| NPGS Base Collection |
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Seed in the NPGS base collection comes from USDA-ARS-NPGS regional or crop specific field sites. At the field sites, seeds are dried to ambient conditions and cleaned to remove empty seeds and chaff. A sample of seed from each accession is retained at the field site for regeneration, multiplication, distribution, characterization and evaluation and comprises an active collection. The NPGS base collection contains all the inventories of each accession including the original sample and earlier regenerations. This consolidated collection of all of NPGS holdings is stored at the NLGRP in secure freezers at -18°C. The viability of stored seeds is periodically monitored using standard germination assays. A fresh sample of seed is obtained if seed supply is too low or germination percent decreases below about 60%. A fresh inventory usually contains between 1500 and 3000 seeds.
As of February 16, 2017 the NPGS base collection stored at the NLGRP consisted of:
| Number of NPGS safety backup samples | 445,722 |
| Number of NPGS unique accessions | 566,345 |
| Number of Non-NPGS (black box) accessions | 324,507 |
| Number of genera | 1,893 |
| Number of species | 9,279 |
| Percent NPGS seed accessions backed-up | 85% |
| Percent NPGS vegetatively-propagated accessions backed-up | 14% |
