20/20 Seed Labs offers the most widely used tests for vigour:
- Cold Germination
- Accelerated Aging
- Controlled Deterioration
- Electrical Conductivity
- Seedling Growth Rate
Which one is used depends on a few factors, including what crop is being tested and what particular information you’re seeking.
Why do a Vigour Test?
Test results are mainly used as a quality assurance tool to rank seed lots for field and/or storage potential. Vigour tests can help predict:
- Rate and uniformity of seed germination and seedling growth
- Field performance, including extent, rate and uniformity of seedling emergence
- Performance after storage and transport, particularly the retention of germination capacity
Vigour testing is not a substitution for germination testing. Both are tests of seed viability, but they measure different sides of that coin.
A germination test tells you what percentage of your seed lot will start to grow under ideal conditions. A vigour test, on the other hand, is an indicator of how that seed will perform under less than perfect environmental conditions, taking into account the seeds’ genetic constitution, size, physiological maturity, and any effects related to production and storage the previous year.
How is a Vigour Test Done?
Cold Germination Test
Cold germination tests assess the seedlings’ ability to withstand the low temperature stress (5 C to 7 C) typically experienced in early spring planting.
This test helps you better assess early season risk. In other words, if test results show the seed is susceptible to cold stress, you can adjust your seeding dates accordingly.
The cold germination test results are reported in two categories:
- Emergence is the percentage of seedlings that developed normally and rapidly under cold conditions.
- Vigour is the percentage of seedlings that have reached the minimum criteria to be considered high vigour.
The benchmark for a high vigour seed lot is 80% emergence and 60% vigour. Expected field performance falls between the vigour and emergence values under a wide variety of field conditions, and is significantly better when field conditions are ideal.
Accelerated Aging Test
This test predicts storage and field planting potential.
High humidity and high temperature stress is imposed on the seed, which is incubated for a period of time under these conditions, then transferred to a growth chamber to assess germination potential.
Seed lots that withstand these conditions, while maintaining a germination rate of 90% or above, are considered high vigour.
Controlled Deterioration Test
Also used to predict storage and field planting potential, the controlled deterioration test is similar to the accelerated aging test in that it imposes a stress factor on the seed.
In this case, seeds are brought to 20% moisture and held at this value constantly during the deterioration period. Again, the seeds are transferred to the growth chamber and the germination potential assessed.
Electrical Conductivity Test
This test is used to determine when seed should be planted, and applies mainly to pulses and large seeded legumes, but can also be used on canola.
The test evaluates the integrity of cell membranes and their ability to repair themselves during the “soak period.” Seed is soaked in de-ionized water for a short period of time, allowing sugars, starches and amino acids to leach from the seed.
The higher the conductivity value of the soak water, the lower the vigour. Seed with high E.C. values should be used with caution.
Seedling Growth Rate Test
This test is closely related to the standard germination test and is useful to figure out field planting potential under optimal or near ideal conditions.
Seeds are planted under optimum conditions and are allowed to grow for an extended period of time, usually several days past the typical germination period. The seedlings are evaluated by their growth characteristics, such as stem length, leaf development or root branching.
The measurements determining strong or poor vigour are highly dependant on the particular cultivar being tested. Some varieties of lentil, for example, may naturally be longer than others. It means our seed analysts have to get very familiar with a lot of different growth characteristics!