Seed-health tests: Germination, viability and vigour in cereals and oilseeds
A crop’s development starts before growth stage 0 – with the production of seed on the parent plant. It is important to understand seed-lot health because it influences approaches to storage and drilling. Find out about the factors that affect seed health and the laboratory tests available.
Factors related to poor seed health
- Inclement weather, especially around harvest
- Presence of disease
- Seed dormancy
- Sprouted grain
- Older seed
- Mechanical or chemical damage
- Low moisture/drying
- Excessive heat (e.g. drying grain at too high a temperature)
Conducted under controlled conditions*, viability, germination and vigour tests indicate the potential health of a seed sample. If the seed is representative of the seed batch, then test results can be used, for example, to adapt seed-drilling rates. However, be aware that performance in tests is usually equal to or, more likely, better than how the seed batch will perform in the field.
*Note: The International Seed Testing Association (ISTA) specifies seed testing requirements and accredits and audits testing laboratories. Seed testing laboratories must meet ISO Guide 25 and EN45001 standards.
A standard germination test – which takes around 7–10 days – shows the percentage of seeds that germinate in a representative seed sample. Conducted under controlled (optimum) conditions, it indicates the maximum seed germination potential.
Diagnostic germination tests provide further information on the amount of viable (normal), abnormal and dead seed. Results are given as a percentage, including damage relating to heat, chemical, disease, mechanical, sprouting and dormant types. Some tests also measure the potential to produce healthy seedlings (i.e. beyond germination potential).
Do not use seed if the germination rate is below 78%.
Seed viability testing is rapid and particularly useful when time is limited. The chemical tetrazolium (TZ) stains living seed tissue to indicate germination potential. A basic/standard tetrazolium (vitascope) test reports the percentage of viable seeds. However, assessment of staining patterns (by trained analysts) can also reveal stress effects, such as heat stress and mechanical damage, alongside seed sprouting. TZ tests do not detect seed abnormalities or other factors that affect germination, including seedborne disease, chemical damage or dormancy.
Vigour tests estimate seed performance under unfavourable conditions. It often provides a better indication of potential performance under field conditions. Such tests aid the matching of seed lots to seedbeds, as well as the suitability for seed storage.
Seed viability and vigour tests are often combined with the percentage of viable seed to produce three seed-vigour categories – ‘high’, ‘medium’ and ‘low’.
For certified seed sources, there are minimum standards for varietal and species purity and germination.