MORFO's reforestation solution is a multi-stage process, focusing on tropical and subtropical regions. Forest ecosystems are restored using drones specially designed to disperse seedpods.
Our catalog currently contains over 200 species that have been or are being studied. For a species to be selected by the MORFO method, it must meet at least 13 different criteria. One of the mandatory criteria is that the seed produced by the plant in question must be an orthodox seed, i.e. one that goes dormant through dehydration. Indeed, compared with recalcitrant seeds that retain their water, orthodox seeds are easy to store, and can be kept easily and for a long time.
This study, on which Emira Cherif, now Head of R&D Ecosystems at MORFO, worked, proves the effectiveness and longevity of Orthodox seed dormancy. She reports on the planting and germination, in 2008, of 2000-year-old seeds from the historic Judean date palm. Lost for millennia on the shores of the Dead Sea, these seeds are a remarkable model for research into seed longevity, given their exceptional storage potential.
In this article you will learn all about seed dormancy and the different methods of breaking it.
The concept of seed dormancy
When a fruit ripens, the embryo in its seeds stops developing and becomes encapsulated and enveloped. It waits for favorable conditions to germinate and give birth to a new plant, thus completing the life cycle. Occasionally, however, the seed goes dormant, a phenomenon common to around two-thirds of all plants. Dormancy is an evolutionary mechanism that protects the perennity of the species by allowing seeds to remain viable for long periods, germinating sporadically under certain conditions.
Some species have differences in shell or tegument thickness between seeds in the same batch, resulting in an irregular exchange of water and gas with the outside environment, necessary for germination. As a result, plants are not all born at the same time, but in a staggered manner, increasing the chances of survival of certain individuals and the establishment of the species as a whole. This process contributes to ecological succession.
Types of seed dormancy
Seed dormancy mechanisms are linked to the adaptation of species to different environments and ecosystem dynamics. In arid climates, many species become dormant in order to survive until the rainy season and start their development. Some seeds need to be washed by rain to eliminate germination-inhibiting substances, and thus remain dormant until the wetter season. In tropical rainforests, seeds can either germinate immediately, or remain dormant due to obstacles to water, oxygen or light.
Dormancy can be caused by a variety of factors, that can sometimes be combined. We can divide these factors into 5 categories.
- Integumentary dormancy: Occurs when the shell or outer part of the seed or fruit is resistant to the gases and liquids needed for germination. This is the most common form of dormancy. For example, if the shell is impermeable or the fruit is too hard for the seed to germinate.
- Physiological dormancy: Although the embryo is fully formed, the seed remains dormant due to factors linked to physiological processes. There may be a lack of substances necessary for germination, or the presence of germination-inhibiting compounds in the seed or fruit.
- Morphological dormancy: Due to the immaturity of the embryo. The embryo is not fully developed and requires specific conditions to complete its development and germinate.
- Combined dormancy: When several factors combine to prevent germination.
- Slow or delayed germination: Some scientists estimate that some seeds can take from 30 days to 12 months to germinate after sowing, which can be considered a form of dormancy.
Techniques for breaking seed dormancy
In nature, seeds start to grow when conditions are right, either thanks to their internal mechanism or to the environment. For example, some dormant seeds are dispersed after passing through the digestive tract of animals that eat their fruit, preparing them to germinate. Rain can also remove substances that prevent germination. However, waiting for germination to occur naturally can take too long to plant. This is why methods to speed up germination, called "dormancy-breaking methods", are used.
There are different techniques for lifting seed dormancy, depending on the type of dormancy.
- Chemical scarification: seeds are soaked in abrasive substances, such as acid, to remove their outer layer without damaging them.
- Mechanical scarification: the outer layer of the seeds is rubbed or scraped so that they can absorb water and oxygen.
- Immersion in hot water or thermal shock: seeds are immersed in hot water and then in cold water to encourage germination.
- Cold water immersion: Seeds are left to soak in room-temperature water for a day to facilitate germination.
- Immersion in running water: Seeds are kept immersed in running water to eliminate substances that prevent germination.
- Cold stratification: Seeds are kept in a cold environment to stimulate growth, then sown.
- Alternating temperatures: Alternate hot and cold temperatures to encourage germination.
- Combined dormancy break: Sometimes, some seeds need more than one method to germinate.
The information in this article is taken from the book "Forest Seeds: A Guide to Germinating 100 Native Species" (2012), written by Fátima C. M. Piña-Rodrigues (Professor and researcher in the Forest Engineering course at the Federal University of São Carlos, Sorocaba campus) and Roberto Bretzel Martins (Agricultural Engineer at Instituto Refloresta).
Image source: MORFO