Seed classes and seed certification
How a new variety's seed is multiplied through breeder, foundation and certified classes, what certification checks, and how seed quality is tested.
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A new variety is only as good as the seed farmers actually sow. Seed certification is the system that keeps a variety true to type and the seed of known quality as it is multiplied from a few kilograms in the breeder's hands to thousands of tonnes sold to farmers.
Seed certification works in broadly the same way in most countries, many of which follow the international OECD Seed Schemes and the testing rules of the International Seed Testing Association (ISTA). The classes of seed, the stages of certification and the quality tests are standard questions in plant breeding and seed technology exams.
Why seed must be certified
Seed can go wrong in two ways:
- Genetic quality: the seed is no longer the variety on the label, because of cross-pollination with other varieties, mechanical mixture at harvest or processing, mutation, or selection pressure over many generations.
- Physical and physiological quality: the seed is mixed with weed seeds, inert matter or other crops, has low germination or vigour, is too moist to store, or carries seed-borne disease.
Certification addresses both, with a chain of custody from the breeder to the bag.
The classes of seed
| Class | Also called | Produced by | Purpose |
|---|---|---|---|
| Nucleus seed | — | the breeder, from selected single plants or lines | the purest source of the variety |
| Breeder seed | pre-basic seed | the breeder or the breeding institution | starting stock for certified multiplication |
| Foundation seed | basic seed | seed agencies or approved growers, under certification | stock for producing certified seed |
| Registered seed | — (used in some schemes) | approved growers | an extra multiplication step |
| Certified seed | C1 (first generation), C2 (second) | seed companies and contract growers | sold to farmers to grow the crop |
The OECD Seed Schemes, established in 1958 and used for international trade by around sixty countries, recognise pre-basic, basic and certified seed (first and later generations). OECD labels are white with a violet stripe for pre-basic, white for basic, blue for first-generation certified and red for second-generation certified seed. North American schemes use foundation (white), registered (purple) and certified (blue) tags. National schemes use their own names and colours, so always check which system a question describes.
The number of generations is limited on purpose. Each multiplication is a chance for contamination and genetic drift; after a set number, a grower must return to fresh foundation or breeder seed.
How certification works
Certification is carried out by a designated authority, often a national seed certification agency, independent of the seed producer.
1. Eligibility
Only varieties officially released or registered can be certified. Release usually requires DUS testing (the variety must be Distinct, Uniform and Stable, the same criteria used for plant variety protection under the UPOV Convention) and, for many crops, VCU testing (Value for Cultivation and Use: yield and quality in official trials).
2. Field inspection
Inspectors visit the seed crop, usually several times, at the stages when contaminants are easiest to see, such as flowering and before harvest. They check:
- that the source seed is of the right class and documented;
- the previous crop on the field, to avoid volunteer plants of another variety;
- isolation: distance (or time) from other fields of the same species that could cross-pollinate or mix. Self-pollinated crops such as wheat or rice need only a few metres; cross-pollinated crops such as maize, sunflower, onion or brassicas need hundreds of metres or more, larger for foundation than certified seed;
- off-types (plants not true to the variety) and pollen shedders in hybrid seed fields, which must stay below set limits;
- objectionable weeds, whose seeds are hard to clean out, and designated seed-borne diseases.
Fields that fail are rejected or downgraded.
3. Processing, sampling and testing
The harvested seed is cleaned, graded and often treated, then divided into seed lots of a maximum size. An official sampler draws a representative sample by set procedures, and a laboratory tests it, usually following ISTA rules:
- Physical purity: the percentage by weight of pure seed, as opposed to other crop seeds, weed seeds and inert matter.
- Germination: the percentage of seeds that produce normal seedlings under standard conditions in a set number of days.
- Moisture content, which governs storage life.
- Other distinguishable varieties, weed seed counts, and sometimes seed health, vigour or genetic purity by laboratory methods.
Each crop and class has minimum standards, for example a pure-seed percentage often around 98 per cent or more and a germination commonly in the range of 75 to 90 per cent depending on the crop.
4. Labelling and sealing
Lots that pass are labelled with the variety, class, lot number, test results and validity date, and sealed so the bag cannot be opened and refilled without breaking the seal.
5. Post-control
Samples of certified lots are grown in grow-out tests to confirm that the seed was the variety claimed and to check certification work after the fact.
Using seed test results
The quality figures on a label are not just compliance: they decide how much seed to sow.
Pure live seed and sowing rate
A recommendation calls for 100 kg/ha of viable seed of a cereal. The seed lot's label shows 98 per cent physical purity and 85 per cent germination.
Pure live seed (PLS) = purity × germination = 0.98 × 0.85 = 0.833, or 83.3 per cent.
Seed to sow = 100 ⁄ 0.833 = 120 kg/ha. With a cheaper lot at 95 per cent purity and 70 per cent germination, PLS is 0.665 and the rate rises to 150 kg/ha, which may cost more than the better seed.
Planning a seed multiplication chain
A seed programme wants enough certified wheat seed to sow 100,000 ha at 100 kg/ha: 10,000 t. Assume a seed yield of 2 t/ha at every stage, so each hectare of seed crop needs 100 kg of seed and produces 2,000 kg, a multiplication ratio of 1 : 20.
- Certified seed area: 10,000 t ⁄ 2 t/ha = 5,000 ha, needing 5,000 × 0.1 t = 500 t of foundation seed.
- Foundation seed area: 500 ⁄ 2 = 250 ha, needing 250 × 0.1 = 25 t of breeder seed.
- Breeder seed area: 25 ⁄ 2 = 12.5 ha, needing 1.25 t of nucleus or earlier breeder seed.
With high-ratio crops (some vegetables yield hundreds of seeds per seed sown) a few kilograms of breeder seed are enough; with low-ratio crops such as groundnut or potato tubers, the chain needs many more steps or years, which is one reason new varieties of such crops spread slowly.
Seed systems beyond certification
Most of the seed sown in the world, especially by smallholders, is not certified: it is saved on farm or exchanged locally, an informal seed system. Many countries also allow an intermediate class, such as quality declared seed (described by FAO), in which producers take responsibility for quality with lighter official checks. Making good seed of improved varieties reach farmers, the "seed replacement" question, is a major policy topic.
Key points
- Seed classes: nucleus → breeder (pre-basic) → foundation (basic) → registered (some systems) → certified.
- Generations are limited to keep varieties true to type; growers return to higher-class seed periodically.
- Only released varieties (tested for DUS and often VCU) can be certified.
- Certification = field inspection (isolation, off-types, weeds, diseases) + sampling and testing (purity, germination, moisture) + labelling and sealing + post-control.
- OECD tags: basic white, certified blue (C1), red (C2); North American: foundation white, registered purple, certified blue.
- Pure live seed = purity × germination; sowing rate = target ÷ PLS.
What the exams ask
- School-leaving and entrance papers: the classes of seed, who produces each, and the colour of tags in a named scheme.
- Degree and research-fellowship entrances: the stages of certification, isolation for self- and cross-pollinated crops, ISTA testing, DUS and VCU, and the role of the OECD Seed Schemes.
- Seed technology and professional examinations: field standards, seed lot sampling, pure live seed and sowing rate calculations, and planning multiplication chains.
Described in general terms: the kind of examination, not a past paper. Laisha never reproduces exam questions.
Questions people ask
Is certified seed always better than farm-saved seed?
It is guaranteed true to variety and tested for germination and purity, which farm-saved seed is not. For hybrids, saved seed loses yield and uniformity. For self-pollinated varieties, carefully saved and cleaned seed can perform well for a few seasons, but quality is not guaranteed.
Why are cross-pollinated crops harder to certify?
Pollen travels from neighbouring fields by wind or insects, so a seed crop of maize or onion can be contaminated from hundreds of metres away. Larger isolation distances and careful timing are needed.
What is the difference between germination and vigour?
Germination is the share of seeds that produce normal seedlings under ideal laboratory conditions. Vigour describes how well they emerge and grow under real, often stressful, field conditions. Two lots with the same germination can differ greatly in vigour.
Sources
- OECD. OECD Seed Schemes: Rules and Regulations. Organisation for Economic Co-operation and Development, updated annually.
- ISTA. International Rules for Seed Testing. International Seed Testing Association, updated annually.
- FAO. Quality Declared Seed System. FAO Plant Production and Protection Paper 185, 2006.
- UPOV. International Convention for the Protection of New Varieties of Plants, 1991 Act. UPOV.
- Copeland, L. O. and McDonald, M. B. Principles of Seed Science and Technology, 4th edition. Springer, 2001.
More in genetics and plant breeding
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