Carya Crop Germplasm Committee Report, June 1997
The Carya genus includes 19* species, 13 of which are native to the U.S. Of the 13, only pecan has major commercial value for nut production, with an annual production of about 125 million kg valued at about 259 million dollars, making it the most valuable native North American nut crop. Pecans are harvested from "native" trees throughout the range of the species (Fig. 1) . The culture of "improved" trees has extended considerably beyond the native range: from Ontario, Canada, south to Oaxaca, Mexico, and from the Atlantic Coast of Virginia and the Carolinas west to California. In addition, the pecan is grown to some extent in Israel, South Africa, Australia, Egypt, Peru, Argentina, and Brazil.
Improved pecan cultivars have traditionally been selected primarily on the basis of nut characteristics, with selections being asexually propagated on seedling rootstocks in orchard configurations where intensive management can be economically justified. Although there are over a thousand documented pecan cultivars (Thompson and Young, 1985), over half of the improved acreage is composed of only 4 cultivars: 'Stuart', 'Western', 'Desirable' and 'Wichita'. Nearly 90% of improved acreage is comprised of only 33 cultivars (Thompson, 1990). With native acreage steadily shrinking and improved acreage comprised of only a few genotypes, the genetic base of this important crop is at risk (Fig. 2).
Numerous selections have been made for large fruited individuals of two other U.S. hickory species, C. ovata and C. laciniosa. The limitations to economically feasible orchard establishment in the hickories are the extremely long period of juvenility (> 10 years), low yields (22 to 45 kg/tree, once in 3 years), and large tree size. These native trees are plagued by many co-evolved disease and insect pests, especially when grown in a "monoculture" having large numbers of trees of a limited number of cultivars. Conventional systems of orchard production have emphasized chemical control of pests, which is both economically and environmentally expensive. Genetic solution of these problems is an attractive alternative.
The value of hickory wood creates an economic incentive to harvest this slowly renewable forest resource. As a result, timber inventories have steadily decreased. Unfortunately, species identity is lost in the forest inventory, as hickories are grouped into two classes, true hickories and pecan hickories. Furthermore, the inventory of standing trees may overestimate the reserve, since many remaining trees are so defective that harvest is not economically justified. Continuous removal of the best individuals from the gene pool is a poor strategy for conservation of germplasm. Policies of timber harvest from National Forests and Parks may contribute to further erosion of this native resource if principles of in-situ conservation are not promptly established. Wise management should integrate the needs of forestry (and economic returns to be gained by meeting those needs) with a long range program of selection for the improvement of the stand.
Among the five Asian species, three (C. cathayensis, C. hunanensis, C. tonkinensis) are reportedly used for food, if not cultivated. Since Asian species, especially C. cathayensis and C. tonkinensis are known to be utilized for the oils produced in their kernels, the potential exists for altering the oil composition and content of pecan cultivars and thus facilitating the development of both domestic and export markets. In addition to their intrinsic ecological value, the remaining species are potentially useful medicinally, for wood production or as specimen plants in the landscape. As more information is gained concerning mechanisms of disease and insect resistance or other genetic adaptations, these species could contribute to the development of the closely related pecan.
* This number reflects the recent re-evaluation of Asian Carya species (Lu et al., in press) and reorganization of the former Carya sinensis Dode of the monotypic section Rhamphocarya, into the new genus Annamocarya.
II. Present Germplasm Activities.
The pecan germplasm collection was begun in the 1930's by Louis Romberg, a former ARS pecan breeder, in order to furnish parents for use in the Pecan Breeding Program. The collection of pecan cultivars was maintained as grafted trees (or as limbs in trees) in orchards at Brownwood, Texas. The collection was designated as the National Clonal Germplasm Repository for Pecans and Hickories in 1984, and a Crop Germplasm Committee (CGC) was formed. Additional collections were recommended by the CGC to represent native pecan populations throughout the range (the Provenance Collection), and to represent other Carya species (the Hickory Species Collection).
There are currently over 300 pecan cultivars being maintained in the Cultivar Collection, with many more being present as nut specimens only. These cultivars represent all pecan growing regions of the United States. This is the largest and most rigorous collection of pecan cultivars in the world. Accessions are maintained as grafted trees, targeting two trees of each cultivar at the Brownwood site, with duplicate collections at the College Station site. Accessions are provided upon request to researchers, and are provided to private growers when commercial nurserymen can not provide wood of a cultivar. Accessions are distributed as graftwood (typically 5 double graft sticks per accession) in January and February. In addition, seed is occasionally distributed from particular accessions for establishment of seedling rootstocks for subsequent grafting. Nut voucher specimens are maintained for each tree to verify identification. In addition nut samples of many cultivars are represented by collections from other orchards. Complete historical passport information on pecan cultivars (Thompson and Young, 1985) and hickory cultivars (Grauke, 1988) has been published. Verified inventories of most pecan cultivars have been characterized with isozyme analysis (Marquard et al., 1994) to provide a method of biochemical verification. The commercial pecan nursery industry needs improved methods of cultivar identification and verification. It is imperative that future biochemical characterizations of cultivars be based on verified accessions. Errors of characterization in the literature, based on incorrectly identified samples from other sources, have been corrected when compared to analyses of verified accessions from this collection. To aid cultivar identification, color photographs of many accessions of the Cultivar collection are available on the Internet at the site maintained by the Pecan Breeding Program (http://extension-horticulture.tamu.edu/carya). Photos are color standardized and are linked to specific inventory trees for which additional evaluation information is available. In addition, the site provides passport information for the most commonly planted cultivars.
Collections of seed have been made from pecan trees growing in native stands from Illinois and Missouri, south to Oaxaca, Mexico. Many of the seedlings arising from those collections have been planted in orchards at the College Station and Brownwood sites and are considered the Provenance collection. Those collections are being used to characterize genetic diversity in relation to seed origin, and are not currently being distributed. The Provenance collection has been found to be more genetically diverse than the Cultivar collection in some ways.
Collections of other Carya species are maintained either as grafted trees (in the case of selected hickory cultivars) or as own rooted trees (in the case of native tree collections). Currently, all hickory cultivars maintained in the repository are available from commercial sources and have not been distributed. Seed collected from native trees has been sent to researchers, but seedlings in repository collections are still juvenile and are not disseminated. The collection provides an excellent foundation for the study of diversity in this genus. In addition, accessions are maintained of the sister genera Annamocarya, Juglans, Pterocarya and Platycarya providing resolution for the study of diversity in the Walnut Family, Juglandaceae.
The ex situ collection provides an abundance of readily available, verified, and well documented plant materials for use in biochemical and molecular characterizations. Isozyme analysis is a useful tool for cultivar verification (Marquard et al., 1994) and for studying population diversity (Grauke et al., 1995). In addition, powerful molecular methods, based on the Polymerase Chain Reaction (PCR) are being developed in cooperation with scientists at the nearby Crop Biotechnology Center of the Texas Agricultural Experiment Station (TAES).
Other germplasm collections
Other collections of pecan and hickory exist in the U.S.A. and other countries (see Bettencourt and Konopka, 1989). Notable U.S. collections include: 1) Southeastern Fruit and Tree Nut Lab, Byron, GA; 2) Pecan Experimental Field, Chetopa, KS; 3) Northern Pecan Research Planting, University of Nebraska, Lincoln, NE; 4) Pecan Research-Extension Station, Louisiana State University Agricultural Center, Shreveport, LA; 5) Alabama Pecan Collection, Fairhope, AL; 6) Pecan Provenance and Hybridity Test, Louisiana State University, Idlewild, LA. Most collections of Carya in other countries are merely small collections of named U.S. cultivars. Notable exceptions include: 1) A collection of cultivars and seedlings of several U.S. Carya species and interspecific hybrids, maintained at the Holden Arboretum, Kirtland, OH; 2) A collection of C laciniosa from Canada, maintained at the University of Guelph Arboretum, Guelph, Ontario, Canada, and 2) a collection of commercial cultivars and landraces of pecan maintained at the Campo Agricola Experimental de La Laguna, Matamoros, Torreon, Mexico.
III. Status of Crop Vulnerability.
Rapidly growing human populations increase the demand for food, fiber, energy, and land. As wetlands are drained and forests are cleared to meet those needs, habitat for other plant and animal life is lost, and the genetic diversity of surviving forest species is reduced. In the United States, the clearing of the temperate southeastern forest largely fueled the growth of this nation. The clearing of North American forests is a continuing process. The 1970's were a period of active forest elimination in Southeastern states such as Louisiana and Arkansas, as increasing acreage was planted to soybeans. Patterns of native pecan production from those states reflect tree loss during that period (Grauke et al., 1995) The stewardship of remaining genetic diversity is imperative, if we are to maintain agricultural productivity and preserve valuable resources for the future.
Stewardship of genetic resources requires knowledge of the extent and distribution of genetic variation. Such knowledge is gained by the systematic sampling of plant populations throughout the distribution of the species, and the evaluation of resulting collections. Understanding the genetic adaptations that equip plants to thrive in particular environments is a prerequisite to the efficient recombination of parental genotypes designed to improve crops for those regions. Information on the spatial distribution of genetic diversity is the foundation of efficient ecosystem management, and is necessary for the design of conservation strategies that can maintain biological and genetic diversity.
The National Clonal Germplasm Repositories (NCGR) as a whole are charged with the maintenance of the diversity of clonally propagated crop plants, and at the same time, given the mandate to collect from "worldwide sources of wild species and domestic cultivars to provide for maximum genetic diversity in each genus" (Westwood, 1986). The National Plant Germplasm System (NPGS) has been clear concerning its motivation: human need is the primary criterion for genetic conservation. Plant species, populations, and cultivars "qualify" for conservation on the basis of utility. Utility is often defined by plant breeders on the basis of what they choose to use, since "plant breeders are usually regarded as the primary managers and users of germplasm collections" (Palmer, 1989). There are inherent efficiencies to be gained by a conservation program dominated by breeders. Namkoong (1991) noted the interrelation of conservation programs with germplasm utilization programs:
"It would be convenient if the gene-conservation problem could be separated from the breeding problem. However, there is a circularity in the maintenance of genetic diversity in breeding for resistance in forest trees. .. Hence, how we plan to conserve genetic diversity affects how we use that variation, and vice versa. The existence of such feedback implies a need for joint analysis of the breeding system, the nature of resistance, and the conservation program."
The interaction between genetic conservation and utilization is necessarily dynamic: conservation and breeding systems must be responsive to changes due to the inputs of the other. Namkoong (1991) suggested that "to develop multiple resistance mechanisms and to use multiple levels of resistance, breeders require more than only maintenance of genetic variation. They require an active combination of directed conservation and breeding". The acquisition of obscure disease resistant pecan cultivars by this Repository has been in response to the needs of the Breeding Program. The development of molecular markers for disease resistance requires structured, controlled cross families of the Breeding Program, but will contribute valuable information if applied to Repository accessions. Selection of parents based on that information could tremendously increase recovery of resistant progeny (Thompson and Grauke, 1994). In addition, the strategy of developing regional ex situ seed banks (described below) could be an effective form of directed conservation that would benefit by refining locally adapted breeding populations and increasing access to climatically adapted seedstocks, while offering cooperators economic incentives.
While the interaction between conservation and breeding is a necessity, curators must see beyond the current crop of breeders to a wider current audience ( all experimental biologists) as well as unpredictable future users. Namkoong (1988) recognized that:
"the person who samples for germplasm collections occupies a very narrow temporal interface between the genetic resources that history has left as our endowment, and the potential uses of those resources with which we endow the future. It is a narrow interface because the genetic resource is eroding rapidly".
The US National Science Board (NSB, 1989) estimates that as many as 25% of the world's species may disappear within the next 25 years. While genetic resources rapidly disappear, funding for the research programs that provide the information base upon which those resources should be conserved is also disappearing. Surviving programs must insure that resources are strategically used. Unfortunately, the current system of evaluating NPGS collections is in relation to frequency of requests for particular accessions, placing undue emphasis on current users and too little on the strategic maintenance of diversity. Wheeler (1995) suggested that public conservation policies were
"inadequately informed by science...We are not likely to have the financial resources or the public will to save so many (threatened) species. Our choices are likely to be between saving a precious few of these species or developing policies that attack the biodiversity crisis on a higher level."
Species are not all equal in their contribution to biological diversity. Wheeler (1995) suggested conserving "as complete a cross-section of phylogenetic diversity as is possible", noting that the last representatives of threatened phylogenetic clades represent greater biological diversity than other less threatened species. Manning (1978) reviewed the organization of the Juglandaceae, as shown in Table 1, and reported that Platycarya had evolved along different lines than the rest of the family, but was advanced when compared to Engelhardia, Oreomunnea and Alfaroa. The latter 3 genera are very closely related and are the most primitive in the family. Of the family, only Juglans and Carya are well represented in U.S. germplasm collections, with Pterocarya being at least minimally represented. By Wheelers (1995) criteria, the single species of Platycarya, representing an anamolous strategy of evolution, would be of singular value for conserving the genetic diversity of this family. The phylogenetically primitive members of the Tribe Engelhardia form a clade that is unrepresented in U.S. collections, and constitute another potentially valuable level of genetic diversity.
Soule' (1990) noted that the "first step in many situations is to describe, inventory, and map biotic diversity." Raven et al. (1992) reiterated that sentiment, noting that "the most basic research requirement is to gain a better, more complete sense of "what's out there"." They called for improved national biological inventories, utilizing professional linkages within existing institutions. This repository should help establish those linkages by coordinating the efforts of individual state conservation efforts aimed at Carya species. To the extent that the ex situ collection and related vouchers represent native distributions, this program provides access to Carya for a broad group of experimental biologists.
Table 1. Organization of the Juglandaceae
Subfamily Tribe Genus # Species Platycaryoide Platycarya 1 ae Juglandoideae Engelhardieae Engelhardia 5 Oreomunnea 2 Alfaroa 7 Juglandeae Juglans 21 Pterocarya 6 Hicorieae Carya 19 Annamocarya 1
Wheeler (1995) suggested targeting the conservation of ecosystems rather than species. This is consistent with the recommendation of the National Research Council (NRC) for the development of in situ reserves (Committee on Managing Global Genetic Resources, 1991). Those authors also recommended that "forest genetic resources programs should conserve species that lack clear present or potential value" as well as those that have known potential value. To efficiently accomplish this, more emphasis should be placed on research contributing to the development of strategies for the long-term, low-input, conservation of genetic diversity (eg. in situ reserves). The ex situ collection of this Repository constitutes an invaluable resource in the development of those strategies.
Within a species, not all populations are equal, although the determination of the distribution of diversity within species is complex. Gilpin and Soule' (1986) suggested that the vulnerability of populations to extinction was a function of the interaction of processes, often in recurring feedback loops involving fragmentation, demographic fluctuations, inbreeding, and loss of adaptability. Gilpin (1987) stressed the key role that spatial structure of populations plays in extinction dynamics, and the need to integrate spatial evaluation in characterizing the minimum viable population (MVP). Allelic distributions often vary in relation to spatial distributions, especially at ecological extremes for the species. Grauke et al. (1995) found an allele for phosphoglucoisomerase that was relatively common in West Texas native pecan populations (and one Illinois site) but was not present in other native populations or in any of the known cultivars of pecan, regardless of origin. We believe that this project can continue to contribute to an understanding of species distribution and diversity. Conservation models developed for pecan may be applicable to other Carya species or other hardwood trees.
The disjunct distribution of Carya myristiciformis, coupled with its scarcity, make it both a candidate for extinction and an excellent test case for in situ conservation. Sargent (1918) described C myristiciformis as "nowhere abundant". Fowells (1965) described it as abundant only near Selma, Alabama. Forest inventory records of the Southern Forest Experiment Station of the Forest Service do not distinguish nutmeg hickory from 'other hickory'. Our distribution records show scattered, disjunct populations including some not previously reported. We have nutmeg hickory accessions from Texas, Louisiana and Alabama, and have herbarium collections from Mexican stands near Cola de Caballo (seed did not germinate). We need to verify the existence of the Kerr Co, TX population, which is suspected to be C. texana. (LJG note: "I visited the UT herbarium in November, 2003. I had no memory of seeing W.L. Bray's 1899 voucher of myristiciformis from Kerr County, but I had annotated it previously, in July 1987. I studied the voucher again in great detail and have no doubt that it is nutmeg hickory. The voucher consists of a single extremely weak shoot. During the previous season, the shoot made only 7 mm growth. The season it was cut, it made 1.5 cm growth. The sample was taken in May, and there was one very weak catkin group present, with the longest catkin being about 2.5 cm. One shoot is hardly evidence to judge a population, but you use what you have. If this shoot is indicative of the vigor of this tree, I would say it was in the process of dying. If that tree was indicative of the stand, it bodes ill for finding surviving representatives.") If it is really myristiciformis, it could be genetically interesting since it is so isolated between US and Mexican populations. We do not have collections from South or North Carolina. Given the pattern of disjunct distribution found in surviving populations, this is a species that would necessitate at least three in situ reserves: in South Carolina, in Alabama, and in the Red River area of either North Texas, Oklahoma, Arkansas or Louisiana. The effects of forest fragmentation might be followed in such populations.
If the underlying purpose of the program is to "make genetic diversity available for use", then the taxonomic and geographic boundaries of the current program need expansion. First, more emphasis should be placed on maintaining diversity. Second "representative collections" of species (or related genera) are needed. From the perspective of an experimental biologist, Palmer (1989) suggested that "germplasm collections must represent as many as possible of the geographic and ecological habitats of a species, whether wild or cultivated". The challenge to developers of a collection is to actively target users, and construct collections that will invite active use. We believe that with relatively minor increases in total accession numbers, the utility of this Repository for experimental biologists can be greatly increased. This must be accomplished without sacrificing the crucially important interaction of the Repository with the Breeding Program.
IV. Germplasm Needs.
A tremendous amount of work can be envisioned relative to this project, all of which could contribute greatly to present and future improvement of world nut and timber production. Unfortunately, we are limited by available resources of personnel and money, and must strategically use those resources. With limited resources, we must be clear concerning priorities for work. Our first priority is to keep the material under our care alive. Individual trees or entire orchards may be at risk, requiring propagation to insure survival of the accession(s). Accessions being transferred by grafting are at risk. In 1991, a fall freeze devastated newly established accessions in Brownwood and killed several accessions in College Station orchards. For that reason, multiple inventories are propagated during a transfer. Once established, pecan trees are very durable, but are still vulnerable to unforeseen calamities, such as extremely high winds or lightning. Maintenance of accessions at both Brownwood and College Station is the insurance against loss under those conditions. Furthermore, our records often include locations of verified inventories of cultivars in orchards owned by other units, agencies, or privately. Our second priority is to maintain the integrity of information associated with an accession. Excellent historic information is associated with most accessions, although many records are in files that have not been completely computerized. Standard procedures of documenting graftwood sources, even for within orchard propagations, have been implemented to allow linkage of inventories to verification procedures (also standardized). The third priority is to maintain the quality of the propagation materials distributed. Propagation of accessions to newly established orchards has greatly increased the quality of graftwood available. Routine management is necessary to insure that accessions are maintained free of insect and disease problems that could threaten recipients of propagation materials. Standard operating procedures for growing season inspections are being implemented with the Texas Department of Agriculture to insure that materials can meet international standards. The fourth priority is to efficiently use the existing collection, by making timely observations of critical parameters. This increases the utility of the existing collection and gives direction for its improvement. Given the lack of standard descriptors for many parameters, it is first necessary to develop confidence in procedures by more rigorous testing than can be accomplished in the Repository collections. The interaction between the goals of the Repository and those of the National Pecan Advanced Clone Testing System (NPACTS) are an advantage in this unit. Fifth, and finally, we must strategically build the collection to insure its use by a broad group of nurserymen, growers and scientists, whose collective work will influence the collection and will contribute to the conservation of its genetic base in other ex situ and wild populations.
The following is organized in relation to the primary objectives of the Repository, with each area subdivided based on the potential for accomplishing the work within present resources.
Collect: Active collection efforts will be curtailed until evaluation of existing accessions reveals gaps that demand addressing. Isolated noteworthy accessions will be added as appropriate. The priority for collection will be species of Carya other than pecan: the current pecan cultivar collection is extensive, and the provenance collection is sufficiently complete to require analysis prior to additional sampling. At the same time, other species are poorly represented in relation to their distribution. Relatively few accessions of each species will add tremendously to the diversity represented in the collection, and to its utility for students of that diversity. Toward that end, isolated accessions of related genera (Platycarya, Engelhardia, Oreomunnea, Alfaroa and Pterocarya,) should be acquired (possibly in conjunction with the National Arboretum). We continually receive unsolicited accessions that require curation.
Will do: Isolated noteworthy accessions will be added as appropriate, with priority on cultivars of other species of Carya.
Will do with cooperation: Target systematic, structured collection of key native populations of U.S. Carya species (C. floridana and C. myristiciformis) based on the overall species distribution.
Should be done, but not possible within resources of the project: Target systematic, structured collection of key native populations of several Asian Carya species, as well as cameo collections of South American species of related genera, based on the overall species distribution.
Herbarium records. Herbarium vouchers are maintained for most wild accessions. Those vouchers are in need of organization to facilitate access, and to inventory for recording in the GRIN database. Recent acquisition of surplus herbarium cabinets and the permanent loss of a technician will make extra organizational space available.
Will do: Vouchers will be organized and inventoried on GRIN. Duplicates will be shared with other interested herbaria.
Will do with cooperation: Translate the distribution information reflected in herbarium vouchers into geographic data sets organized at the county level for electronic generation of revised distribution maps.
Should be done, but not possible within resources of the project: Systematically annotate herbarium records of major collections to correct errors of identification and refine distribution information. Publish range extensions for some species (eg. Carya aquatica), based on documentation in herbarium vouchers. Name the interspecific hybrid families of crosses between pecan and shagbark, and between pecan and nutmeg hickory. Address nomenclatural problems concerning the appropriate name for C. tomentosa.
Isozyme analysis. Materials for isozyme lab analysis have been accumulated over the course of several years, with the intention of establishing that procedure as a standard operation in the verification of cultivar identity. Loss of technician positions prevents full implementation of that strategy.
Will do: Disputed cultivars propagated by the pecan nursery industry will be distinguished using isozyme analysis, in conjunction with passport records related to the cultivars.
Will do with cooperation: Analyze accessions of the Arkansas provenance collection, and the recently acquired Mexican seedling collection, to determine patterns of diversity relative to previously analyzed provenance collections.
Should be done, but not possible within resources of the project: Routinely evaluate accessions using isozyme analysis to verify cultivar identity prior to propagation into the collection or distribution from it.
Molecular techniques. The development of marker aided selection for disease resistance is being investigated using Amplified Fragment Length Polymorphic DNA (AFLPs)] on controlled cross progenies from reciprocal cross families of pecan in the Pecan Breeding Program. The work is a cooperative effort with molecular biologists at the Crop Biotechnology Center, Texas Agricultural Experiment Station (TAES). The procedure is proving to be very successful; it is reproducible and consistent and has resolution to separate cultivars with great power. The technique has been applied to some of the cultivars in the Core, and apparently has resolution to separate provenances as well. Bulk segregant analysis of scab resistant versus susceptible progeny has revealed some bands that may be useful as markers for early selection for nut scab resistance.
The development of DNA marker techniques could contribute tremendously to evaluation of accessions. Specific areas of application include : 1) fingerprinting the cultivars in the National Clonal Germplasm Repository for Pecans and Hickories (NCGR-BRW) as aids to identification and verification; 2) associating genetic profiles with geographic regions of origin and determining genetic relatedness of native pecan populations; 3) refining the selection of parents used for the production of improved progeny families in the breeding program; 4) phylogenetic analysis of species in the genus Carya and 5) phylogenetic analysis of the genera of the Juglandaceae. We recognize the need to engage a broad group of multidisciplinary scientists to pursue some of the more basic botanic goals (eg. 4 or 5) and are encouraged by an increasing cooperation with the botanical community, largely facilitated through cooperation with Dr. Donald Stone of Duke University.
Will do: The development of molecular markers for scab resistance will be extended to parental cultivars in the Repository.
Will do with cooperation: (Pursuing grant for Fund for Rural America) Fingerprinting the cultivars in the National Clonal Germplasm Repository for Pecans and Hickories (NCGR-BRW) using AFLPs as aids to identification and verification will be undertaken if grant money can be obtained.
Should be done, but not possible within resources of the project: Genetic relatedness of broad species groupings should be determined, with more distantly related genera serving as outliers for the analysis.
Ex situ collections. Experts disagree concerning the relative importance of ex situ and in situ preservation of diversity. Some see the need for ex situ collections to compensate for our growing failure with in situ conservation while others fear that ex situ collections serve as an excuse to allow further losses among natural populations (Waller, D. 1992. Priorities for Plants: Review of Genetics and Conservation of Rare Plants. Science 256:1055-1056). We see the need for successive "feedback loops", with collection from native populations establishing ex situ collections, while the evaluation of those collections results in refinement of strategies for both in situ and ex situ conservation. Our existing ex situ collection is heavily weighted in favor of pecan, with excellent representation of both cultivars and native seedlings. The longevity of accessions in the ex situ orchards is a function of their adaptation to local conditions: the more different the climate of the accession's origin from the ex situ orchard site, the more at risk the accession. As a result, pecan collections from the extremes of the range show increased mortality, making the ex situ collection a potentially poor representation of the full species diversity. To offset mortality in the field, accessions can be held in more controlled conditions, increasing the expense of maintenance. The challenge to management is to use the collection wisely, while not viewing its maintenance as an end in itself.
Will do: Recent acquisitions of native pecans from Arkansas and Mexico will be established in 'permanent' orchard sites at the College Station location. Cultivar accessions at the Brownwood worksite that are in jeopardy due to tree or orchard condition will be grafted to new locations.
Will do with cooperation: (Pursuing grant from Fund for Rural America) Develop regional ex situ seed banks: This strategy serves to bridge the gap between the unimproved raw natives that contain high levels of locally adapted genetic diversity, and orchards of improved grafted cultivars, that contain very little diversity. This approach would be targeted at appropriate sites that have been previously cleared, but need to be taken out of rowcrops for conservation purposes (Conservation Reserve Programs in some states). Selected seed would be planted for the establishment of high density pecan "nurseries". Seed would be selected based on regional constraints and would represent families having characteristics predicted to perform well under those conditions. For instance, in the Southeast, where disease is the primary threat, seed from open pollinated seed of many disease resistant seedstocks would be targeted. By planting discrete families of seed from cultivars with improved horticultural traits, the performance and market quality of the seedlings would be predicted to be better than raw natives, while the diversity inherent in seedlings grown from multiple seedstocks could provide cultural advantages as compared to typical 'monoculture' of grafted cultivars. An evaluation period during bearing would allow selection of "improved cultivars" (based on tree and nut characteristics). After the CRP enrollment period, growers would be free to harvest and sell nuts. They would expect to produce greater yields and quality than native pecans, at comparable production costs. "Improved cultivar" selection in regional nurseries would allow increased power of selection for regionally adapted cultivars for propagation and use by the improved pecan industry. The evaluation of "families" of seedlings would result in refinement of seedstocks used for subsequent plantings. The stands could also provide genetically diverse, locally adapted, open-pollinated seed. By maintaining stands in different regions, the possibility of divergent selection for local conditions is increased, while maintaining the genetic diversity of that region. Potential cooperators are available to pursue this approach in Alabama, Arkansas, Kansas and Nebraska.
Should be done, but not possible within resources of the project: Regional ex situ stands for hickory species could also be developed, using seed from several adapted "improved" cultivars. The incentive for economic return is reduced, but the strategy would work for CRP plantings and would contribute both to selection of improved trees and conservation of diversity. Tree improvement could be targeted for timber and/or production/nut quality considerations. Individuals in the Northern Nut Growers Association who have expressed interest in this area should be encouraged to pursue it through private channels.
In situ reserves. Given the large tree size, long generation time, and broad distribution of the hickories, coupled with their status as "keystone" species in ecosystems (Soule'. Ann. Missouri Bot. Gard. 77:4-12. 1990), the strategy of establishing regional in situ reserves is generally applicable for the hickories. The development of a national system of in situ repositories for key Carya species is a long-term goal that will be pursued as resources permit. Resources (of time and money) to pursue those objectives independently are not available.
Ideally the strategy of in situ conservation should reflect the genetic diversity of the species across the geographic, edaphic, and climatic variables of its distribution. We had hoped that the pecan collection could serve as a model for the other Carya species, since we have a much higher sampling density across the pecan's range, and since the information generated by the pecan genetic studies is more immediately translated into economic value. Since gene flow in a given group of trees is a dynamic process sensitive to environmental variation (including co-evolved species) and is influenced by fragmentation of once contiguous populations, there are many questions concerning physiographic boundaries, critical population sizes, and other aspects of practical establishment and maintenance that deserve attention, but that may not be adequately controlled in the first effort. At this point, it is advisable to make a best guess, designate several preserves, and then begin to use those areas as the foundation of characterization to build the datasets that will furnish the models to revise the system.
Will do: We will attempt to form cooperative approaches to pursue the goal of in situ conservation for any Carya species. Data from the characterization of the pecan provenance collection will be evaluated in an effort to refine regional physiographic boundaries for targeted reserves, possibly contributing to model development.
Will do with cooperation: (Pursuing grant from Fund for Rural America) Characterization records of the pecan provenance populations could be evaluated by Geographic Information System to facilitate analysis. Distribution of regionally diverse populations could be evaluated in relation to the distribution of conserved lands to determine target populations for detailed inventory.
Should be done, but not possible within resources of the project: Pecan distributions on the Brazos and Colorado River systems were mapped in 1977 using color remote infrared imaging. Remote sensing of the same areas should be performed to quantify the current status of the resource and change over the twenty intervening years. The information could also help develop target populations of pecan for in situ conservation. The species with the greatest potential for in situ conservation is C. floridana, since it has the most limited distribution, some of which is already included within the Ocala National Forest. Unfortunately, only a small portion of the northernmost part of the native distribution is within the National Forest. The diversity of the conserved population should be evaluated in relation to the diversity of the full range. The population size within the National Forest should be inventoried to insure that it is adequate for sustained maintenance of that diversity. The management of the population should be predicated on long-term maintenance of the genetic diversity. Another species with great potential for in situ conservation is C. myristiciformis. Target populations should be identified for conservation, and detailed ecological inventories of target populations on conserved lands should be developed by multidisciplinary teams.
Refine methods: Much of the evaluation information related to pecan cultivar performance is anecdotal, is rated using different methods by different evaluators, and varies in relation to the year, location, or management system used for trees under observation. Uniform descriptors are needed for most tree and nut characters. Standard procedures have been developed for evaluating pecan kernel color (Thompson and Grauke, 1996). Descriptors are also needed for characterizing tree form and leaf form. Improved methods of evaluating critical phenological stages are needed, specifically, the inception of dormancy in the fall. The development of these descriptors and methods will be pursued as time permits. Insect predation and disease expression are monitored as resources permit. We will continue to encourage specialists in entomology and pathology to use the NPACTS test orchards, as well as Repository orchards, in developing refined methods of monitoring.
Will do: Kernel color standards have been integrated into standard methods of photographing nut samples for the development of digitized images that will be integrated into the computer database. The project is intended as a model for the development of similar records for selected clones in the Breeding Program, and all NPACTS elite clones. Nut quality data collected on multiple trees of approximately thirty cultivars for several years will be analyzed in an effort to refine nut descriptors.
Will do with cooperation: Nut vouchers from hickory species will be characterized for nut and shuck characteristics to insure that descriptors relevant for pecan have resolution in other species.
Germplasm: Procedures for the distribution of seedstocks and graftwood need to be refined, both to improve the product delivered, and to defray the costs of the service. In order to send selected accessions to countries requesting pecan cultivars, we often must first send seed for the establishment of rootstocks. We anticipate the conditions in the area and send the most adapted seedstock. All seed collected from Repository orchards is open pollinated. Seed from northern pecan cultivars collected for use in northern climates that require hardy material may be pollinated with southern pollen, making the seedstock both variable and partially non-adapted. As we increase the collection of other Carya species, the collection will have increasing percentages of interspecific hybrid pollinations.
Will do: Standardize the protocol for production of high quality seed, as well as for high quality graftwood.
Will do with cooperation: Seed to be used in climatically different regions will be obtained from comparable areas through cooperation with researchers in Nebraska and Mexico.
Information: The primary users of the Repository collections currently are personnel of related ARS projects, and state Experiment Station and Extension workers. By increasing documentation on the collection via GRIN, additional users may be developed.
Will do: Records of the Repository will be transferred to the GRIN system.
Will do with cooperation: The image library of pecan cultivars has been made available to GRIN users, along with visual and textual aids to the identification and distribution of Carya species. We have also made cultivar passport information and images available via Internet at our website (http://extension-horticulture.tamu.edu/carya).
1. More emphasis should be placed on maintaining diversity. The priority for collection will be species of Carya other than pecan: the current pecan cultivar collection is extensive, and the provenance collection is sufficiently complete to require analysis prior to additional sampling. At the same time, other species are poorly represented in relation to their distribution. Relatively few accessions of each species will add tremendously to the diversity represented in the collection, and to its utility for students of that diversity. Toward that end, isolated accessions of related genera (Platycarya, Engelhardia, Oreomunnea, Alfaroa and Pterocarya,) should be acquired.
2. Actively target users and construct collections that will invite active use.
3. Continue to make information available on Internet as well as through GRIN.
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