Pea Quality Testing
Germination testing is one method for evaluating seed lots for quality. Germination addresses the seed’s ability to develop into a normal, healthy plant under favourable field conditions. However, this testing can be misleading because seed may germinate well in the lab due to optimum conditions being present or to the fact that the seed has every opportunity to develop into a normal healthy seedling.
Vigour testing, another method, assesses the seed’s potential to withstand unfavourable field conditions by assessing certain factors that influence seed quality. While vigour results represent the lowest germination obtained from the lot, germination testing represents the highest result. Actual field germination would normally fall between the two.
Germination and vigour are influenced by the physiological well-being and anatomical completeness of the seed plus its interaction with a wide range of environmental conditions. Seed vigour is affected by:
- genetic constitution
- seed size and weight
- mechanical integrity and soundness
- stage of maturity
- climatic conditions
In years where unfavourable weather conditions prevail, it is best to combine a vigour test with a germination test to determine seed quality and performance more accurately. Be sure germination results include adequate categorization of the seedling defects and the seedling’s ability to survive adverse conditions.
It’s impossible to predict post-seeding conditions with a vigour test, so seed is placed under a variety of stressful conditions, simulating climatic conditions as closely as possible, including:
- cold temperatures
- wet conditions
- seed soaking
- accelerated aging
Under these conditions, the seed must demonstrate the ability to germinate into a vigorous seedling.
Pea vigour is measured by the Electrical Conductivity Test to assess mechanical damage and evaluate seed lots that remain vigorous during storage. Testing for vigour is an important tool if it is suspected that seed has sustained some injury or that the soil environment will impose stress on the seed. (Research has established a correlation between the Electrical Conductivity Test and actual field results.)
- pea is very susceptible to mechanical injury, such as cracking and chipping, either at harvest or during processing, especially if the moisture level is below 14 per cent
- mechanical injury, such as small seed coat cracks, results in rapid water intake that leads to dead seed cells – this dead tissue then becomes a source of food for invading pathogens
- vigour grades may be used as parameters for sowing times as well as assessing damage:
- 0-20 µs high vigour: little or no mechanical damage – suitable for early sowing
- 20-30 µs medium vigour: some mechanical damage – some seed bed losses may occur in adverse weather conditions but may be used for later drilling in more favourable conditions
- 30-40 µs low vigour: moderate to high mechanical damage – not suitable for early sowing and may fail in cold wet conditions
- 40 µs very low vigour: severe mechanical damage – not suitable for sowing at all
- vigour tests must be combined with germination tests to predict field performance
- the seed may also require 1000 seed weight and disease tests to completely assess the seed’s total quality