Seed Technology
Seed Technology - This domain tests seed structure, germination, viability, vigour, dormancy, purity and seed testing.
Core rules
- Germination percentage = (normal seedlings ÷ total seeds tested) × 100, counted under ISTA rules.
- Viability is the ability to germinate; vigour is the ability to emerge and perform under field stress. A lot can have high viability but low vigour.
- Purity percentage = (pure seed weight ÷ total sample weight) × 100.
- Pure live seed (PLS) = purity × germination, expressed as a fraction.
- Dormancy may be overcome by scarification, stratification, soaking or growth regulators, depending on the cause.
- Seed moisture is measured on a wet basis; safe storage moisture is about 12–14% for cereals.
Worked example
A lot has 98% purity and 90% germination. PLS = 0.98 × 0.90 = 0.882, i.e. 88.2%. If the recommended seed rate is 100 kg/ha of PLS, the bulk seed needed is 100 ÷ 0.882 = 113.4 kg/ha. Reasoning: lower purity or germination means more bulk seed must be sown to achieve the same plant stand.
Traps
- Germination is not the same as viability; tetrazolium staining tests viability without waiting for seedlings.
- Do not calculate PLS by adding purity and germination.
- Hard seeds may be viable but fail to germinate in the standard test.
- Purity is a weight ratio, not a count ratio.
- Seed vigour testing is not the same as the standard germination test.