What is a vigour test?
A vigour test reveals a seed lot’s ability to withstand a variety of different stress factors.
Vigour tests are designed to mimic poor seeding conditions to find out how the seed lot will perform under stress. It’s the exact opposite of a germination test, where seed is grown under optimum conditions.
In a vigour test, the seed is introduced to a stressful environment unfavorable to seedling development. This environment can be cool, cold or warm, or a combination of either high humidity and high temperatures, or heavy moisture at low temperatures.
If the seed lacks vigour, one or more of these created stressors will suppress seedling growth but, if the seed is vigorous, it will withstand one or all of these stressors and grow as if it were on stimulants.
Taken together, vigour and germination test results provide a complete performance profile for a wide range of field conditions and can help guide important seeding decisions, such as when to seed: should you wait for warmer soil temperatures or can this seed survive an earlier planting into cooler soils?
Textbook results for germination and vigour tests are 100% germination and 90% vigour. In reality, we are more likely to see 85% germination and 75% vigour, which completely acceptable.
Remember that the vigour number represents the lowest performance level we would expect to get from the seed lot under stressful field conditions. If seedbed conditions are favorable, then vigour will be closer to germination. Vigour test results factor in field mortality, so it’s important to keep that in mind as you make your seed drill calculations.
What are analysts looking for?
Below are excerpts of two scientific definitions for vigour from the International Seed Testing Association (ISTA) and the Association of Official Seed Analysts (AOSA). All analysts working with vigour are familiar with these two definitions.
ISTA: “Seed vigour is the sum of those properties which determine the potential level of activity and performance of the seed or seed lot during germination and seedling emergence.”
AOSA: “Seed vigour comprises of those seed properties which determine the potential for rapid, uniform emergence and development of normal seedlings under a wide range of field conditions.”
A vigour test must be reproducible and the results must prove to be correlated with a field performance characteristic, such as seedling emergence and environmental stress.
Why is vigour testing important?
Vigour testing is an important component of seed testing because it’s more sensitive test than germination, and becasue loss of vigour may be noted much earlier than loss of germination.
What causes vigour loss?
Vigour loss is due mainly to seed deterioration and aging, which starts as soon as the seed becomes physiologically mature. It’s imperative, therefore, that seed be handled carefully to prevent accelerated reduction in performance through physical damage to cell membranes. This is particularly true of large seeds, such as pulses and legumes, where seed damage is the primary cause of deterioration.
Other associated detrimental factors include:
- enzyme activity in immature and dormant seeds;
- respiration during harvest and storage;
- impaired protein and the use of protein and RNA synthesis during periods of low temperature stress;
- genetic damage;
- accumulation of toxic metabolites.
What can I expect from a vigour test?
These performance characteristics are associated with differences in seed vigour.
- Biochemical processes and reactions during germination, such as enzyme reactions and respiratory activity.
- Rate and uniformity of seed germination and seedling growth.
- Rate and uniformity of seedling emergence and growth in the field.
- Seedling ability to emerge under unfavorable environmental conditions.
Using the appropriate vigour test for the crop kind under analysis will reveal the vigour of the seed.
How do I interpret the results of a vigour test?
A vigour test is usually conducted in conjunction with a germination test because the latter is required before seed can be sold in Canada.
Most producers want to know how their seed will perform at both ends of the spectrum, and these two tests will give them that information.
Naturally, the germination test will almost always have the higher result because the evaluation parameters are more forgiving than those used in the vigour test; so the germination test tells producers how their seed will perform in optimum conditions.
The vigour result will be the lower number because the deliberately applied stress will suppress germination. The vigour test result is likely more consistent with field emergence and tells producers how their seed will perform if it is subjected to stressful field conditions.
Today, vigour testing is very sophisticated and reveals the true quality of the seed. It is one of the most important tools in your box and should be used as a guide to avoid planting into unfavorable conditions.
The bottom line: Early and accurate evaluation of seed quality is essential in the planting and production of a high quality crop. Knowing your overall seed quality will help with important crop input decisions, such as the use of seed treatments, and maximize use of crop inputs, such as herbicides, and ensure a healthy vigorous plant stand.