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United States Department of Agriculture

Agricultural Research Service

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Genebanking Strategies (Plant Focus)
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The research team at NCGRP is called the Plant Germplasm Preservation Research (PGPR) group. PGPR is an integral part of the National Plant Germplasm System (NPGS) infrastructure.  PGPR’s role is to support collections activities by developing strategies and technologies that

 
  • improve the efficiency of ex situ genebanks and
  • expand the potential uses of genebanked samples

     

  •  Diverse varieties of maize are stored in genebanks.

    Genebanking is really an investment for the future. The investment will pay off if we can anticipate the needs of tomorrow’s ever-expanding genebank users and develop genebank strategies that satisfy those needs in an economical way.  Successful genebanking requires linking a physical sample with accurate information about it, and then making sure that the stored sample retains the same properties as the material from which it originated.

    Five strategies pursued within the PGPR group aimed at improved genebanking include:

    1. Maintaining biological integrity
    2. Sampling representatively to accommodate current and anticipated uses and multiple conservation targets
    3. Providing annotation that authenticates, calibrates and characterizes samples
    4. Integrating information systems
    5. Providing germplasm with validated phenotypic and genetic descriptions

    Genebanked samples are used for a variety of reasons by diverse
    customers

    •  Genetic “improvement”
    •  Conservation of  biodiversity
    •  Mechanistic studies of
        adaptation
    •  Systematics and taxonomy
    •  Environmental monitoring
    •  Epidemiology
    •  Forensics
    •  New questions in new
        disciplines
     Understanding the critical parameters of wild rice seed production  Phenotypic data collection on diverse sugarbeet accessions.

     

     

     

     

     

    PGPR also has provided many innovations that have been implemented to improve genebanking worldwide. 

    Some current projects are described below.

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    The PGPR team is charged with trouble-shooting key NPGS operations
    to ensure cost-effective procedures today and relevance and impact of
    NPGS collections in the future:

    1)  Maintaining  biological integrity

    This requires that the physical structure and chemical composition of the stored material remains unchanged through time so that future researchers can test for the presence of compounds or evaluate the appearance of plant cells and organs. Preserving biological integrity usually requires cooling, drying or applying chemical fixatives to samples – all of which can be lethal.

     Freeze fracture image of embryo cells that have been successfully preserved. Freeze fracture image of embryo cells damaged during the preservation process. 

     

    2) Sampling representatively to accommodate current and anticipated uses and multiple conservation targets

    Conservation targets for a genebank include particular genes, genotypes or gene frequencies. Genetic diversity embodied by these different conservation targets should be available to
    future users without oversampling and unnecessary duplication.

     Plant explorers collect wild pepper in Paraguay.

      Preserved pollen is valuable for breeding programs.  Cacao embryos are desiccation sensitive.

     3) Providing annotation that authenticates, calibrates and characterizes samples
     
    Genebank users need information about where, how and when a sample was collected in order to understand why the sample is the way it is.  The information must be standard to avoid misinterpretations and must have a traceable history to ensure accountability.

    Annotation information is valuable for germplasm users, such as taxonomists.DNA samples are gathered in the field during collection trips.

     Wild apples are collected and documented.

     

    4) Integrating information systems

    Databases that describe holdings of repositories from
    all parts of the world must be interoperable to ensure
    that users have access to the full breadth of available
    material and information.

     The GRIN database provides access to annotation.

      5) Providing germplasm with validated phenotypic and genetic descriptions

    Germplasm repositories differ from other genebanks or repositories in that they provide living samples that can be grown out and used further. Providing living samples introduces the risk of change through mortality during the genebanking process or through drift or selection when material is regenerated.

    Regenerating buffalo grass in tissue culture.Diverse lettuce cultivars in field plot.

     Cryopreserved apple buds are recovered by grafting onto rootstock.

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    Innovations developed by the PGPR team have directly improved germplasm repository operations at NCGRP and at genebanks around the world.  Innovations that are now implemented in routine operations include:
    • Low temperature and moisture treatments that maximize seed longevity

     Lettuce seeds stored at 21C for 40 years are dead.Lettuce seeds stored at -12C for 40 years germinate vigorously.

     Propagules are stored in tanks cooled to liquid nitrogen temperatures.
    • cryogenic methods to preserve diverse plant materials

    Shoot tips preserved in a drop of cryoprotectant solution.

     Shoot tips are treated with cryoprotectants for long-term conservation.

     
    • evaluation of containers to ensure sample performance in a variety of storage treatments
    • new ways to evaluate genetic diversity within collections

    Microsatellite markers are used to evaluate genetic diversity.Relationships between cluster assignments and geography determine genetic diversity of wild apples in Kazakhstan.

    Bags, tubes, and vials are compared for water vapor transmission and suitability in liquid nitrogen.

    Network diagram demonstrating relationship among mosquito sampling locations.

    • identification of core subsets of accessions that maximize genetic diversity with the minimum number of individuals

    Hand pollination of apples in a core collection.Diversity of wild apples.Selection of core collection sizes.

    • development of database structures that allow molecular genetic data to be entered and retrieved from NPGS’s database system, GRIN (Genetic Resources Information Network).
    Relationships among molecular tables in GRIN. 

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    Current research projects build on past accomplishments with additional focus on

    • predicting response of diverse germplasm to storage conditions using non-invasive techniques

     Gas chromatography of head space volatiles reveal chemical changes during seed aging.

    Gas Chromatography of head space volatiles.

     Differential scanning calorimetry is used to measure motion of molecules in dry cold cells.

    Differential scanning calorimetry.

     Dynamic mechanical analysis is used to measure elasticity and yield of seeds.

    Temperature-controlled Dynamic mechanical analysis.

    • identifying the physiological basis for differences in response to preservation stresses
    • monitoring cellular responses to the cryopreservation process

     Evaluation of plasmolysis in suspension cells.  Image of plasmolyzed sweet potato cells.

    • identifying genetic and environmental factors that contribute to various responses to preservation stresses

     Diversity of garlic accessions and effects of growth location.  Budwood scored for survival after cryopreservation.  Microarray slide comparing gene expression after cryopreservation treatment.

    • Shoot tips vitrified in cryoprotectant solution.discovering the basis of genetic bottlenecks and change
      in genetic composition of genebanked samples
    • linking diversity measures based on phenotype with
      genotypic measures

     

     

    For further information about NCGRP research contact PGPR principal investigators:

    Dr. Christina Walters (Lead)
     Seed: development, storage, germination
     Biophysics of cellular stabilization 
     Christina.Walters@ars.usda.gov

    Dr. Gayle Volk

     Vegetative propagules: acclimation and growth
     Cellular responses to preservation stress
     Gayle.Volk@ars.usda.gov
    Dr. Chris Richards
     Population and Conservation Genetics
     Chris.Richards@ars.usda.gov

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    Last Modified: 7/12/2011
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