Seed Testing

There are two sets of standards for seed and cone testing: The International Seed Testing Association and the Association of Official Seed Analysts.

Testing conducted at the Tree Seed Centre follows rules set up by ISTA, an organization established to promote the production of high quality seed world wide. ISTA rules and procedures outline a set of methods, calculations and standards for sampling and determining moisture content, percent purity, germination and seed weight.

AOSA is also involved in trying to establish uniformity and accuracy in methods, results, and reports in seed testing.

These groups are currently trying to harmonize their rules. ISTA has a Forest Tree and Shrub Seed Committee and AOSA has a Tree, Shrub, and Native Forb Working Group that address issues specific to forest tree seeds.

There are two types of seedlot tests:

  1. Standard (STD) tests use seed samples that are representative of the entire seedlot. Only standard tests will be displayed on SPAR.
  2. Quality Assurance (QA) tests are performed on a portion of a seedlot, at a specific point in processing, or on a specific request (such as moisture content and germination for sowing requests). Some QA tests may be the same as a STD test, but the material will be sampled from only a portion of the seedlot and the result is not used to characterize the seedlot.

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Seed Sampling

There are several components to seed sampling:

  1. Representative samples of a seedlot are needed for results to be accurate. A test result is only as good as the sample taken. Seedlots are sampled for new tests after the seedlot has been blended to ensure homogeneity. ISTA rules specify, based on seedlot size, how many containers should be sampled and how many samples per container should be taken from a seedlot. These samples are considered primary samples, and are the point at which seed is withdrawn from the seedlot.
  2. Primary samples are combined and thoroughly mixed to form the composite sample. Sub-samples are randomly taken from different areas of the composite sample to get the appropriate submitted sample size. Excess seed is returned to the seedlot.
  3. Seed tests are performed on the working sample, which is a sub-sample of the submitted sample.

Sampling Method and Standard Testing Workflow

New Seedlot Testing

New seedlots must pass some basic testing requirements before they can be placed into freezer storage. The submitted sample for moisture content is made up of two working samples for the two replications of the test. It is critical to determine that the moisture content is within the 4.0 to 9.9 % range to ensure seed can be safely placed into freezer storage.

The second submitted sample is divided into two working samples and used to test the purity of the seedlot. The seedlot must be above 97% pure seed by weight. This ensures efficient seed storage and assists with nursery handling and efficiency.

The moisture content and purity ranges are the physical quality parameters for a seedlot under the Chief Forester's Standards for Seed Use. If a seedlot's purity is less than 97% or the moisture content below 4.0% or above 9.9%, additional processing is required to bring the seedlot to within these standards.

When the moisture content and purity tests are complete and accepted, eight working samples of 100 seeds are drawn for 100-seed weight from the pure seed fraction of the purity test. The seed weight test result is not placed on SPAR as the seeds per gram value that corrects for seedlot purity is more useful. You can convert between these variables using the following formula:

These 100-seed replicates are then used for germination testing performed according to the germination test types by species.

The germination capacity and germination rate are calculated for each seedlot test and an x-ray of one replicate is captured as a record of seed characteristics. For some species, two germination tests types are performed with the superior test type receiving an A-ranked designation on SPAR. This A-ranked germination is used in potential seedling calculations.

If a request to use a seedlot is received before germination testing is complete, a species average (SA) or client-requested seedlot estimated germination (SE) is placed on SPAR and used to calculate potential seedlings and grams required.

Retesting

Germination tests are repeated to maintain an accurate estimate of germination and estimation of potential seedlings in SPAR. The frequency is based on analysis of current and historical germination tests, and results in species being retested at intervals of 18 months to 48 months. Retesting frequency and the types of tests performed depend on species and, in some cases, individual seedlot quality and use. Clients may also request more frequent seedlot retests on a fee-for-service basis.

Fungal Assays

The focus of this program is to identify the presence and rate of infection of major seed-borne pathogenic fungi. Three fungi are considered seed-borne and potential pathogens:

  • Caloscypha fulgens (CAL)
  • Sirococcus conigenus (SIR)
  • Fusarium spp. (FUS)

Not all seedlots are tested for all pathogens. A priority matrix has been established by seed pathologists and this along with collection method, seedlot performance, available balance, usage and concerns expressed by growers, processors, seed owners, and other clients are involved in selecting seedlots for fungal assays. The results of these tests are maintained on SPAR.

Quality Assurance and Research

The testing area provides a large amount of the support required in our Quality Assurance program. This involves germination testing of sowing requests, assessment of pellet quality and measurement of moisture content of cones and seed at various stages of processing or pre‑treatment. Testing also supports research trials at both a basic and operational level to address issues of importance to conifer seed science and technology.