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International Seed Testing Association
International Seed Testing Association
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+41 44 838 60 00
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International Seed Testing Association

FAQ Purity Committee

Purity Testing

  • Correct nomenclature according ISTA?
    ISTA Chapter 3
    Reference 3.2.1 Pure seed
    ….
    1. The following structures ………
    1. Intact seed units
    2. Pieces of seed units larger than one-half their original size.
    Recommendation for action The basis is the size of the seeds, disregarding whether an embryo is present or not. The reason is the best possible uniformity in the application of this rule among ISTA labs. It is regarded as easy and clear for everybody to estimate the original size of a seed and then apply the 50% Rule. To decide about pieces of seed containing pieces of embryos and if they will germinate or not, will be less uniform from analyst to analyst. The agricultural value of broken seeds with/without embryo/pieces of embryo is then determined in the germination test.

    Link List

    Stabilised Plant Names
    Universal List of Species

  • Correct calculation of Purity results: Which weight to use for calculating the percentage of components?
    ISTA Chapter 3
    Reference 3.7 Reporting results
    Recommendation for action ISTA has an agreement with ist stakeholders on a basic stability on plant names of at least 6 years.

    Link List

    Purity Committee

  • How many decimal places for determination and reporting?
    ISTA Chapter 3
    Reference NA
    Recommendation for action For the determination of weight [g] use  the table in: 3.5.1 Working sample, for getting the exact number of decimal places. If your balance shows one (ore more) digit more than indicated in the table: round the next digit according mathematical rules. For the reporting of results [%] use always 1 decimal place, take the second decimal place for rounding according mathematical rules.  Components less than 0,05% must be reported as Trace.

    Link List

    Purity Committee

  • Resources for seed identification
    ISTA Chapter 3.4
    Reference NA
    Recommendation for action

    A list of electronical resources as well as books is published by ISTA PUR.

    Link List

    Purity Committee / See other documents

  • How to report ergots / sand / soil / other things than seeds in a seed quantity deviating from the purity weight?
    ISTA Chapter 3.4
    Reference

    3.1 Object
    3.2.1 Pure seed
    3.2.2 Other seeds
    3.2.3 Inert matter

    Recommendation for action

    The principle of PUR test is to investigate 2500 seeds and report as %. In contrary the OSD with the seed amount of 25000 seeds to be tested and reporting in numbers by weight. But Chapter 4 only talks about seeds, about nothing else. Therefore an investigation on ergots/sand /other things than seeds in any amount deviating from the purity amount has to be reported under: Other determinations.  Additionally a sentence that “this method is not covered by ISTA Rules” has to be added.

    Link List

    Purity Committee

  • Support for determination of seeds
    ISTA Chapter 3.4
    Reference

    NA

    Recommendation for action

    Take informative photos of suitable magnification and quality (resolution and sharpness) from relevant morphological characteristics from your seed. Use a scale bar and give information about the seed size. Tell in which species the seed was found and possibly give information about seed lot origin (country) the seed has been found. Send the photos to the chairperson of ISTA PUR, who will circulate your request. The response will NOT be an authorative seed determination and is not to be used on an ISTA certificate directly. The inquirer is obliged to use the provided information/tools/links being provided to support his own determination of the seed under request. 

    Link List

    Purity Committee

  • Is it possible to report the numbers of other seeds as a purity result?
    ISTA Chapter 3.4
    Reference

    4.2.5 Reduced-limited test;
    4.7 Reporting results

    Recommendation for action

    The number of other seeds found in the purity portion can not be reported under purity. Determination of numbers of seeds is regulated under chapter 4,  OSD tests. The chance to be found in purity is 10 times less  than in the OSD test.By customers request, it could be reported as reduced-limited test according 4.2.5. under "Other determinations" by regarding  4.7 reporting results.

    Link List

    Purity Committee

Use of Balance

  • What kind of balance should be used for Purity testing?
    ISTA Chapter 3
    Reference Some advice regarding calibration of balances:  Moisture Handbook.
    Recommendation for action

    There is no recommendation, because the minimum working weight for purity and OSD depends on the species.  

    When you choose a balance you may consider:

    • Your scope of accreditation 
    • Check the samples weights of those species for which accreditation is held or maybe is intended to be extended in future 
    • In ISTA table 3.5.1 you can see which number of decimal places are needed for the respective species What should be a typical weighing tolerance? 
    • It is up to the lab to set tolerances - that means what does the lab accept as a failure. This can be elaborated by standard deviations or be an agreed level of influence on the results. The tolerance can be different from lab to lab, with the principle of accepted testing accuracy by the lab.

    Link List

    Purity Committee

Other seed determination

  • Correct nomenclature according ISTA?
    ISTA Chapter 4
    Reference 4.7 Reporting results
    Recommendation for action

    ISTA has an agreement with ist stakeholders on a basic stability on plant names of at least 6 years.

    Link List

    Stabilised Plant Names
    Purity Committee

  • How to report species not being included in the ISTA List of stabilised plant names?
    ISTA Chapter 4
    Reference NA
    Recommendation for action

    If a species’ name is not listed in the ISTA Stabilized Names, the species can be reported according to other reputable sources such as:

    GRIN
    Search Taxonomy Data in GRIN-Global

    GBIF

    https://www.gbif.org/species/142637414 LINK DEAD

    Plant list

    http://www.theplantlist.org/  LINK DEAD

    AOSA

    Analyzeseeds
    Mansfeld's Database

    Link List

    Purity Committee

  • Correct nomenclature according ISTA?
    ISTA Chapter 4
    Reference NA
    Recommendation for action

    ISTA has an agreement with its stakeholders on a basic stability on plant names of at least 6 years.

    Link List

    Stabilised Plant Names

Seed collections

  • Where can I buy a seed collection?
    ISTA Chapter 3.4
    Reference Some advice regarding calibration of balances:  Moisture Handbook.
    Recommendation for action

    Special small collections may be available from GEVES/France (see Link). As a member of ISTA you may participate in ISTA proficieny tests, where seeds are provided in the frame of seed dertermination excercises (specific mixture samples). Those you may keep as references. You may establish your seed collection by ordering seeds from botanical gardens, breeders, seed companies. Practise exchange of seeds with your colleagues.

    Link List

    Geves I.D. SEED ®

  • How to establish a seed collection?
    ISTA Chapter 3.4
    Reference NA
    Recommendation for action

    A seed collection may be established according different viewpoints.

    With regard to ISTA accreditation it is important:    

    • To ensure the identity of the material when you insert it in the collection and documentation of inserting new species.
    • To prevent the collection from carry over or from transposition by consciously working with it.
    • To mainain and guarantee the identities also during use (for example opening the boxes is maybe only allowed for special staff members: specialists but not apprentices).
    • ISTA pursues the goal to see in the labs possibly at minimum the species from the “Universal list of species”, if possible try to collect those species as a basis, near the flora that is typical for your samples.
    • Install means of maitenance to prevent the seed collection from damages for example by pests and how to defend in the case of pest attack.

    Link List

    Purity Committee

Thousand seed weight

  • Which method shall I use for determination of thousand seed weight?
    ISTA Chapter 10
    Reference NA
    Recommendation for action

    The two counting methods are regarded as equivalent. There are two working steps with different needs of menpower/machine power: Getting the amount of pure seeds by making a complete purity of xxx g,  possibly having a machine to do the counting  or  the lab has to decide where it likes to invest more in machine or in menpower. “just” taking out 8 x 100 pure seeds from the submitted sample and count by hand.

    Link List

    Purity Committee

Testing coated seeds

  • Testing coated seeds
    ISTA Chapter 11
    Reference NA
    Recommendation for action

    NA

    Link List

    Purity Committee

Testing seeds by weighed replicates

  • Testing seeds by weighed replicates
    ISTA Chapter 13
    Reference NA
    Recommendation for action

    NA

    Link List

    Purity Committee

X-ray-Test

  • X-ray-Test
    ISTA Chapter 14
    Reference NA
    Recommendation for action

    NA

    Link List

    Purity Committee

Rules for size and grading of seeds

  • Rules for size and grading of seeds
    ISTA Chapter 16
    Reference NA
    Recommendation for action

    NA

    Link List

    Purity Committee

Membership

  • How to apply for PUR membership?
    ISTA Chapter NA
    Reference NA
    Recommendation for action

    NA

    Link List

    Becoming a Technical Committee Member

Workshop

  • Request for a workshop on chapters 3, 4, 10, 11, 13, 14 and 16 by offering possibility of hosting one
    ISTA Chapter NA
    Reference NA
    Recommendation for action

    Apply by the chairperson of PUR and ISTA Secretariat.

    Link List

    Purity Committee
    Workshops and Webinars

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