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SEED DORMANCY.pptx

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Seed dormancy
Seed dormancy
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SEED DORMANCY.pptx

  1. 1. ☻ 1
  2. 2. LEARNING OBJECTIVES 2 Describe seed dormancy State the cause of seed dormancy. Mention the advantages of seed dormancy.
  3. 3. INTRODUCTION DORMANCY  During the developmental cycle of the plant, at some phase certain structures like buds, tubers, seeds, go though a period of temporary suspension of growth activity or slow down for a period of time or deep sleep, such a state is called Dormancy.  This minimizes metabolic activity and therefore helps an organism to conserve energy.  Dormant = not active or growing but able to3 become active later.
  4. 4. Seed Dormancy  It is the incapacity of fully developed, mature, viable seed to germinate even under favourable conditions.  In such cases, the completely dry ripe seed is physiologically inactive and is said to be in a resting stage.  The seed is called dormant and the phenomenon is termed Dormancy 4
  5. 5.  The main reason behind this condition is that they require a period of rest before being capable of germination.  This Conditions may vary from days to months and even years. 5
  6. 6. 5
  7. 7. TYPES OF DORMANCY 1) Imposed dormancy or quiescence The dormancy due to unfavourable environmental conditions is called imposed dormancy or quiescence. 2) Innate dormancy or rest The dormancy due to conditions within the dormant plant or organ is called innate dormancy or rest.  It is a condition in which germination or6 growth fails to occur even though the external environmental conditions are favourable.
  8. 8. During the entire process, there may be following three phases of dormancy : 1) Pre-dormancy or early rest : During these phase, the dormant organ has capacity to resume growth by various treatments i.e., capacity of germination or growth is not completely lost. It is called predormancy. 2) Full dormancy or mid rest : When a seed or organ becomes completely dormant and germination or growth cannot be induced by changes environmental conditions, it is called full dormancy or mid 7 rest.
  9. 9. 3) Post dormancy or after rest : When a or organ gradually emerges dormant seed from full germination or growth can be induced dormancy and in it the by changing enviornmental conditions, it is called post-dormancy or after rest.
  10. 10. Causes of Seed Dormancy 1. Seed coat: The seed coat is hard and impermeable and prevents the entry of water and oxygen. 2. Growth inhibitors: Some seeds may contain chemical growth inhibitors like abscisic acid (ABA), coumarin, phenolic acids and short chain fatty acids in the embryo. Endosperm or other tissues may also prevent germination.
  11. 11. 3. Specific light requirement: In certain seeds, dormancy can be broken by exposing them to optimum light (after seeds have been soaked) while in some others, seeds remain dormant as long as they are exposed to light. 4. Optimum temperature: Generally the seeds require a low temperature before germination. It brings about an increase in the gibberellin level. 5. Immaturity of the embryo: At the time of dispersal, some seeds are structurally immature and the embryo is unable to synthesize gibberellic acid.
  12. 12. METHOD TO BREAK SEED DORMANCY Seed coat dormancy can be overcome by weakening the seed coat in a number of ways in various seeds: 1. In some seeds, the seed coat is softened by soaking in water. 2. Hard seed coat can also be softened by certain enzymes present in the digestive tract of birds and animals 3. At times scratching of seed coat called scarification or artificial removal of testa or pricking it with a pin also helps to break the seed dormancy. 4. Certain seed coats can be broken down by soil microorganisms also.
  13. 13. METHOD TO BREAK SEED DORMANCY To break seed dormancy by chemical growth inhibitors, their concentration has to be lowered. It can be achieved by: 1. Exposing the seeds to alternating temperature, chilling, light, placement in running water, treatment of hydrated seeds with oxygen, nitrates, nitrites and thiourea. 2. Treatment with certain hormones or chemicals like gibberellins, cytokinins and ethylene
  14. 14. ADVANTAGES OF SEED DORMANCY 1. It enables the seed to germinate only under favorable conditions, e.g. if the seeds dispersed in summer germinate immediately the seedlings cannot survive the following cold season. 2. It allows seeds to survive through unfavorable conditions and germinate at the onset of favorable season. 3. The dormant seeds can be stored for a long time and the seed dormancy can be broken by giving artificial conditions
  15. 15. ASSIGNMENT 1. Define Seed Dormancy? 2. Mention five (5) causes of Seed Dormancy? 3. Discuss three (3) advantages of Seed Dormancy? 4. Discuss four (4) ways to break seed dormancy?

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