Seed dormancy its alleviation and importance in Agriculture

Introduction

Seed may require proper base/substratum for their germination, when we provide all essentials , adequate water, temperature and air; without the proper base, seeds may be not germinated. Therefore, proper base/substratum should be included under the essentiality for germination and dormancy in seed may be also due to lacking of proper base/substratum. According to Wareing (1965) the term dormancy will be used in the sense where the viable Seed of a given species falls to germinate under conditions of moisture, temperature and oxygen supply which are normally favorable for the later stages of germination and growth of that species. A common misconception of seed dormancy is that it is merely a resting state in the absence of suitable germination condition. This state is often called Quiescence. However, true dormancy is defined as a state in which seeds are prevented from germinating even under environmental conditions normally favorable for germination.

Its Type

Primary dormancy:

May occurs due to chemicals/ anatomical features of seed.
Primary dormancy prevents germination on the mother plant and usually also for some time
After shedding and harvesting. Two types of primary dormancy;

Exogenous/Enforced/relative dormancy:

It is a condition in which the essential germination components which is water, light andtemperature) are not available to seed and thus fails to germinate. This types of dormancy are generally related to physical properties of seed coat.

Endogenous dormancy /Innate/ True Dormancy:

It is the most prevalent dormancy found in seeds and is due to inherent properties of seeds The seed may possess some excess inhibitors that must be removed or reduced prior to germination. The physiological changes such as rudimentary embryo maturation, response to growth regulators, changes in temperature, exposure to light etc., will relieve endogenous dormancy in seed.

Secondary dormancy:

May occurs due to unfavourable environmental conditions.
Eg.: Exposure of dry barley seed to temperature of 50-90 0C
Seven days’ storage of winter barley at high moisture content at 20 0C
Exogenous Dormancy: Dormancy is due to some features of the seed located outside the embryo.
Impermeability of seed coat to water: due to seed coat structure, which is hard enough to restrict the entry of moisture into the seeds, thereby preventing seed germination. Eg, .Malvaceae, Fabaceae, Alliacea
Impermeability of seed coat to gases; is related to the insufficient intake of oxygen by seeds due to impermeability of seed structure enclosing embryo. Eg.Poaceae, fruit crops & forest crops
Mechanical resistances of seed coat: growth of embryo is checked due to extremely hard seed/fruit structure such as seed coat, endosperm per carp etc., eg. Acacia species.

Inhibitors present in seed coat/endosperm: biochemical substances present in seed coat or endosperm block the germination of embryo.

Eg:- Iris app- inhibitors present in the endosperm, Barley- Aflotoxin

Endogenous dormancy:

The reason for dormancy is present within the embryo

Incomplete embryo development: due to an incomplete development of the embryo. In such cases, germination does not occur until the embryos develop to their normal size. Ex: Palmaceae, Amgnoliaceae

Inhibitors present within the embryo: Dormancy arises from metabolic blocks produced by biochemical substances called inhibitors present within the embryo. In such cases can commence only when these inhibitors are leached out of the embryo eg: Xanthium, Fraximus

Combined Dormancy:

dormancy is produced by a combination of two or more factors which act in Complementary fashion. Eg.: Fraximus

Methods of breaking dormancy

Natural breaking of dormancy: in nature dormancy terminates when embryo gets suitable environment such as adequate moisture, aeration and temperature. The impermeable seed coat present in many species became permeable due to the rupturing of softening action of natural agents like microorganism, high or low temperature, humidity ,fiber and abrasion due to wind or digestive tracts of birds and animals which feed on these seeds. Eg: Rhizoctonia damages seed coat

Treatments to break Dormancy: the various treatments for overcoming dormancy may be divided into the following three groups

Seed coat treatments: These treatments aim at making hard seed coat permeable to water or gases either cracking or softening them. The process is usually referred as scarification. These treatments are either physical or chemical in nature.

Scarification

1. Acid scarification: treating seeds with concentrated acids like sulphuric acid, Hydrochloric acid etc,
2. Thermal scarification: the seeds are treated with different temperatures and gases.
3. Mechanical scarification: The seed coat is damaged using mechanical means which is

Embryo treatments

• Exposing seeds to light
• Pressure treatment
• Infra-red radiation treatment
• Magnetic treatment

Significance of dormancy in Agriculture

Advantages

Disadvantages

Writer: Kalpana Poudel (Student, Bsc Ag 4th Sem, Paklihawa Campus)