Seed Grading When There Are Multiple Test Results for the Same Seed Lot
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In order to apply a grade name to a seed lot offered for sale in Canada, a sample of the seed must be tested by a seed laboratory. For kinds in Tables I to VI and XVIII of Schedule I (the Grade Tables) to the Seeds Regulations (the Regulations) the purity examination may be conducted by an accredited grader. The report of seed analysis provided by the laboratory and the results of the purity examination by the grader (for kinds in Tables I to VI and XVIII) form the basis for the grading decision. The seed must meet the minimum quality standards detailed in the Grade Tables for the labelled grade of the seed at the time of sale.
In some cases, single or multiple samples from the same seed lot may be tested by one or more than one laboratory or grader. Differences in reported results from multiple samples and/or tests may be caused by the inherent variability of the seed lot, as well as variations in sampling and testing methods. In addition, if there is a long time period between the initial and subsequent sampling and testing, the germination rate of the seed may have decreased.
Following are guidelines on how to determine which results should be used for the assignment of a grade name when there are multiple reports for the same seed lot.
The grader and the laboratory must have confidence that the sample was drawn according to recognized methods by a competent sampler. Furthermore the grader and the analyst must be confident in the integrity of the sample. The sample must have been intact when received and correctly labelled and identified so that it can be clearly linked to the lot in question. If there is any doubt as to the integrity of the sample then the testing results for that sample are also in doubt and a new sample should be drawn and tested.
The procedures described in the Canadian Methods and Procedures for Testing Seed (M & P) are based on the testing of a single sample from a single sampling operation from a single lot. Where multiple primary samples have been drawn from a lot and mixed and divided to obtain the sample submitted for testing, this is considered a single sampling event and a single sample. If another set of primary samples is drawn and a second sample obtained for testing, then this is considered a second sampling operation and a second sample submitted from the same lot.
Reporting Test Results
a. Multiple tests of the same type by a single lab on a sample from a single sampling operation
If a lab conducts multiple tests of the same type on a sample from a single sampling operation, the M & P requires that:
- for purity test results,
- in the case of percentage tests, the weighted average for the tests that are in tolerance is reported; and
- in the case of tests for numbers of impurities per unit weight, the total number of impurities in the total quantity analysed must be used to calculate the reported number of impurities per unit weight.
- for germination test results,
- the average germination percentage for the tests that are in tolerance is reported.
In many cases, however, the samples are from different sampling operations, and the testing is conducted by different labs or graders and the above direction does not apply.
b. Multiple samples from the same lot from different sampling operations or tested by different labs
In general, where multiple reports are produced from more than one lab or grader testing multiple samples from the same seed lot, the report with the most recent date is considered to be the valid report. This would apply whether the samples were from a single or multiple sampling events.
The International Seed Testing Association (ISTA) provides some rules for these situations if the testing was done by ISTA accredited laboratories.
The reference dates to be used are, in order of priority:
- the date of issuing the certificate (highest priority);
- If more than one ISTA Orange International Certificate (OIC) is issued for the same seed lot under the same reference (i.e., seed lot seal and identification) for the same test(s), then the most recent OIC is considered valid and any previously issued certificates are cancelled.
- the date the test was concluded;
- If both certificates are issued on the same date then the one for which the test was most recently concluded is the valid certificate.
- the date of sampling (lowest priority)
- If both the date of the certificate and the date of the completion of testing are the same for both certificates, then the one with the most recent sampling date is the valid certificate.
The labelled grade name of the seed must reflect the true quality of the seed at the time of sale. It is recommended that, especially in the case of seed carried over from a previous year, and treated seed, the germination test should be repeated prior to sale to verify that the germination of the seed still meets the standards of the labelled grade. Seed must be re-graded and re-labeled prior to sale if the seed lot no longer meets the germination standard of the original labeled grade. In this case, the most recent test results for percentage germination are the valid results.
Note that the seller must, upon written request by the purchaser, supply the purchaser with the seed testing results, including germination test results, within 30 days of receiving the request.
Recommendations for Grading
It is recommended that seed graders follow the guidelines below when there are multiple reports of analysis.
- The most recent purity and germination report of analysis should be used.
- If there is more than one report with the same date, then the results from the most recently concluded test should be used.
- If more than one test was concluded on the same date, then the results of testing of the sample that was most recently drawn should be used.
Despite the guidance provided above, it is recommended that graders establish the grade based on the least favourable purity and germination test results. Using the least favourable test results reduces the risk that the seed would fail to meet the standards for the labelled grade when offered for sale. If a dormancy breaking method was used in a germination test, the results from that test may be used instead of the test result without dormancy breaking.
Germination shopping, that is, repeatedly sampling and testing (in one or more labs) a seed lot in order to obtain the most favourable test results, is highly discouraged. The Regulations are intended to protect the purchaser of the seed. It could be considered false and misleading to apply a more favourable grade name to a seed lot when one is aware of a test result that would require the application of a lower grade.
The Canadian Food Inspection Agency (CFIA) monitors seed in the marketplace and tests samples for compliance with the quality standards stated in the Grade Tables. Should the seed lot be found to not meet the standards for the labelled grade, the seed will be found non-compliant and may be removed from the marketplace for disposal or re-grading and re-tagging.
Prohibited Noxious Weed Seeds
Where any test result indicates the presence of prohibited noxious weed seeds in any sample from a seed lot, the lot may not be offered for sale in Canada. The laboratory or grader who identified the presence of prohibited noxious weed seed(s) in the seed lot must immediately notify the CFIA's Seed Section of the finding of prohibited noxious weed seeds at email@example.com.
For more information contact
Field Crops and Inputs Division
Plant Health and Biosecurity Directorate
Policy and Programs Branch
Canadian Food Inspection Agency
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