Seed dormancy and methods to overcome it

This ppt is related with agriculture and will help to agriculture personal about seed dormancy.

1. A COURSE SEMINAR ON TYPES OF SEED DORMANCY & METHODS TO OVERCOME IT Presented by Abhishek Pati Tiwari Department of Seed Science & Technolgy C. S. Azad University of Agriculture and Technology Kanpur

2. Types of seed dormancy & Methods to overcome it Compete your better with your best

3. Dormency It is inability of viable seed to respond to the favourable enivironmental conditions i.e , temperature , water and oxygen for germination, the phenomenon is known as dormancy. The metabolic activity of dorment seed is similar to non dorment seed . Dormancy is a mechanism to ensure the seed germination after optimum time.

4. A dormant seed is not a 'failure'. The inability of certain seeds to germinate readily even when they are provided with all conditions required for germination. Dormancy may be due to conditions associated either with the seeds itself or with existing environmental factors such as temperature and moisture.

5. Type of dormancy Primary dormancy / innatedormancy the viable seed that does not germinate immediately after maturity under favourabble conditions due to exogenous , endogenous or combination is considered as dormant, it start germination after resting period.

6. Type of primary dormancy Exogenous dormancy dormancy because of unavilability of water , oxygen or mechnical restriction due to physical barrier . Hard seededness Impermeabilty of seed coat to water Impermeabilty of seed coat to oxygen Mechanical dormancy

7. Endogenous dormancy: it is the inherent property of seed . Failure of viable mature embryo to germinate even when it is isolated from the seed coat. Immature embryo Dormant embryo Chemical dormancy (a) presence of inhibitory substance (b) growth regulator induced dormancy

8. Physiological or intermediate seed dormancy Physiological dormancy is a result of seed requiring some type of physiological condition to be met in order to germinate. It may be of following type Osmotic inhibition Metabolic inhibition Secondary dormancy

9. Other type of dormancy Deep dormancy Light dormancy Relative dormancy Combination of dormancy

10. Factor responsible for dormancy Dormancy due to seed coat Dormancy due to rudimentary embryos Dormancy due to chemical inhibitors Dormancy due to internal factors Double dormancy etc..

11. Dormancy due to Seed coat It is due to the seed coats or other tissues covering the embryo which are hard & are impermeable to water & oxygen which prevents germination. E.g. Malvaceae. Also the seed coats are apparently permeable to water & gases but they are so hard to resist the embryo expansion. E.g. Pits of stone fruits, shells of nuts.

12. Dormancy due to rudimentary embryos Some plants shed their fruits before the embryo within the seed has attained the maturity stage to germinate. Such embryos require several weeks to several months after harvest to attain its full maturity so that it can germinate. E.g.. Pinus sp., palms.

13. Dormancy due to chemical inhibitors In certain species specific chemical substances that prevent germination occur in the seed coats, endosperm or the embryo. They are reduced or eliminated by leaching with water or adsorption of water.

14. Dormancy due to internal factors It is due to physiologically dormant embryos. In this case, the dormant embryos do not resume active growth even though all environmental conditions are favourable, unless the seeds are subject to moist, chilling treatments. E.g. Freshly harvested seeds of apple, grapes, peach & apricot.

15. Double dormancy Seeds of some species exhibit both seed coat dormancy & embryo dormancy. E.g. Cercis occidentals

16. Methods to overcome dormancy Mechanical scarification Soaking in water Acid treatment Cold stratification Dry storage Treatment with chemicals

17. Mechanical scarification It includes breaking or scratching the seed coats mechanically to modify the hard or impervious seed coats. This can be done easily by Piercing Chipping Filing

18. Acid scarification : Treatment with conc.sulphuric acid or nitric acid Bio-scarification: use of animal or microorganism Removal of structure around the seed : removal of lemma and palea , hard shell etc with the help of forceps

19. Soaking in water Generally seeds will be soaked in hot water for a few seconds & then soaked for 24 hours in cold water which make the seed coat to get soften & wash off the incubators. E.g. Wattle seeds. In some case, the seeds are soaked in running cold water for a period of 8-12 hours which help in removing the inhibitors.

20. Acid treatment Soaking the seeds for a few seconds (15-60 seconds) in conc. Hydrochloric acid or sulphuric acid modifies the hard or impermeable seed covering. At the end of treatment period, the seeds are washed to remove the remnant acid. E.g. Mucuna bracteata

21. Cold stratification During stratification, seeds are exposed to abundant moisture, ample oxygen & a relatively cool temperature. It consists of placing the seeds in a moist medium of sand, peat or vermiculite & holding at a temperature slightly above freezing. This time varies between 1 to 4 months depending upon the type of seeds. This permits the physiological changes within the embryo to occur. During this process, the level of endogenous growth promoting substances (e.g.. Gibberellins & cytokinins ) increase while the level of growth inhibiting hormones (e.g.. Abscissic acid) decreases, thus removing the block & permitting germination. E.g. Peaches

22. Dry storage It promotes the after ripening in certain seeds which are dormant when freshly harvested. Freshly harvested seeds of many annuals & herbaceous plants fail to germinate until after a period of dry storage. Such post-harvest dormancy may last few days to several months.

23. Treatment with chemicals Soaking in potassium nitrate (0.2%), gibberellic acid (200 to 500 ppm) or thiourea (0.2%) solution prior to sowing has been found to stimulate germination of different kinds of seeds. For instances, soaking of seeds in gibberellic acid stimulates the germination of many citrus species viz. T rifoliate orange, Rangpur lime, Sweet orange, Sour orange etc..

24. SIGNIFICANCE OF DORMANCY The state of dormancy equips seeds to escape deterimental effects of adverse condition. During dormancy physiological activity may be suspended which results in slow down the process of seed deterioration. This increase the chance of survival of seeds. It restrict pre mature germination sseds within ears/pods ( vivipary ) when the crop are exposed to a wet weather fevourable for germination just after harvest.

25. CONCLUSION Seed dormancy may present problems in the determination of seed germination immediately after harvest in such case we have to resort to some effective treatments to overcome the dormancy. A knowledge of dormancy not only helps in understanding the survival of seed under natural condition, it also provides cheap and highly effective means for the protection of crop produce from deterioration due to pre harvest sprouting and enables us to conduct reliable germination tests in such species that exhibit dormancy.

26. T H A N K Y O U