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Similar to Seed dormancy.ppt/Dr K Vanangamudi
Seed dormancy.ppt/Dr K Vanangamudi
- 1. LOGO “ Add yourcompany slogan ” K.VANANGAMUDI Formerly Dean (Agri.), TNAU Dean, Adhiparasakthi Agricultural College, Kalavai Professor & Head, Seed Science & Technology Tamil Nadu Agricultural University, Coimbatore Tamil Nadu CELL WALL H+ H+ H+ H+ H+ H+ H+ H+ H+ ATP PLASMA MEMBRANE Plasma membran Cell wall Nucleus Vacuole Cytop H2O CYTOPLASM
- 2. LOGO “ Add yourcompany slogan ” TERMS AND DEFINITIONS Dormancy – general meaning : lack of growth due to any external or internal cause. Seed dormancy : Failure of a viable seed to germinate even when given favourable environmental conditions. Quiescence : Condition in which seed can germinate upon absorption of water. No internal germination barriers exist.
- 3. LOGO “ Add yourcompany slogan ” TERMS AND DEFINITIONS oAfterripening : Physiological processes that occur in the seed after harvest that enables germination to take place. oPrimary dormancy : Dormancy which develops when the seed is attached to the plant and exists when first harvested. oSecondary dormancy : A condition that develops to prevent germination after the seed has been detached from the plant and is exposed to specific unfavorable environmental conditions
- 4. LOGO “ Add yourcompany slogan ” TERMS AND DEFINITIONS Endogenous dormancy: Any cause of dormancy related to the embryo e.g. immature development or chemical inhibitors Exogenous dormancy: Mechanical resistance, physical impermeability, inhibitors or light sensitivity associated with seed coat Double dormancy or combined dormancy: Two or more dormancy types occur in the seed e.g. fleshy/dry fruits with chemical inhibitors combines with hard endocarp,
- 5. LOGO “ Add yourcompany slogan ” TERMS AND DEFINITIONS Thermo- dormancy: Type of dormancy induced by high temperature (Hartmann et al. 1997). Photo – dormancy: Most seeds having photo dormancy germinate only under light conditions. Such seeds are therefore also called light sensitive (Fig.1) Red light, 660-760nm White light (sunlight): Red/ far-red: 2/1 Pr -------------------------------------------------Pfr (Dormant) (Non dormant) Far red light, 760-800nm
- 6. LOGO “ Add yourcompany slogan ” SEED DORMANCY TYPES I. Primary dormancy A. Exogenous dormancy – Due to factors outside the embryo a. Physical b. Mechanical c. Chemical B. Endogenous dormancy – Due to factors within the embryo itself 1. Morphological a. Rudimentary b. Linear c. Undifferentiated
- 7. LOGO “ Add yourcompany slogan ” 2. Physiological a. Non-deep b. Intermediate c. Deep C. Combinational (two kinds of dormancy) II. Secondary dormancy 1. Thermo-dormancy 2. Photo- dormancy Contd…
- 8. LOGO “ Add yourcompany slogan ” EXOGENOUS DORMANCY - PHYSICAL Seed coats are impermeable to water and oxygen Legumes are an example. The cause of physical dormancy is the structure of the outer cell layer which becomes impermeable to water. Macrosclereid cells, a mucilaginous outer cell layer or a hardened endocarp are the reasons that seed coats become impermeable to water
- 9. LOGO “ Add yourcompany slogan ” MECHANICAL DORMANCY Seed coats are too hard to allow the embryo to expand during germination. Causes: Structure of seed coats or remaining fruit. Occurs in olive. In nature – coats are softened by environmental agents such as acid in guts, microorganisms, warm, and moist environment and forest fires.
- 10. LOGO “ Add yourcompany slogan ” MECHANICAL DORMANCY…. Overcome Abrasive action Scarify with Sandpaper Hot Water Acid scarification @ 100ml commercial grade sulfuric acid/kg of seed Fire (Melts Resins In Cones) Use immature fruits. Softening of hard seed coat: water & O2 enter easily Once scarified water can get in. Have to be careful because the seed is also more susceptible to damage by microorganisms. SST 613 PRE- SOWING SEED MANAGEMENT
- 11. LOGO “ Add yourcompany slogan ” CHEMICAL 3. Chemical Presence of chemical inhibitors in the outer coverings of many fruits and seeds. Occurs in fleshy fruits, hulls, and capsules of many dry fruits. Examples: Apples, citrus, grapes, teak, coriander, spinach Overcome: Water soaking and leaching Heavy Rains Use of Hormones (GA3) Chilling for a few days
- 12. LOGO “ Add yourcompany slogan ” Endogenous dormancy - MORPHOLOGICAL DORMANCY Embryo is not fully developed at time of ripening. Need additional embryo growth after the seed is separated from the plant. Ranunculus, poppy, woody species such as holly, date palms. Often combined with other kinds of dormancy such as hard seed coats.
- 13. LOGO “ Add yourcompany slogan ” MORPHOLOGICAL DORMANCY: TYPES Rudimentary: Pro-embryo stage, Ranunculaceae, Papaveraceae, Araliaceae Linear: Torpedo stage, Umbelliferaea, Ericaceae, Primulaceae Undifferentiated: Orchids To overcome: After ripening Alternate warm and cool temperatures GA3 Extended period at high temperatures Date palms often takes several years to reach full embryo development & germinate. Often high temperatures (100oF) will accelerate this
- 14. LOGO “ Add yourcompany slogan ” PHYSIOLOGICAL - NON-DEEP Often short – termed 1 month to 6 months e. g. Lettuce. Disappears as the seed is stored. Two kinds Photo-dormancy Thermo-dormancy May be due to 1. Inhibitors 2. Control of gas exchange (oxygen). But this light requirement can be substituted by cool temperatures - growing the seeds in the dark below 73ºF.
- 15. LOGO “ Add yourcompany slogan ” NON-DEEP…. To overcome Hormones ABA Kinetin GA3 Photodormancy appears to be through phytochrome. Sunlight (R:FR=2:1) results in phytochrome in the active form. Under foliage (R:FR=0.12:1 to 0.70:1) far red dominates resulting in phytochrome in the inactive form
- 16. LOGO “ Add yourcompany slogan ” INTERMEDIATE Control mechanism to be in seed coat and tissue around embryo e.g. temperate trees, Conifers. Embryo itself is quiescent, not dormant and germinate if excised. Excised embryos exhibit physiologically dwarfing – stunted growth, rosette – like structure. To overcome Chilling Cold Stratification for 1 – several months. Exposing pre moistened seed @ 0-5oC Will respond to GA3 treatment.
- 17. LOGO “ Add yourcompany slogan ” DEEP DORMANCY…. To overcome: Natural stratification Stratification : moist chilling Presoak in water to 50% moisture and kept at 35-45ºF. Note : If temperature is too high, secondary dormancy is induced. Then, another chilling period is required. For apple the temperature is 17ºC (62ºF)
- 18. LOGO “ Add yourcompany slogan ” SECONDARY DORMANCY Secondary Dormancy It prevents the seed from germinating after it absorbs water. Caused by temperature extremes, prolonged darkness, prolonged light, water stress, or oxygen extremes.
- 19. LOGO “ Add yourcompany slogan ” Dormancy Character- istics Example Dormancy breaking stimulus Natural Seed handling Immature embryo Physiologically immature embryo Fraxinus, Gingko biloba Post – dispersal development After ripening Mechanical dormancy Embryo emergence restricted due to hard seed coat Pterocarpus, Terminalias Melias Decomposition of hard structures by termites Mechanical cracking of hard coat Physical dormancy Imbibition impeded due to impermeable seed coat Leguminosae , Myrtaceae Abrasion by sand, high temperatures, ingestion by animals Mechanical scarification, boiling water or acid scarification
- 20. LOGO “ Add yourcompany slogan ” Dorman- cy Characteristics Example Dormancy breaking stimulus Natural Seed handling Chemical dormancy Chemical inhibitory compounds that prevent germination Berries, drupes and pomes Leaching by rain, decomposition of fruit pulp Removal of fruit pulp plus leaching with water. Photo dormancy Seeds fail to germinate unless exposed to appropriate light regimes. Temperate species, Betula, humid tropical pioneer, Spathodea, Eucalyptus Exposure to white light or red light likely to promote germination Exposure to light, during germination, light- dark cycle of variable duration Thermo dormancy Temperatures control Fagus,Quercus, Pinus, tropical- sub tropical pioneers Exposure to low winter temperature, bush or forest fires, diurnal fluctuating temperature Stratification or chilling kiln or light burning, fluctuating temperature