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L. (walnuts and butternuts) is an economically and ecologically important genus in the family Juglandaceae. All are important nut and timber trees. (Common walnut), (Iron walnut), (Chinese walnut), (Ma walnut), and (Manchurian walnut) are native to or naturalized in China. A strongly supported phylogeny of these five species is not available due to a lack of informative molecular markers. We compared complete chloroplast genomes and determined the phylogenetic relationships among the five Chinese using IIumina sequencing. The plastid genomes ranged from 159,714 to 160,367 bp encoding 128 functional genes, including 88 protein-coding genes and 40 tRNA genes each. A complete map of the variability across the genomes of the five species was produced that included single nucleotide variants, indels (insertions and deletions), and large structural variants, as well as differences in simple sequence repeats (SSR) and repeat sequences. Molecular phylogeny strongly supported division of the five walnut species into two previously recognized sections ( and ) with a 100% bootstrap (BS) value using the complete cp genomes, protein coding sequences (CDS), and the introns and spacers (IGS) data. The availability of these genomes will provide genetic information for identifying species and hybrids, taxonomy, phylogeny, and evolution in , and also provide insight into utilization of plants.

The walnut varieties in China are rich, the planting area in the country is wide, and the yield ranks at the forefront of the world. Walnut kernel is the most important application part of the walnut fruit. An in-depth study found that the by-products of walnut, such as green husk and walnut shell, also have great application potential and are cheap raw materials for the extraction of important medical ingredients and the production of industrial products. However, the by-products are often burned or discarded as waste during processing, which not only wastes resources but also causes environmental pollution. To realize the high value-added application of the walnut fruit, a deep processing of each part of the walnut should be considered. Preliminary processing is the key link before walnuts enter the field of intensive processing and consumption. The advanced level of the required technological equipment can help to determine the quality of the walnut products. The preliminary processing of walnuts in China is mainly divided into six steps: green husk removal, walnut drying, walnut size classification, walnut shell-breaking, walnut shell–kernel separation, and walnut kernel skin removal. This paper starts with a presentation of the importance of each link and the existing bottleneck. Then, the paper systematically discusses the analysis of the current situation and the development of devices required for each link. The working mechanism of each link type and its influence on the design of a corresponding device are summarized. On the basis of the corresponding working mechanism, this study classifies and summarizes the characteristics of the core mechanism of the devices for each preliminary process link; then, it evaluates and analyzes the existing typical mechanical devices according to their types. Finally, the influence rule of the various devices for each link in the preliminary processing is analyzed as a means of ensuring high-quality walnuts.

Background Walnut anthracnose caused by Colletotrichum gloeosporioides (Penz.) Penz. and Sacc. is an important walnut production problem in China. Although the long non-coding RNAs (lncRNAs) are important for plant disease resistance, the molecular mechanisms underlying resistance to C. gloeosporioides in walnut remain poorly understood. Results The anthracnose-resistant F26 fruits from the B26 clone and the anthracnose-susceptible F423 fruits from the 4–23 clone of walnut were used as the test materials. Specifically, we performed a comparative transcriptome analysis of F26 and F423 fruit bracts to identify differentially expressed LncRNAs (DELs) at five time-points (tissues at 0 hpi, pathological tissues at 24 hpi, 48 hpi, 72 hpi, and distal uninoculated tissues at 120 hpi). Compared with F423, a total of 14,525 DELs were identified, including 10,645 upregulated lncRNAs and 3846 downregulated lncRNAs in F26. The number of upregulated lncRNAs in F26 compared to in F423 was significantly higher at the early stages of C. gloeosporioides infection. A total of 5 modules related to disease resistance were screened by WGCNA and the target genes of lncRNAs were obtained. Bioinformatic analysis showed that the target genes of upregulated lncRNAs were enriched in immune-related processes during the infection of C. gloeosporioides , such as activation of innate immune response, defense response to bacterium, incompatible interaction and immune system process, and enriched in plant hormone signal transduction, phenylpropanoid biosynthesis and other pathways. And 124 known target genes for 96 hub lncRNAs were predicted, including 10 known resistance genes. The expression of 5 lncRNAs and 5 target genes was confirmed by qPCR, which was consistent with the RNA-seq data. Conclusions The results of this study provide the basis for future functional characterizations of lncRNAs regarding the C. gloeosporioides resistance of walnut fruit bracts.

Background Common walnut ( Juglans regia L.) has a long cultivation history, given its highly valuable wood and rich nutritious nuts. The Iranian Plateau has been considered as one of the last glaciation refugia and a centre of origin and domestication for the common walnut. However, a prerequisite to conserve or utilize the genetic resources of J. regia in the plateau is a comprehensive evaluation of the genetic diversity that is conspicuously lacking. In this regard, we used 31 polymorphic simple sequence repeat (SSR) markers to delineate the genetic variation and population structure of 508  J. regia individuals among 27 populations from the Iranian Plateau. Results The SSR markers expressed a high level of genetic diversity ( H O = 0.438, and H E = 0.437). Genetic differentiation among the populations was moderate ( F ST = 0.124), and genetic variation within the populations (79%) significantly surpassed among populations (21%). The gene flow ( N m = 1.840) may have remarkably influenced the population genetic structure of J. regia , which can be attributed to anthropological activities and wind dispersal of pollen. The STRUCTURE analysis divided the 27 populations into two main clusters. Comparing the neighbor-joining and principal coordinate analysis dendrograms and the Bayesian STRUCTURE analysis revealed the general agreement between the population subdivisions and the genetic relationships among the populations. However, a few geographically close populations dispersed into different clusters. Further, the low genetic diversity of the Sulaymaniyah (SMR) population of Iraq necessitates urgent conservation by propagation and seedling management or tissue culture methods; additionally, we recommend the indispensable preservation of the Gonabad (RGR) and Arak (AKR) populations in Iran. Conclusions These results reflected consistent high geographical affinity of the accession across the plateau. Our findings suggest that gene flow is a driving factor influencing the genetic structure of J. regia populations, whereas ecological and geological variables did not act as strong barriers. Moreover, the data reported herein provide new insights into the population structure of J. regia germplasm, which will help conserve genetic resources for the future, hence improving walnut breeding programs’ efficiency.

In this research, the eco-friendly cationic surfactant modified walnut shell (WNS-CTAB) was synthesised to enhance the uptake for bisphenol A (BPA) and Congo red (CR) from aqueous solution. The characterisation of WNS-CTAB was performed using Fourier-transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), etc. to know its physiochemical properties. The adsorption equilibrium results were best described by the Langmuir isotherm model, which confirmed the monolayer adsorption of the pollutant molecules onto the adsorbent’s surface. The maximum monolayer adsorption quantity of WNS-CTAB was established to be 38.5 mg g –1 for BPA and 104.4 mg g –1 for CR at 303 K, respectively. Pseudo-second-order kinetic models described the adsorption kinetics of both BPA and CR. Furthermore, the intra-particle diffusion was applied to analyse the kinetic results and was established that the rate was not solely controlled by diffusion. The mechanisms associated with BPA and CR adsorption onto the WNS-CTAB may include van der Waals interaction, hydrophobic interaction, and electrostatic force. WNS-CTAB demonstrated a good reusability potential with desorption through three successive adsorption-desorption cycles performed in both experiments. Moreover, in the binary system, the adsorption capacity of BPA witnessed a 66% decrease while CR saw marginal reduction of 8.0 %. This suggests that WNS-CTAB had a higher affinity for binding to CR with higher selectivity as compared with BPA. Therefore, WNS-CTAB has exhibited huge potential to serve as a functional material for practical use in the treatment of wastewater. Graphical abstract

Background Walnut ( Juglans ), cultivated globally for their nuts and timber, holds significant economic and ecological value. The eastern black walnut (EBW, J. nigra ). a diploid species, an important woody species. Key enzymes in the plant lignin biosynthesis pathway include Phenylalanine ammonia-lyase ( PAL ) and Cinnamyl alcohol dehydrogenase ( CAD ). Although the gene families of PAL and CAD have been extensively characterized in various plants, comprehensive genomic resources and expression profiles specific to the EBW remain limited. Results Based on RNA sequencing of shells and kernels from black walnut ( Juglans nigra ) among three development stages, S1 (80 days after flowering, DAF), S2 (111 DAF), and S3(140 DAF) in black walnut shells and kernels, we found the genes related to lignin biosynthesis. genes such as JnPAL , JnC4H , Jn4CL1 , Jn4CL2 , JnHCT , JnCOMT , Jn CAD2, and Jn CAD-like exhibited significant differential expression across all three developmental stages. Both PAL and CAD genes were expressed significantly in walnut shells compared to kernels across three developmental stages. We conducted a genome-wide identification and discovered 7 PAL and 3 CAD proteins in J. nigra and 5 PAL and 3 CAD proteins in J. microcarpa genome, respectively. Transcriptome DEGs (differential expressed genes) analysis and identified three candidates PAL ( JnPAL1 , JnPAL2 , and JnPAL6 ) and 2 CAD genes ( JnCAD2 and JnCAD3 ) were upregulated during the development of walnut kernels and shells. In addition, it was higher expressed of these PAL and CAD genes in the shell than kernel. Conclusions We conducted a comprehensive involving genome-wide identification, transcriptome dynamics, and expression regulation of the key lignin biosynthesis gene families PAL and CAD across three development stages of shells. This study not only constitutes a valuable resource for elucidating the role of PAL and CAD genes in determining shell thickness in black walnut but also holds significant potential for informing gene-assisted breeding strategies in walnut cultivation.

Background Persian walnut, Juglans regia , occurs naturally from Greece to western China, while its closest relative, the iron walnut, Juglans sigillata , is endemic in southwest China; both species are cultivated for their nuts and wood. Here, we infer their demographic histories and the time and direction of possible hybridization and introgression between them. Results We use whole-genome resequencing data, different population-genetic approaches (PSMC and GONE), and isolation-with-migration models (IMa3) on individuals from Europe, Iran, Kazakhstan, Pakistan, and China. IMa3 analyses indicate that the two species diverged from each other by 0.85 million years ago, with unidirectional gene flow from eastern J. regia and its ancestor into J. sigillata , including the shell-thickness gene. Within J. regia , a western group, located from Europe to Iran, and an eastern group with individuals from northern China, experienced dramatically declining population sizes about 80 generations ago (roughly 2400 to 4000 years), followed by an expansion at about 40 generations, while J. sigillata had a constant population size from about 100 to 20 generations ago, followed by a rapid decline. Conclusions Both J. regia and J. sigillata appear to have suffered sudden population declines during their domestication, suggesting that the bottleneck scenario of plant domestication may well apply in at least some perennial crop species. Introgression from introduced J. regia appears to have played a role in the domestication of J. sigillata.

Chile is one of the world’s leading walnut producers, but the endoparasitic migratory nematode Pratylenchus vulnus considerably affects walnut plants and decreases crop yield. This study assessed the biological control effects of three selected native rhizobacteria species (Bacillus weihenstephanensis FB25M, Brevibacterium frigoritolerans FB37BR, and Oerskovia turbata FB55) against P. vulnus and its damage to walnut plants. The direct effect of the bacterial filtrates of the three species on population of P. vulnus was evaluated in vitro for 72 h at 20 °C and nematode mortality registered every 24 h. The antagonistic effect of a bacterial suspension was measured under greenhouse conditions using 3-month-old potted walnut plants. The growing substrate of the plants was inoculated with a suspension of 1 × 106 colony-forming units (CFU/ml) of each rhizobacteria strain or their mixture, followed by P. vulnus inoculation. As control treatments, two commercial products (chemical: cadusafos; and biological: rhizobacterial mix) and unbacterized plants with and without nematodes were used. Results under in vitro conditions showed that after 72 h exposure of P. vulnus to rhizobacterial filtrates, all bacterial treatments were effective in controlling the nematode (P < 0.01), reaching values between 98 and 100% and exhibiting nematicidal and nemastatic effects. The greenhouse experiments had consistent results; rhizobacteria-treated walnut plants exhibited the maximum biocontrol (mortality) values (67–77%) (P < 0.05). Similarly, rhizobacterial treatments demonstrated the highest root weight compared with the untreated and chemical control treatments (P < 0.05). The evaluated rhizobacterial species showed nematicidal and root growth-promoting effects, which can offer a potential alternative for controlling and protecting walnut plants from P. vulnus.

Herein, walnut shell (WS) was utilized as the raw material for the production of purified cellulose. The production technique involves multiple treatments, including alkaline treatment and bleaching. Furthermore, two nanocellulose materials were derived from WS by 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) oxidation and sulfuric acid hydrolysis, demonstrating the broad applicability and value of walnuts. The micromorphologies, crystalline structures, chemical functional groups, and thermal stabilities of the nanocellulose obtained via TEMPO oxidation and sulfuric acid hydrolysis (TNC and SNC, respectively) were comprehensively characterized. The TNC exhibited an irregular block structure, whereas the SNC was rectangular in shape, with a length of 55–82 nm and a width of 49–81 nm. These observations are expected to provide insight into the potential of utilizing WSs as the raw material for preparing nanocellulose, which could address the problems of the low-valued utilization of walnuts and pollution because of unused WSs.