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Breeding Blight-Resistant Chestnuts
Abstract
IntroductionCastanea SpeciesPathology of Chestnut BlightInheritanceBiochemical DifferencesBreeding ApproachesSources of Stocks and Hybrids for a Backcross ProgramPresent Status of the American ChestnutChinese Chestnut Cultivars for Nut ProductionBreeding TechniquesResearch NeedsSummary and Conclusions
Literature Cited
... However, Jaynes and Dierauf (1982) concluded that adequate field resistance was not obtainable among trees that are predominantly (presumably >50%) C. dentata. Later, Anagnostaksis (2001) found this strategy limiting in terms of producing timber quality forest trees and is now actively backcrossing both C. mollissima and C. crenata sources of resistance to C. dentata as originally outlined by Burnham et al. (1986), discussed below. In the early 1980s, a backcross breeding program was proposed to introgress blight resistance genes from Asian chestnuts into C. dentata (Burnham, 1981; Burnham et al., 1986). ...
... Later, Anagnostaksis (2001) found this strategy limiting in terms of producing timber quality forest trees and is now actively backcrossing both C. mollissima and C. crenata sources of resistance to C. dentata as originally outlined by Burnham et al. (1986), discussed below. In the early 1980s, a backcross breeding program was proposed to introgress blight resistance genes from Asian chestnuts into C. dentata (Burnham, 1981; Burnham et al., 1986). The specific steps include making three backcross generations with selection for resistance at each generation to ensure retention of Asian resistance genes, intercrossing the selected BC 3 trees to produce BC 3 F 2 populations fully segregating (i.e., all of homozygote and heterozygote classes) for resistance, selecting in the BC 3 F 2 populations for high resistance (i.e., tree being homozygous for the Asian alleles at all resistance genes), and establishing the selections in seed orchards to produce planting stock for forest planting. ...
... Seeds from the open-pollination in the Type A orchard are planted in the Type B orchard and again exposed to blight, susceptible and intermediate resistant trees are removed, highly resistant trees are allowed to open-pollinate each other to produce highly resistant backcross bred C. dentata nuts for planting in the forest. The American Chestnut Foundation (TACF) was founded to breed C. dentata capable of surviving and reproducing in the forest using the backcross breeding method proposed by Burnham (Burnham et al., 1986; Ellingboe, 1994). Several lines from both the USDA and the CAES breeding programs served to jump-start TACF's breeding program. ...
Introduction American chestnut (Castanea dentata (Marsh.) Borkh. once occurred over much of the eastern deciduous forests of North America (Russell, 1987), with a natural range exceeding 800,000 km 2 (Braun, 1950) (Figure 1). Castanea dentata was a dominant tree species throughout much of its range, comprising between 25-50% of the canopy (Braun, 1950; Foster et al., 2002; Russell, 1987; Stephenson, 1986). Particularly in the Appalachian region, C. dentata filled an important ecological niche (Ellison et al., 2005; Youngs, 2000). The wood of C. dentata has a straight grain, is strong and easy to saw or split, lacks the radial end grain found on many hardwoods and is extremely resistant to decay (Youngs, 2000). Historically, C. dentata wood served many specialty use purposes including telephone poles, posts, and railroad ties, as well as construction lumber, siding, and roofing (Smith, 2000; Youngs, 2000). Due to the high tannin content, both the wood and bark were used to produce tannin for leather production. The nuts, which are edible raw or roasted, were collected throughout the fall to provide a dietary supplement and were also used as a commodity for sale or trade on U.S. streets (Steer, 1948; Youngs, 2000). Figure 1: Original natural range of Castanea dentata in eastern North America, as adapted from Little (1977). Chestnut blight disease, caused by Cryphonectria parasitica (Murr.) Barr (= Endothia parasitica (Murr) Anderson and Anderson) (Anagnostakis, 1987), rapidly annihilated C. dentata throughout its range (Roane et al., 1986). The introduced pathogen is thought to have been 2
imported on Castanea spp. seedlings from Asia and was first discovered in 1904 on infected chestnut trees at the Bronx Zoological Park in New York City (Anderson and Rankin, 1914; Murrill, 1906; Roane et al., 1986). By 1950, the disease had spread throughout the range of C. dentata, and by 1960 had killed an estimated 4 billion trees; essentially extirpating the species from the canopy (Anagnostakis, 1987; Hepting, 1974; McCormick and Platt, 1980). Since the discovery of chestnut blight, many groups have worked to develop blight-resistant C. dentata through diverse strategies including biocontrol of the fungus, breeding and selection of large surviving C. dentata trees, inter-species backcross breeding with resistant Asian chestnut species, and genetic modification. Continuing and recent progress in these areas suggest a large-scale re-introduction program is imminent (Diskin et al., 2006; Jacobs, 2007). Because C. dentata disappeared decades before the development of modern principles of forest ecology (Paillet, 2002), our knowledge of basic biological and ecological characteristics of the species is rudimentary (Jacobs, 2007; Paillet, 2002). Much of our understanding regarding establishment and growth of C. dentata originates from historical observations or growth of stump sprouts (Paillet, 1982; 1984; 2002). With the successful advancement of C. dentata breeding programs leading to the verge of reintroduction, there has been increased prioritization for research examining C. dentata establishment and growth in planted and natural forests (Jacobs, 2007). This progress, combined with continued advances in genetic technologies for production of blight-resistant C. dentata trees for reintroduction, implicates the need for an updated critical synthesis to aid in further developing protocols for disease resistance breeding and subsequent germplasm deployment. Thus, the purpose of this technical review is to synthesize the current state of knowledge regarding 1) C. dentata biology and natural history 2) the development of blight-resistant C. dentata trees and 3) the ecology of C. dentata pertinent to pending restoration programs. These knowledge areas as well as understanding of their considerable overlap will contribute to the formulation of a viable restoration plan for the ecologically and socially important C. dentata (Figure 2).
... This natural genetic resource is used for hybridization of American chestnut and blight-resistant Asian chestnut species (Hebard 2001;Anagnostakis 2012). The American Chestnut Foundation (TACF) is one program that uses a backcross breeding approach directed towards producing trees with the form, phenology, and growth characteristics of the American chestnut, while incorporating blight resistance from the Chinese chestnut (Castanea mollissima Blume) (Burnham et al. 1986;. The most advanced breeding generation currently available for testing from TACF is the third intercross of the third backcross generation, commonly referred to as the BC 3 F 3 generation. ...
... These same dependent factors have been frequently used to determine success of particular genotypes or breeding lines in tree improvement or breeding programs of Fagaceae species in the US (Kriebel et al. 1988; and around the world Fernández-López 2012, 2015). BC 3 F 3 generation seedlings were predicted to grow similar to American chestnuts with stable blight resistance from Chinese chestnut (Burnham et al. 1986;Hebard 2006). We, therefore, focused on specific comparisons between BC 3 F 3 generation seedlings, and American and Chinese chestnut species. ...
... The Chinese chestnut family was from a controlled pollination of a Chinese chestnut mother tree at the Meadowview orchard. Families from hybrid generations were produced through backcross breeding (Burnham et al. 1986) in seed orchards at Meadowview, and each generation had unique lineages. Different mother trees were used in each backcross of each generation, and the same backcrosses from early generations were not used in later generations (cf. ...
European and American chestnut species (Castanea) have been decimated by
exotic species, most notably chestnut blight (Cryphonectria parasitica), since the early
nineteenth century. Backcross breeding programs that transfer blight disease resistance
from Chinese chestnut (C. mollissima) into American chestnut (C. dentata) offer promise
for chestnut restoration, particularly for the American chestnut which was a keystone
species in eastern North America. Nursery prescriptions and conformity to desired
American chestnut traits following planting must be tested, however, before blight resistance
can even be evaluated. We tested early field performance of American and Chinese
chestnut and hybrid seedlings from the third backcross generation (e.g., BC3F3) in twoaged
regeneration harvests on highly productive sites in the southern Appalachians, USA.
We also tested a common nursery prescription of grading seedlings by size prior to
planting. BC3F3 seedlings had similar 4-year survival to American chestnut seedlings, but
generally had smaller stem heights and ground-line diameters (GLD). Although blight had
not yet substantially challenged some sites, the BC3F3 seedlings had blight incidence
similar to the Chinese chestnut which was lower than the American chestnut. Visual
seedling grading affected planting shock and stem height and GLD by the end of year 4.
Large size-class seedlings had more stem dieback and 5 % lower survival compared to
small size-class seedlings, but larger trees exhibited the same height in year 3 as small trees
in year 4. Advanced breeding material (BC3F3) was successfully established during the
stand initiation phase of forest development on highly productive sites, but deviations in desired growth rate of the American chestnut was evident. Visual grading of seedlings affected establishment of breeding material, and should be considered in the restoration process.
... When the chestnut blight was first introduced, the now defunct USDA Bureau of Plant Industry began crossing American chestnut to Asian species to produce timbertype trees with blight resistance (Graves 1942, Clapper 1954. The work was then transferred to the Connecticut Agricultural Experiment Station (CAES) in the 1940s, but the research was largely unsuccessful (Burnham et al. 1986). The backcross breeding method was not proposed in American chestnut breeding programs until 1986 (Burnham et al. 1986). ...
... The work was then transferred to the Connecticut Agricultural Experiment Station (CAES) in the 1940s, but the research was largely unsuccessful (Burnham et al. 1986). The backcross breeding method was not proposed in American chestnut breeding programs until 1986 (Burnham et al. 1986). Three major breeding programs currently exist to combat chestnut blight and ink diseases: the CAES, the American Chestnut Cooperators Foun-dation (ACCF), and the American Chestnut Foundation (TACF). ...
... Three major breeding programs currently exist to combat chestnut blight and ink diseases: the CAES, the American Chestnut Cooperators Foun-dation (ACCF), and the American Chestnut Foundation (TACF). The CAES program is the oldest in the country and creates complex hybrids using backcross breeding to transfer resistance to chestnut blight, Asian gall wasp (Dryocosmus kuriphilus Yasumatsu), and ink disease from the Asian chestnut species, Japanese chestnut (Castanea crenata Siebold and Zucc.) and Chinese chestnut (Castanea mollissima Blume), while maintaining desired American chestnut characteristics (Burnham et al. 1986, Anagnostakis et al. 2011, Anagnostakis 2012. The CAES program incorporates hypovirulent chestnut blight strains that contain a virus that reduces blight virulence (discussed below). ...
American chestnut restoration depends on a multitude of biological, administrative, and technological factors. Germplasm traditionally bred for resistance to the chestnut blight disease caused by the exotic pathogen Cryphonectria parasitica has been deployed on national forests
in the Eastern and Southern Regions of the National Forest System (NFS) since 2009. Trees were challenged by biological factors, primarily deer browse and ink disease (caused by Phytophthora cinnamomi). Because of these problems, inferences regarding resistance or tolerance to blight
are premature. Mitigation to improve success includes improved technology in seedling production for planting and selection of appropriate test sites with limited management restrictions. We suggest that chestnut restoration within the USDA Forest Service be conducted through deployment of
a series of long-term multidisciplinary tests. Limitations in resources required for this effort necessitate partnership building both within and outside the agency. Vegetation establishment targets that include chestnut test plantings within the NFS should be developed.
... Early attempts to recover American chestnut focused on hybridizing C. dentata with Asian species of the genus, which carry genes for blight resistance. Two breeding programs were initiated in the 1920s: one by the United States Department of Agriculture (USDA) and one by the Brooklyn Botanic Garden, later transferred to the Connecticut Agricultural Experiment Station (CAES) (Burnham et al. 1986;Anagnostakis 2012). Breeding work in both programs stopped in the early 1960s, and neither succeeded in reaching its objective of combining the blight resistance of Asian chestnut with the growth and form of American chestnut (Jaynes 1978;Burnham et al. 1986). ...
... Two breeding programs were initiated in the 1920s: one by the United States Department of Agriculture (USDA) and one by the Brooklyn Botanic Garden, later transferred to the Connecticut Agricultural Experiment Station (CAES) (Burnham et al. 1986;Anagnostakis 2012). Breeding work in both programs stopped in the early 1960s, and neither succeeded in reaching its objective of combining the blight resistance of Asian chestnut with the growth and form of American chestnut (Jaynes 1978;Burnham et al. 1986). ...
... A new strategy for breeding blight-resistance into C. dentata was proposed by Charles Burnham, a maize geneticist, beginning in the early 1980s (Burnham 1981(Burnham , 1988Burnham et al. 1986). Burnham and others created The American Chestnut Foundation (TACF) for the purpose of raising funds for the project, and breeding activities were consolidated on land in Meadowview, Virginia, in 1989. ...
Following the near-obliteration of American chestnut (Castanea dentata [Marsh.] Borkh.) by the chestnut blight early in the last century, interest in its restoration has been revived by efforts to develop a blight-resistant form of the species. We summarize progress and outline future steps in two approaches: (1) a system of hybridizing with a blight-resistant chestnut species and then backcrossing repeatedly to recover the American type and (2) transformation of American chestnut with a resistance-conferring transgene followed by propagation and conventional breeding. Several decades of effort have been invested in each approach. More work remains, but results indicate that success is within practical reach. The restoration of C. dentata to its native habitat now appears to be less a matter of time and conjecture than ever before in 90 years of work by public and private entities. The difficult and protracted task of incorporating extraspecific genes for resistance into a tree species with lethal susceptibility to a naturalized pathogen represents perhaps the most extreme of restoration challenges. Its pursuit by a small non-governmental organization supported primarily by philanthropy and volunteers may serve as a model for other species threatened by exotic pathogens or insects.
... Today, an estimated 431 million American chestnut stems survive as seedlings and collar sprouts, but their stems rarely flower and almost never produce viable seed before being re-infected with the blight (Dalgleish, Nelson, Scrivani, & Jacobs, 2016). Publicly funded breeding programs, initiated in the 1920s by the U.S. Department of Agriculture and the Brooklyn Botanical Garden, hybridized C. dentata with Asian Castanea species that are tolerant of chestnut blight (Anagnostakis, 2012;Burnham, Rutter, & French, 1986). However, these F 1 hybrids were not sufficiently competitive in the mixed hardwood forests typical of the historical C. dentata range (Schlarbaum, Hebard, Spaine, & Kamalay, 1998), and these early chestnut breeding programs were largely discontinued by the 1960s (Jaynes, 1978). ...
... In 1983, the American Chestnut Foundation (TACF) was founded and backcross breeding was proposed to generate hybrids that combined the blight resistance of Chinese chestnut (Castanea mollissima) with the timber-type form of American chestnut (Burnham, 1981(Burnham, , 1988Burnham et al., 1986). Backcrossing C. mollissima × C. dentata hybrids to C. dentata over three generations was expected to generate BC 3 F 1 hybrids that inherited an average of 15/16ths (93.75%) of their genome from C. dentata. ...
... Incomplete dominance of blight resistance was surmised from the observation that F 1 hybrids develop blight cankers that are intermediate in size and severity between C. mollissima and C. dentata (Graves, 1950). Burnham et al. (1986) hypothesized that blight resistance segregates at two loci based on observations of Clapper (1952) that F 1 hybrids backcrossed to C. mollissima segregate at a ratio of three small cankered trees (blight-tolerant) to one large cankered tree (susceptible). Later, Kubisiak et al. (1997Kubisiak et al. ( , 2013 found that three QTLs on three linkage groups (B, F, and G) explained 40% of the variation in canker severity in a full-sib (C. ...
American chestnut was once a foundation species of eastern North American forests, but was rendered functionally extinct in the early 20th century by an exotic fungal blight (Cryphonectria parasitica). Over the past 30 years, The American Chestnut Foundation (TACF) has pursued backcross breeding to generate hybrids that combine the timber‐type form of American chestnut with the blight resistance of Chinese chestnut based on a hypothesis of major gene resistance. To accelerate selection within two backcross populations that descended from two Chinese chestnuts, we developed genomic prediction models for five presence/absence blight phenotypes of 1,230 BC3F2 selection candidates and average canker severity of their BC3F3 progeny. We also genotyped pure Chinese and American chestnut reference panels to estimate the proportion of BC3F2 genomes inherited from parent species. We found that genomic prediction from a method that assumes an infinitesimal model of inheritance (HBLUP) has similar accuracy to a method that tends to perform well for traits controlled by major genes (Bayes C). Furthermore, the proportion of BC3F2 trees’ genomes inherited from American chestnut was negatively correlated with the blight resistance of these trees and their progeny. On average, selected BC3F2 trees inherited 83% of their genome from American chestnut and have blight resistance that is intermediate between F1 hybrids and American chestnut. Results suggest polygenic inheritance of blight resistance. The blight resistance of restoration populations will be enhanced through recurrent selection, by advancing additional sources of resistance through fewer backcross generations, and by potentially by breeding with transgenic blight‐tolerant trees.
... In the TACF backcross program, blight resistance genes are introduced to AM chestnut via crosses with CH chestnut (Burnham et al. 1986). Starting with these F 1 hybrids, AM chestnut traits are recovered through a series of backcrosses with AM chestnuts. ...
... In third generation backcross (BC 3 ) trees, the AM chestnut complement of the genome should on average be 94% (15/16th AM chestnut and 1/16th CH chestnut) and fourth backcross (BC 4 ) trees 97% (31/32th AM chestnut and 1/32th CH chestnut). The theoretical model (based upon two or three independently segregating, incompletely dominant genes) that formed the basis for the TACF backcross program predicted that backcross trees should harbor intermediate levels of blight resistance (Burnham et al. 1986). Theoretically, full resistance is to be recovered by intercrossing BC 3 (or BC 4 ) trees to produce BC 3 F 2 (BC 4 F 2 ) trees, a small percentage of which may be genetically fixed for blight resistance. ...
... Selected BC 3 parent trees at Berry College (Supplement 1) had been previously shown to exhibit adult morphological characteristics indistinguishable from those of AM chestnut (Cipollini et al. 2017). It should be noted that most of the BC 3 F 2 and BC 4 F 2 seeds used in this study are not expected to carry the full complement of blight-resistance genes of the parent trees; the theoretical framework suggests that only a fraction of the offspring might carry significant blight resistance (Burnham et al. 1986). ...
American chestnut (Castanea dentata) was a foundation species in the eastern United States until chestnut blight (Cryphonectria parasitica) infestation resulted in range-wide catastrophic reduction. Since 1983, The American Chestnut Foundation (TACF) has engaged in a breeding program aimed at restoring C. dentata to the wild. The primary goal has been to introduce blight resistance from Castanea mollissima while recovering a C. dentata phenotype via successive backcrosses. To diversify the genetic base, state chapters of TACF have been producing BC3 and BC4 (third and fourth backcross) lines using C. dentata from across its native range. This study focuses on morphology and chemistry of seeds, and morphology and early growth of seedlings derived from BC3 and BC4 trees selected for blight resistance in state chapters. Our primary comparisons were among backcross, pure C. mollissima, and pure C. dentata lines. Seed traits included a suite of morphological characters known to differ between C. dentata and C. mollissima, as well as dry matter, total carbohydrate, sugar, protein, lipid, and phenolic content. Seedling traits included variables such as stem basal diameter and height, leaf variables such as number and area, and relative growth in key parameters such as stem volume. C. mollissima lines tended to differ significantly from C. dentata and backcross lines in most parameters, while C. dentata and backcross types tended to overlap broadly in traits. These results suggest that seed and seedling characteristics of backcross hybrids studied here are likely to be sufficiently similar to C. dentata for use in restoration programs.
... In 1922, breeding work for blight resistance also began under the United States Department of Agriculture (USDA) Office of Forest Pathology, with American chestnut and Chinese chestnut hybrids selected for timber-type growth form (tall and straight, a hallmark of the American chestnut) and blight resistance (Burnham et al. 1986). From that effort, several promising first-generation Chinese x American hybrid trees were generated, including what has become known as the "Clapper" tree, which for several decades did exhibit good growth and slower progression of chestnut blight, yet eventually did die from it. ...
... None of these early programs succeeded in producing a fast growing, timber-type tree with good blight resistance; every candidate fell short in at least one of these respects (Diller and Clapper 1969;Burnham et al. 1986;Anagnostakis 2012). Hybrid breeding can also result in complications, with respect to a restoration tree, such as internal kernel breakdown (IKB) (Fulbright et al. 2014), male sterility (Sisco et al. 2014), and intermediate traits (Cipollini et al. 2017). ...
... In 1983, TACF was founded as a coalition of plant scientists and laypersons interested in the preservation of the species. Soon thereafter, three of the foundation's scientists published an extensive paper describing the foundation's breeding plan to incorporate resistance genes from the Chinese chestnut (Burnham et al. 1986). Although earlier programs had the goal of replacing American chestnuts with simple hybrids or pure Asian species (Hepting 1974), the "Burnham plan" proposed a systematic program of backcrossing F1 hybrid trees with pure American chestnut trees, selecting for blight resistance and American phenotype at each step. ...
An invasive fungal pathogen has reduced the American chestnut (Castanea dentata), once a keystone tree species within its natural range in the eastern United States and Canada, to functional extinction. To help restore this important canopy tree, blight-tolerant American chestnut trees have been developed using an oxalate oxidase-encoding gene from wheat. This enzyme breaks down oxalate, which is produced by the pathogen and forms killing cankers. Expressing oxalate oxidase results in blight tolerance, where the tree and the fungus can coexist, which is a more evolutionarily stable relationship than direct pathogen resistance. Genetic engineering (GE) typically makes a very small change in the tree's genome, potentially avoiding incompatible gene interactions that have been detected in some chestnut hybrids. The GE American chestnut also retains all the wild American chestnut's alleles for habitat adaptation, which are important for a forest ecosystem restoration program.
... Mitigation of resident exotic pests has often involved intraspecific or interspecific breeding for disease resistance, which can take many decades in tree species (Schlarbaum, 1999;Sniezko, 2006), and breeding for disease resistance in American chestnut, has been evolving for over 100 years (Van Fleet, 1914;Burnham et al., 1986;Anagnostakis, 2012). Asian Castanea Mill. ...
... mollissima Blume) exhibiting the highest resistance (Clapper, 1954). Remnant wild American chestnut and germplasm from early breeding programs of the United States Department of Agriculture (USDA), Connecticut Agricultural Experiment Station (CAES), and The American Chestnut Foundation (TACF) have been used to produce hybrid seedlings using a backcross breeding method (Burnham et al., 1986;Anagnostakis, 2001Anagnostakis, , 2012. Backcross breeding introgresses blight resistance from Chinese chestnut into a predominately American chestnut genome to produce trees that contain Asian genes for disease resistance, yet retain desirable American chestnut phenotype. ...
... Backcross breeding introgresses blight resistance from Chinese chestnut into a predominately American chestnut genome to produce trees that contain Asian genes for disease resistance, yet retain desirable American chestnut phenotype. After multiple breeding generations, including backcrossing and intercrossing, and selections for phenotype and blight resistance, the BC 3 F 3 generation (third generation of the third backcross) was predicted to have sufficient resistance for forest test plantings (Burnham et al., 1986;Hebard, 2001Hebard, , 2006Anagnostakis, 2012). ...
The loss of American chestnut (Castanea dentata) in eastern North America to chestnut blight, a disease caused by the fungal pathogen Cryphonectria parasitica, has devastated ecological and utilitarian processes and functions. A backcross breeding approach has been developed to confer disease resistance to hybrid seedlings, and forest reintroduction trials will provide important information on performance and durability of resistance in real-world forest conditions. Three plantings were established in 2009 in mesic, even-aged regeneration harvests (site index averaged 23 m for Quercus rubra) and were examined for eight-year blight resistance. These plantings are the first forest field trials to test blight resistance of the most advanced breeding generation currently available, the third generation of the third backcross (BC 3 F 3), against less advanced breeding generations (BC 1 F 3 , BC 2 F 3), disease-resistant Chinese chestnut (C. mollissima), and disease-susceptible American chestnut. We also examined if C. parasitica infection was related to tree size and growth. The pathogen infected 36 percent of trees across locations by year 8, but 31 percent of trees died prior to detection of infection. Non-pathogen related mortality was probably due to factors that are typical of hardwood plantings, including repeated deer browsing and native and non-native pest damage. The BC 3 F 3 generation exhibited resistance more similar to the Chinese chestnut than the American chestnut, but exhibited significantly lower resistance than Chinese chestnut at the location with the highest blight incidence; genetic family differences among BC 3 F 3 progeny were significant at this location. Interactions between planting location and breeding generation affected resistance rankings, suggesting additional or longer-term testing is needed to determine resistance of a particular breeding line across a variety of sites. Probability of disease incidence was positively related to ground-line diameter (GLD), but this relationship depended on location and breeding type. At two locations, American chestnut had 50 percent probability of C. parasitica infection when GLD was approximately 70 mm, and the BC 3 F 3 had 50 percent probability when GLD was between 93 and 126 mm. The Chinese chestnut maintained low probability of disease incidence (< 35 percent) across all GLD sizes, regardless of location. While a relatively high level of disease resistance was associated with the most advanced breeding generation, BC 3 F 3 , the plantings are too young to determine durable blight resistance.
Full text available at https://www.fs.usda.gov/treesearch/pubs/57357
... The restoration of Castanea dentata is perhaps the largest and most advanced reintroduction project involving disease-resistant hybrids, and it is considered a model for plant species reintroduction (Jacobs et al. 2013). For nearly 100 years, public and private programs have been breeding for blight resistance (Anagnostakis 2012), and most recently, Castanea hybrids produced through a backcross breeding technique (Burnham et al. 1986) are being tested in forest field trials (Clark et al. 2014(Clark et al. , 2016(Clark et al. , 2019. This method uses Asian chestnut species, most notably Castanea mollissima Blume (Chinese chestnut), as the initial source of blight resistance. ...
... This method uses Asian chestnut species, most notably Castanea mollissima Blume (Chinese chestnut), as the initial source of blight resistance. After subsequent backcrosses to C. dentata, followed by intercrossing, hybrids are theoretically 15/16 C. dentata in their genetic make-up, but maintain C. mollissima genes for blight resistance (Burnham et al. 1986;Anagnostakis 2012). Throughout the breeding process, trees are selected for their level of blight resistance and C. dentata-like growth form and phenotypic characteristics (Diskin et al. 2006;Cipollini et al. 2017). ...
The reintroduction of disease‐resistant hybrids is a commonly proposed solution to the introduction of pathogens and pests that weaken or eliminate native plant species. Plant interactions with soil biota result in plant–soil feedbacks (PSFs), which have consequences for individual plant growth and survival as well as broader community‐level processes, such as species diversity and coexistence. Because of their importance, species reintroduction should consider these interactions, yet little work has integrated this perspective. Here, we investigate the effects of hybrid Castanea (chestnut) reintroduction on PSFs and how these mechanisms may influence the recruitment of other species in contemporary forests. We also examine how blight‐resistant Castanea hybrids perform in the soil conditions of contemporary forests and we compare their below‐ground interactions with those of C. dentata. We conducted a reciprocal greenhouse experiment testing the effect of species‐specific soil inoculum on the growth and survival of C. dentata, Castanea hybrids and other forest dominants. Our results suggest that C. dentata and hybrids had similar belowground interactions and were regulated by negative PSFs, meaning soil microbial communities reduced conspecific growth and survival. These negative PSFs may involve the presence of the non‐native pathogen Phytophthera cinnamomi. Soil inoculum of C. dentata and Castanea hybrids had similar effects on heterospecific growth, suggesting Castanea restoration will have neutral effects on natural regeneration in restoration plantings. We conclude that Castanea hybrids may fill a similar below‐ground niche to their parent species, and that site selection, screening for soil pathogens, and site planting density will be important to restoration.
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... Building on hybrid breeding work initiated during the chestnut blight epidemic of the early 20th century, TACF aims for the restoration of chestnut to the forests of eastern North America (Burnham, Rutter, & French, 1986;Gravatt, Diller, Berry, Graves, & Nienstaedt, 1953). First detected in 1905, chestnut blight, caused by the ascomycete Cryphonectria parasitica, spread rapidly throughout the native range of the American chestnut (Castanea dentata Marsh. ...
... TACF is in the process of backcrossing interspecific hybrids to American chestnut for three generations, and intercrossing the third backcross progeny with putative elevated resistance to produce a generation of progeny (BC 3 F 2 ) in which a few recombinant individuals are supposed to be homozygous for all three major resistance genes. To accomplish this, large numbers of BC 3 F 2 trees must be evaluated (~1,200 per family) because the desired recombinants are rare (1/64 of the F 2 progeny), and a large range of phenotypes from highly susceptible to highly resistant are present (Burnham et al., 1986;Fitzsimmons et al., 2014). The most resistant, putatively homozygous recombinants should be similar to American chestnut, but true-breeding for blight resistance; that is, they will transmit equally strong blight resistance to their offspring. ...
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.
... Chestnut blight causes necrotic cankers on the branch and trunk surfaces leading to girdling and eventual mortality in susceptible trees. To restore the chestnut to eastern North American forests, a backcross breeding approach has been developed in an attempt to confer blight resistant genes from Asian chestnut species, most often the Chinese chestnut (Castanea mollisima Blume), into the American chestnut using conventional breeding (Burnham et al. 1986;Anagnostakis 2012). Such breeding programs aim to generate progeny that exhibit American chestnut phenotypic form and growth characteristics as well as maintain durable blight resistance (Hebard 2001;Diskin et al. 2006;Sniezko 2006;Anagnostakis 2012). ...
... Hereafter, a Bfamily^refers to progeny from a single open-pollinated orchard tree with a distinct lineage and limited pollen contamination from outside sources (Hebard 2006). The Chinese chestnut family was located on private property with limited pollen contamination (Paul Sisco, TACF, Asheville, NC, USA, personal communication) (Burnham et al. 1986). The TACF hybrids (D22, W3, W4, W5, and W6) are theoretically 94% C. dentata and 6% C. mollissima (Hebard 2006), whereas the CAES hybrid (4-75) is theoretically 90% American chestnut with remaining 10% a mix of Chinese chestnut, European chestnut (Castanea sativa), and Japanese chestnut (Castanea crenata) (Anagnostakis 2012). ...
Restoration of the American chestnut (Castanea dentata) is underway using backcross breeding that confers chestnut blight disease resistance from Asian chestnuts (most often Castanea mollissima) to the susceptible host. Successful restoration will depend on blight resistance and performance of hybrid seedlings, which can be impacted by below-ground fungal communities. We compared fungal communities in roots and rhizospheres (rhizobiomes) of nursery-grown, 1-year-old chestnut seedlings from different genetic families of American chestnut, Chinese chestnut, and hybrids from backcross breeding generations as well as those present in the nursery soil. We specifically focused on the ectomycorrhizal (EcM) fungi that may facilitate host performance in the nursery and aid in seedling establishment after outplanting. Seedling rhizobiomes and nursery soil communities were distinct and seedlings recruited heterogeneous communities from shared nursery soil. The rhizobiomes included EcM fungi as well as endophytes, putative pathogens, and likely saprobes, but their relative proportions varied widely within and among the chestnut families. Notably, hybrid seedlings that hosted few EcM fungi hosted a large proportion of potential pathogens and endophytes, with possible consequences in outplanting success. Our data show that chestnut seedlings recruit divergent rhizobiomes and depart nurseries with communities that may facilitate or compromise the seedling performance in the field.
... Its broad adaptability to soil and climatic conditions in eastern North America has made it commercially more valuable for nut production than the Japanese species (Hunt et al. 2009;Fei et al. 2012); however, there is still a desire to recapture the economical and ecological value of C. dentata as a forest tree and timber species. Current chestnut breeding programmes aimed at re-establishing American chestnut via hybridization of C. dentata and C. mollissima (and other Castanea), which are being carried out by organizations such as The American Chestnut Foundation and the Connecticut Agricultural Experiment Station (Burnham et al. 1986;Hebard 2001;Anagnostakis 2012). These breeding programmes aim to transfer resistance to chestnut blight from the genome of Asian Castanea species into Asian × American chestnut hybrids (Jacobs 2007;Anagnostakis 2012). ...
... The presence of blightsusceptible C. mollissima individuals requires an explanation as to why natural selection in China has not purged blight-susceptible alleles from the population. Current hypothetical models for the genetics of blight resistance (Burnham 1981;Burnham et al. 1986;Hebard 1994Hebard , 2006 do not account for the variability in blight resistance in C. mollissima over evolutionary time. ...
With the transport of plants around the globe, exotic species can readily spread disease to their native relatives; however,
they can also provide genetic resistance to those relatives through hybrid breeding programmes. American chestnut (Castanea dentata) was an abundant tree species in North America until its decimation by introduced chestnut blight. To restore chestnut in
North America, efforts are ongoing to test putative blight-resistant hybrids of Castanea dentata and Chinese chestnut (Castanea mollissima), but little is known about the ecology of C. mollissima. In a forest in northeastern USA in which C. mollissima has become established, we explored questions of stand dynamics, health and genetic relationships of C. mollissima offspring to an adjacent parent orchard. We found that C. mollissima was adapted and randomly distributed among native species in this relatively young forest. The genetics of the C. mollissima population compared with its parents indicated little effect of selection pressure as each of the parent trees contributed
at least one offspring. The ease with which this exotic species proliferated calls to question why C. mollissima is rare elsewhere in forests of North America. It is likely that a time window of low animal predation allowed seedlings
to establish, and the shallow soil at this site limited the maximum forest canopy height, permitting the characteristically
short-statured C. mollissima to avoid suppression. Our results indicate that because C. mollissima exhibited pioneer species characteristics, hybrids between C. mollissima and C. dentata have the potential to be successful pioneer species of future forests in North America, and we challenge the paradigm that
exotic tree species are wholly detrimental to native biodiversity. We contend that exotic tree species should be assessed
not only by their level of threat to native species, but also by their potential positive impacts on ecosystems via hybrid
breeding programmes.
... Breeding programs provide a means to introduce resistance into populations of native species following the introduction of non-native pathogens (Sniezko 2006;Ingwell and Preisser 2010). In an effort to produce material for restoring chestnut as a canopy tree within its natural range, The American Chestnut Foundation (TACF) initiated a backcross breeding program that introgresses blight resistant genes of an Asian chestnut parent, primarily Chinese chestnut (Castanea mollissima Blume), into American chestnut through multiple backcrosses to the American parent (Burnham et al. 1986;Hebard 2005). After the third generation of the third backcross (BC 3 F 3 ), the resultant progeny should exhibit high levels of blight-resistance (from the Chinese chestnut parent) but maintain the phenology, morphology, and growth characteristics of the American parent. ...
Backcross breeding programs have been used to transfer disease resistance and other traits from one forest tree species to another in order to meet restoration objectives. Evaluating the field performance of such material is critical for determining the success of breeding programs. In eastern North America, The American Chestnut Foundation has a backcross breeding program that uses Chinese chestnut (Castanea mollissima Blume) to introduce resistance of the fungal pathogen chestnut blight [Cryphonectria parasitica (Murr.) Barr.] to the native American chestnut [Castanea dentata (Marsh.) Borkh.]. We compared physiological and morphological characteristics among seedlings of American chestnut, Chinese chestnut, and BC1F3, BC2F3, and BC3F3 hybrid chestnuts during their fourth growing season after field-planting. American chestnut and the BC3F3 breeding generation displayed photosynthetic light-response curves that were similar to each other but different from Chinese chestnut. Rates of photosynthesis were higher for American chestnut and the BC3F3 breeding generation when compared to Chinese chestnut for light levels ≥800 μmol m−2 s−1 photosynthetic photon flux density and for maximum photosynthetic capacity. Leaf morphology variables were not different between American chestnut and any of the breeding generations, but leaf area (on a per leaf basis) of Chinese chestnut was lower than that of any other chestnut type. Our results suggest that backcross breeding can be used to transfer desirable traits for restoration of native species threatened by non-native pathogens.
... However, breeding research undertaken by the American Chestnut Foundation has produced resistant hybrids by crossing with the Chinese chestnut (Castanea mollissima). Furthermore, through backcrossing these hybrids with the American chestnut, they have developed putatively resistant chestnuts having all the timber qualities of the American variety (Burnham et al., 1986; for details see www.acf.org ). We have been using these chestnut seedlings for testing efficacy of mycorrhizal fungi for their survival and establishment on reclaimed mined sites. ...
Plant-microbe community dynamics influence the natural succession of plant species where pioneer vegetation facilitates the establishment of a distantly related, later successional plant species. This has been observed in the case of restoration of the American chestnut (Castanea dentata) on abandoned mine land where Virginia pine (Pinus virginiana) facilitated the establishment of chestnut seedlings. This was apparently due to the natural mycorrhizal networks of pine, which aided the survival and growth of chestnut seedlings. In this study, we assessed the survival and propensity of introduced mycorrhizal fungi on Virginia pine to colonize pure American and backcrossed American chestnut. Seedlings were planted in Perry State Forest located in southeastern Ohio. This area was mined for coal in the 1950s and had very little reclamation done aside from experimental tree plantings. The selected site, with little topsoil or organic matter, was characterized by high concentrations of Al, high soil temperatures, and a pH of 3.6. Virginia pine seedlings were inoculated using ectomycorrhizal (ECM) cultures of Amanita rubescens, Laccaria laccata, and Pisolithus tinctorius via liquid media. After three months, roots were tested for the presence of mycorrhizae. They were then transplanted and grown for two years in the greenhouse. After verifying mycorrhizal colonization, 600 pines were out planted in May of 2005. Chestnut seedlings (100 one-year-old seedlings) inoculated with P. tinctorius by the Ohio state tree nursery had been planted by other researchers at the same time. After eight growing seasons, pines and chestnuts were measured and sampled for ECM colonization. Growth measurements showed that pines and hybrid chestnuts had significantly more aboveground biomass compared to pure American chestnut (P = 0.01). Eleven fungal species were detected using DNA sequencing. With the exception of Amanita, the inoculum that were out planted with both chestnut and Virginia pine were replaced after 8 field seasons by fungi native to the site. More fungal species were sampled from the Virginia pines than from chestnut roots, which contributed to the significant differences in ECM fungal community composition between the two species (P = 0.005).
... The American Chestnut Foundation (TACF) is a non-profit organization attempting to restore this species using a backcross breeding program that was first initiated in the 1980s (Burnham et al., 1986;Hebard, 2005). In theory, the first putatively blight-resistant generation, the BC 3 F 3 generation, is 94% American chestnut, 6% Chinese chestnut, and is predicted to have the desired phenotypic characteristics of the American chestnut parent while maintaining blight resistance of the Chinese chestnut parent (Hebard, 2005). ...
Production of American chestnut (Castanea dentata) resistant to the chestnut blight fungus (Cryphonectria parasitica) is being conducted currently through traditional breeding and genetic transformation. Sufficient material for field testing is currently available from The American Chestnut Foundation's backcross breeding program. We planted approximately 4500 chestnut seedlings into forest test plantings on three National Forests over three years, beginning in 2009. Early survival and growth was dependent on disease pressure from exotic pathogens, primarily, root rot caused by Phytophthora cinnamomi. Plantings that contained seedlings not exhibiting symptoms of this disease had high survival (>75%) and fast rates of height growth (0.5 m/yr). We documented other non-native pests negatively affecting chestnuts including Asiatic oak weevil (Cyrtepistomus castaneus) and the Asian chestnut gall wasp (Dryocosmus kuriphilus). Native pest problems included browsing of the terminal leader by deer (Odocoileus virginianus) and defoliation caused by the chestnut sawfly (Craesus castaneae). Restoration of American chestnut will require not only blight-resistance, but adaptation to forest environments with intense vegetation competition and strategies to address other native and exotic insects and pathogens.
... The forests of the eastern United States have been permanently altered due to another invasive species, chestnut blight. This non-native, invasive pathogen [Cryphonectria parasitica (Murrill) Barr] is responsible for the decimation of American chestnut trees and the subsequent altered forest landscapes of North America(Burnham et al. 1986). At present, the United States (US) is battling multiple invasions on multiple fronts, including the emerald ash borer (Agrilus plannipennis Fairmaire), gypsy moth (Lymantria dispar Linnaeus), and cogon grass (Imperata cylindrical Linnaeus) in the eastern US, and leafy spurge (Euphorbia esula Linnaeus) and the Asian longhorned beetle (Anoplophora glabripennis Motschulsky) in the western US, just to mention a few.Human health and economies can also be dramatically affected by invasive pests. ...
An invasive insect, hemlock woolly adelgid (HWA), has initiated widespread hemlock
decline and mortality in the Great Smoky Mountains National Park (GSMNP). Riparian hemlock
mortality impacts on vegetative and aquatic systems of first-order, headwater streams were
evaluated. Reference sites for this study were representative of the best available conditions
within the GSMNP, with initial stages of HWA presence. Impacted sites were defined as areas
with over 90 percent hemlock mortality. Impacted streams had decreased canopy coverage and
increased light availability. Residual red maple, yellow birch, and sweet birch capitalized on the
loss of hemlock, with increases in relative basal area and species importance values. Rosebay
rhododendron responded with increased density and height at impacted sites, thereby preventing
woody regeneration. Since long-term regeneration and post-mortality canopy recruitment are
limited, alterations of vegetative composition and structure in the stream riparian zone are
expected. A seasonal assessment (Sept. 2009 – March 2010) of aquatic impacts revealed
increased diurnal variation in stream temperature and exhibited cooler temperatures during the
colder months than reference streams. Impacted streams exhibited greater amounts and larger
size classes of large woody debris (LWD). Higher concentrations for several nutrients, including
silicon, sodium, potassium, magnesium, chlorine, and copper were detected in impacted streams
than detected in reference streams. Impacted streams were characterized by higher pH and
increased acid neutralization capacity, while reference streams exhibited nitrate concentrations
three times higher than impacted stream concentrations. Reference streams were experiencing
the initial stage of HWA-induced defoliations, increasing stream nitrate concentrations, while
impacted sites had levels suggesting nitrate concentrations have returned to pre-infestation levels. A seasonal assessment of macroinvertebrates found species diversity, abundance, and taxa
richness were not affected by hemlock mortality. Impacted streams had a lower density of
Chironomidae and Ephemeroptera when compared to reference streams, while Pleuroceridae
snails were virtually eliminated at impacted stream sites. Reference streams were dominated by
the collector/filter functional feeding group (FFG), while impacted streams were dominated by
the scraper FFG. Hemlock mortality induced by the presence of HWA has resulted in short-term
impacts to vegetative and aquatic dynamics in stream riparian areas of the Great Smoky
Mountain National Park.
... The American Chestnut Foundation (TACF), formed in 1983, is breeding surviving American chestnut with blight-resistant Chinese chestnuts (Castanea mollissima) (Burnham et al., 1986). Highly blight-resistant progeny of the backcrosses are then selected for further backcrossing to American chestnut (Hebard, 2005). ...
The development of Chestnut backcrosses by The American Chestnut Foundation has resulted in seeds and seedlings that are now being planted on coal surface mines in the Appalachian Region. In West Virginia, two studies were established. The first study, initiated in 2008, involved planting seeds of two parental species of chestnut and three breeding generations (100% American, 100% Chinese, and B1F3, B2F3, and B 3F2 backcrosses) into loosely-graded mine soils at the Glory surface mine in West Virginia. First year survival was Chinese 81%, American 66%, and backcrosses between 69 and 74%. After the 4th year, survival had declined further for all chestnut stock types except for Chinese: Chinese 80%, American 40%, B1F3 55%, B2F 3 40%, and B3F2 44%. Average height after the 4th season was not significantly different among seed stock types: Chinese 45 cm, American 49 cm, B1F3 48 cm, B 2F3 53 cm, and B3F2 48 cm. Significantly lower survival was found when seeds were planted with peat (44%) compared to seeds without peat (60%), and lower survival resulted when seeds were not protected with tree shelters. The second study, initiated in 2009, involved planting seeds and seedlings of these same five chestnut parental species and breeding generations into two substrates (brown sandstone (pH 4.5) and gray sandstone (pH 6.6)). Only six out of 250 seeds germinated, which was surprising with the good germination results on the Glory study the year before. Planted chestnut seedlings, however, showed much better establishment. After the 3rd year on brown sandstone and gray sandstone, respectively, seedling survival was American 77 and 80%, Chinese 84 and 100%, B 1F3 88 and 72%, B2F3 70 and 68%, and B3F2 68 and 48%. Average height after the 3rd season for brown and gray sandstone substrates, respectively, was American 92 and 71 cm, Chinese 112 and 79 cm, B1F3 77 and 55 cm, B2F3 68 and 52 cm, and B3F2 82 and 39 cm.
... While the American chestnut is susceptible to the blight causing fungus, its counterpart from Asia the Chinese chestnut (Castanea mollissima), is resistant to the blight fungus. In order to restore the American chestnut to forests, researchers have been engaged in breeding programs to develop a blight-resistant American chestnut (Burnham et al., 1986; for details see www.acf.org). The reason for seeking a resistant American species for restoration instead of using the already resistant Chinese species is largely due to differences between the two species with respect to stature. ...
We have been planting blight resistant American chestnut seedlings on reclaimed coal mined areas in Southeastern Ohio, which was once within the natural range of the American chestnut. Towards the goal of restoring the American chestnut, we are testing suitable sites that can aid survival, growth and establishment of planted seedlings pre-inoculated with ectomycorrhizal fungi. Prior to the arrival of the chestnut blight fungus, pathogens of the genus Phytophthora were introduced in the USA that were responsible for the "ink disease" or "root-rot" resulting in wide-spread death of chestnut trees in southern states. Although these pathogens were not observed elsewhere, recent reports indicate their presence in some northern states, including Ohio. We have been testing each location targeted for chestnut plantings for the presence of Phytophthora, specifically P. cinnamomi. The work reported here shows results obtained from seven different sites in southeastern Ohio where reclamation was done 3-20 years ago. Soil was collected at a depth of 4-5 inches at several locations within each site. A positive control containing ∼4 cfu/10 g soil was used in the analysis. We used two different techniques for identifying the pathogen: 1. Direct isolation of the pathogen from the soil using selective media; 2. Using chestnut leaves as a baiting technique followed by selection on plates. In both cases, final identification was done by DNA isolation and sequencing using Phytophthora-specific primers. Our results showed that, at least in the locations we tested, P. cinnamomi was not detected. Because most of these lands were only recently reclaimed, it is possible that the pathogen may not have established there yet. However, samples from locations that were reclaimed more than 2 decades ago also showed absence of this fungus. Results suggest that this pathogen is either not as wide-spread in Ohio as in southern states or mined sites are not favorable for its existence and spread.
... Number of backcross generations required to reduce donor segment length by the indicated proportion (black solid lines) if a recipient genome marker at the indicated distance (cM) is used to assist selection. into state chapters that sought surviving American chestnut trees for intermating with resistant crosses with the goal of introducing locally adapted genotypes into each state's breeding population (Burnham et al. 1986). ...
Throughout the latter part of the nineteenth century and early portion of the twentieth century, there were widespread declines in wildlife species in North America due to unregulated harvest for commercial, regulatory, and private uses as well as dramatic changes in land-use practices (Moulton&Sanderson 1999). Despite recognition of the grave situation facing many of the most popular and common wildlife species, resulting in the initiation of continent-wide conservation and management programs for both game and nongame species, many of these species were critically imperiled by the time such programs were initiated (Mackie 2000). The history of wildlife management and conservation programs in the United States is intrinsically tied to this point in time, in that many of the practices and values that are in existence today stem from the recognition that wildlife resources are not inexhaustible and that active management and protection efforts must be implemented to offset the negative impacts that our species exerts on natural resources. One of the most effective and widely used tools employed by wildlife management and conservation organizations to recover and redistribute wildlife species within suitable habitats is the practice of species translocation (International Union for Conservation of Nature [IUCN] 1987). Indeed, species-translocation programs targeted at reintroducing or introducing wildlife species to areas of suitable or reclaimed habitat were used extensively in attempts to recover decimated species across North America beginning in the early portion of the twentieth century (Griffith et al. 1989; Fischer&Lindenmayer 2000). Early in the development of these translocation programs, most emphasis was placed on elucidating the ecology of species targeted for recovery; locating potential source populations from which to draw individuals for translocation; identifying areas of habitat suitable for population establishment; and developing viable capture, handling, and veterinary protocols for species targeted for translocation (IUCN 1998). As the logistical considerations of translocation have been optimized for growing numbers of species, the utilization of this tool has grown to encompass not only species recovery and reintroduction programs but also numerous additional applications, including population supplementation, population expansion, and nuisance-animal management (Griffith et al. 1989; Linnell et al. 1997).
... Figura 6 -Diagrama de uma inflorescência com três flores femininas (adaptado de Schad, 1952) Cada inflorescência de flores femininas possui em geral 3 flores, 1 terminal e 2 laterais secundárias (Camus, 1929;Fenaroli, 1945;Breisch, 1995;Nienstaedt, 1956;Bergamini, 1975;Valdiviesso et al., 1993), envolvidas numa cúpula anteriormente desenvolvida durante a floração, (Solignat e Chapa, 1975;Jaynes, 1978) e que se fendilha em 2 a 4 (ou 8) valvas (Coutinho, 1936;Guerreiro, 1948). Noutras inflorescências podem, por vezes, atingir até 7 flores (Bergamini, 1975;Solignat e Chapa, 1975), característica que depende da cultivar de castanheiro considerada. ...
In this work, we established the phenology in four Castanea sativa chestnut Portuguese cultivars (Amarelal, Longal 5, Verdeal and Martainha 2). The unisexual and androgenic flower differentiation was determined: June of the previous vegetative cycle and May of the vegetative cycle, respectively.
The more relevant morphological aspect of the inflorescence was the presence of hermaphroditic flowers in all the studied cultivars. We could determine that only the terminal zone of the style corresponds to the stigmatic region. For the first time, it was referred the presence of the secretory cells, which layered the aperture of the stigma, at full receptivity. This secretion is important in the process of pollen adhesion and germination. Histochemical characterisation of the secretion revealed the presence of polysaccharides and lipids. A new model for hermaphroditic flowers with anthers and stigma location was described.
The receptivity period of each stigma is restricted to a few days (about 2 days), corresponding to the presence of the mucilaginous secretion. The receptivity is not synchronised, only one style at a time becomes receptive. If it is successfully pollinated, the other styles of that flower will arrest the final development. If not, the next becomes receptive and so on. The pollen tubes inside the style reach the ovule after 10 to 12 days. During this period, the final steps of ovule development occur. Only a few pollen tubes reach the ovary, and only one ovule seems to be fertilised and develop a normal seed.
Best results for in vitro pollen germination were obtained with a modified F-medium (0.01% H3BO3, 0.04% MgSO4 7H2O, 0.1% Ca (NO3)2 3 H2O, 0.025% K2PO4, and 0.025% KCl) at pH 7.0 and 20% of sucrose.
Patterns of phenotypic and phenetic variability in six Portuguese cultivars of chestnut (Castanea sativa Mill.) were evaluated cultivares (Amarelal, Longal 5, Longal 6, Verdeal, Martainha 1 and Martainha 2). Morphological characterisation was based on the quantification of seventeen quantitative traits, for a five years period. Variance analysis showed significant differences among cultivars, and cultivar year, for all the traits studied, and tree within cultivar, showed also some significant differences, for some of the morphological variables. A significant correlation was obtained between length of the leaf blade and the percentage of unisexual and androgynic inflorescence with the effective thermal index, accumulated rainfall from April to October and from July to October, or the accumulated temperature below seven during the dormant period. Principal Component and cluster analyses were performed to group the cultivars, according to their similarity coefficients, one group formed by Verdeal, Martainha 1 and Martainha 2 and the other by Amarelal, Longal 5 and Longal 6.
For molecular characterisation, 125 RAPD polymorphic markers were amplified using 28 primers. Three groups were formed: Amarelal/Longal 5, Verdeal/Martainha 1 and Longal 6/Martainha 2. Martainha 1 and Martainha 2 (81,6% of similarity) and Longal 5 and Longal 6 (83,6% of similarity) might be different cultivars. Martainha 1 and Verdeal (97,7% of similarity) have probably the same identity.
... The chestnut (Castanea Miller) belongs to the beech family (Fagaceae), which also includes the beech (Fagus), the oak (Quercus), and the chinquapin (Castanopsis). The thirteen Castanea species are native to the temperate zone of the Northern Hemisphere: five to East Asia, seven to North America and one to Europe (Burnham et al., 1986). The European chestnut (Castanea sativa Mill.) is widespread throughout Europe and southwest Asia. ...
Here we report phenotypic and genotypic differences among 14 Turkish chestnut genotypes. The genotypes were analyzed both genetically and for 30 morphological criteria comprising 12 qualitative and 18 quantitative characteristics. The phylogenetic relationships were determined between different chestnut genotypes selected from Sinop, Samsun, Artvin and Bartin provinces of Black Sea Region in Turkey. Morphological criteria were investigated biometrically using multivariate analysis. Ten morphological criteria were found to be effective for discrimination between the genotypes. Five morphological criteria accounts for 64.1% of the variability. These morphological criteria were the ratio of length of teeth to width of teeth, the ratio of length of hilum to length of fruit, cross section of leaves, the ratio of height of fruit to length of fruit and peeling of testa. The discrimination of morphological criteria was shown using cluster analysis, which created four main groups. Dice's coefficient was used to evaluate the genetic similarity by RAPD analysis, which created three main groups. The UPGMA method was used for the determination of phylogenetic trees. The genetic and morphological dendrograms were compared using the Mantel test, which gave a correlation of r=-0.33. The discrimination of morphological criteria was shown using cluster analysis, which created four main groups. Dice's coefficient was used to evaluate the genetic similarity by RAPD analysis, which created three main groups. The UPGMA method was used for the determination of phylogenetic trees. The genetic and morphological dendrograms were compared using the Mantel test, which gave a correlation of r=-0.33. This study illustrates that the selected chestnut genotypes might be valuable genetic resources for future chestnut breeding programs.
... An intensive breeding program was initiated in the 1980s to develop and restore a blight-resistant chestnut to forests of the eastern United States, (Burnham et al. 1986). Blightresistant hybrid cultivars (genetically 94% American chestnut and 6% Chinese chestnut [C. ...
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.
... In the late 20 th century, backcross breeding programs were implemented to produce hybrids from pathogen resistant Asian chestnut species, primarily Chinese chestnut (Castaneamollissima) and American chestnut [14]. The hope is that the sixth generation (B 3 F 3 ) carries American chestnut morphology characteristics [15] but also resistance to the blight from Chinese chestnut [16]. ...
... ❖ www.esajournals.org 2 April 2017 ❖ Volume 8(4) ❖ Article e01773 2002). A backcross hybrid chestnut for reintroduction that is genomically 94% American chestnut has been produced through breeding with blightresistant Chinese chestnut (Castanea mollissima) (Burnham et al. 1986). The hybrid is morphologically indistinguishable from pure American chestnut for a host of physiological and morphological traits (Diskin et al. 2006, Knapp et al. 2014, although it may differ from purebred chestnuts at other functional traits (Blythe et al. 2015), and additional generations of breeding will be needed to ensure blight resistance (Steiner et al. 2017). ...
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.
... The highly competitive mode of American chestnut has been demonstrated in the wild, outside the Holocene maximum range of the species (Paillet and Rutter 1989). It may portend the rapid recovery of chestnut's former prominence if blightresistant strains emerge (Burnham et al. 1986) or if the viroid-induced decline in the virulence of the blight fungus becomes widespread (Anagnostakis 1987). ...
The research addressed parallel hypotheses about what maintains tree species diversity in upland, moist-temperate forests: (1) resources are distributed in mesic, upland, temperate forests such that the environment is fine grained for adult trees and coarse grained for seedlings and (2) co-occurring tree species differ in abilities to exploit resources as seedlings, resulting in changes in seedling performance rank by species with small-scale resource variation. Spatial variation in growth rate ranking among species, through competition, may translate into patterns of relative species abundances of tree seedlings that could persist in the community composition of adult trees. Thus, the maintenance of adult tree species diversity may depend on processes occurring at the seeedling stage. Spatial autocorrelation analysis indicates that resources limiting to plant growth in this ecosystem--light, available nitrogen, and soil moisture--are far more patchily and unevenly distributed among growing sites that are the size of small plants, including tree seedlings, than among areas covered by large, adult trees. Greenhouse and forest growth experiments showed that 11 tree species which co-occur as adults in uniform habitat differ in their abilities to exploit resources as seedlings. When ranked by seedling growth characteristics associated with competitive ability, the hierarchy among 9 of the species changed with amounts of resource variation typically found among tree-seedling sized patches on the forest floor and over time. Seedlings of American chestnut, Castanea dentata (Marsh.) Borkh., responded most strongly to resource gradients and ranked highest in traits associated with competitive ability over the broadest range of combinations of resource levels of all species studied. The apparent competitive superiority of chestnut seedlings over a wide range of resource conditions may have contributed to the species' rapid, post-glacial invasion and capture of canopy dominance across a major portion of the eastern North American, moist-temperate forest biome.
... Mill.) has been placed in the Fagaceae family which includes beech (Fagus), oak (Quercus) and Castanopsis. In total, 13 Castanea species are recognized and are native to the temperate zone of the Northern Hemisphere; five in East Asia, seven in North America and one in Europe (Burnham et al., 1986). All Castanea species and their hybrids are edible and some are used in commercial nut production around the world. ...
Morphological and phenological characteristics of the chestnut (Castanea sativa Mill.) cultivar (cv) 'Serdar' were examined and compared to the cv 'Marigoule', a European × Japanese (C. sativa × C. crenata) hybrid. Morphological characteristics such as tree vigor and growth habit, shoot, leaf, flower, bur and fruit characteristics and phenological characteristics such as time of bud break, flowering, nut ripening and leaf fall were studied. Three trees per genotype and 10-50 samples per tree were examined for each quantitative characteristic. Cultivar 'Serdar' was represented by vigorous trees with semi-upright growth similar to cv 'Marigoule'. Shoots of 'Serdar' were thinner and the shoot bark was browner than 'Marigoule'. 'Serdar' had a higher lenticel density than 'Marigoule' and 'Serdar' had relatively short internodes similar to 'Marigoule'. 'Serdar' initiated break bud 11 days later than 'Marigoule', bloomed 1-2 days later than 'Marigoule', and nuts ripened 20 days later than nuts from 'Marigoule'. Leaf fall of cv 'Serdar' was one day earlier than cv 'Marigoule'. The lamina, petioles and leaves of the 'Serdar' were longer than those of 'Marigoule'; however, 'Serdar' had a lower ratio of lamina width/lamina length and lamina width/leaf length. 'Serdar' and 'Marigoule' were placed in the same group with respect to all flower characteristics investigated. 'Serdar' had globular burs with long spines. Its density of spine was also higher than 'Marigoule'. 'Serdar' had very bright, reddish brown coloured shells, with light cream coloured kernels; and, the fruit had good flavor. Peeling of the seed coat of 'Serdar' was easier than that of 'Marigoule'. The fruit of 'Serdar' was smaller than those of 'Marigoule' and the relative size of the hilum in relation to the upper part of fruit was intermediate in 'Serdar' and large in 'Marigoule'. 'Serdar' showed a higher propensity for splitting of the pericarp although both cultivars were placed within the same group. The cv 'Serdar' can be recommended for new chestnut orchards due to some of its positive advantages such as earlier bearing, blooming twice in a single growing season, resistance to spring frosts and its low susceptibility to chestnut blight.
... These lines were: pure American, pure Chinese, and three individual hybrid lines from the American Chestnut Foundation's breeding program (B1F3, B2F3, B3F1). These hybrids represent a successive order of "advancement" in the American Chestnut Foundation's breeding scheme (Burnham et al. 1986) toward the goal of a tree that is morphologically indistinguishable from and functionally equivalent to the American parent but still retains the Chinese parent's blight resistance where B1F3 trees are closest to the Chinese parent tree and B3F1 trees are closest to the American parent in terms of the assumed percentage of genetic material. We planted the five seeds in random order around the "shoulder" of each mound (where the semi-flattened top transitions to the side slope), spaced roughly 1 m apart. ...
Surface mining for coal represents a significant form of anthropogenic disturbance on the landscape. Currently there are more than one million hectares of former mined land in the United States. New reclamation procedures are being examined to accelerate forest succession on former coal mine sites in eastern Appalachia. Our study was conducted on public lands that had been previously surface-mined for coal, reclaimed in 1978, and re-mined and reclaimed using new methods in 2007. We planted 535 American chestnut seeds in March 2008 at the study site in 107 blocks. Each block contained five seeds from five different genetic lines including Pure American, Pure Chinese, and three intergraded hybrid Chinese-American lines. We saw few significant differences in performance between pure American chestnuts and more advanced backcrossed generations of hybrid trees. However, Chinese chestnut and early-generation hybrids showed significantly better growth and survival measurements. The American Chestnut Foundation's breeding program appears to have been successful at capturing a morphological fidelity between the latest hybrids and pure American trees. Trees with a greater percentage of Chinese parental material possess a suite of leaf characters that may make those hybrids better suited for the arid, high light conditions found on reclaimed mine sites (particularly thickness, length to width ratio, and pubescence). Development of goal-specific cultivars by the American Chestnut Foundation might aid in more successful restoration attempts but also may limit genetic diversity in those lines if intensive inbreeding or cultural cloning is utilized. Additionally, restoration at end-dump sites may need to pursue a phased system of introduction after initial extreme environmental conditions have been ameliorated by the use of early successional species in order to ensure the success of desirable species.
... These drawbacks led Charles Burnham and Lawrence Inman to oppose making F 2 s until the third backcross was in hand (F.V.H., personal information). Presumably, the drawbacks were the reason for departure from the conventional backcross method (Burnham et al. 1986), which calls for an F 2 generation after the initial hybridization, as well as an F 2 generation at B 3 and B 6 (Allard 1960). Traditionally during backcrossing, plants have been selected for recurrent type using morphological and other macroscopic traits. ...
Biotechnology has been practiced on chestnuts (Castanea spp.) for
many decades, including vegetative propagation, controlled crossing
followed by testing and selection, genetic and cytogenetic mapping,
genetic modifi cation, and gene and genome sequencing. Vegetative
propagation methods have ranged from grafting and rooting to
somatic embryogenesis, often in coordination with breeding efforts
and programs. More recently, particularly in the United States, chestnut
biotechnology has included the analysis of genes and genomes with the
goal of characterizing and fi nding disease resistance genes and utilizing
them for developing resistant Castanea dentata (American chestnut)
for use in species conservation programs. In this chapter we review
chestnut biotechnology, especially with respect to its development
in the United States, with emphasis on producing resistant C. dentata
using various resistant sources of C. mollissma (Chinese chestnut) and
C. crenata (Japanese chestnut).
... Hybrid chestnut plantings were conducted in Connecticut and Virginia during the 1970s and 1980s. The American Chestnut Foundation (TACF), formed in 1983, continued the restoration program to breed American chestnut with blight-resistant Chinese chestnut (Castanea mollissima Blume) (Burnham et al. 1986). Hybrids were selected for repeated backcrossing to American chestnut to produce a BC 3 F 3 chestnut (94% American chestnut and 6% Chinese chestnut) (Hebard 2005). ...
Reclamation of surface mined sites to forests is a preferred post-mining land use option, but performance of planted trees on such sites is variable. American chestnut (Castanea dentata (Marsh.) Borkh.) is a threatened forest tree in the eastern USA that may become an important species option for mine reclamation. Chestnut restoration using backcross hybrids that incorporate blight resistance may be targeted to the Appalachian coal mining region, which corresponds closely with the species’ native range. Thus, it is important to understand how chestnut hybrids perform relative to progenitors on reclamation sites to develop restoration prescriptions. Seeds of parents and three backcross generations of chestnut (100% American, 100% Chinese, and BC1F3, BC2F3, and BC3F2 hybrids) were planted into mine soils in West Virginia, USA with shelter treatments. Survival for all stock types was 44% after 8 years (American 39%, Chinese 77%, BC1F3 40%, BC2F3 28%, and BC3F2 35%). Height for all stock types was 33 cm after 8 years (American 28 cm, Chinese 67 cm, BC1F3 30 cm, BC2F3 21 cm, and BC3F2 20 cm). At another site a year later, seedlings of the chestnut stock types were planted into brown (pH 4.6) or gray sandstone (pH 6.3) mine soils and seedling survival across all stock types was 58% after 7 years. Chinese had the highest survival at 82%, while the others ranged from 38 to 66%. Height was 63 cm for all stock types after 7 years. More advanced backcross hybrids (BC2F3 and BC3F2) had the lowest vigor ratings at both sites after 7–8 years. Our results indicate that surface mines in Appalachia may provide a land base for planting blight-resistant chestnuts, although Chinese chestnut outperformed American chestnut and later generation backcross hybrids. As blight-resistant chestnuts establish and spread after planting, chestnut trees may become a component of the forest canopy again and possibly occupy its former niche, but their spread may alter future forest stand dynamics.
... A small, branchy tree is more manageable in an orchard setting than a very tall one, especially in locales where chestnuts are picked by hand after climbing the tree (Rutter et al., 1991). Chinese chestnut in general has a shorter stature and less-pronounced apical dominance than the non-domesticated American chestnut (Clapper, 1954) which is a major consideration in the backcross blight resistance breeding program being carried out by the American Chestnut Foundation (Burnham et al., 1986). In forest settings, C. mollissima grow to 20-25 m in height (Fei et al., 2012), so the short stature of orchard trees may be, at least in part, an artificially selected trait. ...
Chestnuts (Castanea) are major nut crops in East Asia and southern Europe, and are unique among temperate nut crops in that the harvested seeds are starchy rather than oily. Chestnut species have been cultivated for three millennia or more in China, so it is likely that artificial selection has affected the genome of orchard-grown chestnuts. The genetics of Chinese chestnut (Castanea mollissima Blume) domestication are also of interest to breeders of hybrid American chestnut, especially if the low-growing, branching habit of Chinese chestnut, an impediment to American chestnut restoration, is partly the result of artificial selection. We resequenced genomes of wild and orchard-derived Chinese chestnuts and identified selective sweeps based on pooled whole-genome SNP datasets. Sweeps identified from pooled data were validated in an independent sample of individual whole-genome sequences of orchard chestnuts. Several putative sweeps aligned to domestication-associated regions in other woody plants. Annotations of predicted genes in putative sweep regions could indicate their usefulness in chestnut improvement.
... Yeasts from the Ustilaginales have been documented as endophytes (Abdel-Motaal et al., 2009). The ecological effects of novel endophyte associations in chestnut hybrids could affect the ecological success of chestnut blight-resistant backcrossed chestnuts (Burnham et al., 1986) if they are restored to the eastern North American deciduous forest. ...
High-throughput sequencing of DNA barcodes, such as the internal transcribed spacer (ITS) of the 16s rRNA sequence, has expanded the ability of researchers to investigate the endophytic fungal communities of living plants. With a large and growing database of complete fungal genomes, it may be possible to utilize portions of fungal symbiont genomes outside conventional marker sequences for community analysis of short-read data. We designed a bioinformatics pipeline to identify putative fungal coding sequences from 100 bp Illumina reads of DNA extracted from several angiosperm species (Castanea, Juglans, and Ulmus). Reads remaining after a two-step filtering process made up a small fraction of total reads (2–100 putative fungal reads per 10,000 plant reads) and were assigned to fungal genera and orders based on similarity to proteins from complete fungal genomes. Some of the taxa identified are known to be ubiquitous class 2 endophytes. We detected some differences in endophyte community composition based on ITS sequence data versus results from the short-read pipeline, particularly among Ulmus. ITS results in Juglans and Castanea, however, closely reflected results from the short-read pipeline, and both methods portrayed similar intergeneric differences in endophyte community composition.
... The American Chestnut Foundation (TACF) has conducted a 25-year program to breed a blight-resistant chestnut tree (Burnham et al. 1986). The backcross-breeding program seeks to incorporate the blight-resistance of the Chinese chestnut (Castanea mollissima Blume) into a tree that will be functionally equivalent to the American parent (i.e., a tall-growing, straight-trunked timber tree) (Disken et al. 2006). ...
Microsite availability is crucial for recruitment success in natural populations as well as populations being established for restoration projects. Understanding the specific microsite requirements of a particular species targeted for restoration will increase the probability of success of any restoration project. Surface mining for coal represents one of the largest anthropogenic disturbances to the forests of the eastern United States. The original natural range of the American chestnut (Castanea dentata (Marsh.) Borkh.) overlaps the extent of the Appalachian Coal Basin. With American chestnut being readied for reintroduction trials, we sought here to determine some of the effects of microsite conditions on the establishment success of American chestnut on mine sites reclaimed using new, compaction-reducing techniques (i.e., "end-dump" reclamation) that create a series of loosely dumped mounds roughly 8-m diameter and 3-m tall to serve as a planting substrate. Specifically, we examined the effects of distance from existing forest edge, amount of existing cover of vegetation, small-scale topographic position, and a small set of soil variables on the growth and survival over three seasons of American chestnut seedlings planted on a reclaimed mine site in east-central Ohio. We found decreased tree survival adjacent to existing forest edges and greater annual growth rates at distances of 20 and 50 m from the existing forest edge. Microtopographic position had a significant effect on seedling growth and survival seedlings planted higher on mounds had increased mortality and lower growth than those on the side slopes of those mounds. The amount of existing vegetative cover also affected survival and growth; trees growing in plots with higher vegetative cover values showed increased growth and survival. The compaction-reducing reclamation approach used here is relatively new and novel. Promising results that have been observed to date using American chestnut and this method seem to indicate that the combination may be very effective at restoring functional forests on lands degraded by surface mining.
... In North America, molecular breeding approaches have been used solely within the context of Castanea dentata restoration efforts (Burnham et al. 1986;Diskin et al. 2006;Westbrook 2018a, b;Westbrook et al. 2019;Wheeler and Sederoff 2009;Worthen et al. 2010). In an early paper describing his plan to use the backcross method to introgress blight resistance from C. mollissima into C. dentata, Burnham (1988) proposed that restriction fragment length polymorphisms (RFLPs) could be used to accelerate the breeding program by selecting backcross progeny that most closely resemble the genotype of the C. dentata recurrent parent, then subjecting the marker-selected progeny to phenotypic selection for chestnut blight resistance. ...
The chestnuts and chinquapins are a group of about seven species of trees and shrubs in the genus Castanea. They are of considerable importance ecologically in all the areas of their natural occurrence, and the chestnuts especially are of great economic value for their lumber and for their nut crop wherever they are cultivated. Two catastrophic diseases, chestnut blight caused by the ascomycete fungus Cryphonectria parasitica (Murr.) Barr and Phytophthora root rot (ink disease) caused primarily by the soil-borne oomycetes Phytophthora cinnamomi Rands and P. cambivora (Petri) Buisman, have severely impacted chestnut in Europe and North America. Therefore, much of the breeding work continues to focus on breeding for resistance to these two diseases. The most serious insect pest of Castanea is the Asian chestnut gall wasp, Dryocosmus kuriphilus Yasumatsu. Variation in host tolerance to D. kuriphilus has led to development of new gall-resistant chestnut cultivars. Interspecific hybridization offers great opportunity to combine the most favorable traits found in the ample genetic diversity of the genus through introgression into locally-adapted populations. Chestnut breeders in eastern Asia have made great strides towards improvement of chestnut fruit quality and crop yields, and researchers in all chestnut growing regions have made gains in disease resistance by using molecular markers and other genomic tools to assist selection. Biotechnologies that include transmissible hypovirulence as a biocontrol for chestnut blight, tissue culture and other micropropagation techniques, and genetic engineering and transformation technologies are complementary to classical plant breeding programs.
... Barr, a backcross breeding approach has been developed to restore the chestnut in North American forests. Blight resistant genes from Asian chestnut species, most often the Chinese chestnut (Castanea mollisima Blume), were bred with the American chestnut (Burnham et al. 1986;Anagnostakis 2012). ...
Although agriculture focuses on row crops in the Midwestern US, chestnut (Castanea) would be a possible multipurpose agroforestry crop in erodible locations within this region. As ectomycorrhizal (ECM) colonization is often crucial for tree establishment and production, we addressed the importance of ECM colonization on chestnut performance by assessing: (1) natural ECM colonization in an established chestnut orchard, and (2) the effect of ECM inoculation on seedling establishment and drought response in a greenhouse. We selected 50 Chinese American hybrid chestnuts trees in a commercial orchard and assessed their level of mycorrhizal colonization in relation to distance from an adjacent forest, the source of inoculum. In the green house, we grew 80 seedlings from this orchard with and without mycorrhizal inoculation. Half were harvested to assess inoculation success and biomass; the remainder were subjected to experimental water stress which was evaluated with chlorophyll fluorescence using Fv/Fm values. In the orchard planted with uninoculated plants, ECM colonization decreased with distance from adjacent oak forest (P = 0.015), the putative ECM source, with an average of 29% root tips colonized. ECM inoculation increased seedling aboveground biomass by 16.4% in the greenhouse and generated 1.14 times more, but smaller stomata on leaves. Water stress in ECM inoculated seedlings also recovered faster from an experimental drought having significantly higher Fv/Fm value (P = 0.004) than uninoculated seedlings. Our study clearly indicates that ectomycorrhizal colonization can help chestnut trees in their early growth and stress tolerance and should be included into field plantings to minimize dependence on agricultural amendments.
... The fact that the genetic correlations were significantly different from zero suggested that resistance to multiple diseases is possible. In forest tree species, breeding programs in American chestnut are seeking to improve resistance to chestnut blight (Cryphonectria parasitica) and to phytophthora dieback (Phytophthora cinnamomi) through backcrossing between American and Chinese chestnut (Burnham et al., 1986). However, no evidence of multiple disease resistance has been found to chestnut blight and phytophthora dieback in the first-year American chestnut and Chinese chestnut hybrids (Westbrook et al., 2019). ...
Increasing resistance against foliar diseases is an important goal in the Pinus radiata D.Don breeding program in New Zealand, and screening for resistance has been in place for some time, since the late 1960s. The current study presents results of four progeny trials within the breeding program to investigate whether multiple disease resistance could be detected against three different needle diseases in P. radiata: Dothistroma needle blight (DNB) caused by Dothistroma septosporum, Cyclaneusma needle cast (CNC) caused by Cyclaneusma minus, and red needle cast (RNC) caused by Phytophthora pluvialis. Four progeny trials in the North Island of New Zealand were available to estimate heritabilities and between-trait genetic correlations. Two of the trials were assessed for DNB, involving 63 full-sib families. A third trial was assessed for CNC, involving 172 half-sib families, and a fourth trial was assessed for RNC, involving 170 half-sib families. Disease resistances had moderate estimates of heritability (0.28-0.48) in all trials. We investigated the potential for multiple disease resistance to the three foliar diseases by estimating genetic correlations between disease resistances using a spatial linear mixed model. The correlation between DNB and CNC resistance was favorable and strong (0.81), indicating that genotypes that are highly resistant to DNB also have a high resistance to CNC. These results suggest that selection based on resistance to DNB could allow for simultaneous indirect selection for resistance to CNC, usually only expressed at a later age. This would allow selections to be made earlier due to the earlier expression of DNB than CNC and reduce the number of expensive disease assessments being undertaken. Conversely, genetic correlation estimates for RNC with DNB and CNC were close to zero, and very imprecise. As such, later-age assessments for this disease would still be required.
Restoration of the functionally extirpated American chestnut (Castanea dentata) to landscapes of the eastern United States is planned with the successful propagation of a blight-resistant hybrid tree. Predicting the response of rodent seed consumers to this novel source of mast will be critical to restoration success, as rodents are important seed predators and dispersers in forests that once included chestnut. In particular, frequency-dependent foraging responses by rodents could affect the rate of spread of rare chestnuts following reintroductions. We conducted field trials to test for seed preferences and frequency-dependent selection by fox squirrels (Sciurus niger) when combinations of American chestnut and two common associates [northern red oak (Quercus rubra) and white oak (Q. alba)] were available in varying frequencies. Fox squirrels tended toward positive frequency-dependent seed predation when combinations of white oak and chestnuts were available, consuming more common mast items at a higher rate than expected based on availability. No preferences were observed between American chestnut and either red or white oak independent of frequency, but red oak was preferred over white oak. Frequency-dependent consumption of more common white oak acorns could benefit rarer chestnut during restoration, as squirrels would feed disproportionately on established white oak; however, this management strategy should only be considered following larger-scale and longer-term studies that consider impacts on white oak regeneration. Lack of preference or frequency dependence for chestnut when paired with red oak suggests that negative impacts of fox squirrel consumption on restoration will vary with the relative availability of the two seed types.
Chestnuts (Castanea sp.) belong to the family Fagaceae, comprising more than 900 species of trees and shrubs. The family Fagaceae is dominated by temperate forest trees like oaks (Quercus spp.) and beeches (Fagus sp.), which are found mainly in the Northern Hemisphere countries of the world (Manos et al. 2008). From time to time coevolution among different Castanea sp. and biodiversity found among these species have ensued the extent of these opulent and diverse Castanea sp. to spread all over the world, particularly in high altitude areas. The elasticity and adaptability of various chestnut species to different agro-climates and the extensive genetic base of these species determined the range of various ecotypes in the wild. During the course of many decades, human population has selected, maintained, and utilized these diverse genotypes for many uses, such as garden-fresh consumption, production of flour, timber production, and physical nourishment, thus promisingly making contribution towards the preservation of natural biodiversity of these species and giving an outstanding model for horticultural crop conservation. However, presently the genomic diversity of the species is in danger of extinction and huge number of cultivars are liable of being vanished as a result of various phytosanitary issues like Pseudomonas syringae causing canker blight, Phytophthora palmivora causing ink disease, gall wasp, Cryphonectria parasitica, Phytophthora spp., and Dryocosmus kuriphilus. These issues have resulted in the decline and desertion of chestnut cultivation and loss of male chestnut as well. In recent times, numerous research programs have strived to improve policies for the preservation of Castanea sp. biodiversity. The main goal of this chapter is to present the research studies on genomic variability and preservation of Castanea sp. germplasm to pave way for conservation and development of resilient chestnut varieties.
One of the most difficult processes of micropropagation is rooting and acclimatizing in vitro shoot cultures, especially for hardwood tree species. As more transgenic lines of potentially blight-resistant American chestnut (Castanea dentata) are developed, we expect to produce thousands of tiny shoots to be rooted, transferred to potting mix, and grown to a large enough size for planting outdoors. Many shoots are lost during rooting and acclimatization, so pinpointing factors that enhance survival is extremely important. Five factors were examined in relation to acclimatization success — light intensity, light color, time in rooting medium, temperature, and presence of activated charcoal. The percentage of plantlets surviving from rooting initiation to 16 weeks in the growth chamber was increased from 33 to 67% by rooting the shoots in darkness instead of on a light bench. The best combination of rooting factors was to place shoots in rooting medium containing activated charcoal in complete darkness for only four days at 25C. This combination of factors increased plantlet survival from approximately 33% using the original rooting protocol to 73%. Finding that American chestnut plantlets have better acclimatization survival after being placed in rooting medium for only four days should enhance many laboratory practices. Shortening the time in rooting medium and including a period in darkness will increase the survival of novel transgenic American chestnut lines, allowing them to be planted in field trials more quickly.
Turkey ranked third place in the world for chestnut production after China and South Korea and the country has unique chestnut forests including valuable and diverse chestnut genotypes. This study was conducted to select superior chestnut genotypes within seedling populations found in natural wild grown chestnut forest located in Isparta province in Turkey during 2010–2011 years. A total of 2500 wild grown chestnut trees were examined on the field first year and among them the most promising 22 genotypes were chosen according to relatively high yield capacity, earliness, tolerance to chestnut blight (Cryphonectria parasitica), ink disease (Phytopthora cambivora), and fruit quality characteristics. The selected 22 genotypes were evaluated for their detailed morphological, phenological and pomological traits in 2010 and 2011. According to average of 2 years, nut weight, the number of nut per kilogram, nut width, nut length, nut height and nut shell thickness of 22 promising genotypes ranged from 10.26 to 22.32 g, 97.47 to 44.80/kg, 26.80 to 42.47, 16.92 to 25.91, 27.74 to 39.73, and 0.26 to 1.01 mm, respectively. The ash, crude protein, and total fat content of kernels were between 0.85 to 1.94, 3.69 to 7.06 and 1.32 to 4.52, respectively. The genotypes were evaluated with weighted ranking method and the highest general quality score was observed in genotypes of IY17, IY01, IY42, IY43 and IY12. © 2015 Northeast Forestry University and Springer-Verlag Berlin Heidelberg
Charles Burnham hypothesized in 1981 that the blight resistance of Castanea mollissima could be backcrossed to C. dentata to produce a tree that would perform in the forest like the formerly dominant American chestnut. The American Chestnut Foundation (TACF) was formed in 1983 to test this hypothesis using a traditional plant breeding program. Two B1 chestnut trees, 'Clapper' and 'Graves,' produced by former breeding programs of the U.S. Department of Agriculture and the Connecticut Agricultural Experiment Station, were used to jump-start the program. These former breeding programs identified Chinese chestnut as the most promising source of blight resistance and developed most of the methods used in the current program. 'Clapper' and 'Graves' each were backcrossed into approximately thirty American chestnut from the vicinity of Sugar Grove, Virginia, backcrossed again then intercrossed twice. Prior to each cross, trees were selected for blight resistance and recurrent morphological traits. The resultant B3F3 seedlings were planted into the forest for testing beginning in 2009. Tests of the parents of these B3F3s suggested that their blight resistance will fall somewhere between an intermediate and a high level. We are midway through selection in B3F2 seed orchards and resistance among B3F3 progeny should increase as more trees are culled. The ultimate blight resistance of these trees in the forest will be influenced by their adaptation and also may be affected by hypoviruses and other factors; it may take decades for a clear picture to emerge. In addition to 'Clapper' and 'Graves,' 'Nanking' Chinese chestnut has been backcrossed into twenty American backgrounds. More than twenty other sources of blight resistance from Chinese chestnut have been backcrossed, to varying degrees, into American chestnut but into only a few backgrounds; by themselves they do not constitute a viable breeding population. Other Castanea species, C. crenata, C. henryi and C. sequinii have been used to a lesser extent, as well as large, surviving American chestnut trees. This breeding program has been extended throughout the range of the American chestnut in TACF's network of seventeen state chapters. Through the efforts of those chapters, the effective size of our core population (Ne) should exceed five hundred. The chapters also plan to develop viable breeding populations from the additional sources of blight resistance mentioned above.
Rooting and acclimatization are two difficult stages of plant tissue culture, requiring an efficient system to reduce losses in plant materials, supplies and labor. This is especially important when working with vital transgenic cultures. Two modifications to a standard American chestnut rooting procedure, removing the activated charcoal and adding a period of darkness, were examined to see whether they would increase rooting, the number of roots per plant, and the overall survival of the plantlets ex vitro in growth chambers. Plantlets rooted in the dark, with 2.0 g/L activated charcoal in the medium, had the highest rate of rooting and overall survival with 76% of plantlets growing well after 16 weeks in the growth chamber. A period of darkness during the rooting period is therefore recommended when micropropagating American chestnut. This technique may also be adapted to other chestnut species or members of the Fagaceae family as well.
The prolonged juvenility period common to woody perennial plants, often ranging from 3 to 10 years or more, is a major impediment to breeding. It seriously undermines the ability to make positive crop improvements or react to emerging threats in a reasonable time frame. Recently, precocious flowering in perennial trees has been induced through the ectopic expression of a number of genes involved in the induction and formation of flowers. Transgenic plants overexpressing these flowering regulatory genes display significantly shorter juvenility periods, typically 1 year or less. These modified plants have been used successfully in apple and plum to develop rapid cycle breeding programs that enable trait introgression in a few years rather than a few decades. While the breeding system leverages genetically engineered plants to accelerate breeding, the output is conventional cultivars as the ectopically expressed flowering gene can be selected against to yield non-transgenic progeny.
Calcification, a kind of quality deterioration, occurs in chestnut due to fast water loss when stored at low relative humidity (RH) and room temperature. In this study, the relationship between water loss rate and plasma membrane lipid oxidation in chestnut stored at low (50–55%) RH and high (85–90%) RH at 25 °C has been investigated to understand the mechanism of calcification. Water loss rate per day in chestnut at low RH was 6% and 1.5 times that at high RH, while the calcification index at low RH was 0.4 and 3.5 times that at high RH. At low RH, the activities of plasma membrane lipase and lipoxygenase (LOX), the content of malonaldehyde (MDA) and saturated fatty acid (SFA) in chestnut were higher than those at high RH. Meanwhile, unsaturated fatty acid (UFA) index decreased in low RH, but increased in high RH. The correlation coefficient (r) between MDA content and calcification index in chestnut stored at low RH and high RH was 0.928** and 0.937** respectively, which implied that the plasma membrane lipid oxidation induced by fast water loss might be related closely to occurrence of calcification in chestnut. In contrast, at high RH, the moisture content in chestnut decreased slowly and the hydrolysis and oxidation of membrane lipid were a low, and was associated with better maintenance of quality.
Aim of this study was to determine morphometric differences of fruits between selected sweet chestnuts (Castanea sativa Mill.). The 28 genotypes (referred as CS-01 to CS-28) were introduced by seeds from Czech Republic, Carpathians, Kyrgyzstan. Genotypes of sweet chestnut are grow more than 30 years in Forest-Steppe of Ukraine in the M.M. Gryshko National Botanical Garden of NAS of Ukraine. They are well adapted to the climatic and soil conditions. The fruits were collected at the period of their full maturity (September). The population differs in weight, shape, size and color of fruits. Their morphometric parameters were following: weight from 1.70 g (CS-26) to 18.60 g (CS-20), length from 8.07 mm (CS-28) to 33.39 mm (CS-11), width from 16.34 mm (CS-28) to 40.95 mm (CS-11), thickness from 9.02 mm (CS-26) to 28.70 mm (CS-11) and hilum length from 6.62 mm (CS-26) to 31.30 mm (CS-07), hilum width from 6.50 mm (CS-23) to 19.99 mm (CS-07). The shape index of the fruits was found in the range of 0.81 (CS-20) to 0.98 (CS-12). The shape index of the hilum was found in the range of 1.48 (CS-04) to 2.03 (CS-23). The outcome of the research point to the fact that the genepool Ukrainian sweet chestnut is a rich source of genetic diversity and might be used in selection for creation a new genotypes and cultivars.
Tree species world-wide are under increasing threat from diseases and insects, many of which are non-native. The integrity of our natural, urban and plantation forest ecosystems, and the services they provide are seriously imperiled. Breeding programs that harness the natural genetic resistance within tree species can provide a durable solution to these threats. In many cases, genetic resistance offers the key to restoration of forests and may even prevent extinction of some tree species. The potential use of genetic resistance is often widely discussed, but the development of applied programs and use of resistant seed has only taken place in a relatively few species. The reflections here from some of the most advanced applied resistance programs, as well as some of the unknowns and limitations of implementing a resistance program will provide a guide to managers considering this approach. In any such program, there is a research component, a tree improvement component and a restoration and reforestation component. These three components, along with sustained management and public support, need to be linked for any genetic resistance program to be fully successful in facilitating the recovery of healthy forests. Other management activities and newly developing technologies may serve to complement genetic resistance or to expedite its development, but premature, over-emphasis on some of these may slow the operational program. An understanding of the level, frequency, durability and stability of resistance and its limitations are necessary to management planning.
Pecan is the only major nut crop native to North America; however, many important wild relative species of nut crops, including chestnut, hazelnut, pecan, pistachio, and walnut, are native to North America and are important sources of useful genes. This chapter briefly covers the history and use of temperate nut crops and more thoroughly discusses the occurrence, potential usefulness, and conservation status of North American crop wild species that have potential value in nut crop improvement.
Chitosan (CHI) and whey protein are usually used to prepare edible films for food preservation. However, the composite film composed of the two components does not yield satisfactory properties for chestnut preservation. In this study, nano‐cellulose and cinnamaldehyde (CMA) were added to CHI and whey protein, creating a new composite film with strong water retention, bacteriostatic, and mechanical properties. The water vapor permeability (WVP) of the film decreased by 21.61% with the addition of 0.5% (w/v) nano‐cellulose, and 23.02% with the addition of 0.3% (w/v) CMA. Furthermore, water solubility (WS) decreased 22.05%, and the density of the film was significantly improved with the addition of 0.3% (w/v) CMA. The optimized formula of the film was CHI 2.5% (w/v), whey protein 3.0% (w/v), nano‐cellulose 0.5% (w/v), CMA 0.3% (w/v), and pH 3.8, as determined by orthogonal testing L9(34), with fuzzy comprehensive assessment, of WVP, WS, tensile strength, and elongation at break. The film clearly inhibited the growth of E. coli, S. aureus, and Chinese chestnut fungus, destroying the mycelial structure of the fungus. In addition, coating effectively reduced the weight loss, mildew rate, and calcification index during 16 days of storage of chestnuts at 25 °C.
The Asiatic oak weevil, Cyrtepistomus castaneus Roelofs (Coleoptera: Curculionidae), is a nonnative defoliator of trees in the Fagaceae family in the United States but has not been studied on Castanea species in the southern Appalachian Mountains. Planted trees of Castanea dentata (Marsh.) Borkh. (Fagales: Fagaceae), Castanea mollissima Blume (Fagales: Fagaceae), and four hybrid breeding generations were evaluated in 2012 for insect defoliation and C. castaneus abundance and frequency. Defoliation was visually assessed throughout the growing season at two sites in the southern Appalachian Mountains (western North Carolina and eastern Tennessee). C. castaneus abundance and frequency were monitored on trees using beat sheets and emergence was recorded from ground traps. Asiatic oak weevils were more abundant and more frequently collected on American chestnut (Ca. dentata) and its most closely related BC3F3 hybrid generation than on the Asian species Ca. mollissima. In most months, C. castaneus colonization of hybrid generations was not significantly different than colonization of parental species. Frequency data for C. castaneus suggested that adults were distributed relatively evenly throughout the study sites rather than in dense clusters. Emergence of C. castaneus was significantly higher under a canopy dominated by Quercus species than under non-Quercus species or open sky. C. castaneus emergence began in May and peaked in late June and early July. These results may be useful for resource managers trying to restore blight-resistant chestnut to the Southern Appalachians while minimizing herbivory by insect pests.
There are fewer than 162 ha of commercial Chinese chestnut orchards in the United States, with approximately half of these in the Southeast. Large numbers of Chinese chestnut seedlings are planted annually in the United States for home and game food production; however, knowledge about chestnut propagation, fertilization, pests, harvest, storage and marketing is not adequate. There is little commercial marketing of U.S.-grown Chinese chestnuts through roadside markets and local farmers’ markets as the supply is low and unpredictable. However, we yearly import 4.5 mill kg of European chestnuts to satisfy the U.S. market. Successful chestnut orchards will require vegetatively propagated selections, intensive management, mechanical harvesting, and control of insect and disease pests.
Stems of many woody ornamental plant taxa were collected in midwinter and hardened to their maximum capability under laboratory conditions. Hardiness levels were determined and compared to zone recommendations as listed in Hortus III and Rehder’s Manual of Cultivated Plants . Many woody plants had a greater midwinter cold tolerance than their hardiness ratings would infer.
The genus Juglans is an economically important group grown for timber and nuts. The breeding of walnut species has been reviewed by Forde (1975), but breeding for nut production in Persian walnut (Juglans regia) was stressed.
Studies are described on the in vitro multiplication of chestnut axillary buds from 3- month-old seedlings and 5-year-old trees grown in containers. In attempts to eliminate the autointoxication of expiants by tannins released into the culture medium, both the importance of dipping in sterile water before culture, and of the age and the bud position on the twig was established. Murashige and Skoog’s medium with BAP (1 mg 1_1) permitted the multiplication of juvenile as well as adult material. Lowering the pH to 4, with the Ca and Mg concentrations doubled, promoted multiplication and elongation. Whereas the multiplication medium permitted the elongation of leafy shoots taken from buds, it did not do so for buds originating from adult material. For the latter it was necessary to add auxin, adenine and activated charcoal to halt multiplication and allow elongation. Some roots were obtained, but only on the juvenile material.
The present distribution of chestnut sprout clones in Andover, Massachusetts, includes areas with abundant stumps from canopy trees killed by blight before 1922, and former abandoned pastures adjacent to woodlots that once contained mature chestnut trees Sprout densities range from less than 1 to more than 200 living clones per hectare Greatest densities occur in areas with abundant logs and stumps from preblight chestnut tress, but some areas with abundant chestnut wood have very few living sprouts Limited numbers of chestnut sprouts were found with living stems growing from small knobs of cambium on the root collars of otherwise completely dead stumps of former canopy trees More than 95 per cent of all observed chestnut sprouts show no connection with remains of preblight trees, and almost all appear to have been through several cycles of blight infection The distribution pattern of these sprouts indicates that they originated as suppressed seedlings established before 1922 and not as sprouts from the roots of canopy dominants No signs of recent seedling establishment or vegetative reproduction by sprouting from roots away from the root collar on either small live sprouts or long dead chestnut stumps were found Vegetative reproduction is now occurring by relatively rare instances of layering, and by slow expansion and division of root crowns at a rate which probably more than offsets the low mortality of entire clones Chestnut sprouts that have escaped blight for many years indicate that the natural growth condition of suppressed chestnut seedlings is a single stem with controlled release of individual basal buds This process involves a complex mechanism for apical control of the entire clone that appears to be part of a definite reproductive strategy
This study was initiated in 1939 on the SW slope of Beanfield Mountain, Giles Co., Virginia, and was repeated in 1970. Prior to the chestnut blight [Endothia parasitica (Murr.) A. and A.], which reached a peak about 1920, the study area was covered by an oak-chestnut forest except for low-elevation cove forests. Dominant oak species included chestnut oak (Quercus prinus L.), northern red oak (Q. rubra L. var. borealis) (Michx. f.) and white oak (Q. alba L.). Following the blight these oak species partially filled canopy openings and persisted as codominants for a quarter century. In 1939, at elevations above 850 m, the mountain was covered by an oak complex dominated by northern red oak. On the basis of trends observed in 1953, Catherine Keever speculated that, eventually, oak-hickory forests would replace chestnut-oak forests in the region. Results of our 1970 study support Keever's predictions. By 1970, pignut hickory (Carya glabra, Mill.) had replaced chestnut, red maple (Acer rubrum L.) invaded clearings and sugar maple (A. saccharum Marsh.) became a dominant species in mixed mesophytic forests at low elevations. A half century following the chestnut blight, the oak-chestnut forest has been replaced by an oak-hickory forest.
Sprouts from the root systems of American Chestnut (Castanea dentata (Marsh) Borkh) have been increasing in numbers and size in the successional forests of Connecticut in spite of the chestnut blight Chestnut stems are especially impressive in defoliation-induced canopy gaps where they sometimes attain a diameter greater than 15 cm and appear to reach canopy level only a few years after release Five sites containing natural openings of various sizes and one site subjected to selective logging were investigated by coring chestnut stems and surrounding canopy trees All chestnut sprouts subjected to strong release under natural canopy openings exhibited cores with one to three decades of slow growth followed by very rapid diameter increase The relatively good form of these chestnut stems therefore resulted from rapid changes in stem form and not by resprouting from root systems It is proposed that initial suppression in shrublike form was a natural step in canopy emplacement for the chestnut This reproductive strategy appears especially effective under severe competition with shrubs on poor sites. Modern study of chestnut ecology is important because an increase in the proportion of chestnut pollen is a characteristic indicator of the most recent climate zone inferred from pollen profiles in New England The role of chestnut as a climatic indicator is explained best by a complex process of soil impoverishment and organic litter build-up analogous to a widely accepted theory for the late Holocene development of blanket bogs in western Europe
JONES, C., G. J. GRIFFIN, and J. R. ELKINS. 1980. Association of climatic stress with blight on Chinese chestnut in the eastern United States. Plant Disease 64:1001-1004. In commercial and home plantings of Chinese chestnut in Georgia, North Carolina, Tennessee, Virginia, West Virginia, and New York, 23% of the trees had main stem cankers incited by the chestnut blight fungus, Endothiaparasitica. The average main stem canker size was 28 X 55 cm. Fifteen percent of the trees had infection over 50% or more of the limb circumferences. Only two blighted trees were killed. In general, main stem canker incidence (13-93%) was higher in plantings of the Appalachian Mountain region than in plantings of the Piedmont region (2-13% incidence). Trees that were damaged most by E. parasitica cankers were located in high-wind and cold-winter areas of the Appalachian Mountains.
The Chinese chestnut (Castanea mollissima) is important internationally in the nut industry and in the study of resistance to the sympatric chestnut blight fungus (Cryphonectria parasitica). The chestnut blight devastated American chestnut (C. dentata) populations in Eastern North America and is a major pathogen on European chestnut (C. sativa) as well. Chinese chestnut is serving as donor for breeding of resistance in C. dentata. We have sequenced and assembled a first draft of the Chinese chestnut genome, covering 724.4 Mbp of the estimated 800 Mb chestnut genome in 41,270 scaffolds. A total of 38,146 genes were predicted, annotated, and confirmed with expression data. BAC clones tiling the three major blight resistance QTL were sequenced to great depth, revealing 782 genes with a diversity of molecular functions and biological processes, including app. 200 genes in the GO stress-response classification, and 15 known defense response genes. The genome scaffolds were integrated with the Chinese chestnut genetic and physical maps, including telomeric and centromeric chromosomal assignment by FISH of mapped BAC clones. Blocks of syntenies were found between the genomes of Chinese chestnut and ten model plant species, as well as micro-synteny among disease-resistance QTL. We hope that the Chinese chestnut genome will advance breeding and research with chestnuts, and lead to a better understanding of canker disease-resistance and –susceptibility in trees. The chestnut genome project was supported by The Forest Health Initiative (www.foresthealthinitiative.org).
Kuhlman, E. G., Bhattacharyya, H., Nash, B. L., Double, M. L., and MacDonald, W. L. 1984. Identifying hypovirulent isolates of Cryphonectria parasitica with broad conversion capacity. Phytopathology 74:676-682. When 118 virulent (V) and 27 hypovirulent (H) isolates of Cryphonectria parasitica were paired in culture, 95% of the V isolates were converted to the hypovirulent condition by at least one of the H isolates. The 118V isolates in 54 vegetative compatibility (v-c) groups included representatives from West Virginia, North Carolina, Virginia, Tennessee, and Italy. The average conversion capacity of the 27 H isolates was 15% and ranged from 0 to 41 %. Eight cluster analyses based on different similarity functions were performed to group V isolates according to their susceptibility to conversion. The most useful cluster analysis was based on the square root of the number of sectors converted by individual H isolates and formed nine conversion groups and left only eight isolates ungrouped. Twenty-eight of the 54 v-c groups had more than one V isolate, and isolates in 15 of these v-c groups were also together in conversion groups. Clustering appears useful for determining relatedness among v-c groups. Conidial or mycelial slurries
This study investigated the potential of birds and mammals to vector the chestnut blight fungus in today's mixed hardwood forests. Animals were shot or trapped in established woodland plots in southern Connecticut where densities of American chestnut sprouts were high, brought back to the laboratory, and examined for the presence of Endothia parasitica. Results showed that birds and mammals can transport virulent and hypovirulent-like strains of E. parasitica in today's forest community. Two birds, a mouse, and a shrew were identified as carriers of the blight fungus; the shrew harbored a hypovirulent-like strain introduced onto the plot 2 years earlier.
Stands of American chestnut trees have survived in Michigan in spite of the presence of Endothia parasitica. Cankered trees were evaluated in eight groves in seven of which two types of abnormal cankers were observed. These abnormal cankers resulted when diseased periderm was replaced by wound periderm. Endothia parasitica isolated from abnormal cankers often differed from E. parasitica isolated from normal cankers in that the isolates had abnormal culture morphology, reduced virulence, and contained double-stranded ribonucleic acid (dsRNA). These characteristics are similar to those of hypovirulent strains of E. parasitica found in Europe, except that four different dsRNA banding patterns were found in Michigan isolates, indicating different dsRNA genomes. Pathogenicity tests showed that host resistance or tolerance probably is not responsible for the prolonged life of infected trees in certain groves. Therefore, native Michigan hypovirulent isolates of E. parasitica may be responsible for the recovering American chestnut groves in Michigan.
After 10 to 25 years, 5 Chinese chestnut accessions (from northeastern China) and 10 Asiatic-American chestnut hybrids--in 4 of 8 plant growth regions in the eastern United States--produced trees of forest-tree form, grew rapidly, and had high resistance to the chestnut blight. Successful plots occurred on well-drained, moist sites in Van Dersal Regions 25 and 27. Less successful plots occurred in Regions 22 and 28. All plots are located between 32° and 41° latitude. Most of the chestnut accessions and hybrids failed, or grew unsatisfactorily in the 5 plots located in northern New York and southern New England--where once the American chestnut thrived. We recommend that forest timber-plots be established with clones of the outstanding Clapper chestnut hybrid, and with clones of the elite Chinese (PI-58602) chestnut, when the vegetative propagation of chestnuts becomes more efficient.
We conducted surveys of insects associated with American chestnut stems and chestnut blight cankers, and of the abilities of these insects to carry inoculum of virulent and cytoplasmically hypovirulent isolates of Endothia parasitica (Murrill) Anderson. Chestnut stems and blight cankers were found to have a large, diverse insect fauna; the majority of 495 insect species captured were from 'families of Coleoptera and Diptera that spend part or all of their life cycles associated with woody tissue or decaying vegetation. E. parasitica was isolated from 69 insect species (mostly Coleoptera) representing four orders. Species of insects capable of carrying E. parasitica were present throughout the growing season. Eleven isolates of E. parasitica obtained from insects exhibited abnormal in vitro morphology. Double-stranded (ds)-RNA was detected in two of these. Three other isolates obtained from insect traps also contained detectable ds-RNA. Old blight cankers colonized by Ceratocystis microspora and C. eucastaneae were more attractive to insects than were young blight cankers without Ceratocystis or healthy bark. Furthermore, attachment of Ceratocystisladen blighted bark to healthy chestnut stems and plastic posts increased the attractiveness of these substrates to insects compared with that observed on controls. These results suggest that Ceratocystis contributes to the increased attractiveness of old blight cankers to insects.
A Chinese chestnut planting of PI 58602 stock was established successfully 40 years ago in Killingly, Conn. In 1965, 36 of the original 50 trees were alive and fruiting. Five acres of an adjacent old field were sampled for the amount of chestnut regeneration. Natural regeneration of chestnut has occurred in the old pasture for at least 15 years, averages about 50 chestnut trees per acre, and occurs up to 700 feet from the original planting. Some of the older volunteers have already begun to fruit. Stem form is poor both for the original trees and the seedlings even though they have developed in situations ranging from full exposure to heavy shade. The value of Chinese chestnut trees as nut producers for wildlife is stressed.
During the first half of this century, the chestnut blight fungus, Endothia parasitica, destroyed stands of the American chestnut, Castanea dentata, throughout the tree's natural range. Conventional methods of controlling plant diseases have been ineffective. An approach being studied is the use of viruslike cytoplasmic hypovirulence agents to reduce the ability of the fungus to cause blight. Individual cankers have been controlled by treating them with strains containing these agents, but neither the agents nor the strains containing them appear to have spread naturally. Persistent cankers containing these agents may be required to provide long-term sources of inoculum for spread.
Introduction and Historical PerspectiveFloral Structure and ReproductionGermplasm Sources and PreservationVariation and InheritanceBreeding StrategiesSeed OrchardsProduction and Distribution of Improved StockFuture DirectionsLiterature Cited
This paper reviews initiation and execution of the selection program for blight-resistant chestnut trees in Switzerland. Important information about predisposition, resistance, and inoculation methods gained during the preliminary studies forms the basis for selection and interpretation of test results. During the last 25 years over 120000 native and Asian chestnut trees and their hybrids were tested in inoculation experiments. Now about 40000 of the selected trees are being further tested in gene banks and are being subjected to additional selection procedures.
Report (M.S.)--Virginia Polytechnic Institute and State University, 1975.
After 77 years of being attacked by the chestnut blight fungus, American chestnut trees continue to sprout from gradually declining root systems. The blight fungus in Italy is now associated with virus-like agents that limit its pathogenicity, and attempts have been made to introduce these controlling agents into the blight fungus in the United States. If a way can be found to help the spread here of strains of the fungus with controlling agents, it may be possible to save the American chestnut trees in our eastern forests.
Blossoming characteristics of horticultural varieties and seedling progenies of Chinese chestnuts
- J W H L Mckay
- Crane
A method of controlling the chestnut blight on partially resistant species and hybrids of Castanea
- A H Graves
1963 Location of F 1 Chinese-American chestnut hybrids produced by U
- J W Mckay
WITCHER 1971 Evaluation of the 24-year-old Table Rock (South Carolina) chestnut plot for growth and disease resistance and proposed breeding program for its use
- C R R E W Schoenike
WOOD 1982 Chinkapins, a promising nut crop in the South
- J A J D W Dutcher B