– integumentary or exogenous numbness
a) Acid scarification
The seeds are immersed in sulfuric acid for a certain time, which varies according to the species, at a temperature between 19ºC and 25ºC, then washed in running water and placed to germinate.
b) Immersion in water
Immersion in hot water: Immersion in hot water is an efficient way to overcome the seed dormancy of some forest species. The water is heated to an initial species-varying temperature where the seeds are immersed and remain for a varying period of time according to each species;
Immersion in cold water: seeds of some species have difficulties to germinate without being dormant. Simply soaking the seeds in water at room temperature (25ºC) for 24 hours eliminates the problem, which usually results from long storage periods, which causes the seeds to overdry, preventing them from absorbing water and starting the process. germinal process.
c) Mechanical scarification
This method has been shown to be very effective in overcoming dormancy of some forest species, especially legumes. The procedure basically consists of subjecting the seeds to abrasion, through rotating cylinders, lined internally with sandpaper which will wear down the integument, providing conditions for it to absorb water and start the germination process;
In order to obtain positive results in the use of the process, some precautions are necessary, such as the exposure time of the seeds to scarification and the purity of the lot, since seeds with impurities compromise the efficiency of the treatment.
Embryonic or endogenous numbness
a) Cold stratification The seeds of some forest species have immature embryos, which do not germinate under favorable environmental conditions, requiring stratification to complete their development. For stratification, the medium in which the seeds will be placed should have good moisture retention and be free of fungi. Normally well-washed sand with grains around 2.0 mm in diameter (average) is used to facilitate further separation of seeds by sieving.
The container in which the medium will be placed should allow good drainage avoiding the accumulation of water at the bottom which causes the seeds to rot.
The temperature required for cold stratification is between 2oC and 4oC, which can be obtained in a refrigerator or cold room. The seeds are placed between two 5 cm thick layers of sand. The stratification period varies from 15 days for some species to 6 months for others. Once the stratification period is over, the seeds should be sown immediately, as if they are dried they can be induced to secondary dormancy.
b) Hot and cold stratification
Fruit ripening of some species occurs in late summer and early fall, with lower ambient temperatures. The hot and cold stratification aims to reproduce the environmental conditions that occurred during the fruit ripening.
The procedure is exactly the same as described for cold stratification, changing high temperatures (25ºC for 16 hours and 15ºC for 8 hours) for one period, and low temperatures (2ºC to 4ºC) for another period.
Some species have seeds with integumentary and embryonic dormancy. In these cases, the seed is initially submitted to the treatment to overcome the integumentary dormancy, and then to overcome the embryonic dormancy. In some cases, only cold stratification is sufficient to overcome both.