|Preservation and Quality Assessment of Plant Genetic Resources (PGRPP)|
Stephanie Greene, Seed Curator: Stephanie.Greene@ars.usda.gov
Maria Jenderek, Clonal Cryopreservation: Maria.Jenderek@ars.usda.gov
The Plant Genetic Resources Preservation Program maintains NPGS's entire collection of genetic resources. (Plant Collections) This centralized collection provides efficiency for managing the > 10,000 plant species within NPGS as well as greater security for the collections that are currently maintained only in fields, orchards or nature reserves. The program also provides long-term back-up storage for microbial collections. Management of PGRPP collections fall along cross-cutting issues of ownership and ease of preservation. Seeds are stored under so-called "conventional" storage conditions of optimized relative humidity (25% RH at 5°C) and -18°C and are expected to maintain viability for several decades to centuries, depending on species. These conditions are lethal to vegetative propagules (such as woody buds or meristematic shoot tips), and complex cryoprotective procedures followed by storage at liquid nitrogen temperatures are required to maintain viability. Assessments of health of newly-received materials and periodic monitoring to detect changes in viability are required to alert NPGS curators when inventories need regeneration. NLGRP provides training opportunities for germplasm preservation methods and repository infrastructure.
PGRPP seeks to provide safe long-term storage of plant and microbial germplasm under conditions that optimize longevity and economic efficiency.
Objective 1. Maintain seed viability for decades to centuries for accessions received at NPGS with necessary passport information, including seeds within the National Plant Germplasm System (NPGS) and non-NPGS plant genetic resources such as international collections, Plant Variety Protection, Crop Science plant registration materials, genetic stocks, and plant genetic resources endemic to the US. Detect losses in seed vigor within the NPGS base collection through periodic viability monitoring.
Objective 2. Develop, adapt, modify and/or apply methods for secure long-term back-up preservation of selected vegetatively-propagated crops, especially Allium, Fragaria, Ipomoea, Humulus, Musa, Prunus, Pyrus, Rubus and Ribes.
Objective 3. Initiate comprehensive and strategic long-term secure back-up storage of priority U.S. microbial collections.
Objective 4. Collaborate, coordinate and consult with regional and foreign genebanks to aid technology transfer of preservation technologies.
Need for Research
As the guardians of the base collection for the NPGS, the PGRPP has the responsibility of ensuring that the methods employed for long-term preservation of the genetic resources are the best possible for maintaining a viable and healthy collection. About 89% of the species within NPGS produce seeds that tolerate sufficient desiccation to survive freezer conditions (termed orthodox seed). Deterioration progresses in the freezer, albeit slowly, and some accessions of a species age faster than others for unknown reasons. These changes are detected by differences from initial seed germination percent, which is measured on all samples entering the base collection using the Association of Official Seed Analysts guidelines.
Despite goals of 100% back-up of NPGS collections, about 22% of seed accessions and 85% of the vegetatively-propagated accessions are not at NLGRP. These "un-secured" accessions are at risk from tornado, hurricane, flood, pandemic disease or climate change. The PGRPP works with curators within NPGS and across the world to identify at-risk seed and vegetatively maintained collections to back them up securely.
Vegetative propagules are more difficult to cryopreserve than seeds. They often require aseptic culture, application of cryoprotectants, or encapsulation and desiccation to a certain level of moisture content. Procedures have only been developed for selected species and often optimization for specific genotypes within a collection is needed.
Microbial genetic resources are used for research on food safety, plant productivity,diversity of soil microflora and plant diseases. These valuable collections need back-up storage to ensure against loss. PGRPP is coordinating with various microbe collection curators to create culture collections at NLGRP.
This research focuses on working with NPGS curators to provide high quality genetic resources for the development of new cultivars, genetic stocks, germplasm releases, and bioproducts. This program provides critical information to determine when accessions are declining and in need of regeneration and develop a pipeline with curators to ensure safe long-term storage of our crops and microbes. In addition, this program works to ensure information and protocols for storage of various plant species are provided to customers, stakeholders and others involved in genetic resources preservation worldwide.