For every farmer when you have seeds that take too long to germinate, there are some methods of overcoming seed dormancy for planting. But you will first need to know what dormancy really mean before you take any step.
Seed dormancy is the inability of seeds to germinate under the required conditions for germination. It may be due to physical or physiological conditions of a viable seed. Seed dormancy affects crop establishment, growth and harvest and uniformity of seed development and maturation. The un-germinated dormant seed that remain in the soil will produce unwanted plants or volunteer plants in future.
In some crops, dormancy may be desirable when it prevents pre-harvest and post-harvest sprouting or germination during wet weather thereby maintaining seed quality or quality of planting material. Dormancy also protects the entire crop against total loss during drought.
Causes of seed dormancy
Certain factors may cause seed dormancy too and this could be due to;
- Immature embryo. E.g. lettuce
- Seed coat impermeable to water. E.g. okra, mungbean and amaranthus
- Seed coat impermeable to gas. E.g. cucumber, lettuce and beets
- Presence of germination inhibitors. E.g. phenolic compounds such as abscissic acid (ABA) and caffeic acid. These acids can be found in beets.
- Physiological immaturity (absence of some growth substances or excess amount of inhibitors than promoters)
- Light sensitivity
- Mechanical restriction to seedling growth by seed coat. E.g. amaranthus and corchorus.
Examples of growth inhibitors include; cyanide, ammonia compounds, mustard oil, alkaloids (e.g. caffeic acid and cocaine), organic acids or compounds, unsaturated lactose, phenolic compounds, synthetic growth retarders and essential oils.
Overcoming seed dormancy
- Use of suitable temperature regime:
Use the correct optimum temperature and alternating temperatures. E.g. 8hrs at 300C and 16hrs at 200C. Pre-chilling moist seeds at 5-80C.
Modification of seed coat:
It can be modified by cutting e.g. mango, milling to remove apparent appendages, scarification by abrasion or use of chemicals, e.g. acetone, alcohol, hydrogen peroxide, sulfuric acid, hydrochloric acid and sodium hydroxide. The use of chemicals requires that correct dosage per species is applied to avoid injury.
- Removal or neutralization of growth inhibitors
Chemical treatment of the seed;
E.g. potassium nitrate, hydrogen peroxide, plant growth regulators (PGR) such as GA3 (Gibberellins), Auxins, cytokinins and ethylene.