Japanese Walnut Research Articles

Morph-specific mating patterns in a low-density population of a heterodichogamous tree, Juglans ailantifolia

Heterodichogamy, including protandrous (PA) and protogynous (PG) morphs, is considered a mechanism to avoid selfing and promote disassortative mating. Although morphotypes are usually present in a population at a 1:1 ratio, this ratio may be biased in a low-density population by demographic stochasticity, resulting in a deficiency of mating partners in a neighbourhood dominated by a single morph. In this study, we determined morph ratio of the heterodichogamous tree species, Juglans ailantifolia by observing flowering in a low-density population during 2 years. The morph ratio (PG: PA) of 2.56:1 deviated significantly deviated from 1:1. We genotyped 59 reproductive trees and 405 offspring derived from eight PG-mother and three PA-mother trees with 11 microsatellite markers. Paternity analysis was conducted to clarify the effects of mother morph on the proportion of intra-morph mating. Then, we applied the Bayesian mixed effect mating model (MEMM) to clarify mating system, pollen dispersal, and individual fecundity of PG- and PA-mother trees. We found that the selfing rate and the distance of pollen dispersal were not clearly different between PG- and PA-mother trees. In contrast, the proportion of intra-morph mating was higher in the majority-morph (PG) mother trees than in the minor-morph (PA) mother trees. The MEMM indicated that mean dispersal distance of PG-mother trees was larger than that of PA-mother trees with large variance. Furthermore, we observed individuals with unusually high intra-morph fecundity for majority-morph (PG) trees. These findings indicate that intra-morph mating may occur when majority-morph mothers suffer a deficiency of potential inter-morph mates.

Human‐impacted landscapes facilitate hybridization between a native and an introduced tree

Spatial and temporal dynamics of hybridization, in particular the influence of local environmental conditions, are well studied for sympatric species but less is known for native-introduced systems, especially for long-lived species. We used microsatellite and chloroplast DNA markers to characterize the influence of anthropogenic landscapes on the extent, direction, and spatial distribution of hybridization between a native North American tree Juglans cinerea (butternut) and an introduced tree Juglans ailantifolia (Japanese walnut) for 1363 trees at 48 locations across the native range of butternut. Remarkably, admixture in anthropogenic sites reached nearly 70%, while fragmented and continuous forests showed minimal admixture (<8%). Furthermore, more hybrids in anthropogenic sites had J. ailantifolia seed parents (95%) than hybrids in fragmented and continuous forests (69% and 59%, respectively). Our results show a strong influence of landscape type on rate and direction of realized gene flow. While hybrids are common in anthropogenic landscapes, our results suggest that even small forested landscapes serve as substantial barriers to hybrid establishment, a key consideration for butternut conservation planning, a species already exhibiting severe decline, and for other North American forest trees that hybridize with introduced congeners.

Historical Effects on Local Variation in Walnut-Feeding Behavior by the Japanese Wood Mouse, Apodemus speciosus

The Japanese wood mouse Apodemus speciosus eats large, hard-walled walnuts of Juglans ailanthifolia immediately after finding or after hoarding them. However, not all individuals can efficiently eat the nuts. In this study, to examine local variation in the ability to eat walnuts, feeding behavior was compared among nine wood mouse populations, four from mainland Honshu, where the walnut tree is distributed, and five from the Izu Islands (30-100 km south of Honshu), which lack the tree species. To avoid the effects of pre-capture experience with walnuts, mice from areas lacking the walnut trees were used for testing, even in the Honshu sites. Most mice from Honshu were able to eat walnuts after a 14-day training period, whereas most insular mice could not, with the exception of mice on Kouzushima Island. An analysis of the population genetic structures of these mice based on sequences of the mitochondrial control (D-loop) region revealed that the four insular populations are genetically distinct from the mainland populations, whereas the Kouzushima population remains genetically similar to the mainland populations. The relatively recent colonization of Kouzushima may explain why mice from this island were able to feed on walnuts despite the lack of walnut trees on the island. Thus, walnut-feeding ability appears to have some innate basis in the Japanese wood mouse, and this trait would be selected for in a walnut-available environment as it would better enable mice to survive during food shortages.

First Report of the Walnut Witches'-Broom Phytoplasma on Japanese and Black Walnut in Iowa.

A single Japanese walnut (Juglans ailantifolia Carrière, an ornamental, deciduous tree) with symptoms of witches'-brooms and branch dieback, consistent with those associated with the walnut witches'-broom (WWB) phytoplasma (1), was observed near Ames, IA. No other Japanese walnut trees were present in the planting and the numerous black walnut (Juglans nigra L.) trees were asymptomatic. Leaf samples were collected in September 2009 from witches'-brooms as well as from two asymptomatic branches from the Japanese walnut tree and from three branches each from two nearby (10 m and 100 m away, respectively) black walnut trees. The presence of phytoplasma was tested using DNA extracted (sodium dodecyl sulfate and potassium acetate methods) from the midvein of individual leaves and PCR with universal phytoplasma primers P1 and P7, which amplify from the beginning of the 16S rDNA to the beginning of the 23S rDNA gene (4). Each of the five symptomatic leaves yielded a PCR product, but the two asymptomatic leaves from the sole Japanese walnut tree did not. One of the three asymptomatic leaves from a black walnut tree (100 m away) was also positive. In a subsequent round of PCR, with the nested primers R16F2 and R16R2 (4), three additional asymptomatic leaves from the two black walnut trees were positive. The P1/P7 or R16F2/R16R2 products from each of the three trees were directly sequenced or cloned into a TA vector and sequenced using vector primers. The BLAST searches (v. 2.2.2.4) of these sequences most closely matched the sequences of the WWB phytoplasma and other members of the 16SrIII group (peach X-disease). The closest matches for the full P1/P7 sequence from the Japanese walnut (GenBank Accession No. HQ221553, 1,814 bp) were with those of phytoplasmas associated with WWB from two black walnut trees in Georgia (AF190227, 1,812 of 1,815 bp matching; and AF190226, 1,808 of 1,815 bp matching), spiraea stunt (AF190228, 1,808 of 1,814 bp), and western X (AF533231, 1,807 of 1,814 bp). The iPhyClassifier restriction fragment length polymorphism similarity coefficient was 0.99 for L33733 (Canadian peach X phytoplasma) and 0.98 for AF190226. Sequence HQ221553 differed by 10 bp from the sequence from the asymptomatic black walnut tree that was 100 m away (HQ221554, 1,815 bp), which matched closest to one of the black walnut samples from Georgia (AF190227, 1,807 of 1,816 bp). A 1,029-bp fragment from the second black walnut tree (10 m away) differed by 1 or 2 bp from the Georgia WWB accessions. To our knowledge, this is the first report of WWB symptoms in Iowa and the first identification of the WWB phytoplasma outside of Georgia (1). The disease, however, is more widely known (Illinois, Indiana, and Ohio) and may cause serious reduction in nut production (1-3). It can be lethal to Juglans spp., especially to exotic species such as Japanese walnut (2,3). The native black walnut is thought to be relatively resistant to tolerant of WWB (2,3) and may only show growth decline with no symptoms, except for broom production from cut surfaces (3). Care should be taken in moving planting stock of black walnut (4) because asymptomatic trees may harbor the phytoplasma.

Homonymy, synonymy and hybrid misassignments in butternut (Juglans cinerea) and Japanese walnut (Juglans ailantifolia) nut cultivars

Butternut (Juglans cinerea), a tree native to North America and Japanese walnut (J. ailantifolia), native to Japan, form the basis for a small but growing specialty nut crop industry in the eastern United States and Canada. Over the last century, Canadian and American nut tree growers, academic plant breeders and nursery owners have clonally propagated cultivars and freely exchanged scion wood, creating the possibility of misidentification. To detect homonymy, synonymy and hybrid misassignments, we used 12 highly polymorphic microsatellites to genotype most of the butternut and Japanese walnut cultivars grown in the United States and Canada. Bayesian clustering and identity analyses revealed high levels of homonymies (genetically different cultivars with the same name) and synonymies (genetically identical cultivars with different names). Over 41% of the butternut cultivars and 45% of the Japanese walnut cultivars tested had homonymies, and a majority of the cultivars in both species also had synonymies. Further, 43 entries (~15%) identified by the contributors as either J. cinerea or J. ailantifolia were interspecific hybrids. Given our results we recommend that any comparative studies on the cultivars of either species or their hybrids include reference genetic fingerprints as a part of the study.

Effects of root architecture, physical tree characteristics, and soil shear strength on maximum resistive bending moment for overturning Salix babylonica and Juglans ailanthifolia

Effects of root architecture, physical tree characteristics, and soil shear strength on overturning moment due to flooding were investigated using Salix babylonica and Juglans ailanthifolia, exotic and invasive plants in Japanese rivers. Tree-pulling experiments that simulated flood action were conducted, and the resulting damage was examined to assess the effects of physical tree characteristics and root architecture on the maximum resistive bending moment (M max) for overturning. In situ soil shear strength tests were conducted to measure soil strength parameters. The effects of species differences on the M max were examined by analyzing root architecture. S. babylonica has a heart-root system that produces a greater overturning moment due to the strong root anchorage and the large amount of substrate that must be mobilized during overturning. J. ailanthifolia has a plate-root system that produces a smaller overturning moment. However, trees with the plate-root system may withstand overturning better due to an increased root:shoot ratio. The results of the study show that the M max of a tree for overturning had significant (P < 0.05) correlations with a tree’s physical characteristics, including height (H), trunk diameter at breast height (D bh), D bh 2 , height multiplied by the second power of D bh (trunk volume index H × D bh 2 ), and root–soil plate depth (R d), and root–soil plate radius (R r). Considering the strategy of J. ailanthifolia to increase the root:shoot ratio for anchoring in the substrate, the trunk volume index (H × D bh 2 ) is a better parameter than D bh 2 because it indirectly involves the difference in below-ground volume and surface area. Different soil cohesion values were found at different experimental sites, and the average M max for overturning each species decreased linearly with increasing soil cohesion.

Population differences and learning effects in walnut feeding technique by the Japanese squirrel

Feeding efficiency is an important factor explaining diet selection in seed-eating animals. Behavioral adaptation to process and consume the seed is advantageous to improve their feeding rate. The Japanese walnut (Juglans ailanthifolia), which has a nutritious kernel surrounded by a hard shell, is an important food for the Japanese squirrel (Sciurus lis) in lowland mixed-species forests in Japan. In the present study, population differences in feeding technique were examined. In all squirrels captured from the Takao population (with wild Japanese walnuts in their habitat), the optimal feeding technique for quickly opening the walnut shell was observed. However, only 8% of the squirrels from the Fuji population (without walnuts in their habitat) processed the walnuts by the optimal feeding technique. By a repetitive provision of walnuts for 50 days, 14% of squirrels from the Fuji population acquired the optimal feeding technique. Learning effects did not differ significantly between solitary (without a demonstrator) and social conditions (with a demonstrator). The effects of age on learning the feeding technique were examined using individuals from a zoo population that had been naive for Japanese walnuts. All five individuals aged 6 months old, and half the individuals aged 1–2 years old, ate walnuts by the optimal feeding technique after a 2-month learning period, but none of the individuals older than 3 years did. Consequently, the walnut feeding techniques of the Japanese squirrel are not entirely genetically fixed behavior and can be improved by learning at a young age.

DNA markers identify hybrids between butternut (Juglans cinerea L.) and Japanese walnut (Juglans ailantifolia Carr.)

Butternut (Juglans cinerea L.) is a temperate deciduous hardwood native to the eastern USA and southern Canada valued for its nuts and wood. Butternut’s survival is threatened by butternut canker, a disease caused by the exotic fungus Sirococcus clavigignenti-juglandacearum Nair, Kostichka & Kuntz. Field observations indicate that trees commonly called buartnut (a hybrid of butternut and its close congener Japanese walnut (Juglans ailantifolia × J. cinerea)) may be more resistant to butternut canker than is either parental species. Hybrids are difficult to distinguish morphologically from butternuts, and scientists have expressed concern over the possibility of range-wide genetic invasion by Japanese walnut via hybridization with butternut. We used pair-wise combinations of 40 random primers to screen bulked DNA pools of butternut, Japanese walnut, and buartnuts to identify genomic regions unique to Japanese walnut. We ultimately identified one ITS region marker, one chloroplast marker, one mitochondrial marker, and six nuclear markers. The utility of the markers for identifying hybrids was tested and verified using more than 190 genotypes. The markers will be used to identify buartnut hybrids based on the presence of introgressed genomic fragments inherited from Japanese walnut. We confirmed that hybrids have a complex genetic history and present features of the parental species in all possible combinations. These results will assist in the identification and testing of (non-hybrid) butternut for breeding and reintroduction of the species to its former habitats.

Reclassification of the butternut canker fungus, Sirococcus clavigignenti-juglandacearum, into the genus Ophiognomonia

Sirococcus clavigignenti-juglandacearum (Sc-j), which causes a canker disease on butternut, is largely responsible for the decline of this tree in the United States and Canada. The original description of the species was based on anamorphic characters because the teleomorph is unknown. Recent phylogenetic investigations have found that Sc-j is not a member of the genus Sirococcus, and accurate taxonomic classification is required. The objective of this study is to use sequence data to determine the phylogenetic placement of Sc-j within the Gnomoniaceae, Diaporthales. Isolates were recovered from infected Juglans ailantifolia var. cordiformis (heartnut), Juglans cinerea (butternut), and Juglans nigra (black walnut) in Ontario and the eastern United States. The genes coding for β-tubulin, actin, calmodulin, internal transcribed spacers 1 and 2, and the translation elongation factor 1-alpha from 28 isolates of Sc-j and representatives of the major lineages within the Gnomoniaceae were evaluated. There was no difference in the sequences of the five genes among the isolates of Sc-j studied, indicating a recent introduction followed by asexual reproduction and spread via conidia. The phylogenetic analyses demonstrate this fungus does not belong to the genus Sirococcus, and provides strong support (99% MP and 100% NJ bootstrap values, and 100% Bayesian posterior probabilities) for its inclusion in the genus Ophiognomonia, thereby supporting a reclassification of the butternut canker fungus to Ophiognomonia clavigignenti-juglandacearum.

Host‐associated pre‐mating reproductive isolation between host races of Acrocercops transecta: mating site preferences and effect of host presence on mating

1. A correlation between habitat and mating site preference is crucial for reproductive isolation between populations with different ecological requirements in the absence of any other barriers to gene flow. In phytophagous insects, host‐plant preference of ovipositing females has been postulated to directly influence the extent of assortative mating. 2. Although this pleiotropic effect of host preference is commonly postulated in both theoretical and empirical studies in phytophagous insects, few studies have assessed the mating site preferences of both sexes. In herbivorous insects, it is crucial whether males have the same host preference as ovipositing females. 3. This study examines whether males and females have preferences for mating sites and assesses the effects of host presence on mating activity in a leaf‐mining moth, Acrocercops transecta Meyrick (Gracillariidae). This species consists of two host races, which are associated with Juglans ailanthifolia Carr. (Juglandaceae) and Lyonia ovalifolia (Wall.) Drude (Ericaceae). The two host races clearly differ in host preferences of ovipositing females. 4. In an experiment of mating site selection, Lyonia‐associated host race females significantly preferred Lyonia, while males of the Lyonia‐associated host race and both sexes of the Juglans‐associated host race did not show a preference for either plant. The mating activity of the Lyonia‐associated host race was not reduced in the absence of host plants. In the Juglans‐associated host race, however, the proportion of successful matings was significantly reduced when the host was absent. 5. These laboratory experiments provide empirical evidence that the different host associations in A. transecta do not directly lead to host‐induced assortative mating between the two host races as a pleiotropic effect. However, the present results suggest that the combined effects of the mating‐site preference of Lyonia‐associated females and the mating propensity of Juglans‐associated females could contribute to reproductive isolation between the two host races.

Geographically extensive hybridization between the forest trees American butternut and Japanese walnut

We investigate the question of naturally occurring interspecific hybrids between two forest trees: the native North American butternut (Juglans cinerea L.) and the introduced Japanese walnut (Juglans ailantifolia Carrière). Using nuclear and chloroplast DNA markers, we provide evidence for 29 F(1) and 22 advanced generation hybrids in seven locations across the eastern and southern range of the native species. Two locations show extensive admixture (95% J. ailantifolia and hybrids) while other locations show limited admixture. Hybridization appears to be asymmetrical with 90.9 per cent of hybrids having J. ailantifolia as the maternal parent. This is, to our knowledge, the first genetic data supporting natural hybridization between these species. The long-term outcome of introgression could include loss of native diversity, but could also include transfer of useful traits from the introduced species.

Four cleaved amplified polymorphic sequence (CAPS) markers for the detection of the Juglans ailantifolia chloroplast in putatively native J. cinerea populations

Hybridization between butternut (Juglans cinerea), a forest tree native to eastern North America, and Japanese walnut (J. ailantifolia), a tree tolerant to the lethal fungal disease butternut canker, casts doubt on the genetic identity of the remaining butternuts. We report a diagnostic test to distinguish the J. cinerea chloroplast from the J. ailantifolia chloroplast using cleaved amplified polymorphic sequences resolvable in 1.5% agarose gels. J. ailantifolia maternal ancestry in naturally regenerated stands provides a site selection criterion for studies of introgression dynamics when the non-native parent and the hybrids tolerate a disease to which the native species is susceptible.

Morphological and molecular methods to identify butternut (Juglans cinerea) and butternut hybrids: relevance to butternut conservation

Butternut (Juglans cinerea L.) is a native, cold-tolerant, hard-mast species formerly valued for its nuts and wood, which is now endangered. The most immediate threat to butternut restoration is the spread of butternut canker disease, caused by the exotic fungus Sirococcus clavigignenti-juglandacearum Nair, Kostichka & Kuntz. Other threats include the hybridization of butternut with the exotic Japanese walnut (Juglans ailantifolia Carr.) and poor regeneration. The hybrids, known as buartnuts, are vegetatively vigorous, highly fecund, more resistant than butternut to butternut canker disease and difficult to identify. We review the vegetative and reproductive morphological traits that distinguish butternut from hybrids and identify those that can be used by field biologists to separate the taxa. No single trait was sufficient to separate butternut from hybrids, but pith color, lenticel size, shape and abundance, and the presence or absence of a notch in the upper margin of leaf scars, can be used in combination with other traits to identify butternuts and exclude most hybrids. In at least one butternut population, reduced symptoms of butternut canker disease were significantly associated with a dark barked phenotype. We also describe two randomly amplified polymorphic DNA (RAPD) markers that differentiate butternuts from hybrids based on DNA polymorphism. Together, these results should assist in the identification and testing of non-hybrid butternut for breeding and reintroduction of the species to its former habitats.

Seed Dispersal by Rodents and Seedling Establishment of Walnut Trees (Juglans ailanthifolia) in a Riparian Forest.

Seed Dispersal by Rodents and Seedling Establishment of Walnut Trees (Juglans ailanthifolia) in a Riparian Forest.

Host race formation in the leaf-mining moth Acrocercops transecta (Lepidoptera: Gracillariidae)

Genetic differentiation in ecological traits plays an important role in the reproductive isolation of phytophagous insects. The present study aims to elucidate the genetic changes involved during the process of host shifts, by combining analyses for (1) host adaptations, (2) pre- and postmating isolation, and (3) phylogeney among populations, using a leaf-mining moth, Acrocercops transecta. This species is associated with Juglans ailanthifolia and Lyonia ovalifolia. Transplantation of the larvae demonstrated that the Juglans-associated population completely failed to survive on Lyonia, whereas the Lyonia-associated population survived on Juglans as well as on Lyonia. Females of respective host-associated populations oviposited on their natal host plant only. An mtDNA-based phylogeny clearly separated the Lyonia-associated population from the Juglandaceae-associated population, and indicated that the Lyonia-associated population once evolved from the Juglandaceae-associated population. These results indicate that the processes of host shifting from juglandaceous species to Lyonia involved genetic changes both in larval ability to use host plants and in host preference of females. The derived Lyonia-associated population has retained the potential to assimilate the ancestral host, Juglandaceae. Mating between the two host-associated populations was successful for both directions of crossing, and there were no significant differences in egg hatchability between hybrids and control crosses. No adults emerged when the F1 hybrid larvae were maintained on Lyonia; however, on Juglans the F1 hybrid larvae grew to adulthood as well as in the control, suggesting a lack of genomic incompatibilities between the two host-associated populations. In conclusion, the results showed that the two host-associated populations are host races that are partially reproductively isolated, and that the differences in performance and preference function as strong barriers against gene flow between the host races. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 93, 135–145.

Diaporthe eres (Phomopsis oblonga) as a Pathogen of Butternut (Juglans cinerea) in Connecticut

Butternut seedlings from North Carolina (S. Schlarbaum, University of Tennessee) were planted during the spring of 2005 in an open space at the edge of the Mattatuck State Forest in Plymouth, CT. There were mature butternuts with visible cankers that were at the forest edge and out of reach. In May 2006, some seedlings had died and many small, dark lesions were found on the twigs and stems of living seedlings. Stems with lesions were surface sterilized with 10% bleach, rinsed with sterile water, the epidermis peeled away, and slices of the wood were placed on the surface of 2% water agar plates. From these, we consistently isolated a Phomopsis sp. that grew well on potato dextrose agar (PDA) at 28°C and produced alpha and beta spores (average 8 × 2 μm and 25 × 1 μm, respectively). A mixture of six such isolates on autoclaved pieces of butternut stem supported by water agar produced perithecia after 6 months with ascospores that matched the description of Diaporthe eres (two-celled, slightly constricted at the septum, and averaged 12 × 3 μm). Two of our isolates of Diaporthe eres, both of which were weakly pathogenic and recovered from the lesions, were inoculated into cut, dormant stems of butternut 'Buckley' in the laboratory, This ascomycete was reported to be a pathogen of Juglans ailantifolia and J. regia var. orientes in Japan (1) but has not been reported on J. cinerea. There is a rather vague report of Diaporthe spiculosa on other species of Juglans and Phomopsis juglandina on twigs (with a question mark) of J. regia (with a question mark) in California (2). These were not reported by T. Kobayashi.

Geographic variation in walnut seed size correlates with hoarding behaviour of two rodent species

AbstractSeeds of the Japanese walnut, Juglans ailanthifolia, are usually scatter‐hoarded by two rodent species, the Japanese squirrel Sciurus lis and the field mouse Apodemus speciosus, but only by the latter in several areas where S. lis is absent. We examined seed‐size‐mediated interactions of these three species across a wide geographic range. Field tracking of walnuts with miniature radio‐transmitters revealed that squirrels hoarded larger seeds more frequently and at greater distances than smaller seeds. In contrast, mice hoarded smaller seeds more frequently and transported them farther than larger seeds. These seed dispersers could affect the evolution of seed size because seeds hoarded at sites farther from source trees are known to survive better until germination and as seedlings. We expect that larger seeds may be advantageous in regeneration if the main seed dispersers are squirrels, whereas smaller seeds may be advantageous if mice are the dominant dispersers. These predictions were supported by the fact that seed size was smaller on islands inhabited only by mice and at the edge of the squirrel distribution, compared to areas where mice and squirrels are both common.

Fatty Acid Profiles, Tocopherol Contents, and Antioxidant Activities of Heartnut (Juglans ailanthifolia Var. cordiformis) and Persian Walnut (Juglans regia L.)

The fatty acid and tocopherol compositions of three heartnut (Juglans ailanthifolia var. cordiformis) varieties (Imshu, Campbell CW1, and Campbell CW3) were examined and compared with those of two Persian walnut (Juglans regia L.) varieties (Combe and Lake). The major fatty acids found in heartnuts and walnuts were identified by gas chromatography as linoleic (18:2n-6), alpha-linolenic (18:3n-3), oleic (18:1n-9), palmitic (16:0), and stearic acid (18:0). Polyunsaturated fatty acids were the main group of fatty acids found in both heartnut and walnut, ranging from 73.07 to 80.98%, and were significantly higher in heartnut than in Persian walnuts (P < 0.001). In addition, heartnuts had significantly higher levels of 18:2n-6 and lower levels of 18:3n-3 compared to the Persian walnuts. gamma-Tocopherol was the main tocopherol homologue present in both types of nuts, followed by delta- and alpha-tocopherol. The highest concentration of gamma-tocopherol was found in Combe Persian walnut at 267.87 mug/g, followed by Lake Persian walnut and Imshu, Campbell CW1, and CW3 heartnut at 205.45, 187.33, 161.84, and 126.46 mug/g, respectively. Tocopherols, particularly the gamma-tocopherol, were found to contribute the most to the strong total antioxidant activities of both walnut and heartnut oils using either the free radical 2,2-diphenyl-1-picrylhydrazyl assay or the photochemiluminescence method.

Polyphenolic Profiles and Antioxidant Activities of Heartnut (Juglans ailanthifolia Var. cordiformis) and Persian Walnut (Juglans regia L.)

The polyphenolic compositions of three heartnut (Juglans ailanthifolia var. cordiformis) varieties (Imshu, Campbell CW1, and Campbell CW3) were examined and compared with those of two Persian walnut (Juglans regia L.) varieties (Combe and Lake). The nuts were defatted, extracted, and separated into three different fractions, the free phenolic acid (FPA), acid-hydrolyzable phenolic acid (AHPA), and bound phenolic acid (BPA) fractions. The total phenolic contents (TPCs) in both FPA and AHPA of the Persian walnuts were significantly higher (P < 0.001) than those of the heartnuts, but not in the BPA (P = 0.20). LC-ESI-MS(n)() studies revealed that except for the FPA fraction, the major polyphenolics in both heartnut and Persian walnut were ellagic acid and valoneic acid dilactone. Persian walnuts contained an average of 0.29 and 1.31 mg of ellagic acid/g nut in the 80% methanol extractable fractions FPA and AHPA, respectively. Heartnuts contained an average of 0.16 and 0.60 mg of ellagic acid/g nut in the respective fractions. Bound ellagic acid in the residue was 0.93 and 0.70 mg/g of nut in the Persian walnut and in the heartnut, respectively. Valoneic acid dilactone was tentatively identified and quantified as milligrams of ellagic acid equivalent per gram of nut. These components were found to contribute to the strong total antioxidant activities measured using ferric reducing antioxidant power and photochemiluminescence methods.

Improving disease resistance of butternut (Juglans cinerea), a threatened fine hardwood: a case for single-tree selection through genetic improvement and deployment

Approaches for the development of disease-resistant butternut (Juglans cinerea L.) are reviewed. Butternut is a threatened fine hardwood throughout its natural range in eastern North America because of the invasion of the exotic fungus, Sirococcus clavigignenti-juglandacearum Nair, Kostichka and Kuntz, which causes butternut canker. Early efforts were made to identify and collect putatively resistant germ plasm, identify vectors and to characterize the disease. More recently, molecular techniques have been employed to genetically characterize both the pathogen and the resistant germ plasm. Much of the host resistance may originate from hybridization with a close Asian relative, Japanese walnut (Juglans ailanthifolia Carr.), and from a few natural phenotypic variants. Further genetic characterization is needed before classical breeding or genetic modification can be used to produce canker-resistant trees.