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Seed dormacy: It's defination, classification, types, description
- 1. Topic : Dormancy RaviYadav Department of horticulture(Vegetable Science) CoA,Tikamgarh(M.P) 1 16-04-2019
- 2. Content •Introduction,meaning,definition •Classification of seeddormancy •Factors causing dormancy of seeds •Methods to overcome seed dormancy 2 16-04-2019
- 3. Dormancy Introduction, meaning, defination •Dormancy: is a period in an organism's life cycle when growth, development, and (in animals) physical activity are temporarily stopped. • This minimizes metabolic activity and therefore helps an organism to conserve energy. • Dormancy tends to be closely associated with environmental conditions. 3 16-04-2019
- 4. Dormancy Introduction,meaning,defination • During thedevelopmental cycle of the plant, at some phase certain structures like buds, tubers, seeds, go through a period of temporary suspension of growth activity, such a state is called dormancy. • It is derived Dormant word. • Dormant means sleeping “Seed dormancy is defined as a state in which seeds are unable to germinate even under Environmental conditions normally favorable for germination.” 4 16-04-2019
- 5. Classification of seeddormancy Types of dormancy include: a) Primary dormancy: Physical dormancy Mechanical dormancy Chemical dormancy • Secondary dormancy: Physiological dormancy • Morphological dormancy 5 16-04-2019
- 6. Primary dormancy • Exogenousdormancy is a result of factors imposed form outside the embryo for example the seed coat and or the fruit parts. • This material surrounding the embryo may inhibit imbibition of water, or limit oxygen to the embryo, or prevent inhibitor leaching or conversely supply inhibitors to the embryo. 6 16-04-2019
- 7. Physical dormancy • Dormancythat is caused by an impermeable seed coat. • It is the result of impermeable layer that develops during maturation and drying of the seed or fruit. • It prevents the seed from taking up water or gases. • As a result, the seed is prevented from germinating until dormancy is broken. • Generally, physical dormancy is the result of one or more palisade layers in the fruit or seed coat. 7 16-04-2019
- 8. Mechanical dormancy, Chemical dormancy •Mechanical dormancy: • Mechanical dormancy occurs when seed coats or other coverings are too hard to allow the embryo to expand during germination. • Chemical dormancy- • Presence of inhibitors within the seed (seed coat) can cause dormancy. •E.g.: Coriander seed pericarp contains Coumarin •Paddy hull contain Abscisic acid •Tomato juice circulic acid 8 16-04-2019
- 9. Physiological dormancy • Physiologicaldormancy prevents embryo growth and seed germination until chemical changes occur. • Photo dormancy: light sensitivity affects germination of some seeds. These photoblastic seeds need a period of darkness or light to germinate. • Thermo dormancy : seed sensitivity to heat or cold. • Some seeds germinate only at high temperature like Amaranth. 9 16-04-2019
- 10. Morphological dormancy • Inmorphological dormancy, the embryo is underdeveloped or undifferentiated. 10 16-04-2019
- 11. Factors causing dormancyof seeds • Hard seed coat • Dormancy due to temperature • Immature Embryo • Light Sensitive Seed • Dormancy due to growth inhibitory chemicals 11 16-04-2019
- 12. Dormancy due tohard seed coat • Testa of some seeds are hard and multilayered (Leguminaceae, Solonaceae). • Hard seed coat prevents the entry of water into the seed.because waxy coating(Lignin,cutin) in seed coat. Breaking seed coat ;soil fungus,Bacteria. • seed coat impermeable to oxygen.Ex-Xanthium, Oat. 12 16-04-2019
- 13. Dormancy due totemperature • Some seeds require chilling treatment for germination. • Examples are apple, walnut,pear,cherry. Such seeds need chilling temperature (1 -5 ºC) for few weeks. • Immature Embryo • Embryo is not matured at the time of harvesting for maturity of such embryo, resting period is required. • Example: Caltha palustris,apple,pea,cherry 13 16-04-2019
- 14. Light Sensitive Seed •There two type of seeds for light sensitivity: • Positive photoblastic seeds: Seeds of some species like lettuce,tabboco,carrot. remain dormant in the dark, they germinate when they are exposed to light. • Negative photoblastic seeds: Seeds of some species like Phlox, Nemophila and Silene remain dormant when exposed to light. They germinate only in the dark. 14 16-04-2019
- 15. Dormancy due togrowth inhibitory chemicals • There are several naturally occurring compounds which inhibit germination of seeds, like Coumarin, Cyanides,Ammonia, Dinitrophenols, Organic acid, Aldehydes, Alkaloids, Fluorides. • Example: Tomato fruit pulp – Circulic acid, Caffeic acid and Ferulic acid which induce dormancy. 15 16-04-2019
- 16. Methods to overcomeseed dormancy • Mechanical scarification • Impaction • Cold stratification • Removal of inhibitors • Treatment with growth hormones • Specific light requirement • Pressure 16 16-04-2019
- 17. Mechanical scarification • Scarification: Any treatment i.e. physical or chemical that weakens the seed coat. (A)Piercing • Chipping • Rubbing • Chilling: cabbage, sunflower. • Pre-drying: maize, lettuce. • Pre-soaking: bean. (B)Acid Treatment: Sulphuric acid, nitric acid. 17 16-04-2019
- 18. Stratification • Treatment ofseed at low temperature Under, well aeration moist condition. • Temperature 0-10 centigrade • Growth promoting hormones increases and Growth retarding hormones decreases. Ex: Rosaceae (Peach,Apple,Cherry etc) 18 16-04-2019
- 19. • 4. Removalof inhibitors: Growth inhibiting chemicals removed by repeated washing with water. Ex sugerbeet, xanthium etc. • 5. Treatment with growth hormones: Gibberellins substitute the cold treatment requirement in many seeds. Cytokinin promotes germination of many seeds.Gibberelic acid @ 0.05% 1L. Water. • 6. Pressure: Dormancy can be broken by exposing seeds to high atmospheric pressure. E.g. Sweet Clover or lucern seeds subjected to hydraulic pressure of 200 atm favors the increase in germination at 18 ºC. 19 16-04-2019
- 20. Thank you forlessening …………. 20 16-04-2019