Seed Dormancy and its breaking of seed dormancy and helping in seed germination.pptx

Seed dormancy

1. Seed Dormancy Presented by: Anshika Singh M.Sc. Ag (Horticulture) I Sem.

2. Contents Introduction Causes of Seed Dormancy Types of Seed Dormancy Methods of breaking seed dormancy Importance of Seed Dormancy References

3. Introduction Seed Dormancy is a condition where seeds will not germinate even when the environmental conditions such as water, temperature and air are favourable for germination. Dormant = not active or growing but able to become active later. The main reason behind this condition is that they require a period of rest before being capable of germination.

4. Seed refers to the fertilized, matured ovule that contains an embryonic plant, food reserves, all enclosed within a protective seed coat.

5. Causes of the Seed Dormancy Light Temperature Hard Seed Coat Period after ripening Germination inhibitors Immaturity of the seed embryo Impermeability of seed coat to water Impermeability of seed coat to oxygen Mechanically resistant seed coat Presence of high concentrate solutes (lower the osmotic potential)

6. Types of Seed Dormancy Primary Dormancy: Exogenous Dormancy Endogenous Dormancy Combinational Secondary Dormancy: Thermo Dormancy Conditional

7. Primary Dormancy Exogenous dormancy is a result of factors imposed from 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.

8. Therefore exogenous dormancy may be physical or chemical. Physical dormancy: seeds with such dormancy fail to germinate due to seed coats that are impermeable to water. Eg the Malvaceae family- okra. Chemical dormancy: chemicals that are present in the flesh of fruits and seed coverings may inhibit germination . Eg ABA in flesh and seed coats. Endogenous dormancy (physiological) results from characteristics of the embryo that prevent germination . The basis of this type of dormancy is that the embryo lacks the growth potential. Growth potential is the force exerted by the radicle to penetrate the seed coat.

9. Types of endogenous dormancy Physiological Seeds cannot germinate unless they have received a dormancy breaking treatment. Morphological Found in seeds with underdeveloped embryos that must differentiate before germinating. Morphophysiological Physiological dormancy developed in seeds with underdeveloped embryos (morphological dormancy). Photodormancy : seeds requiring light or the absence of light (darkness) are referred to as photodormant or photoblastic. Combinational dormancy is a result of the combination of exo and endogenous dormancy. The seed coat may be hard coupled by physiological dormancy (lack of growth potential).

10. Secondary Dormancy Secondary dormancy is due to germination conditions. It is a further adaptation to prevent germination of an imbibed seed if other environmental conditions are not favourable . These conditions can include unfavourably high or low temperature, prolonged darkness and water stress. It is of two types: I) Thermo dormancy: High temperature induced dormancy. II) Conditional dormancy: Change in ability to germinate related to time of the year.

11. Methods of breaking Seed Dormancy Seed coat treatment: Scarification Embryo treatments: Stratification High temperature treatment Chemical treatments: Hormonal treatment

12. 1. Scarification Scarification is the process of breaking, scratching, mechanically altering or softening the seed covering to make it permeable to water and gases. i . Mechanical Scarification : Chipping hard seed coat by rubbing with sand paper, cutting with a file or cracking with a hammer are simple methods useful for small amount of relatively large seeds.

13. Scratching by knife Shaking by sand paper By chemical

14. ii. Acid Scarification : Dry seeds are placed in containers and covered with concentrated Sulphuric acid (H 2 SO 4 ) or HCl in the ratio of one part of seed to two parts of acid. The acid treated seeds can either be planted immediately when wet or dried and stored for later planting. Large seeds of most legume species, brinjal and tomatoes are reported to respond simple sulphuric acid treatment.

15. iii. Hot water Scarification : Drop the seeds into 4-5 times their volume of hot water with temperature ranging from 77 to 100 o C. The heat source is immediately removed, and the seeds soaked in the gradually cooking water for 12 to 24 hours. Following this the unswollen seeds may be separated from the swollen seeds by suitable screens. Then seeds are sown immediately. iv. Warm Moist Scarification : The seeds are placed in moist warm medium for many months to soften the seed coat and other seed coverings through microbial activity. This treatment is highly beneficial in seeds having double seed dormancy.

16. 2. Stratification Seeds of some trees and shrubs from the temperate zone do not germinate unless they are exposed to chilling temperatures. E.g peach and apple. This can be accomplished artificially by a practice called stratification. As the chilling process prolongs levels of ABA decrease as levels of GA rise.

17. The following procedure is usually successful: 1. Put sand or vermiculite in a clay pot to about 2-3 cm from the top. Place the seeds on top of the medium and cover with 1 cm of sand or vermiculite. 2. Wet the medium thoroughly and allow excess water to drain through the holes in the pot. Place the pot containing the moist medium and seeds in a plastic bag and seal. 3. Place the bag in a refrigerator. Periodically check to see that the medium is moist, but not wet. Additional water will probably not be necessary. 4. After 10 to 12 weeks, remove the bag from the refrigerator. Take the pot out and set it in a warm place in the house. Water often enough to keep the medium moist. 5. When the young plants are about 5-7 cm tall, transplant them into pots to grow until time for planting at their permanent sites.

18. 3.Leaching of inhibitors It is established fact that some inhibitors and phenolic compounds are present in seed coverings of many species, which inhibit germination. Therefore, soaking of seeds in the running water for 12-24 hours or placing them in water for few hours help in leaching off the inhibitors and phenolic compounds, which help in easy seed germination.

19. 4. Pre- chilling: In seeds of certain plant species, dormancy can be overcome by pre-chilling treatment. In this treatment, the imbibed or soaked seeds are kept at a temperature of 5-10 C for 5-7 days before sowing. After that seed can be sown in the field immediately. 5. Pre-drying:  This is also a useful practice in some seeds to overcome seed dormancy. In this treatment, the dry seeds are subjected to a temperature of 37-40 C for 5-7 days prior to sowing. After this, seed can be sown in the field.

20. 6.Treatment with chemicals : Some compounds other than hormones are also used to break dormancy but their role is not clear. Thiourea is one example known to stimulate germination in some kinds of dormant seeds. The seeds are soaked in 0.5 – 3 per cent solution of thiourea for 3-5 minutes. Afterwards seeds are rinsed with water and are sown in the field. Similarly, potassium nitrate and sodium hypochlorite also stimulate seed germination in many plant species.

21. 7. Hormonal Treatment Among various hormones, GA3 is commercially used for breaking seed dormancy in different types of seeds. The concentration of GA3 depends upon the kind of seed but generally a concentration of 200-500 ppm is most widely used. Cytokinin is another group of hormones used for breaking physiological dormancy and stimulating germination in seeds of many species. Kinetin and BA(6-benzyle aminopurine ) are commercial preparations of cytokinin used for breaking seed dormancy. Soaking seeds in 100 ppm solution of kinetin for 3-5 minutes is highly effective concentration for overcoming seed dormancy of many species. Etheral also stimulates germination in seeds of some species.

22. Crop Chemical/hormone Concentration Apple Thiourea 5000 ppm Kinetin 25 ppm GA 50 ppm Ethrel 100-200 ppm Pear GA 150 ppm Thiourea 5000 ppm Peach Thiourea 5000 ppm GA 400 ppm BA 400 ppm Walnut GA 250 ppm Ethrel 1000 ppm Recommended concentrations of growth hormones in temperate fruits for increasing seed germination:

23. Hormonal changes during  stratification : A reduction of ABA Increased synthesis of cytokinin and gibberellins Reduction in hormone synthesis in preparation for germination. In general, gibberellins promote germination in dormant seeds, while ABA inhibits germination. Pre-sowing treatments with certain seeds not only reduce the  stratification  requirement and improve the seed germination but also enhances seedling growth in a number of temperate fruits.

24. Importance of Seed Dormancy It follows the storage of seeds for later use by animals and man. It helps in the dispersal of the seeds through the unfavourable environment. Dormancy induced by the inhibitors present in the seed coats is highly useful to desert plants. Allows the seeds to continue to be in suspended animation without any harm during cold or high summer temperature and even under drought conditions. Dormancy helps seeds to remain alive in the soil for several years and provides a continuous source of new plants, even when all the mature plants of the area have died down due to natural disasters.

25. References Textbook of Plant Physiology- V. Verma Textbook of Basic Horticulture- Jitendra Singh http://ecoursesonline.iasri.res.in/pluginfile.php/101028/mod_resource/content/1/Lecture_-_2.pdf https://www.slideshare.net/MaitriThakor/seed-dormancy-213436624 https://slideplayer.com/slide/13548671/

26. Thank You