Dormancy

introduction,meaning,definition, classification of seed dormancy,factors causing dormancy of seed , methods to overcome seed dormancy , dormancy due ti growth

1. Topic : Dormancy Ravi Yadav Department of horticulture(Vegetable Science) CoA,Tikamgarh (M.P) 1 16-04-2019

2. Content Introduction,meaning,definition Classification of seed dormancy 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 the developmental 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 seed dormancy Types of dormancy include: Primary dormancy: Physical dormancy Mechanical dormancy Chemical dormancy Secondary dormancy: Physiological dormancy Morphological dormancy 5 16-04-2019

6. Primary dormancy Exogenous dormancy 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 Dormancy that 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 Physiological dormancy 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 In morphological dormancy, the embryo is underdeveloped or undifferentiated. 10 16-04-2019

11. Factors causing dormancy of 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 to hard 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 to temperature 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 to growth 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 overcome seed 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 of seed 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 . Removal of 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 for lessening …………. 20 16-04-2019