Germination and sleep breaking in seeds
Seed dormancy is a process characterized by delayed germination, when seeds even under favorable conditions (humidity, temperature, light and oxygen) do not germinate. About two thirds of the tree species have some kind of dormancy, a phenomenon that is common in temperate species (cold regions), as well as in tropical and subtropical plants (warm regions). The phenomenon of seed dormancy comes from an adaptation of the species to the environmental conditions that it reproduces, which may be of high or low humidity, direct light incidence, low temperature, etc. It is therefore a resource used by plants to germinate in the most favorable season for their development, seeking through this the perpetuation of the species (guarantee that some individuals settle) or colonization of new areas. Therefore, when faced with this phenomenon there is a need to know how species overcome the dormancy state in natural conditions, so that through it we can look for alternatives for a rapid and homogeneous germination, this process is called SLEEP BREAK.
The seed dormancy phenomenon can be divided into primary and secondary dormancy:
- Primary dormancy is the one that already manifests when the seed completes its development, that is, when we harvest the seeds they already have dormancy.
- Secondary dormancy is when mature seeds do not have dormancy, ie they germinate normally, but when exposed to unfavorable environmental factors are induced to the dormancy state.
Main causes of seed dormancy:
Impermeable integument: seeds with these characteristics are called hard shell seeds, because they cannot absorb water and / or oxygen.
Physiologically immature or rudimentary embryo: in the process of seed maturity the embryo is not fully formed and favorable conditions need to be developed for its development.
Inhibiting substances: These are substances in seeds that can prevent their germination.
Dormant Embryo: The embryo itself is in a state of dormancy, usually in this case dormancy is overcome with thermal shock or light.
Combination of causes: Seeds do not necessarily have only one type of dormancy, but there may be more than one cause of dormancy in the same species.
Seed dormancy breaking processes:
Chemical Scarification: It is a chemical method, usually made with acids (sulfuric, hydrochloric etc.), which allows the seeds to perform exchanges with the medium, water and / or gases.
Mechanical scarification: is the abrasion of seeds on a rough surface (sandpaper, rough floor etc). It is used to facilitate the absorption of water by the seed.
Stratification: consists of a humid treatment at low temperature, assisting the seeds in embryo maturation, gas exchange and water soaking.
Temperature shock: It is made with alternating temperatures varying in approximately 20ºC, in periods of 8 to 12 hours.
Hot water: It is used in seeds that have an integument impermeability and consists of immersion of the seeds in water at a temperature of 76 to 100ºC, with a specific treatment time for each species.