Seed Dormancy.pptx

Seed Dormancy.pptx

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  NAME : YASIRAHMAD C.NO : 64 SEMESTER : 2nd DEPARTMENT : AGRONOMY ASSIGMENT NO : 06 DEGREE : M.SC ( AGRONOMY) SUBMITTED TO : PROF. DR. INAMULLAH
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  Seed dormancy • Seed dormancyrefers to a condition in which a seed fails to germinate under favorable environmental conditions. In other words, it is a period of arrested growth and development of a seed even when all the necessary conditions for germination are present. Seed dormancy is an adaptive mechanism that allows seeds to remain viable and capable of germination for extended periods, ensuring their survival in unfavorable conditions.
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  Breaking seed Dormancy: •To break primary dormancy and promote germination in dormant seeds, specific treatments or conditions can be applied. Here are some common methods used to break primary dormancy:
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  1. Stratification: • Someseeds with primary dormancy require a period of cold stratification. This involves subjecting the seeds to a cold and moist environment for a specific duration, simulating winter conditions. Cold stratification helps overcome the inhibitory effects of ABA, allowing the embryo to complete its development and germinate when favorable conditions return.
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  2. Scarification: • Mechanicalor chemical scarification techniques can be employed to break primary dormancy. By physically scratching or chemically treating the seed coat, the barriers that prevent water and gases from entering the seed can be weakened or removed. This allows for water imbibition, rehydration of the embryo, and subsequent germination.
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  3. Moisture and Temperature Manipulation: •Adjusting the moisture and temperature conditions can also influence the breaking of primary dormancy. Seeds may require specific levels of moisture or temperature for dormancy release and germination. Adequate moisture and suitable temperature conditions activate physiological processes within the seed that lead to the breakdown of dormancy and the initiation of germination.
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  4. Light Exposure: • Someseeds with primary dormancy require exposure to light to break dormancy. Light acts as a signal to stimulate germination. Seeds that have a light requirement for germination will not germinate when buried too deep in the soil but will only germinate when placed near or on the soil surface where they can receive sufficient light.
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  TYPES OF DORMANCY 1. PhysicalDormancy (Seed Coat Dormancy): • Also known as hard seed coat dormancy, this type of dormancy is caused by a hard or impermeable seed coat that prevents water and gases from entering the seed. The seed coat acts as a physical barrier, protecting the embryo from unfavorable environmental conditions. Over time, natural weathering processes or physical abrasion can break down the seed coat, allowing water and oxygen to penetrate and initiate germination.
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  TYPES OF DORMANCY 2. PhysiologicalDormancy: • This type of dormancy is controlled by physiological factors within the seed itself. It occurs when the embryo is not fully developed and requires specific conditions to trigger germination. Physiological dormancy is often influenced by hormones and growth inhibitors present in the seed. For germination to occur, the inhibitors must be degraded or diluted, and hormone balances need to shift favorably. Factors such as temperature fluctuations, light exposure, and the presence of certain chemicals can break physiological dormancy.
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  TYPES OF DORMANCY 3. MorphologicalDormancy (Embryo Dormancy): • Morphological dormancy occurs when the embryo of the seed is not fully developed and requires additional time or specific environmental cues to complete its growth. This type of dormancy is often found in seeds of woody plants, such as trees and shrubs. Environmental factors like cold stratification (exposure to cold temperatures), fire, or digestion by animals can scarify the seed coat and stimulate embryo growth, allowing germination to take place.
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  TYPES OF DORMANCY 4.Morphophysiological Dormancy: Morphophysiological dormancy combines both morphological and physiological dormancy characteristics. Seeds with morphophysiological dormancy have underdeveloped embryos and may require specific conditions such as exposure to light, temperature fluctuations, or other environmental triggers to break dormancy and complete embryo growth.
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  TYPES OF DORMANCY 5.Combined Dormancy: • Some seeds exhibit a combination of different types of dormancy. For example, a seed may have physical dormancy due to a hard seed coat, as well as physiological dormancy due to the presence of growth inhibitors. In such cases, both the seed coat barrier and the physiological factors need to be overcome for successful germination.