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Black walnut ,Juglans Nigra L, is native to the eastern United Sates. It is prized as a multipurpose species as it provides high-quality timber, edible nut and is attractive to wild life.

A recently developed detached-leaf blight resistance assay has generated interest because it could reduce the amount of time needed to evaluate backcrossed hybrid trees in the American chestnut blight resistance breeding programme. We evaluated the leaf inoculation technique on a sample of advanced progeny from the Indiana state chapter American Chestnut Foundation breeding programme, along with susceptible American chestnut ( Castanea dentata), the recurrent parent, and resistant Chinese chestnut ( Castanea mollissima), the donor parent for blight resistance. In experiments over 2 years using two pathogen isolates, we found no biologically meaningful relationship between leaf lesion size and the size (length and width) or severity (1-5 canker severity rating) of stem cankers on 5-year-old trees. Chinese chestnuts did develop significantly smaller leaf lesions than American or backcrossed chestnuts. We conclude that while the detached-leaf assay may have utility in some chestnut breeding applications, it is not a suitable proxy for the established practice of stem inoculations. [ABSTRACT FROM AUTHOR]

Juglans regia L. 'Sorrento' is the most important Italian walnut variety. It is cultivated for both nuts and timber in the Campania Region. 'Sorrento' is a mixture of genetic entities and is best characterized as a 'landrace', which affects the homogeneity of important commercial parameters such as fruit size and yield. To clarify the genetic variability in walnuts grown in Campania and labelled as 'Sorrento', we analyzed ten plants that originated from 'Sorrento' seeds and six grafted 'Sorrento' clones, and compared them with six other walnut cultivars using Simple Sequence Repeats (SSRs) DNA markers. Primers derived from I nigra L. amplified alleles at six SSR loci in Persian walnut. A total of 33 putative alleles were detected, nine of which were unique to one genotype. Two loci, WGA5 and WGA27, were particularly useful for distinguishing walnut varieties. Cluster analysis clarified the relatively large genetic distance between most of the 'Sorrento' plants and some genotypes labelled as 'Sorrento'. Despite the genetic diversity found among seed and vegetatively propagated plants, 'Sorrento' landrace trees can be identified and distinguished from other walnut varieties. These data present a starting point for characterising the range of genetic variability among 'Sorrento' plants. [ABSTRACT FROM AUTHOR]

With the advent of affordable and more accurate third-generation sequencing technologies, and the associated bioinformatic tools, it is now possible to sequence, assemble, and annotate more species of conservation concern than ever before. Juglans cinerea, commonly known as butternut or white walnut, is a member of the walnut family, native to the Eastern United States and Southeastern Canada. The species is currently listed as Endangered on the IUCN Red List due to decline from an invasive fungus known as Ophiognomonia clavigignenti-juglandacearum (Oc-j) that causes butternut canker. Oc-j creates visible sores on the trunks of the tree which essentially starves and slowly kills the tree. Natural resistance to this pathogen is rare. Conserving butternut is of utmost priority due to its critical ecosystem role and cultural significance. As part of an integrated undergraduate and graduate student training program in biodiversity and conservation genomics, the first reference genome for Juglans cinerea is described here. This chromosome-scale 539 Mb assembly was generated from over 100 × coverage of Oxford Nanopore long reads and scaffolded with the Juglans mandshurica genome. Scaffolding with a closely related species oriented and ordered the sequences in a manner more representative of the structure of the genome without altering the sequence. Comparisons with sequenced Juglandaceae revealed high levels of synteny and further supported J. cinerea's recent phylogenetic placement. Comparative assessment of gene family evolution revealed a significant number of contracting families, including several associated with biotic stress response., Competing Interests: Conflicts of interest The author(s) declare no conflict of interest., (© The Author(s) 2023. Published by Oxford University Press on behalf of The Genetics Society of America.)

Walnut ( Juglans ) species are used as nut crops worldwide. Eastern black walnut (EBW, Juglans nigra ), a diploid, horticultural important woody species is native to much of eastern North America . Although it is highly valued for its wood and nut, there are few resources for understanding EBW genetics. Here, we present a high-quality genome assembly of J. nigra based on Illumina, Pacbio, and Hi-C technologies. The genome size was 540.8 Mb, with a scaffold N50 size of 35.1 Mb, and 99.0% of the assembly was anchored to 16 chromosomes. Using this genome as a reference, the resequencing of 74 accessions revealed the effective population size of J. nigra declined during the glacial maximum. A single whole-genome duplication event was identified in the J. nigra genome. Large syntenic blocks among J. nigra , Juglans regia , and Juglans microcarpa predominated, but inversions of more than 600 kb were identified. By comparing the EBW genome with those of J. regia and J. microcarpa , we detected InDel sizes of 34.9 Mb in J. regia and 18.3 Mb in J. microcarpa , respectively. Transcriptomic analysis of differentially expressed genes identified five presumed NBS-LRR ( NUCLEOTIDE BINDING SITE-LEUCINE-RICH REPEAT ) genes were upregulated during the development of walnut husks and shells compared to developing embryos. We also identified candidate genes with essential roles in seed oil synthesis, including FAD ( FATTY ACID DESATURASE ) and OLE ( OLEOSIN ). Our work advances the understanding of fatty acid bioaccumulation and disease resistance in nut crops, and also provides an essential resource for conducting genomics-enabled breeding in walnut., Competing Interests: None declared., (© The Author(s) 2023. Published by Oxford University Press on behalf of Nanjing Agricultural University.)

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., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2022 Luo et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

Background: The walnut family (Juglandaceae) contains commercially important woody trees commonly called walnut, wingnut, pecan and hickory. Phylogenetic relationships and diversification within the Juglandaceae are classic and hot scientific topics that have been elucidated by recent fossil, morphological, molecular, and (paleo) environmental data. Further resolution of relationships among and within genera is still needed and can be achieved by analysis of the variation of chloroplast, mtDNA, and nuclear genomes., Results: We reconstructed the backbone phylogenetic relationships of Juglandaceae using organelle and nuclear genome data from 27 species. The divergence time of Juglandaceae was estimated to be 78.7 Mya. The major lineages diversified in warm and dry habitats during the mid-Paleocene and early Eocene. The plastid, mitochondrial, and nuclear phylogenetic analyses all revealed three subfamilies, i.e., Juglandoideae, Engelhardioideae, Rhoipteleoideae. Five genera of Juglandoideae were strongly supported. Juglandaceae were estimated to have originated during the late Cretaceous, while Juglandoideae were estimated to have originated during the Paleocene, with evidence for rapid diversification events during several glacial and geological periods. The phylogenetic analyses of organelle sequences and nuclear genome yielded highly supported incongruence positions for J. cinerea, J. hopeiensis, and Platycarya strobilacea. Winged fruit were the ancestral condition in the Juglandoideae, but adaptation to novel dispersal and regeneration regimes after the Cretaceous-Paleogene boundary led to the independent evolution of zoochory among several genera of the Juglandaceae., Conclusions: A fully resolved, strongly supported, time-calibrated phylogenetic tree of Juglandaceae can provide an important framework for studying classification, diversification, biogeography, and comparative genomics of plant lineages. Our addition of new, annotated whole chloroplast genomic sequences and identification of their variability informs the study of their evolution in walnuts (Juglandaceae)., (© 2021. The Author(s).)

Manchurian walnut (Juglans mandshurica Maxim.) is a synonym of J. cathayensis, a diploid, vulnerable, temperate deciduous tree valued for its wood and nut. It is also valued as a rootstock for Juglans regia because of its reported tolerance of lesion nematode. Reference genomes are available for several Juglans species, our goal was to produce a de novo, chromosome-level assembly of the J. mandshurica genome. Here, we reported an improved assembly of J. mandshurica with a contig N50 size of 6.49 Mb and a scaffold N50 size of 36.1 Mb. The total genome size was 548 Mb encoding 29,032 protein coding genes which were annotated. The collinearity analysis showed that J. mandshurica and J. regia originated from a common ancestor, with both species undergoing two WGD events. A genomic comparison showed that J. mandshurica was missing 1657 genes found in J. regia, and J. mandshurica includes 2827 genes not found in of the J. regia genome. The J. mandshurica contained 1440 unique paralogues that were highly enriched for flavonoid biosynthesis, phenylpropanoid biosynthesis, and plant-pathogen interaction. Four gene families related to disease resistance notable contraction (rapidly evolving; LEA, WAK, PPR, and PR) in J. mandshurica compared to eight species. JmaPR10 and JmaPR8 contained three orthologous gene pairs with J. regia that were highly expressed in root bark. JmaPR10 is a strong candidate gene for lesion nematodes resistance in J. mandshurica. The J. mandshurica genome should be a useful resource for study of the evolution, breeding, and genetic variation in walnuts (Juglans)., (© 2021 John Wiley & Sons Ltd.)

Tapiscia sinensis (Tapisciaceae) possesses an unusual androdioecious breeding system that has attracted considerable interest from evolutionary biologists. Key aspects of T. sinensis biology, including its biogeography, genomics, and sex-linked genes, are unknown. Here, we report the first de novo assembly of the genome of T. sinensis. The genome size was 410 Mb, with 22,251 predicted genes. Based on whole-genome resequencing of 55 trees from 10 locations, an analysis of population genetic structure indicated that T. sinensis has fragmented into five lineages, with low intrapopulation genetic diversity and little gene flow among populations. By comparing whole-genome scans of male versus hermaphroditic pools, we identified 303 candidate sex-linked genes, 79 of which (25.9%) were located on scaffold 25. A 24-kb region was absent in hermaphroditic individuals, and five genes in that region, TsF-box4, TsF-box10, TsF-box13, TsSUT1, and TsSUT4, showed expression differences between mature male and hermaphroditic flowers. The results of this study shed light on the breeding system evolution and conservation genetics of the Tapisciaceae.

Southwestern (SW) China is an area of active tectonism and erosion, yielding a dynamic, deeply eroded landscape that influences the genetic structure of the resident populations of plants and animals. Iron walnut ( Juglans regia subsp. sigillata ) is a deciduous tree species endemic to this region of China and cultivated there for its edible nuts. We sampled 36 iron walnut populations from locations throughout the species' range in SW China and genotyped a total of 765 individuals at five chloroplast DNA regions and 22 nuclear microsatellite loci. Species distribution models were produced to predict the evolution and historical biogeography of iron walnut and to estimate the impacts of climate oscillations and orographic environments on the species' demography. Our results indicated that J. regia subsp. sigillata had relatively low genetic diversity, high interpopulation genetic differentiation, and asymmetric interpopulation gene flow. Based on DIYABC analysis, we identified two lineages of J .  sigillata in southwestern China. The lineages (subpopulations) diverge during the last glacial period (~1.34 Ma). Southwestern China was a glacial refuge during the last glacial period, but increasingly colder and arid climates might have fostered the fragmentation of J .  regia subsp. sigillata within this refugium. Finally, we found that recent habitat fragmentation has led to a reduction in population connectivity and increased genetic differentiation by genetic drift in isolated populations. Our results support a conclusion that geological and climatic factors since the Miocene triggered the differentiation, evolutionary origin, and range shifts of J .  sigillata in the studied region., Competing Interests: None declared., (© 2019 The Authors. Ecology and Evolution published by John Wiley & Sons Ltd.)

Common walnut ( Juglans regia L.) is an economically important hardwood tree species cultivated worldwide for its high quality wood and edible nuts. It is generally accepted that after the last glaciation J . regia survived and grew in almost completely isolated stands in Asia, and that ancient humans dispersed walnuts across Asia and into new habitats via trade and cultural expansion. The history of common walnut in China is a matter of debate, however. We estimated the genetic diversity and spatial genetic structure of 31 walnut populations sampled across its Chinese range using 22 microsatellite markers (13 neutral and 9 non-neutral). Using historical data and population genetic analysis, including approximate Bayesian analysis (ABC), we reconstructed the demographic history of J . regia in China. The genetic data indicated the likely presence of J . regia in glacial refugia in the Xinjiang province (Northwest China), Northeastern China (Beijing, Shandong, and Changbai Mountains), Central China (Qinling and Baishan Mountains and Xi'an), and Southwestern China (Tibet, Yunnan, Guizhou, and Sichuan provinces). Based on DIY-ABC analysis, we identified three ancient lineages of J. regia in China. Two lineages (subpopulation A and subpopulation B+C) diverged about 2.79 Mya, while Southwestern China, and Qinling and Baishan Mountains lineages diverged during the Quaternary glaciations (about 1.13 Mya). Remnants of these once-distinct genetic clusters of J. regia may warrant ecological management if they are to be retained as in situ resources. A population size expansion in Northeastern China was detected in the last five centuries. The present distribution of walnut in China resulted from the combined effects of expansion/contraction from multiple refugia after the Last Glacial Maximum and later human exploitation.

Genomic data are a powerful tool for elucidating the processes involved in the evolution and divergence of species. The speciation and phylogenetic relationships among Chinese Juglans remain unclear. Here, we used results from phylogenomic and population genetic analyses, transcriptomics, Genotyping-By-Sequencing (GBS), and whole chloroplast genomes (Cp genome) data to infer processes of lineage formation among the five native Chinese species of the walnut genus (Juglans, Juglandaceae), a widespread, economically important group. We found that the processes of isolation generated diversity during glaciations, but that the recent range expansion of J. regia, probably from multiple refugia, led to hybrid formation both within and between sections of the genus. In southern China, human dispersal of J. regia brought it into contact with J. sigillata, which we determined to be an ecotype of J. regia that is now maintained as a landrace. In northern China, walnut hybridized with a distinct lineage of J. mandshurica to form J. hopeiensis, a controversial taxon (considered threatened) that our data indicate is a horticultural variety. Comparisons among whole chloroplast genomes and nuclear transcriptome analyses provided conflicting evidence for the timing of the divergence of Chinese Juglans taxa. J. cathayensis and J. mandshurica are poorly differentiated based our genomic data. Reconstruction of Juglans evolutionary history indicate that episodes of climatic variation over the past 4.5 to 33.80 million years, associated with glacial advances and retreats and population isolation, have shaped Chinese walnut demography and evolution, even in the presence of gene flow and introgression., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Genomic analysis in Juglans (walnuts) is expected to transform the breeding and agricultural production of both nuts and lumber. To that end, we report here the determination of reference sequences for six additional relatives of Juglans regia : Juglans sigillata (also from section Dioscaryon ), Juglans nigra , Juglans microcarpa , Juglans hindsii (from section Rhysocaryon ), Juglans cathayensis (from section Cardiocaryon ), and the closely related Pterocarya stenoptera While these are 'draft' genomes, ranging in size between 640Mbp and 990Mbp, their contiguities and accuracies can support powerful annotations of genomic variation that are often the foundation of new avenues of research and breeding. We annotated nucleotide divergence and synteny by creating complete pairwise alignments of each reference genome to the remaining six. In addition, we have re-sequenced a sample of accessions from four Juglans species (including regia ). The variation discovered in these surveys comprises a critical resource for experimentation and breeding, as well as a solid complementary annotation. To demonstrate the potential of these resources the structural and sequence variation in and around the polyphenol oxidase loci, PPO1 and PPO2 were investigated. As reported for other seed crops variation in this gene is implicated in the domestication of walnuts. The apparently Juglandaceae specific PPO1 duplicate shows accelerated divergence and an excess of amino acid replacement on the lineage leading to accessions of the domesticated nut crop species, Juglans regia and sigillata ., (Copyright © 2018 Stevens et al.)