Seed Dormancy: Causes, Types, Methods, Methods and Protocols

Definition Of Seed Dormancy

Seed dormancy is a state in which seeds do not germinate even if placed in suitable environmental conditions. This is, therefore, a key determinant of plant survival, allowing seeds to tolerate unfavourable conditions and germinate only when conditions are more likely to support seedling establishment. Dormancy prevents seeds from sprouting prematurely, under which they have poor survival rates, to align germination with favourable environmental cues in enhancing the possibility of successful plant development.

Types Of Seed Dormancy

The types of seed dormancy are discussed below-

Innate Dormancy

Intrinsic to the seed itself, innate dormancy will not germinate when conditions are favourable because of factors within the seed. It often results from the physiological state of the seed or hard seed coat and is observed in many species, including black locusts. This type of dormancy makes sure that seeds germinate under the most optimal circumstances for survival and reproduction only.

Induced Dormancy

Induced dormancy is a state in which seeds go dormant as an effect of external environmental conditions, usually temperature or the presence of water. In this regard, the dormancy is short-term and may be observed in certain species, such as the tomato—Solanum lycopersicum—that may exhibit dormancy due to stress or unsuitable conditions to prevent untimely germination.

Enforced Dormancy

Enforced dormancy occurs with seed germination forbidding factors, which are usually mechanical or severe environmental. For example, enforced dormancy occurs in the seeds of the fireweed (Epilobium angustifolium) by extreme heat from fires, required to trigger its germination naturally.

Causes Of Seed Dormancy

The causes are described below-

Physical Dormancy

Physical dormancy occurs when the seed coat acts as a physical barrier to water and gas reaching the embryo. Examples include the legume family, including peanuts (Arachis hypogaea), where the impermeable seed coat is the major factor in dormancy. Scarification is one such method for physically altering the seed coat, often employed to overcome this type of dormancy.

Physiological Dormancy

Physiological dormancy is induced by factors in the seed itself, such as hormone imbalance or other stages of development of the seed. Abscisic acid, ABA, and Gibberellins, GA, are the two primary hormones affecting this kind of dormancy. For instance, Lettuce, Lactuca sativa seed, undergoes physiological dormancy that is controlled by the mentioned hormones, through inducing certain environmental factors, breaking the dormancy.

Morphological Dormancy

One of the types of morphological dormancy includes underdeveloped embryos that need further development before germination. For instance, the coconut (Cocos nucifera) requires the embryo to take some time and develop enough in the seed. In most cases, this kind of dormancy calls for certain conditions regarding development to be broken.

Combination Dormancy

Combination dormancy refers to the combination of physical, physiological, and morphological factors that inhibit germination. For example, in the common buckwheat (Fagopyrum esculentum) there may be a hard seed coat with physiological dormancy, and more than one treatment may thus be required to achieve the germination of such seed.

Mechanisms of Overcoming Seed Dormancy

The mechanism is described below-

Scarification

Scarification is a process of mechanically or chemically weakening the seed coat to allow for water absorption. Mechanical scarification includes abrasion and nicking, while chemical scarification involves the action of acids in weakening the seed coat. The practical applications are in agriculture, where scarification improves the germination rate for seeds with hard coats.

Stratification

It's the process of subjecting seeds to cold or warm temperatures to break dormancy by imitation of natural seasonal conditions. Cold stratification, like storing seed lots at low temperatures, is used for species like maple (Acer spp.), while warm stratification refers to the process of exposing the seeds to higher temperatures. Such methods are fundamental in manipulating seed germination in controlled environments.

Light And Temperature Treatments

Light and temperature treatments are such that the exposure of seeds to specific light conditions and temperature ranges triggers germination. In other words, some seeds have to be exposed either to light or to a change in temperature to break dormancy. For instance, practical applications include the use of growth chambers where optimal conditions for seed germination can be provided.

Hormonal Treatments

Hormonal treatments involve the use of plant hormones, including gibberellins, to break physiological dormancy, which stimulates the growth and development of seeds. The application of gibberellins to seeds aims at breaking dormancy to enhance germination. Practical applications of hormonal treatments are utilised in horticulture and agriculture to ensure efficient propagation of seeds.

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