Certification Of Seed
To be certified, all seed varieties have to be registered. That means it has to be listed on one of the Danish, EU or OECD Plant variety catalogues. However, to be sold in the EU, the variety must be listed on the Danish or EU Catalogues.
Seed only gets a listing on a plant variety catalogue having first undergone comprehensive technical analysis in the laboratory.
- Standards must be met for:
- Fitness for purpose, or agricultural value (if applicable) based on:- Quality characteristics, response to the environment, resistance to harmful organisms and yield.
The standard of certification depends on the generation or category of a seed. Firstly, a small portion of breeder material is selected for reproduction. This material is not nec-essarily produced under official control of a certification authority, although all follow-ing generations must be. Requirements for first generation seed, called pre-basic and basic seed, are higher than for later generations of certified seeds, referred to as C1 and C2. These later generations are the basis on which pure, uniform, certified seeds of the highest quality are produced.
Uniformity of the variety of seed is kept stable by keeping a ‘standard sample’ of every variety. The standard is a living example of how each variety should perform. Compar-ing later certified samples of seed to the standard sample is known as post control. Samples of certified seed are sown next to the standard sample. By comparing the two throughout the growing process, verification can be provided that the certified samples perform exactly like the standard sample as a guarantee of uniformity.
All fields used for seed breeding have to be inspected by official or authorised field in-spectors. As stated earlier, the inspectors apply the most demanding standards at this stage. Rigorous checks are made for:-
- Purity of species
- Purity of variety
- Presence of wild oats and weeds
- Proximity to cross pollination
All seed that passes the field inspections is then harvested and cleaned. The seed lot is then sealed and labelled by an authorised seed sampler, who also takes samples for seed quality tests.
All seed testing takes place at ISTA laboratories, where they send their results direct to the regulating authorities. If the sample fails to meet EU standards, the seed lot cannot be certified and the labels will be removed.
Seed Quality Tests
Seed tests in the laboratory aim to provide accurate guidance as opposed to absolute answers or predictions. Viability, germination and vigour tests all produce results that are usually greater than, or at best equal to, how the seed will actually perform in the field – as in the lab, all test parameters are at an optimum.
The test results can however, help to maximise the understanding of the planting value or storage potential of the seed. Calculation of sowing rates can be achieved by having both a germination test and a thousand grain weight test. If sowing at the wrong time of year is required, a vigour test may be useful. If time is of the essence, or heat damage is suspected, the tetrazolium (viability) test is useful in this situation.
Seed Germination Test
This test measures the number of healthy seedlings under optimum laboratory conditions, not just if a root has emerged from the seed. For this reason, a germination test will take at least a week for cereals and up to 4 weeks for grasses. In the field, many factors such as temperature, water availability, oxygen, light, etc can all affect the seeds capability of producing healthy seedlings. For this reason, a germination test is more a measure of potential growing ability in perfect conditions rather than a measure of absolute accuracy of seedling emergence.
A standard lab test is based on 200 seeds. Dormancy breaking measures are applied. Distinctions are made between normally and abnormally germinated seed and also dead seed. Tests can be quite lengthy in some species. Results are reported as a % germination and also a % of dormant seed (where relevant) at a relatively low cost. Sowing rate can be calculated when this test is undertaken along with a 1000 grain weight test.
Diagnostic Germination Test
A more expensive diagnostic test, also based on 200 seeds is available which gives results reported as % germination, % dead seed, % abnormal seedlings and % damaged seed (heat damage, disease, etc). Again, when performed alongside a 1000 grain weight test, sowing rates can be calculated in accordance. A diagnostic test will note quality problems for the sample in detail. 400 seed samples can also be tested, which will improve the accuracy of the test slightly at more cost.
1000 Grain Weight
This is exactly as it sounds. Once the sample has been screened to simulate what the seed lot would be like once cleaned and processed. 1000 seeds are then weighed in grams and this result can be used to accurately calculate sowing rates when used alongside a germination test result.
The formula used is as follows:-
Seed rate (kg/ha) = (target plants/m2 x 1000 grain weight in grams x 100) /(Germination % x Potential Field Establishment %)
The potential field establishment % chosen for the calculation depends on the condition of the seedbed. As a guide, rates of 80% are generally.
Seed Viability (Tetrazolium) Test
If a germination test (which takes a week or longer) is too long and time is of the essence, a viability test represents the best alternative. This test uses a chemical called tetrazolium which determines which tissues are alive inside the seed therefore showing the potential to germinate. Tetrazolium is a colourless chemical that reacts with living cells and stains them red. Living tissue in seed embryos can then be distinguished from non-living tissue. It will not detect seed abnormalities, it only highlights which tissues are alive or viable. Occasionally, a tetrazolium test and a germination test will differ significantly.
This is because any factor that affects the seed as it actually geminates is not detected by tetrazolium tests. Factors include chemical damage, dormancy and disease. Tetrazolium tests are very good for detecting heat-damaged seeds as these show a unique staining pattern that can be interpreted by a trained analyst to determine germination potential. The deterioration of heat-damaged seed can occur over a period of time. If the seed sample is tested for germination immediately after the point of damage, the seed may not have fully deteriorated and the germination potential may be over-estimated. With a tetrazolium test, it is possible to detect the very earliest signs of heat damage.
Seed Vigour Tests
Considered the closest measure of potential field performance. Seedlings that have been classified as ‘normal’ by a germination test, will in fact differ in their ability to perform well under a wide range of environmental conditions. Vigour testing aims to measure the ability of the seed to perform well under unfavourable conditions. Vigour testing is used for two main reasons:- To assess seed lots for storage suitability, To as-sess seed lots for planting value (Eg. To promote synchronous emergence and maximising performance under sub-optimal seedbed conditions.)
Common Problems With Seed Quality
• Wheat & Barley tend to show good germination, but seedling diseases can affect germination tests, especially in wet years. Mechanical damage can be problematic, especially in dry years.
• Large seeds, such as Field Beans, are susceptible to mechanical damage, again, especially in dry years.
• Oilseed Rape quality can be problematic for a number of reasons, such as heat damage, mechanical damage, chemical damage and occasionally disease.
• All seed is at risk of heat damage, due to excessively hot weather at harvest, or poor artificial drying techniques.
• Germination of seed that has been overwintered is likely to deteriorate, especially if storage conditions are less than ideal.
• Seed stored in areas of previous chemical activity can have an effect on the germination of the seed that has come into contact with it. Seeds are likely to be alive, but will germinate abnormally and are less likely to produce healthy plants in the field, especially in less than optimum conditions. Chemical damage can be identified with a germination test, but tetrazolium tests cannot do this and are likely to over-estimate potential field emergence.