1.4 Flashcards
Germination tests
Percentage germination capacity
Seeds are submitted for testing at accredited labs to measure the number of healthy, well developed seedlings in a sample.
Seeds are germinated under optimum conditions, appropriate dormancy breaking measures are applied.
Results are given as germination percentage
More sophisticated reporting can include percentage of dead/abnormal seedlings and percentage and type of damage to seed
Germination percentage of laboratory grown seeds will generally be higher than field emergence because of tilth, prevailing weather and disease factors.
Tetrazolium test
Tetrazolium is a chemical that reacts with living cells and stains them red so that living cells can be distinguished from non- living tissue visibly.
Seeds are cut, stained in tetrazolium and visually assessed.
Staining patterns can be interpreted to indicate seed vigour.
Results reported as percentage of viable seeds with sub categories for high/med/low seed vigour.
Cutting test
Simple guide to seed viability.
Cut along side of each seed to view embryo, if embryo is fresh, the seed is considered viable.
Results reported as percentage of viable seed.
Float test
Basis of test is that dense, viable seeds sink when placed in water.
Seeds that sink are then dried and counted.
Result report as percentage of viable seeds (seeds that sank in water)compared to seeds that floated.
Only suitable for fresh seeds as most dried seed will float, even if viable.
Not suitable for plants that disperse their seed in water. Many species have seeds that normally float eg. Rosa spp.
Reasons for Priming
Regulates process of seed germination by managing temperature and seed’s water content.
Priming Allium porrum
Phase 1
Seed placed in suitable warm environment with regulated moisture
Phase 2
Given these conditions the seed is activated, emerging from dormancy to start germination process. Roots and hypocotyl begin to develop and emerge.
This phase is interrupted; seed is dried out before root emerges.
Phase 3
When conditions are correct seed is sown, germination is reactivated, resulting in faster germination.
Advantages of seed priming
Seedlings emerge faster and in a more uniform fashion. Yields are likely to be higher and more reliable.
Fluid sowing
Seed example
Pastinaca sativa
Fluid sowing involves?
Seed germination in optimum environmental conditions.
Mixing selected pre-germinated seeds in a gel-type medium to protect and suspend seed for uniform sowing.
Using a specialist fluid drill seeder (or modified plastic bag) into growing medium.
Advantages of pre germination
Early, concentrated seedling emergence.
Better stand, more uniform growth, crop maturity and harvest.
Especially advantageous in cold soils, emergence is usually significantly earlier.
Advantages of carrier gel.
Protects seed.
Separates seed for more even distribution when sown.
May retain moisture around seed when sown.
Additives such as plant nutrients, growth stimulants and pesticides maybe added.
Example of seed that may have a pesticide treatment.
Zea mays
Treatment of Zea mays
Dried, sorted and graded.
Treated with polymer together with appropriate fungicide eg.thiram
Seed dressings
Advantages
Small amount of chemicals needed.
Seed coloured to deter birds.
Higher seed vigour and germination rates.
Improvements in shoot and root length.
Coating/pelleting
Prills
Examples of seed
Bergonia semperflorens Cultorum Group
