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Gnomoniopsis castaneae is an important, destructive pathogen of Castanea species, initially identified as the primary agent of nut rot in Europe and Oceania. Although a decade of research has focused almost exclusively on its association with and activity in chestnuts, it has been identified as a mild pathogen or endophyte in multiple other hardwood species, whose roles as potential reservoirs and hosts have remained unexplored. Although the origin of the disease is unknown, it is thought to be a ubiquitous endophyte that has potentially shifted to pathogenic activity as a result of global climate change. Yet there is evidence of the expansion of the range of the pathogen as it continues to be identified in new regions, suggesting some degree of introduction is occurring. Its recent discovery in the United States brings a new urgency to the need to understand the full range and epidemiology of G. castaneae and to examine potential methods of detection and mitigation. [ABSTRACT FROM AUTHOR]

The iconic American chestnut (Castanea dentata) once spanned a large portion of eastern North America before its functional extinction in the early 20th century due primarily to non‐native fungal pathogens. The pronounced loss of this species likely resulted in an abrupt alteration of many ecological processes, including fire. The potential to resurrect this species through resistance breeding or other methods holds promise, but more information on the fire ecology of American chestnut may provide helpful information to assist restoration. Here we summarize the existing direct and indirect research on the fire history and fire ecology within the former range of American chestnut. We found multiple lines of evidence to suggest fire was frequent throughout much of its historical range. A broadscale analysis of historical fire frequency revealed that 88% of the American chestnut range had a mean fire return interval of 20 yr or less, corresponding to finer‐scale fire history and forest structure studies. In much of the historical range of American chestnut, the stand structure was much more open, fire scar studies of associated species were very frequent (mean fire return interval ranged between 1.9 and 19.8 yr), and, in many cases, charcoal abundance and American chestnut pollen were positively related. This evidence coupled with American chestnut's suite of traits associated with tolerance of frequent fire, such as highly flammable litter, tall stature, rapid growth, and resprouting ability, reinforce concepts that fire was historically an important component of many woodlands and forests containing American chestnut. While these lines of evidence are strongly suggestive, we provide potential areas of further inquiry to expand and refine our understanding of American chestnut fire ecology. [ABSTRACT FROM AUTHOR]

Societal Impact Statement: Over four billion American chestnut trees have been killed as a result of an introduced pathogen, the chestnut blight fungus. Recently, transgenic blight‐tolerant American chestnut trees have been produced by inserting a gene from wheat into the American chestnut genome. Pending federal approval to use these transgenic trees for large‐scale forest restoration, this would be the first instance where a transgenic approach has been used to restore a tree species that has been rendered functionally extinct by an introduced pathogen. With the help of citizen scientists, we estimate that large‐scale forest restoration using blight‐tolerant American chestnut trees is possible within the next few decades. SummaryBreeding transgenic blight‐tolerant American chestnuts with susceptible wild‐type (WT) trees is potentially an efficient method to rescue the genetic diversity and adaptive capacity of the American chestnut population for large‐scale restoration.To develop a breeding plan to diversify a transgenic blight‐tolerant population, we simulated pedigrees to estimate inbreeding coefficients and effective population size in scenarios involving outcrossing 1–4 transgenic founders to a maximum of 1,500 WT trees over 1–5 generations. We also simulated marker‐assisted introgression scenarios to minimize the extent of the transgenic founder genome, especially on the transgene carrier chromosome.Simulations suggest that the effective population size may be increased to >500, and the average inbreeding coefficient reduced to <0.01, by outcrossing a single transgenic founder over five generations to 2, 25, 50, 150, and 450 (677 total) WT parents. Three generations of marker‐assisted introgression is predicted to decrease the length of the founder genome to between 7% and 13% of the transgene carrier chromosome length as compared to 42% with event selection (ES) only. Transgenic outcross selections may be intercrossed to select progeny homozygous for the transgene for planting in seed orchards.A diversified population of transgenic blight‐tolerant American chestnut is estimated to be available for use in large‐scale forest restoration 20–35 years after federal approval to distribute the trees. In contrast, trees from earlier generations would be available almost immediately after federal approval for personal or horticultural plantings. Methods to accelerate pollen production and outcrossing are discussed. [ABSTRACT FROM AUTHOR]

Biotechnology offers a new approach for the restoration of tree species affected by exotic pathogens; however, nontarget impacts of this novel strategy on other organisms have not been comprehensively assessed. We evaluated the effect of transgenic American chestnut (Castanea dentata) leaf litter on the growth and survival of larval wood frogs (Lithobates sylvaticus), a forest‐dwelling amphibian species widely sympatric with American chestnut, that forage almost entirely on periphyton and litter detritus that accumulate in temporary vernal pools in forests. We reared wood frog larvae on Castanea leaf litter (American chestnut genetically engineered for blight tolerance, nontransgenic American chestnut, Chinese chestnut [Castanea mollissima], and an American–Chinese chestnut hybrid) and litter from two non‐Castanea, nontransgenic "control" tree species, coupled with two levels of supplementary food. We observed no differences in growth or survival of wood frog larvae reared on transgenic versus nontransgenic American chestnut leaves. Without supplementary food, wood frog larvae provided leaves from American chestnut (both types) developed faster and grew larger than those exposed to other leaf litter treatments. Results of this study provide preliminary evidence that (1) American chestnut may have formerly been an important source of food for forest‐dwelling amphibians and (2) transgenic American chestnut litter generated as part of chestnut restoration efforts is unlikely to present direct novel risks to developing amphibian larvae in the forest environment. [ABSTRACT FROM AUTHOR]

American chestnut (Castanea dentata) was once an important component forests in the central Appalachians (USA), but it was functionally extirpated nearly a century ago. Attempts are underway to reintroduce blight‐resistant chestnut to its former range, but it is uncertain how current forest composition, climate, and atmospheric changes and disturbance regimes will interact to determine future forest dynamics and ecosystem services. The combination of novel environmental conditions (e.g. climate change), a reintroduced tree species and new disturbance regimes (e.g. exotic insect pests, fire suppression) have no analog in the past that can be used to parameterize phenomenological models. We therefore used a mechanistic approach within the LANDIS‐II forest landscape model that relies on physiological first principles to project forest dynamics as the outcome of competition of tree cohorts for light and water as a function of temperature, precipitation, CO2 concentration, and life history traits. We conducted a factorial landscape simulation experiment to evaluate specific hypotheses about future forest dynamics in two study sites in the center of the former range of chestnut. Our results supported the hypotheses that climate change would favor chestnut because of its optimal temperature range and relative drought resistance, and that chestnut would be less competitive in the more mesic Appalachian Plateau province because competitors will be less stressed. The hypothesis that chestnut will increase carbon stocks was supported, although the increase was modest. Our results confirm that aggressive restoration is needed regardless of climate and soils, and that increased aggressiveness of chestnut restoration increased biomass accumulation. The hypothesis that chestnut restoration will increase both compositional and structural richness was not supported because chestnut displaced some species and age cohorts. Although chestnut restoration did not markedly enhance carbon stocks, our findings provide hope that this formerly important species can be successfully reintroduced and associated ecosystem services recovered. Forests under novel environmental conditions (e.g., climate change), reintroduced species and modified disturbance regimes (e.g., exotic insect pests) with no analog in the past require mechanistic models to robustly project future forest dynamics. We used a forest landscape model based on physiological first principles to test hypotheses about the interactions among climate change, disturbance and land type on nascent efforts to restore blight –resistant American chestnut in the eastern U.S. Climate change should favor chestnut, but chestnut restoration will only modestly increase carbon stocks. Chestnut restoration will likely decrease both compositional and structural richness because chestnut will displaced some species. [ABSTRACT FROM AUTHOR]

American chestnut (Castanea dentata) was a dominant species in eastern North America prior to the importation of chestnut blight. In light of recent efforts to restore viable populations of chestnut in eastern forests, an increased understanding of its association with other co‐occurring, disturbance‐adapted oak species is necessary. We evaluated crown architecture and leaf morphology in juvenile chestnut and red oak (Quercus rubra) to assess potential differences in establishment strategies of both species. We also investigated differences in nonstructural carbohydrate reserves and whole tree biomass partitioning between species. Seedlings of both species were planted in forest stands treated either with midstory removal or small patch cuts, simulating potential restoration plantings. After 5–7 years, chestnut's allocation to its root system was lower than red oak's, with chestnut saplings instead diverting resources to branches and foliage. Chestnut had lower leaf area index, greater crown projection area, and higher specific leaf area than red oak, indicating the species may have an advantage in shaded understories. There were only minor differences in nonstructural root carbohydrate reserves, between red oak and American chestnut, indicating that chestnut may respond similarly to oak by resprouting after disturbances topkill young saplings. We suggest that American chestnut has morphological and physiological attributes that allow it to function as an opportunistic and plastic species that can utilize gaps to facilitate its canopy recruitment, yet still persist after occasional surface fire. This knowledge can guide restoration strategies for this iconic species of the eastern temperate forest region. [ABSTRACT FROM AUTHOR]

Abstract: Both seed predators and herbivores can have profound effects on individual plant growth, reproduction and survival, but their population‐level effects are less well understood. While most plants interact with a suite of seed predators and herbivores over their life cycle, few studies incorporate the effects of multiple interacting partners and multiple life stages on plant population growth. We constructed a matrix model using 6 years of data from a rare, seed‐producing population of American chestnut (Castanea dentata). We combined field demographic data with published experimental results on the effects of pre‐dispersal seed predators (weevils) and post‐dispersal seed predators (scatter‐hoarding vertebrates) and incorporated the effect of vertebrate herbivores estimated from the field data. We explored the impact of these three different animal interactions for short‐term (transient) and long‐term (asymptotic) tree population growth. In addition, we used the model to explore the conditions under which scatter hoarding would function as a mutualism. Seed predators had greater effect on both short‐ and long‐term population growth than herbivores. Although weevil infestation can greatly reduce the probability of germination, pre‐dispersal seed predators had smaller effects on both short‐ or long‐term population growth than post‐dispersal predators. The elasticities of weevil‐related parameters were also small. The effect of browsers on both the short‐ and long‐term population growth rate were the smallest of the effects studied. Post‐dispersal seed predation affected population growth the most in the interactions studied. The probability of seed removal was among the largest elasticities, similar in magnitude to survival of large trees. Synthesis. Our results indicate that neither weevils nor the intensity of browse damage observed at our study site are likely to hinder tree regeneration or reintroduction, although both reduced population growth. Although researchers and forest managers often assume that seeds are unimportant for long‐lived tree populations, our test of this assumption shows that scatterhoarders and other post‐dispersal seed consumers can significantly limit natural regeneration. Forest management that alters scatterhoarder behaviour could have significant effects on tree population dynamics that are largely unexplored. [ABSTRACT FROM AUTHOR]

Hybrid chestnut (Castanea dentata × C. mollissima) has the potential to provide a valuable agroforestry crop on formerly coal mined landscapes. However, the soil interactions of mycorrhizal fungi and buried metals associated with mining are not known. This study examined soil, plant tissue, and ectomycorrhizal (ECM) root colonization on eight-year-old hybrid (BC1F3 and BC2F3) and American chestnuts on a reclaimed coal mine in Ohio, USA. Chestnut trees were measured and ECM colonization on roots was quantified. Leaves, flowers, and soil were analyzed for heavy metals. Differences were not detected among tree types regarding metal accumulation in plant tissue or ECM colonization. BC2F3 hybrids had greater survival and less cankers than American chestnuts (P = 0.006 and <0.0001). Taller trees were associated with greater ECM root colonization and correlated with an increase in Al uptake (P = 0.02 and 0.01). When comparing tissue, manganese and aluminum were in higher concentrations in leaves than flowers, where copper and selenium were significantly higher in floral tissue (P < 0.05). All trees were flowering at this time meriting further examination in nut tissue. Block effects for selenium and zinc indicate the variability in reclaimed soils requiring further monitoring for possible elemental transfer to nut and wood tissue. [ABSTRACT FROM AUTHOR]

Transgenic hypovirulent strains of Cryphonectria parasitica, the chestnut blight fungus, engineered to contain a chromosomally integrated full-length infectious cDNA copy of virulence-attenuating hypoviruses, differ from natural hypovirulent strains in the ability to transmit hypoviruses to ascospore progeny and with 100% efficiency through asexual spores. We report the results of a long-term field study that examined whether these properties result in enhanced hypovirulence establishment, dissemination and persistence under field conditions. Informed by previous field results using a severe hypovirus, this study that employed 144 American chestnut trees was designed to provide improved inoculum formulation and delivery and to include the use of a mild hypovirus isolate (less debilitating) CHV-1/Euro7 in an attempt to increase dissemination. Isogenic transgenic hypovirulent ( TG), non-transgenic cytoplasmic hypovirulent ( CH) or virus-free virulent (V) treatment strains were applied to artificially initiated and natural C. parasitica cankers three times each year for 7 years. Reservoirs of treatment inoculum also were initiated and refreshed annually for the first 6 years of the study. Sampling of 111,000 individual ascospores from 4,500 perithecia confirmed hypovirus-containing spermatia successfully transmitted TG hypoviruses to ascospore progeny under field conditions. Surprisingly, TG ascospore progeny were recovered 3 years after the last annual application of treatment inoculum. Repeated sampling of over 440 cankers revealed dissemination of both CH and TG hypovirulent strains. However, no significance differences in establishment or dissemination were observed for the two hypovirulent strains. The results are discussed in terms of the contribution of ascospore progeny to infection, competition by endemic virulent C. parasitica, size of inoculated trees and the biological control potential of TG hypovirulent strains. [ABSTRACT FROM AUTHOR]

In the eastern United States, American chestnut (Castanea dentata) was historically a major component of forest communities, but was functionally extirpated in the early 20th century by an introduced pathogen, chestnut blight (Cryphonectria parasitica). Because chestnut is fast-growing, long-lived, and resistant to decay, restoration of American chestnut using blight-resistant stock could have the potential to increase carbon sequestration or storage in forested landscapes. However, carbon dynamics are also affected by interspecific competition, succession, natural disturbance, and forest management activities, and it is unknown how chestnut restoration might interact with these other processes. We used the PnET-Succession extension of the LANDIS-II forest landscape model to study the implications of chestnut restoration on forest composition and carbon storage in the context of other disturbances, including timber harvest and insect pest outbreaks. Our results imply that it could take a millennium or more for chestnut to fully occupy landscapes without aggressive restoration efforts. When successful, chestnut restoration activities displaced other species approximately in proportion to their abundance on the landscape, rather than replacing a single species or genus (e.g., Quercus). Insect pests increased the rate of chestnut colonization by reducing the abundance of competitors, and also had a dominant effect on carbon dynamics. Although chestnut is fast-growing, moderately shade-tolerant, and decomposes very slowly, our results suggest that it can only modestly increase the carbon storage potential of eastern forests. However, our results also demonstrate that compositional changes in forest communities can have noticeable effects on biomass accumulation, even with the large uncertainties introduced by invasive pests. [ABSTRACT FROM AUTHOR]

ABSTRACT Range-wide declines of the Allegheny woodrat ( Neotoma magister) have been attributed, in part, to reductions in mast associated with extirpation of American chestnut ( Castanea dentata) and transition to oak ( Quercus)-dominated forests prone to periodic mast failure. Chestnuts produce mast more consistently than oaks; hence, efforts to restore a blight-resistant hybrid chestnut may facilitate woodrat recovery. Our goal was to describe the implications of chestnut restoration for imperiled Allegheny woodrat populations. Our objectives were to evaluate woodrat preferences for American chestnuts, blight-resistant hybrid chestnuts, and other hard mast items and to describe the response of woodrats to artificial increases in mast availability. From 2011 to 2013, we conducted a series of cafeteria-style experiments among woodrat populations in southern Indiana in which we used remote cameras to quantify woodrat preferences for various mast items. Additionally, we introduced an abundance of mast into occupied den sites and evaluated differences in apparent survival, apparent recruitment, population growth rate, and body mass between mast-supplemented and control populations. Discrete choice modeling revealed that woodrats preferentially removed northern red oak ( Q. rubra) and black oak ( Q. velutina) acorns over chestnuts and other seed types (i.e., hickories [ Genus spp.], walnuts [ Genus spp.]). Further, woodrats preferred American over hybrid chestnuts, suggesting that these seeds were not perceived as equivalent food resources. Apparent survival, apparent recruitment, population growth rate, and body mass did not differ between supplemented and control populations. Although chestnuts, as annually consistent mast producers, may benefit woodrat populations by reducing the risk of complete mast failure, our results suggest that the restoration of chestnut mast is unlikely to benefit woodrat populations during years of abundant acorn production. Accordingly, managers should foster a diverse and abundant oak community to ensure sufficient acorn resources are available to sustain woodrat populations as chestnut restoration efforts progress. © 2015 The Wildlife Society. [ABSTRACT FROM AUTHOR]

Recent field trials on blight-resistant hybrids ( BC3F3) of American chestnut ( Castanea dentata) and Chinese chestnut ( C. mollissima) have intensified planning for widespread restoration of Castanea to eastern U.S. forests. Restoration will likely rely on natural seed dispersal from sites planted with chestnut; however, we do not know how dispersal agents such as granivorous rodents will respond to hybrid chestnuts. At one extreme, excessive seed consumption may impede restoration. Alternatively, scatter-hoarding rodents might facilitate the spread of chestnut by dispersal of seeds from restoration plantings. We conducted trials with five rodent species to quantify foraging preferences and to evaluate the potential role of granivores in chestnut restoration. Specifically, we presented seeds from American and hybrid chestnuts ( BC3F2) with other common mast species and recorded the proportion of seeds removed and the fates of tagged seeds. Mice, chipmunks, and flying squirrels harvested both chestnut types preferentially over larger, tougher black walnut, hickory, and red oak seeds, but fox squirrels and eastern gray squirrels preferred larger seeds to chestnuts. All rodents consumed a greater proportion of the chestnuts than other seed types. American and hybrid chestnut also differed in important ways: except for fox squirrels, rodents preferentially removed American chestnuts over hybrid chestnuts, but we estimated that fox squirrels carried a greater proportion of hybrid chestnuts beyond our tag search area, suggesting that hybrids may be dispersed farther and cached more often than American chestnut. These differences indicate that hybrid chestnut may not be functionally equivalent to American chestnut with regard to seed-granivore interactions. [ABSTRACT FROM AUTHOR]

The objective of this research was to evaluate soil subsurface methods that may aid in seedling establishment and encourage root colonization from a diverse group of ectomycorrhizal (ECM) fungi during restoration projects., American chestnut Castanea dentata Marsh. Borkh. and backcrossed chestnuts seedlings were planted on a reclaimed coal mine site in central Ohio, USA. Roots from chestnut seedlings planted in the plots that were cross-ripped, plowed and disked, or a combination of treatments were sampled for ECM fungi and compared with control plots. The presence and identification of native ECM were determined by fungal DNA sequencing of the internal-transcribed (ITS) region., After two growing seasons, mechanical soil treatments resulted in seedlings with significantly more ECM species when compared to seedlings grown in the control plots ( P < 0·0001). A nonmetric multidimensional scaling ordination followed by a permutational manova confirmed significant dissimilarities in community composition between the control and mechanically treated plots ( F = 0·24, P = 0·015)., Ectomycorrhizal root colonization was significantly higher on the chestnut seedlings sampled from the mechanically treated plots when compared to the control plots ( F = 10·63, P < 0·0001). Differences did not exist among the three mechanical treatments. There was also a significant increase in above-ground seedling growth in the plots that were treated with a surface soil method ( F = 15·72, P < 0·0001). It is not clear whether ECM activity was the driver of plant growth; regardless, both are strong indicators of healthy tree establishment., Synthesis and applications. This study illustrates that the use of soil subsurface methods increased ectomycorrhizal (ECM) activity and seedling growth. Employing methods that encourage the root colonization by beneficial ECM and promote healthy seedling establishment may aid the long-term survival of chestnuts in restoration projects. This can be applied to other hardwood seedlings used in reforestation in soils compacted after anthropogenic disturbances. [ABSTRACT FROM AUTHOR]

I.II.III.IV.V.References Summary: We propose a conceptual framework for restoration of threatened plant species that encourages integration of technological, ecological, and social spheres. A sphere encompasses ideas relevant to restoration and the people working within similar areas of influence or expertise. Increased capacity within a sphere and a higher degree of coalescing among spheres predict a greater probability of successful restoration. We illustrate this with Castanea dentata, a foundation forest tree in North America that was annihilated by an introduced pathogen; the species is a model that effectively merges biotechnology, reintroduction biology, and restoration ecology. Because of C. dentata's ecological and social importance, scientists have aggressively pursued blight resistance through various approaches. We summarize recent advancements in tree breeding and biotechnology that have emerged from C. dentata research, and describe their potential to bring new tools to bear on socio‐ecological restoration problems. Successful reintroduction of C. dentata will also depend upon an enhanced understanding of its ecology within contemporary forests. We identify a critical need for a deeper understanding of societal influences that may affect setting and achieving realistic restoration goals. Castanea dentata may serve as an important model to inform reintroduction of threatened plant species in general and foundation forest trees in particular. [ABSTRACT FROM AUTHOR]

Aim Chestnuts ( Castanea spp.) are ecologically and economically important species. We studied the general biology, distribution and climatic limits of seven chestnut species from around the world. We provided climatic matching of Asiatic species to North America to assist the range-wide restoration of American chestnut [ C. dentata (Marsh.) Borkh.] by incorporating blight-resistant genes from Asiatic species. Location North America, Europe and East Asia. Methods General chestnut biology was reviewed on the basis of published literature and field observations. Chestnut distributions were established using published range maps and literature. Climatic constraints were analysed for the northern and southern distribution limits and the entire range for each species using principal component analysis (PCA) of fourteen bioclimatic variables. Climatic envelope matching was performed for three Chinese species using Maxent modelling to predict corresponding suitable climate zones for those species in North America. Results Chestnuts are primarily distributed in the warm-temperate and subtropical zones in the northern hemisphere. PCA results revealed that thermal gradient was the primary control of chestnut distribution. Climatic spaces of different species overlap with one another to different degrees, but strong similarities are shown especially between Chinese species and American species. Climatic envelope matching suggested that large areas in eastern North America have a favourable climate for Chinese species. Main conclusions The general biological traits and climatic limits of the seven chestnut species are very similar. The predictions of Chinese species climatic range corresponded with most of the historical American chestnut range. Thus, a regionally adapted, blight-resistant, introgressed hybrid American chestnut appears feasible if a sufficiently diverse array of Chinese chestnut germplasm is used as a source of blight resistance. Our study provided a between-continent climate matching approach to facilitate the range-wide species restoration, which can be readily applied in planning the restoration of other threatened or endangered species. [ABSTRACT FROM AUTHOR]

This study evaluated the influence of planting sites on the establishment and ectomycorrhizal (ECM) colonization of American chestnut (Castanea denetata (Marsh.) Borkh.) on an abandoned coal mine in an Appalachian region of the United States. Root morphotyping and sequencing of the fungal internal transcribed spacer (ITS) region were used to identify the ECM species associated with the chestnut seedlings. Germination, survival, ECM root colonization, and growth were assessed in three habitats: forest edge, center (plots without vegetation), and pine plots (a 10-year-old planting of Pinus virginiana). Seedlings in pine plots had higher survival (38%) than the other plot types (center 9% and forest edge 5%; P = 0.007). Chestnuts found colonized by ECM within the pine plots were larger (P = 0.02), contributed by a larger root system (P = 0.03). Forest edge and pine plots had more ECM roots than seedlings in center plots (P = 0.04). ITS fungal sequences and morphotypes found among chestnut and pine matched Scleroderma, Thelephora, and Pisolithus suggesting these two plant species shared ECM symbionts. Results indicated that the presence of P. virginiana had a greater facilitative effect on growth and survival of chestnut seedlings. [ABSTRACT FROM AUTHOR]

The American chestnut ( Castanea dentata (Marshall) Borkh.), once a major component of eastern forests from Maine to Georgia, was functionally removed from the forest ecosystem by chestnut blight (an exotic fungal disease caused by Cryphonectria parasitica (Murr.) Barr), first identified at the beginning of the twentieth century. Hybrid-backcross breeding programs that incorporate the blight resistance of Chinese chestnut ( Castenea mollissima Blume) and Japanese chestnut ( Castenea crenata Sieb. & Zuc.) into American chestnut stock show promise for achieving the blight resistance needed for species restoration. However, it is uncertain if limitations in tissue cold tolerance within current breeding programs might restrict the restoration of the species at the northern limits of American chestnut's historic range. Shoots of American chestnut and hybrid-backcross chestnut (i.e., backcross chestnut) saplings growing in two plantings in Vermont were tested during November 2006, February 2007, and April 2007 to assess their cold tolerance relative to ambient low temperatures. Shoots of two potential native competitors, northern red oak ( Quercus rubra L.) and sugar maple ( Acer saccharum L.), were also sampled for comparison. During the winter, American and backcross chestnuts were approximately 5°C less cold tolerant than red oak and sugar maple, with a tendency for American chestnut to be more cold tolerant than the backcross chestnut. Terminal shoots of American and backcross chestnut also showed significantly more freezing damage in the field than nearby red oak and sugar maple shoots, which showed no visible injury. [ABSTRACT FROM AUTHOR]

In restoring species, reasons for introducing limited numbers of individuals at different locations include costs of introduction and maintenance, limited founder supply, and risk “bet hedging.” However, populations initiated from few founders may experience increased genetic drift, inbreeding, and diversity loss. We examined the genetic diversity of an isolated stand of more than 5,000 American chestnut trees relative to that of the 9 surviving stand founders (out of 10 total) planted in the 1880s. We used minisatellite DNA probes to reveal 84 genetic markers (circa 24 loci) among the nine founders, and their genetic diversity was compared with three separate plots of descendant trees, as well as with two natural stands. The descendants were circa 7.3% more heterozygous than the founders (mean estimated H= 0.556 vs. 0.518, respectively; p < 0.0001). Genetic differentiation was not pronounced ( FST < 0.031), and no markers, including those at low frequency among the founders, were lost in the descendants. The founders and natural transects were not significantly different in H or similarity (mean proportion of bands shared). Special planting or mating protocols for establishment of a vigorous American chestnut population from a low number of founders may not be required to avoid strong effects of genetic drift and inbreeding. These results demonstrate that loss of genetic diversity following reintroduction of a limited number of founders is not always inevitable, such as this case where the species is highly outcrossing, expression of heterozygous advantage may occur, the original founders remain as gene contributors over generations, and the establishing population expands constantly and rapidly. [ABSTRACT FROM AUTHOR]

1 Matrix models were used to evaluate the effect of chestnut blight infection on transition probabilities and population growth rates for American chestnuts. Disease-free, epidemic and recovering (i.e. pathogen infected with a double-stranded (ds) RNA hypovirus) populations were compared. 2 Population growth rates (λ) did not differ significantly over time or with disease status. However, predicted stable stage distributions differed between population types, with disease-free and recovering populations more similar to each other than either was to epidemic populations. 3 Survival had the highest proportional contribution to population growth rates as revealed by elasticity analyses. However, reductions in stasis of the largest trees contributed most to reductions in population growth rate when comparing diseased with disease-free populations using LTRE. 4 The presence of hypovirus reduces pathogen virulence, allowing individual American chestnut trees to increase in size. Where dsRNA has spread, chestnut populations in Michigan have attained population dynamics similar to those found in disease-free populations. 5 Matrix models and life table response experiments can be used to detect important pathogen-mediated changes in the dynamics of host populations. Journal of Ecology (2004) 92, 675–685 [ABSTRACT FROM AUTHOR]

Natural blight cankers on grafted American chestnut Castanea dentata trees were inoculated with one French-derived hypovirulent Cryphonectria parasitica strain, with a predominantly orange-pigmented colony phenotype and three Italian hypovirulent C. parasitica strains, with a predominantly white colony phenotype, in 1982 and 1983. Cryphonectria hypovirus 1 (CHV1) dsRNA was extracted from the four inoculated strains and from 11 predominantly white or orange pigmented C. parasitica isolates recovered from blight-controlled cankers on the grafted trees during 1994–2000; cDNAs were made by reverse transcriptase-polymerase chain reaction for two hypovirus regions: (i) an 844-bp region in the helicase domain of open reading frame B (ORF B), designated OB and (ii) an 894-bp region that included part of the 5′ non-coding region and part (p29) of ORF A (5′OA). Nucleotide sequence analysis indicated that hypovirus isolates from the grafted trees and Italian inoculated strains had high homologies (identities) to each other and high homologies for OB (98.7–99.9%) and 5′OA (99.2–99.6%) to reference hypovirus, CHV1-Euro7; homologies to reference hypovirus, CHV1-EP713, were low (≤89.8%). In contrast, the hypovirus from the predominantly pigmented, French-derived inoculated strain had high homologies for OB (99.1%) and 5′OA (99.7%) to reference CHV1-EP713, and low homologies (87.7–89.7%) to the predominantly pigmented grafted-tree isolates. These results provide strong evidence that hypoviruses present in the two predominantly pigmented isolates and nine predominantly white isolates of C. parasitica from the grafted trees were of Italian inoculated hypovirulent strain origin. For the Phe(25) through Gln(73) phenotype-determinant region in p29 of 5′OA, hypovirus isolate amino acid sequences were dependent on whether they were CHV1-Euro7 or CHV1-EP713 hypoviruses, but predominantly white and predominantly pigmented phenotypes within CHV1-Euro7 or within CHV1-EP713 had identical amino acid sequences. Grafted-tree hypovirus isolates infecting the predominantly pigmented C. parasitica isolates may originate from chance transmission and replication of a CHV1-Euro7 hypovirus variant or variant mixture, possibly present in one or more of the Italian inoculated hypovirulent strains, such as Ep 49. [ABSTRACT FROM AUTHOR]

The American chestnut (Castanea dentata; Fagaceae) was a dominant canopy tree in the Appalachian Mountains of North America. Since the introduction of the chestnut blight fungus (Cryphonectria parasitica; Valsaceae) in America, the American chestnut has been reduced to a predominantly clonal, understory species. Our objective was to determine whether the ecological changes and absence of new recruits have influenced the population genetics of American chestnut. Leaf samples were collected from four populations in southwestern Virginia. Electrophoretic data from five polymorphic loci were used to determine the genetic diversity and population structure of the populations and subpopulations. Growth data and infection status were recorded for one of the populations to determine their relationship with heterozygosity. F statistics revealed a significant amount of differentiation among subpopulations and an excess of heterozygotes within subpopulations. Heterozygous individuals also had higher rates of vegetative growth. The superior performance and excess of heterozygotes suggests that selection favors heterozygous individuals. The prolonged absence of sexual reproduction in C. dentata has allowed subtle fitness differences to accumulate to the extent that they have had significant effects on the genetics of chestnut populations. [ABSTRACT FROM AUTHOR]

Summary American chestnut trees, grafted in 1980 from large survivors, were inoculated in 1982 and 1983 with four white (European) hypovirulent strains of Cryphonectria parasitica , infected with C. hypovirus 1 (CHV1); this hypovirus has been shown to be capable of moving rapidly within the mycelium of a vegetative compatibility (vc) type of C. parasitica in blight cankers. Using a 49-cell lattice plot, 17.8×17.8 cm, the spatial patterns and frequencies of white and pigmented isolates and white and pigmented vc types were investigated within superficial cankers on the grafts located outside the hypovirulent-strain-inoculated zone. Four of six cankers assayed contained white isolates, and three of the four had random spatial patterns of white isolates, based on join-count statistics. Vc tests, using pigmented isolates and pigmented single-spore colonies of white isolates, indicated that the majority of white and pigmented isolates recovered from each of two cankers assayed were in one vc type. White and pigmented lattice-plot cells of the same vc type were frequently in contact with each other, indicating incomplete movement of CHV1 within a vc type. Nine and 10 vc types were found in the two cankers; it is hypothesized that small, white vc type areas in each canker may be a source of CHV1 transmission to the major vc types. Based on join-count statistics, the spatial pattern of the single, major vc type in one canker was non-random (aggregated), whereas the other canker had a random major vc type pattern. White and pigmented in vitro variants (sectors) of C. parasitica , that resemble white and pigmented in vivo variants in spatial contact and vc compatibility, were intermediate hypovirulent and virulent on forest American chestnuts, and dsRNA positive and negative, respectively. Incomplete movement of CHV1 within a vc type could be a major cause of the prevalence of pigmented isolates in superficial cankers on chestnut trees. [ABSTRACT FROM AUTHOR]

Abstract Aim The character and distribution of American chestnut (Castanea dentata ) populations in New England are analysed to identify the extent to which the introduced chestnut blight and historic land use practices have affected chestnut distribution and life history. Location The study focuses on chestnut in Connecticut and Massachusetts but includes analysis of data related to other Castanea species in North America and Europe. Methods The ecology and palaeoecology of chestnut is investigated using a range of techniques, including examination of the growth form of chestnut trees in plantations located away from blight, mapping of chestnut sprouts and blight-killed trees at various locations, anatomical examination of chestnut stems, analysis of early forestry practices, identification of changes in the relative abundance of chestnut pollen in Holocene lake sediments and comparison of American chestnut with other Castanea species. Results Examination of chestnut sprouts surviving in the former range of that species shows that most sprouts originated from suppressed seedlings and that environmental factors severely limited the survival of sprouts from large blight-killed trees. Palynological data show that chestnut was either present in very low populations or entirely absent from New England and only became abundant after about 2500 years ago. All factors suggest that chestnut abundance is related to the natural disturbance cycle, while human-induced transformations of the landscape and the introduction of chestnut blight have further transformed the character of chestnut in New England. Main conclusions Most surviving chestnut sprouts in New England forests represent old seedlings that have continued to re-sprout since establishment before the introduction of blight nearly 100 years ago. The growth form of these sprouts ensures a minimal substrate of bark tissue for blight establishment so that blight has a relatively minor effect on... [ABSTRACT FROM AUTHOR]

A mixture of hypovirulent strains of Cryphonectria parasitica , including four white (European) strains infected with Cryphonectria hypovirus1 (CHV1), was used in 1982 and 1983 to inoculate natural blight cankers located within a zone ranging from the ground to 183 cm on grafted American chestnut trees. These four white strains belonged to three vegetative compatibility (vc) types. Using pigmented, single-spore colonies from white isolates, 48 vc types were identified among 110 white isolates recovered in 1996, 1998, and 1999 from cankers located outside the inoculated zone. Twenty-five of the 48 white vc types consisted of two or more isolates. The 25 major white vc types were vegetatively incompatible with all four of the original white hypovirulent strains, providing evidence for spread of CHV1 but not for spread of the original inoculated strains. Forty-five vc types represent the minimum number of `new' vc types into which CHV1 had spread. The ratio of white vc types to white isolates tested (S/N) and Shannon diversity index were 0.436 and 3.64, respectively. The spatial pattern of white vc types on the grafts was found to be non-random (p=0.019). White single-spore colonies of white isolates were placed into four cultural morphology (CM) groups. The two largest groups contained 37 (CM group 3) and 33 (CM group 1) isolates. Single-spore colonies from the original, white inoculated strain, Ep 49, were classified into CM groups 3 and 1, and colonies of Ep 51 W were classified into CM group 1. [ABSTRACT FROM AUTHOR]

This article focuses on the evaluation of superficial canker instability for hypovirulent Cryphonectria parasitica inoculated on American chestnut trees. The results of this study indicate that cankers produced following inoculation of American chestnut trees with hypovirulent strains of Cryphonectria parasitica were unstable for a character important to biological control of chestnut blight: canker superficiality. Since chestnut trees are perennial and must survive for several decades, this character must be reasonably stable or the cankers may eventually kill the trees, as found here.

Ten American chestnut (Castanea dentata) trees were wounded at 53, 99, and 145 cm above the ground and inoculated with Cryphonectria parasitica in May. Canker area was measured in August and the surfaces of longitudinal dissections of stem wood were stained with I2KI to reveal the presence of starch. Mean canker area was greatest (7.5 ± 4 cm²) in sections with no starch, and smallest (1.8 ± 0.6 cm²) in sections with moderate amounts of starch. Starch reserves may play a role in the chestnut's ability to respond to infection by C. parasitica. [ABSTRACT FROM AUTHOR]

Provides an allozyme and a random amplified polymorphic deoxyribonucleic acid (DNA) (RAPD) analysis of the genetic diversity and geographic variation in wild populations of the American chestnut (Castanea dentata). Information on the species; Composition of the genus Castanea species; Reference to breeding efforts conducted by the United States Department of Agriculture; Details on the success of breeding programa launched.