. This study explores the relationship between plant available nutrients in soil and walnut fruit nutrient content as affected by future temperature changes. Methods The soil samples were collected in the walnut forests of Southern Kyrgyzstan from top- and subsoils at three elevation levels (1000, 1300, and 1600 m above sea level). The walnut samples were collected from the same sampling sites and both soil Mehlich-3 extracts and acid digests of walnut fruits analyzed by ICP-OES. Results The results revealed no consistent relationship between Mehlich-3 extractable elements and walnut extractable elements, except for a weak negative correlation with zinc (Zn). Stronger relationships were observed among soil elements, but no clear associations with elevation levels were found. The walnut kernel ionome exhibited differences, particularly in calcium (Ca) and potassium (K) concentrations, with the low elevation site showing higher Ca and lower K concentrations compared to the high elevation site. Conclusions Differences in average temperature as caused by elevation did not affect available plant nutrients in the soil but altered the walnut kernel ionome and thus affected the walnut quality in the investigated forest systems. Future investigations should focus on climate change effects, such as altered precipitation patterns and drought, which may impact walnut fruit development and kernel properties.

Effect of Extracted Walnut Pomace Cake Edible Coating and Packaging Type on Quality Parameters of Walnut (Juglans regia L.) Kernels During Long Storage Periods

Walnuts are highly valued for their rich nutritional content, but their quality degrades during storage due to oxidation and other quality reducing processes. This study investigated the use of bioactive compounds extracted from walnut pomace, a by-product of walnut oil production, to develop an edible coating that extends the shelf life of ‘Milotai 10’ walnut kernels. Walnut kernels were stored for eight months in four different packaging materials (PE, PP, MPP, PLA) and three treatments were used (air or without treatment, nitrogen gas, and walnut pomace extract coating). The effects of these combinations on walnut quality parameters, including polyphenol content, vitamin E, fatty acids, peroxide value, and color, were analyzed. The results show that the combination of metallized polypropylene packaging under nitrogen treatment or with atmospheric air and walnut pomace extract (MPP-A-E+) best preserves walnut quality, making it a promising option for extending shelf-life.

Detection of walnut internal quality via improved YOLOv5 and x‐ray imaging

AbstractThis study proposes a walnut target detection algorithm based on improved YOLOv5 and x‐ray imaging to meet the demand for internal quality detection and removal in the Xinjiang walnut industry. By replacing the C3 module in the backbone layer with the C2f module and the couple‐head in the head layer with the decouple‐head, the algorithm reduces computational complexity, enhances robustness and generalizability, and retains more spatial information, thereby improving the performance of multicategory small target detection. In addition, this paper replaces the original CIOU loss function with the EIOU loss function to improve the convergence speed of the algorithm's accuracy and boundary aspect ratio. Compared with the original model, the improved model, improved YOLOv5, maintains the same average precision for normal walnuts while increasing the average precision for shriveled walnuts and empty‐shell walnuts by 8.2% and 0.4%, respectively. Compared with other mainstream models, such as VGG16, ResNet50, YOLOv5s, YOLOv7, YOLOv8s, YOLOv9s, and YOLOv10s, this model achieves the highest detection accuracy and good detection performance, with a single‐image detection time of 11.9 ms, meeting the requirements for real‐time detection. This work lays a foundation for automatic robot detection of the internal quality and removal of walnuts, showing practical application potential.Practical applicationsXinjiang stands as a prominent producer of walnuts; however, due to the decentralized nature of its cultivation and management processes, a notable prevalence of internal empty shells and shrinkage is observed, which substantially diminishes their commercial value. The integration of YOLOv5 with x‐ray imaging technology promises to enhance the precision of internal quality assessments of walnuts. The improved YOLOv5 model, as delineated in this study, exhibits the highest detection accuracy when benchmarked against a multitude of other models. It achieves a detection latency of merely 11.9 ms per image, thereby satisfying the stringent demands for real‐time detection applications. This model is designed for integration into x‐ray systems with an adjunctive sorting mechanism, which facilitates the inspection and exclusion of defective walnuts on conveyor belts.

Foliar application of biostimulants improves nutritional and bioactive quality of walnuts.

Owing to their health benefits, walnuts are attracting interest as a good option for nutritious meals, thereby promoting their production. Furthermore, the adoption of ecologically and environmentally friendly agriculture strengthens biostimulant use as a sustainable complement to traditional fertilizers. This study evaluated the effects of different foliar-applied biostimulants in walnut tree orchards, in northeastern Portugal, on walnuts' chemical composition and bioactivity. Walnut samples were rich in fat (particularly the polyunsaturated linoleic acid), dietary fiber and protein. Sucrose was the most prevalent soluble sugar, followed by glucose and fructose. Studied samples also showed an antioxidant activity comparable (or superior) to that of Trolox. Some plant biostimulants (e.g. Sprint Plus®) had a positive impact on the nutritional composition of walnuts, more specifically by boosting tocopherol levels, besides improving the bioactivity of walnut extracts against specific bacteria. Overall, this research demonstrated that important quality traits of walnuts can be improved using sustainable agricultural bioproducts and practices. © 2024 Society of Chemical Industry.

Effects of leaf scorch on photosynthetic characteristics, fruit yield, and quality of walnuts

Effects of leaf scorch on photosynthetic characteristics, fruit yield, and quality of walnuts

A dual RNA-seq analyses revealed dynamic arms race during the invasion of walnut by Colletotrichum gloeosporioides

BackgroundWalnut anthracnose caused by Colletotrichum gloeosporioides seriously endangers the yield and quality of walnut, and has now become a catastrophic disease in the walnut industry. Therefore, understanding both pathogen invasion mechanisms and host response processes is crucial to defense against C. gloeosporioides infection.ResultsHere, we investigated the mechanisms of interaction between walnut fruits (anthracnose-resistant F26 fruit bracts and anthracnose-susceptible F423 fruit bracts) and C. gloeosporioides at three infection time points (24hpi, 48hpi, and 72hpi) using a high-resolution time series dual transcriptomic analysis, characterizing the arms race between walnut and C. gloeosporioides. A total of 20,780 and 6670 differentially expressed genes (DEGs) were identified in walnut and C. gloeosporioides against 24hpi, respectively. Generous DEGs in walnut exhibited opposite expression patterns between F26 and F423, which indicated that different resistant materials exhibited different transcriptional responses to C. gloeosporioides during the infection process. KEGG functional enrichment analysis indicated that F26 displayed a broader response to C. gloeosporioides than F423. Meanwhile, the functional analysis of the C. gloeosporioides transcriptome was conducted and found that PHI, SignalP, CAZy, TCDB genes, the Fungal Zn (2)-Cys (6) binuclear cluster domain (PF00172.19) and the Cytochrome P450 (PF00067.23) were largely prominent in F26 fruit. These results suggested that C. gloeosporioides secreted some type of effector proteins in walnut fruit and appeared a different behavior based on the developmental stage of the walnut.ConclusionsOur present results shed light on the arms race process by which C. gloeosporioides attacked host and walnut against pathogen infection, laying the foundation for the green prevention of walnut anthracnose.

Genome-Wide Analysis of Transcription Factor R2R3-MYB Gene Family and Gene Expression Profiles during Anthocyanin Synthesis in Common Walnut (Juglans regia L.).

The R2R3-MYB gene family, encoding plant transcriptional regulators, participates in many metabolic pathways of plant physiology and development, including flavonoid metabolism and anthocyanin synthesis. This study proceeded as follows: the JrR2R3-MYB gene family was analyzed genome-wide, and the family members were identified and characterized using the high-quality walnut reference genome "Chandler 2.0". All 204 JrR2R3-MYBs were established and categorized into 30 subgroups via phylogenetic analysis. JrR2R3-MYBs were unevenly distributed over 16 chromosomes. Most JrR2R3-MYBs had similar structures and conservative motifs. The cis-acting elements exhibit multiple functions of JrR2R3-MYBs such as light response, metabolite response, and stress response. We found that the expansion of JrR2R3-MYBs was mainly caused by WGD or segmental duplication events. Ka/Ks analysis indicated that these genes were in a state of negative purifying selection. Transcriptome results suggested that JrR2R3-MYBs were widely entangled in the process of walnut organ development and differentially expressed in different colored varieties of walnuts. Subsequently, we identified 17 differentially expressed JrR2R3-MYBs, 9 of which may regulate anthocyanin biosynthesis based on the results of a phylogenetic analysis. These genes were present in greater expression levels in 'Zijing' leaves than in 'Lvling' leaves, as revealed by the results of qRT-PCR experiments. These results contributed to the elucidation of the functions of JrR2R3-MYBs in walnut coloration. Collectively, this work provides a foundation for exploring the functional characteristics of the JrR2R3-MYBs in walnuts and improving the nutritional value and appearance quality of walnuts.

Screening and Characterization of Antioxidant Film Applicable to Walnut Kernels from Juglans sigillata.

Walnuts play a positive role in human health due to their large amounts of unsaturated fatty acids, whereas lipid oxidation can easily occur during storage. Herein, three natural antioxidants (epicatechin, sesamol, and myricetin) were added to the composite film cross-linked with chitosan and soy protein peptide, and the antioxidant film appropriate for the preservation of walnut kernels from Juglans sigillata was screened to improve the storage quality of walnuts. The results showed that three antioxidant films could all enhance the storage performance of walnut kernels, with sesamol being the best. The characterization of antioxidant film cross-linked with chitosan and soy protein peptide containing sesamol (C/S-ses film) revealed that the composite film improved the slow release and stability of sesamol; in addition, the presence of sesamol could effectively reduce the light transmittance and water vapor permeability of the composite film, together with significantly enhancing the antioxidant and antimicrobial activities, resulting in an effective prolongation of the storage period of walnut kernels. These findings indicated that C/S-ses possess excellent potential for retarding the oxidative rancidity of unsaturated fatty acids and will provide an effective strategy for the preservation of walnut kernels.

Design and Development of Walnut Dehuller-cum-washer

Traditional manual practices of walnut dehulling and washing are tedious, laborious, and time consuming. Power-operated and manual-operated walnut dehuller-cum-washers were designed, developed, and evaluated in comparison to existing manual methods. The performance parameters evaluated in the present study differed significantly (p<0.05) in all three tested methods. Highest throughput capacity (340 kg.h-1) was observed for power-operated walnut dehuller-cum-washer (M1), followed by 16.25 kg.h-1 by manual-operated walnut dehuller-cum-washer (M2), and12.54 kg.h-1 by manual dehulling and washing (M3). Labour requirement was lowest in M1 (2.94 man.h.t-1), followed by M2 (61.53 man.h.t-1), and M3 (79.74 man.h.t-1). Highest dehulling and washing efficiency was in case of M1 (96.82%), followed by M3 (85.17%), and M2 (82.60%). Furthermore, M1, M2, and M3 yielded fully dehulled walnut percentages of 97.20, 81.20, and 94.56; partially dehulled walnut percentages of 1.87, 7.80, and 4.74%; and un-hulled walnut percentages of 0.9, 9.5, and 0.5%, respectively. Broken walnut percentage was least (0.02%) in case of M1, followed by M3 (0.20%), and M2 (0.50%). Hardness of walnut was highest with M1, and lowest for M3. Peroxide value and free fatty acid content were lowest in case of walnut processed by M1, followed by M2, and M3. Brightness (L*) of un-shelled walnut as well as kernel were highest for M1; whereas redness (a*) and yellowness (b*) were minimum in walnut processed by M1. Adoption of the developed prototypes in walnut dehulling and washing can significantly enhance the throughput capacity with drastic reduction of labour requirement, besides improving the quality of whole walnut as well as its kernel.

Physical and chemical characteristics of walnut (Juglans regia L.) kernels with different skin lightness.

Walnuts undergo rigorous grading before being sold to customers. There are multiple parameters used for the grading, including skin lightness. Walnuts with light skin receive superior grades while walnuts with dark skin are given poor grades or even rejected. However, information on the quality and physicochemical properties of walnuts with varying skin lightness levels is minimal. Therefore, we studied the quality of kernels of varying skin lightness from three common cultivars grown in California, USA (Chandler, Howard, and Tulare). The samples were subjected to size and weight, fat content, free fatty acid, peroxide value, oxidative stability, volatiles, tocopherols, fatty acid profile, and phenol measurements. The dark kernels had significantly lower weight and fat content, higher oxidative stability, and more volatiles than their light counterparts. The dark kernels had higher concentrations of some phenolics but low procyanidin B1 and non-existent epicatechin gallate, compared to the light kernels, indicating that these two phenolics were likely involved in an antioxidant mechanism. Oxidation and depletion of epicatechin gallate likely contributed to the darkening of walnut color.

Transcriptomic Evidence of a Link between Cell Wall Biogenesis, Pathogenesis, and Vigor in Walnut Root and Trunk Diseases.

Crown gall disease (Agrobacterium tumefaciens), crown/root rot disease (Phytophthora spp.), root lesion disease (Pratylenchus vulnus) and tree vigor are key traits affecting the productivity and quality of walnuts in California. Unchallenged hybrid rootstocks were analyzed by RNA-seq to examine pre-formed factors affecting these traits. Enrichment analysis of the differentially expressed genes revealed that the increased expression of cell wall biogenesis-related genes plays a key role in susceptibility to A. tumefaciens, susceptibility to Phytophthora spp. and increased vigor. Analysis of the predicted subcellular loci of the encoded proteins revealed that many gene products associated with vigor and susceptibility were targeted to the plasma membrane and extracellular space, connecting these traits to sustaining barrier function. We observed that RNA processing and splicing, along with predicted nuclear targeting, were associated with resistance to A. tumefaciens, resistance to Phytophthora spp. and low vigor. Four genes within the J. microcarpa QTL region for resistance to A. tumefaciens and Phytophthora spp. were represented among our transcripts, with two of the genes being differentially expressed in association with resistance to A. tumefaciens and decreased vigor. No differential expression related to Phytophthora spp. or P. vulnus resistance was observed in this region. Additionally, the J. microcarpa haplotype expressed more transcripts associated with resistance to A. tumefaciens, Phytophthora spp. and low vigor, but not P. vulnus, than the J. regia haplotype. We also report unique and shared hormone and defense responses associated with each trait. This research suggests a link between cell wall biogenesis, vigor and critical root diseases of walnut.

Walnut phosphatase 2A proteins interact with basic leucine zipper protein JrVIP1 to regulate osmotic stress response via calcium signaling.

Walnut is an important economic tree species that is susceptible to osmotic stress. Scientific cultivation management is an important way to improve the yield and quality of walnuts, which requires understanding the regulatory mechanisms in response to osmotic stress. Therefore, in this study, 15 protein phosphatase 2A (PP2A) genes were identified from the walnut transcriptome (named JrPP2A01~15) and their potential function responses to osmotic stress were elucidated. The open reading frame (ORF) of JrPP2A01~15 ranges from 651 to 1,764 bp in length, the molecular weight of the encoded proteins are 24.15-65.61 kDa, and the theoretical isoelectric points are 4.80-8.37. These JrPP2As were unevenly distributed on 10 chromosomes and divided into five groups based on the composition of conserved domains, motifs, and exon/intron organizations. The five groups are JrPP2AAs, JrPP2AB's, JrPP2AB''s, JrPP2AB55s, and JrPP2ACs, including 1, 5, 2, 3, and 4 members, accordingly. The cis-elements in JrPP2As' promoters were involved in responses to hormone and abiotic stress. Most JrPP2A genes, excluding JrPP2A01, JrPP2A02, JrPP2A05, JrPP2A06, and JrPP2A13, could be induced significantly by PEG6000, NaCl, CaCl2 and ABA. JrPP2A02, JrPP2A05, JrPP2A07, JrPP2A09, and JrPP2A14, could independently interact with a bZIP transcription factor JrVIP1. Moreover, overexpression of JrPP2A07, JrPP2A09, and JrPP2A14 could significantly decrease ROS accumulation while increasing calcium (Ca) uptake exposed to PEG6000 and NaCl stresses, which was mediated by exogenous CaCl2 and ABA. These results suggested that JrPP2A genes play potential key roles in walnut response to drought and salt-inducing osmotic stress involving Ca- and ABA-dependent signaling pathways.

Physiological and transcriptomic analyses of response of walnuts (Juglans regia) to Pantoea agglomerans infection.

Walnut blight is a serious bacterial disease that affects the yield and quality of walnuts. Pantoea agglomerans is one of the main causative agents of walnut blight. However, there have been few studies on the response of walnuts to P. agglomerans infection. In this study, the soluble sugar, photosynthesis, antioxidant enzyme activities, and secondary metabolites were measured, and the transcriptomic analysis was performed to determine the response of walnut tissue cultures to P. agglomerans infection. After pathogen inoculation, the soluble sugar content decreased, and photosynthesis was inhibited. Antioxidant enzyme (superoxide dismutase and peroxidase) activities and secondary metabolites (phenol and flavonoid) contents increased, especially in the early stages of inoculation. Transcriptomic analysis revealed that the phenylpropanoid biosynthesis pathway is induced after infection, and pathogen infection promotes ABA and ethylene signal transduction and inhibits auxin signaling. In addition, SA and JA-related gene expression was altered after inoculation with P. agglomerans, and the FLS- and calcium-mediated disease resistance signaling pathways were activated. Furthermore, our results suggested an involvement of the R-protein RPM-mediated disease resistance pathway in the response of walnuts to bacterial infections. Our findings indicated that phenylpropanoid biosynthesis, hormone signal transduction, and plant-pathogen interaction have key roles in pathogenic inoculation, which provide insights into the molecular mechanisms in the response of walnuts to P. agglomerans infection.

Postharvest drying of walnuts: Effect of drying methods on walnut quality

It has been demonstrated that drying can significantly promote the antioxidant active substances of fresh walnut, as well as enhance lipid content and conversion of glycerol phospholipids to lysophospholipids in walnut. Currently, oven drying (OD) and natural air drying (NAD) are the two most commonly used drying methods for walnut. However, the differences in their effects on the quality of the final product remain unclear. This study investigated the effect of OD and NAD on the phenotypic and physiological properties and lipid oxidation of four main walnut varieties W10, W179, W185, X2 in Xinjiang, China, and determined the correlations among these properties. The results showed that OD could maintain plump and yellowish white kernels, whereas NAD led to noticeably darker and more wrinkled kernels at the end of drying. In addition, an analysis of quality-related metabolites revealed that two representative lipids PC (18:2_18:2) and PC (18:1_16:0) had completely different patterns under OD and NAD, and the metabolites highly relevant to these two lipids were mainly enriched in amino acid and ascorbate metabolism pathways. Comprehensive physiological and metabolite analysis indicated that OD outperforms NAD in maintaining walnut quality, and may be applied to industrial walnut drying.

Genome-wide identification and molecular expression profile analysis of FHY3/FAR1 gene family in walnut (Juglans sigillata L.) development

BackgroundJuglans sigillata L. (walnut) has a high economic value for nuts and wood and has been widely grown and eaten around the world. Light plays an important role in regulating the development of the walnut embryo and promoting nucleolus enlargement, which is one of the factors affecting the yield and quality of walnut. However, little is known about the effect of light on the growth and quality of walnuts. Studies have shown that far red prolonged hypocotyl 3 (FHY3) and far red damaged response (FAR1) play important roles in plant growth, light response, and resistance. Therefore, FHY3/FAR1 genes were identified in walnuts on a genome-wide basis during their growth and development to reveal the potential regulation mechanisms involved in walnut kernel growth and development.ResultsIn the present study, a total of 61 FHY3/FAR1 gene family members in walnuts have been identified, ranging in length from 117 aa to 895 aa. These gene family members have FHY3 or FAR1 conserved domains, which are unevenly distributed on the 15 chromosomes (Chr) of the walnut (except for the Chr16). All 61 FHY3/FAR1 genes were divided into five subclasses (I, II, III, IV, and V) by phylogenetic tree analysis. The results indicated that FHY3/FAR1 genes in the same subclasses with similar structures might be involved in regulating the growth and development of walnut. The gene expression profiles were analyzed in different walnut kernel varieties (Q, T, and F). The result showed that some FHY3/FAR1 genes might be involved in the regulation of walnut kernel ripening and seed coat color formation. Seven genes (OF07056-RA, OF09665-RA, OF24282-RA, OF26012-RA, OF28029-RA, OF28030-RA, and OF08124-RA) were predicted to be associated with flavonoid biosynthetic gene regulation cis-acting elements in promoter sequences. RT-PCR was used to verify the expression levels of candidate genes during the development and color change of walnut kernels. In addition, light responsiveness and MeJA responsiveness are important promoter regulatory elements in the FHY3/FAR1 gene family, which are potentially involved in the light response, growth, and development of walnut plants.ConclusionThe results of this study provide a valuable reference for supplementing the genomic sequencing results of walnut, and pave the way for further research on the FHY3/FAR1 gene function of walnut.

Rapid and accurate detection of multi-target walnut appearance quality based on the lightweight improved YOLOv5s_AMM model.

Nut quality detection is of paramount importance in primary nut processing. When striving to maintain the imperatives of rapid, efficient, and accurate detection, the precision of identifying small-sized nuts can be substantially compromised. We introduced an optimized iteration of the YOLOv5s model designed to swiftly and precisely identify both good and bad walnut nuts across multiple targets. The M3-Net network, which is a replacement for the original C3 network in MobileNetV3's YOLOv5s, reduces the weight of the model. We explored the impact of incorporating the attention mechanism at various positions to enhance model performance. Furthermore, we introduced an attentional convolutional adaptive fusion module (Acmix) within the spatial pyramid pooling layer to improve feature extraction. In addition, we replaced the SiLU activation function in the original Conv module with MetaAconC from the CBM module to enhance feature detection in walnut images across different scales. In comparative trials, the YOLOv5s_AMM model surpassed the standard detection networks, exhibiting an average detection accuracy (mAP) of 80.78%, an increase of 1.81%, while reducing the model size to 20.9 MB (a compression of 22.88%) and achieving a detection speed of 40.42 frames per second. In multi-target walnut detection across various scales, the enhanced model consistently outperformed its predecessor in terms of accuracy, model size, and detection speed. It notably improves the ability to detect multi-target walnut situations, both large and small, while maintaining the accuracy and efficiency. The results underscored the superiority of the YOLOv5s_AMM model, which achieved the highest average detection accuracy (mAP) of 80.78%, while boasting the smallest model size at 20.9 MB and the highest frame rate of 40.42 FPS. Our optimized network excels in the rapid, efficient, and accurate detection of mixed multi-target dry walnut quality, accommodating lightweight edge devices. This research provides valuable insights for the detection of multi-target good and bad walnuts during the walnut processing stage.

Quantification and characterization of biological activities of glansreginin A in black walnuts (Juglans nigra).

Glansreginin A has been reported to be an indicator of the quality of walnuts (Juglans spp.). However, bioactive properties of glansreginin A have not been adequately explored. In the present study, we quantified concentrations of glansreginin A in black walnuts (Juglans nigra) using high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) and performed an array of in vitro bioassays to characterize biological activities (e.g., antibacterial, antioxidant, anticancer capacities) of this compound. Results from HPLC-MS/MS analysis indicated that glansreginin A was presented in all 12 black cultivars examined and its contents were variable among black walnut cultivars, ranged from 6.8mg/kg (Jackson) to 47.0mg/kg (Hay). Glansreginin A possessed moderate antibacterial activities against Gram-positive pathogens (Staphylococcus aureus and Bacillus anthracis). This compound exhibited no antioxidant activities, did not induce the activity of antioxidant response element signaling pathways, and exerted no antiproliferative effects on tumorigenic alveolar epithelial cells and non-tumorigenic lung fibroblast cells.

A Raspberry Pi-Guided Device Using an Ensemble Convolutional Neural Network for Quantitative Evaluation of Walnut Quality

A Raspberry Pi-Guided Device Using an Ensemble Convolutional Neural Network for Quantitative Evaluation of Walnut Quality

Trunk rot of Juglans regia caused by Myrmaecium fulvopruinatum in China.

Walnut (Juglans regia) is a deciduous tree of the Juglandaceae family, widely cultivated in China, and provides value in a variety of ways, including the usage of the wood and nuts, and offers substantial economic, social, and environmental advantages (Wang et al, 2017). Nevertheless, a fungal disease of causing walnut trunk rot was observed in approximately 30% of 50 counted ten-year-old J. regia in Chongzhou City (30°33'34″N, 103°38'35″E, 513 m), Sichuan Province, China, and this disease has greatly delete healthy growth of walnut. The infected bark exhibited purple necrotic lesions, and the sick parts were surrounded by water-soaked plaques. From 10 trunks of the 10 diseased trees, 20 isolated fungal colonies were the same. The ascospores placed in 60 mm plates were almost entirely covered with mycelium within 8 days, colonies on the PDA changed from initial pale to white, ad then turned yellowish to light orange or rosy to yellow-brown (25℃, 90% relative humidity, 12-h photoperiod). On the host, Ectostromata were immersed to erumpent, globose to subglobose, purple and brown, and measured 0.6 - 4.5 × 0.3 - 2.8 mm (x̄ = 2.6 × 1.6 mm, n = 40); Ascomata were flask-shaped to subglobose, dark brown, and measured 0.1 - 0.6 × 0.1 - 0.4 mm (x̄ = 0.35 × 0.25 mm, n = 40); Asci were numerous, cylindrical to subclavate, contained 8 uniseriate ascospores, and measured 80 - 150 × 10 - 20 μm (x̄ = 115 × 15 μm, n = 40), and Ascospores were ellipsoid, 2-celled, dark brown to black, plump or attenuated towards, apices with 1 large drop per cell, and measured 14 - 20 × 6.5 - 9 μm (x̄ = 17 × 7.8 μm, n = 40). These morphological characteristics are consistent with the species Myrmaecium fulvopruinatum (Berk.) Jaklitsch & Voglmayr (Jaklitsch et al. 2015). The genomic DNA of a representative isolate SICAUCC 22-0148 was extracted. The ITS, LSU region, tef1-α, rpb2 genes region were amplified using the primer pairs ITS1/ITS4 primers (White et al. 1990), LR0R/LR5 (Moncalvo et al. 1995), EF1-688F/986R (Alves et al. 2008), fRPB2-5f/fRPB2-7cr (Liu et al. 1999), respectively. The sequences were deposited in NCBI with accession numbers ON287043 (ITS), ON287044 (LSU), ON315870 (tef1-α), and ON315871 (rpb2), rspectively, which showed 99.8, 99.8, 98.1, and 98.5% identities with M. fulvopruinatum CBS 139057 holotype (accession numbers KP687858, KP687858, KP688027, and KP687933 respectively). Based on the analyses of phylogenies and morphologies, the isolates were identified as M. fulvopruinatum. The pathogenicity of SICAUCC 22-0148 was tested by inoculating surface-sterilized trunk wounds of four-year-old trees of J. regia with a mycelial plug (Desai et al. 2019). Sterile PDA plugs were used as controls. Wounds were covered with a film, to ensure humidity and prevent contamination. Each inoculation was repeated twice and included two plants, control and inoculated. A month later, the symptoms observed on inoculated trunks were similar to those in the wild, and M. fulvopruinatum was re-isolated from the inoculated trunk, confirming Koch's postulates. Previous research has reported M. fulvopruinatum as an important fungal species that cause canker delete symptoms on Chinese sweet chestnut in China (Jiang et al. 2018). We carried the taxonomy work of the fungi that caused trunk rot on walnut, and this is the first time that M. fulvopruinatum has been linked to walnut trunk rot on J. regia. Trunk rot of walnut will not only cause weakening of trees, but also affect the yield and quality of walnuts, bringing huge economic losses. This study was supported by the Sichuan Science and Technology Program under Grant 2022NSFSC1011.

Influence of irrigation regime and seasonal temperatures on nut quality and the oil fatty acid profile of walnuts (Juglans regia L.)

Walnut production is expanding worldwide due to the high demand for natural products with proven nutraceutical properties. This expansion includes new growing areas, such as central–western Argentina, where crop water requirements have yet to be determined and little is known about the response in terms of production quality to the water regime. The aim of this study was to assess the effects of four irrigation regimes (at 50, 75, 100, and 125 % of crop evapotranspiration) and the weather conditions over two consecutive seasons in a young Chandler walnut orchard in terms of in–shell and kernel caliber, kernel color, oil concentration, and fatty acid profile. Quality production characteristics were not significantly affected by irrigation regimes within each season. In contrast, the quality parameters achieved were significantly different between seasons. The first season (S1) was wetter (462 mm) and cooler (17.05 °C mean air temperature in the oil accumulation period) and produced more extra–light kernels (92%). The second season (S2) was drier (326 mm) and warmer (19.02 °C) and produced a lower proportion of extra–light kernels (82.2%). In addition, during the second season, walnuts produced larger kernels with a higher oil concentration (62.7%; +3.5% of S1) and a better omega–6/omega–3 ratio (3.25 in S2 vs. 3.70 in S1). These results suggest that kernel quality was more sensitive to the seasonal temperature than the irrigation studied regimes. The nutritional quality of walnuts may increase significantly in warmer seasons/environments despite the deterioration of kernel color.