Methods of breaking dormancy

This presentation describes about the dormancy, types of dormancy (seed dormancy and bud dormancy) as well as methods to overcome the bud and seed dormancy in detail.

1. METHODS OF BREAKING DORMANCY

2. Contents Dormancy Seed Dormancy Reasons for Seed Dormancy Methods of Breaking Seed Dormancy Advantages of Seed Dormancy Disadvantages of Seed Dormancy Bud Dormancy Reasons for Bud Dormancy Methods of Breaking Bud Dormancy Seed and Bud Dormancy

3. dormancy A period in which a plant does not grow, awaiting necessary environmental conditions such as temperature, moisture, nutrient availability, etc. In plant physiology, dormancy is a period of arrested plant growth. A state when organisms are in unfavourable conditions, and slow down their metabolic processes to a minimum to retain resources until conditions are more favourable.  Plants may do this when their is a lack of water, while animals, such as the garden dormouse, hibernate, which is also a form of dormancy.

4. SEED DORMANCY Many seeds are unable to germinate even under ideal conditions of oxygen, water and temperature. It is due to internal conditions. The resting stage of seed before germination is termed as seed dormancy.

5. SEED DORMANCY Seed dormancy can be defined as the state or a condition in which seeds are prevented from germinating. Even under the favourable environmental conditions for germination including, temperature, water, light, gas, seed coats, and other mechanical restrictions. The main reason behind these conditions is that they require a period of rest before being capable of germination. These conditions may vary from days to months and even years. These conditions are the combination of light, water, heat, gases, seed coats and hormone structures.

6. REASONS FOR SEED DORMANCY Some seeds are shed before the maturation of embryo. Such seeds are not fit to grow. They require a period during which certain changes occur within the seed, such as enzymatic activity and respiratory activation,. Germination occurs only when the embryo development is complete. Dormancy due to immature embryo is common in Orchidaceae, Ranunculus, Fraxinus etc In some seeds chemical acts as inhibitors for germination. In tomato fruits, ferulic acid is an inhibitory substance. Certain inhibitory substances are phenolic acids, abscisic acid, coumarine and para -ascorbic acid, they are found in different kinds of fruits. It is the most common factor for seed dormancy. It prevents the absorption of water and gaseous exchange. In addition o hard seed coat, seeds of many members of Leguminaceae have external waxy coating. Hard seed coat Immature embryo Chemical inhibitors

7. REASONS FOR SEED DORMANCY Chemical inhibitors Immature embryo Hard seed coat

8. METHODS OF BREAKING SEED DORMANCY

9. The natural breaking of Seed Dormancy Nature of dormancy stops when the embryo gets appropriate environment such as adaptive moisture and temperature. The seed coat that exists in many species becomes permeable due to the rupturing of smoothing action of natural agents like microorganism, temperature, and abrasion by the digestive tract of birds and animals that feed on these seeds. Other natural methods include: Completion of the over-ripening period. Leaching of inhibitors present in the seed coat. Inactivation of inhibitors by the supply of cold, heat, and light. Leaching of the excess and highly concentrated solutes from the seeds. Production of growth hormones which can neutralize the effect of inhibitors. Artificial Overcoming of Seed Dormancy Some of the artificial methods used for breaking seed dormancy are listed below: Action with hot water for termination of waxes, surface inhibitors, etc. Rupturing of seed coats by filing, chipping, or threshing through machines. Exposure to heat, cold or light, depending upon the type of seed dormancy. By applying Hydraulic pressure for 5 to 20 minutes in order to weaken the tough seed coats. Seed coats are treated with concentrated sulphuric acid for removing all traces of the mineral acid.

10. SCARIFICATION Scarification involves weakening, opening, or otherwise altering the coat of a seed to encourage germination.

11. SCARIFICATION When the dormancy is due to hard coat, it is impermeable to water and oxygen. The scarification method is used to break the dormancy of seed. In this method, the seed coat becomes permeable to water and oxygen. By cutting or breaking the seed coat or by chemical treatment. In this way, scarification is either mechanical or chemical.

12. Mechanical scarification It is a technique for overcoming the effect of an impermeable seed-coat. It can be done by rubbing seeds between two pieces of sandpaper, or using a file, a pin, or a knife to rupture the seed coat. Seed may also mixed with the coarse sand and shaken vigorously in a jar. Even a vise can be used to squeeze seeds along the suture until they crack open. After the seeds have been cut of rubbed soak them in cold water for 24 hours before sowing.

13. a Mechanical Scarification

14. Chemical scarification It involves the use of one or more chemicals to promote the germination. It can involve imbibing or soaking seeds in precisely concentrated acidic or basic solutions for varying amounts of time. Wear goggles and protective clothing at all times. Acid treatments are often used to break down especially thick impermeable seed coats. In this method, seeds are dipped into strong acid or into organic solvents such as acetone or alcohol. Seeds are placed in concentrated H 2 SO 4 will become charcoal in time.

15. Chemical scarification The temperature of the acid and the length of the time in which seeds are soaked are very important. The acid should be used at room temperature for a period of few minutes to several hours depending on the seed type. The seeds should be immersed in acid in a glass or china dish. It should be stirred occasionally with a glass rod. The seeds should be removed from the acid just before any acid penetrates the seed coats. Then washed it under cold water for 10-15 minutes to remove any remaining acid.

16. Chemical Scarification

17. THERMAL SCARIFICATION Thermal scarification can be achieved by briefly exposing seeds to hot water, which is also known as hot water treatment. In some chaparral plant communities, some species' seeds require fire and/or smoke to achieve germination.

18. HOT WATER TREATMENT This is by far the most common and one of the easiest ways of scarification. Place a teaspoon of seed in a cup then fill the cup with boiling water, leave to cool. Let the seed soak in the water for twenty four hours and then sow. You can usually tell the seed that has been impregnated with water as it will have started to swell. Any seed that is not showing sign of impregnation can be left soaking for a couple of days and if it still hasn’t started to swell then it can be retreated with boiling water. The container used for this treatment should not be made of aluminum as it may be toxic for the seeds.

19. HOT WATER TREATMENT

20. Seeds Sowing

21. Dry heat fire Oven or dry heat is not often recommended and the temperature required are more suitable to an incubator than a kitchen oven. In this method, seeds should be placed in shallow containers in a preheated incubators or oven. The specific temperature and duration depend on the species. The temperature suggested is between 1800-2120F. Seeds of some genera have tough, thick seed coats and germinate best when subjected to the heat of fire. Seeds should be sown in the fall in a slightly moist medium but not watered. A layer of dry pine needles, four to six inches deep, should be placed over the top of the seedbed. A few small pieces of wadded paper will help to ignite the material. One or two strips of aluminum foil placed over the exposed edges of wood container will prevent it from burning.

22. STRATIFICATION Stratification is a treatment given to seeds of some plants species that requires a period of cold temperatures (40C-80C) in order to germinate. For example, some seeds of species like peach, apple, plum, cherry etc. They only germinate when they are exposed to well aerated moist conditions under low temperatures for weeks or months. It is believed that embryos of those seeds which require stratification are immature in the sense. It requires some chemical changes must take place to initiate seed germination. Natural stratification occurs when seeds are shed, they are covered with soil, debris and snow. In artificial stratification, the layers of seeds are kept in sand or any other material.

23. Cold STRATIFICATION Some seeds contain germination inhibitors that break down when exposed to cold temperatures. This is nature’s way of preventing the seed from germinating before spring arrives. Soaking the seeds in cold water for 6–12 hours immediately before placing them in cold stratification. Stratification exposes the seeds to cold temperatures in the refrigerator, simulating a short winter. When brought back to room temperature, they germinate readily. Large seeds are easy to stratify by placing them between moist paper towels or in a jar of moist sand in the refrigerator. It’s best to plant small seeds in a tray of soil before refrigerating them. It takes between two and six weeks of cold temperatures to break down the inhibitors, depending on the type of seed. Seeds require moisture, cold and oxygen.  In general, this period of time allows an undeveloped embryo to mature. This cold moist period triggers the seed's embryo; its growth and subsequent expansion eventually break through the softened seed coat in its search for sun and nutrients.

24. COLD STRATIFICATION

25. REFRIGERATOR

26. Warm stratification Warm stratification means to place seeds in contact with warm, moist soil (usually to simulate the end of summer and usually followed by cold stratification). Warm stratification requires temperatures of 15-20°C (59-68°F). In many instances, warm stratification followed by cold stratification requirements can also be met by planting the seeds in summer in a mulched bed for expected germination the following spring. Some seeds may not germinate until the second spring..

27. stratification Seeds may be kept outdoors through the winter in lined pits or raised beds.  They must be protected from freezing, drying and rodent predation (use wire netting in the soil).  Pits or beds are layered with clean sand, medium with seeds, more clean sand, etc.   Outdoor Planting is that some categories of seeds may simply be planted outdoors in the fall and natural stratification is allowed to happen. Outdoor Stratification Outdoor Planting

28. IMPACTION Impaction means to strike something with force. This method implies to the vigorous shaking of the seeds. This method is used when the micropyle is blocked by a cork-like substance, strophiolar plug, which prevents the penetration of oxygen and water.

29. GROWTH REGULATORS Three chemical that have proven very helpful in breaking certain types of dormancy. Gibberellic acid (GA3) conc. Of 100 ppm, Potassium nitrate (0.2 %) and Thiourea (0.5 to 3%). The aqueous solution of these chemicals should be used at room temperature. The concentration and the length of the treatment depends on the species to be treated. Seeds soaked in GA3, or thiourea should be stirred occasionally and not rinsed afterwards, unless specified, but sown immediately. After this soaking they can also be air-dried and stored for short periods and then sown or given a subsequent treatment. The no-rinse afterwards also applies to the use and potassium nitrate and hydrogen peroxide, other chemicals occasionally as aids to germination.

30. gibberellins Induction and release of seed dormancy is mainly under the control of abscisic acid (ABA) and gibberellic acid (GA). ABA promotes seed dormancy and germination inhibition. Action of ABA is counteracted by GA, which promotes seed germination at appropriate time. Gibberellins (GAs) break seed dormancy and promote germination (1, 2), and several other hormones, including brassinosteroids, ethylene, and cytokinin, have also been shown to promote seed germination (3, 4). However, abscisic acid (ABA) is the only hormone known to induce and maintain seed dormancy.

31. Water mulch The mulch treatment hastens the microbial breakdown or softening of the seed coats. For the occasional species whose seed coats contain readily water-soluble, germination-inhibiting chemical, this substance can be removed by soaking the seeds in tap water or by leaching the seeds in slowly tap water for various lengths of time just prior to soaking .

32. Advantages of seed dormancy Dormancy allows the seeds to remain in suspended animation without any harm during drought, cold or high summer temperature. Dormancy help seeds to remain alive in the soil for several years provide a continuous source of new plants even when all the mature plants of the area have died down due to natural disasters. It ensures the seeds only germinates under the favourable conditions. In temperate zones, the dormancy of seeds helps the plants to tide over severe cold which may be injurious for their vegetative and reproductive growth. In tropical regions, the dormancy of seeds resulting from their impermeable seed coats ensures good chances of survival during water stress.

33. It also enables the proper dissemination (dispersal) seeds to distant places from the unfavourable environment. It also ensures the agricultural seeds to be stored artificially. Dormancy of seeds in many cereals is of utmost important to mankind. If these seeds would germinate immediately after harvest in the field, they will become useless to man for consumption as food. Rain, at that time of harvest or maturity, may spoil entire produce by initiating germination. Thus it enables storage of seeds for later use by animals and man. Advantages of seed dormancy

34. Disadvantages of seed dormancy No uniform germination. It is difficult to maintain plant population. It interferes in seed testing procedures. Seed remain naked during dormant period they get shabby look.

35. BUD DORMANCY

36. BU D DORMANCY A dormancy process in which dormancy is induced, maintained or broken in a bud. Bud dormancy is a suspension of most physiological activity and growth that can be reactivated. It may be a response to environmental conditions such as seasonality or extreme heat, drought, or cold. The exit from bud dormancy is marked by the resumed growth of the bud.

37. what is Bud? Bud is a undeveloped or embryonic shoot and normally occurs in the axil of leaf or at the tip of stem. Once form a bud may remain for sometime in condition, or it may form a shoot immediately. Buds may be specialized to developed flowers or a short shoot, or may have potential for general shoot development. The buds of many woody plants, especially in temperate or cold climates, are protected by a covering of modified leaves called scales. Which tightly enclose the more delicate parts of the bud. Many bud scales are covered by a gummy substance which serves as added protection.

38. ` Reasons for bud dormancy Perennial plants like shrubs, trees have to go through different seasons in a year. The onset of winter is always an unfavourable season for the growth and even survival of plants become difficult. Environmental signals such as temperature and light play crucial roles in regulating development and release of bud dormancy. Physiological signals including phytochrome, phytohormones, and sugar are associated with changes in dormancy status that occur when plants perceive environmental signals. Those of major importance in contributing to the onset of bud dormancy include changes in temperature and photoperiod and the availability of food, water, oxygen, and carbon dioxide. The winter season is an unfavorable season for the growth and survival of the plants. In order to overcome the cold conditions the buds undergoes a period of suspended growth also known as the bud dormancy.  This season stimulates the synthesis of growth inhibiting compounds abscissin which dominates. ABA which induces the dormancy on meristematic tissues of the plant body.

39. Reasons for Bud Dormancy

40. METHODS OF BREAKING BUD DORMANCY

41. Methods of breaking bud dormancy Chilling method to break bud dormancy. Photoperiod to break bud dormancy. By using growth promoting hormones to break bud dormancy such as gibberellins, cytokinin and ethylene. By providing alternate temperature such as high or low temperature also break the bud dormancy.

42. Chilling treatment Chilling treatment can break the bud dormancy. By providing very low temperature to the plant, so their enzymatic activity created. The chilling requirement (exposure to temperature between 5 and 10°C) for breaking dormancy of flower buds differs among species and cultivars. The cold exposure of plants also releases them from dormancy and buds start sprouting. The natural exposure to low temperature is during the winter or during seasonal cool spells. The stimuli developed in response to low temperature are accumulated in the buds which normally is expressed as an effect on the quantitative increase in the growth of buds in response to the increasing chilling duration.

43. Photoperiodic effect The photoperiodic effect either in breaking the dormancy or induction of dormancy is explained on the basis of phytochrome involvement. When long day conditions prevail, more amount of PfR form of phytochrome accumulates in the cells. It initiates not only the synthesis of more GA and but also it facilitates the release of it from the plastids into the cytoplasm.  Once GA is released, it brings about the activation of dormant cells, and thus GA breaks bud dormancy.  It is really very fascinating to understand the three way interaction between phytochrome, photoperiod and GA/ABA synthesis in imposing bud dormancy or breaking it.

44. Low and high temperature treatment Temperature regulates bud dormancy and environmental stimuli perceived by the plant and their correlation of environmental signals with the built up of plant hormones and nucleic acids levels lead to the further control of bud dormancy. Bud dormancy can also be induced by exposing the plant firstly with low temperature and then with high temperature. So this alternating temperature treatment break the bud dormancy.

45. Growth promoters The dormant buds can be induced to sprout again by treating with cytokinins and gibberellins.  But in natural course, the onset of spring and long photoperiods, the dormant buds become active and develop into branches. Cytokinins are known to be synthesized in root tips but under cold conditions because of the snow fall, the root meristems are very inactive and they don’t synthesize sufficient quantities of cytokinin required for the buds to be active.  That is probably one of the reasons why buds remain dormant.  As soon as cytokinins are provided to dormant buds, mitotic activity is initiated and buds start sprouting.  Besides, cytokinins also counteract ABAs inhibitory effect of the metabolic activity level and promote growth activity. Another class of phytohormones, which overcomes the bud dormancy, is Gibberellins.  Now it is certain that Gibberellin synthesis takes place in plastids.  Moreover, the synthesis of GA and ABA starts from the same precursor called mevolonate.  Under short day conditions, the pathway from mevolonate is directed towards ABA synthesis and GA synthesis is inhibited, but during long day photoperiods it is directed towards GA synthesis and ABA synthesis is blocked.  That is the reason why gibberellins under long day conditions or not light treatment, break bud dormancy and nullify the effect of ABA present in such dormant buds.

46. Methods of Breaking Bud Dormancy

47. Seed Dormancy Bud Dormancy Seed dormancy is the phenomena where the seed does not germinate for specific period of time. Seed dormancy is also the phenomena where the bud does not grow for specific period of time. Gibberellins , cytokinin and ethylene break seed dormancy. Gibberellins , cytokinin and ethylene break seed dormancy. Abscissic acid promotes seed dormancy. Abscissic acid promotes seed dormancy. seed and bud dormancy

48. references Dr. Muhammad Fareed Akhtar, Botany For Degree Classes Paper C&D https://en.wikipedia.org/wiki/Dormancy https://www.britannica.com/science/dormancy https://www.biologydiscussion.com/seed/seed-dormancy/seed-dormancy-meaning-types-and-effects-biology/34493 https://en.wikipedia.org/wiki/Seed_dormancy https://homeguides.sfgate.com/methods-break-seed-dormancy-73304.html https://biologyboom.com/methods-of-breaking-seed-dormancy/ https://thefactfactor.com/facts/pure_science/biology/seed-dormancy/2123/

49. references https://www.slideshare.net/gohilsanjay3/bud-dormancy https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/bud-dormancy https://www.frontiersin.org/articles/10.3389/fpls.2018.00657/full https://plantcellbiology.masters.grkraj.org/html/Plant_Growth_And_Development12-Physiology_Of_Dormancy.htm#:~:text=Breaking%20Bud%20Dormancy%3A,active%20and%20develop%20into%20branches . https://www.biologydiscussion.com/plant-physiology-2/bud-dormancy/mechanism-involved-in-releasing-bud-dormancy-plant-physiology/40323