Exercise 5

Exercise 5: Seed treatments for breaking seed dormancy and Inducing vigorous seedling growth
    Exercise: Seed treatments for breaking seed dormancy and inducing vigorous seedling growth.
    Materials Required: Seed, sand, stratification box (pit), sand paper, moss, hessian cloth, water, bavistin, labels, and glass containers
    Procedure:
    Methods of Breaking Dormancy:
    Scarification: Scarification is any process of breaking, scratching, mechanically altering or softening the seed covering to make them permeable to water and gases. Three types of treatments are commonly used as scarification treatments.
    Mechanical scarification:
    • It is simple and effective if suitable equipment is available.
    • 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.
    • For large scale, mechanical scarifiers are used. Seeds can be tumbled in drums lined with sand paper or in concrete mixers containing coarse sand or gravel.
    • The sand gravel should be of different size than the seed to facilitate subsequent separation.
    Acid scarification:
    • Dry seeds are placed in containers and covered with concentrated sulfuric acid (H2SO4) or HCl in the ratio of one part seed to two parts acid.
    • The amount of seed treated at any time should be restricted to not more than 10kg to avoid uncontrollable heating.
    • The containers should be of glass, earthenware or wood non metal or plastic. The mixture should be stirred cautiously at intervals during the treatment to produce uniform results.
    • The time may vary from 10 minutes to 6 hours depending upon the species. With thick-coated seeds that require long periods, the process of scarification may be judged by drawing out samples at intervals and checking the thickness of the seed coat.
    • When it becomes paper thin, the treatment should be terminated immediately.
    • At the end of the treatment, the acid is poured off and the seeds are washed to remove the 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 respond to simple sulfuric acid treatment.
    Hot water scarification:
    • Drop the seeds into 4-5 times their volume of hot water with temperature ranging from 77 to 100oC.
    • The heat source is immediately removed, and the seeds soaked in the gradually cooking water for 12 to 24 hours.
    • The unswollen seeds may be separated from the swollen seeds by suitable screens. The seed should be sown immediately after hot water treatment.
    Stratification:
    • Stratification is a method of handling dormant seed in which the imbibed seeds are subjected to a period of chilling to after ripen the embryo in alternate layers of sand or soil for a specific period. It is also known as moist chilling.
    • The seeds can be planted immediately after stratification in the field.
    5.1 5.2
    Plate 5.1 Open field stratification Plate 5.2.Refrigirated Stratification
    • Seeds with a hard endocarp, such as Prunus spp. (the stone fruit including cherry, plum and peaches) show increased germination if planted early enough in the summer or fall to provide one to two months of warm temperature prior to the onset of chilling.
    Refrigerated stratification:
    • An alternative to outdoor field stratification is refrigerated stratification. It is useful for small seed lots or valuable seeds that require special handling.
    • Dry seeds should be fully imbibed with water prior to refrigerated stratification. Twelve to twenty four hours of soaking at warm temperature may be sufficient for seeds without hard seed coats.
    • After soaking seeds are usually mixed with well washed sand, peat moss or vermiculite. A good medium is a mixture of one part coarse sand to one part peat, moistened and allowed to stand 24 hours before use.
    • Seeds are placed in alternate layers of sand or medium. The usual stratification temperature is 0-10oC.
    • At higher temperature seeds sprout prematurely and low temperature delay sprouting.
    • During stratification seeds should be examined periodically, if they are dry, the medium should be remoistened.
    • The stratified seed is separated from the medium prior to sowing in nursery beds.

    5.3 5.4
    Plate 5.3 Stratified seed of apple(Plump and swollen Plate5.4. Stratified seed of apple( inside view)
    Stratification period and percentage of germination in seeds of temperate fruits.
    Kinds of Fruit
    		 Stratification period (days)
    		 % Germination
    Apple
    		 70-75
    		 70-75
    Kainth (Pyrus patia)
    		 30-35
    		 90-95
    Peach
    		 60-70
    		 55-60
    Apricort
    		 45-50
    		 75-80
    Almond
    		 45-50
    		 85-90
    Walnut
    		 95-100
    		 80-85
    Pecan
    		 70-75
    		 75-80
    The stratification of seeds results in quick and uniform germination and therefore the seed should be subjected to stratification invariably under all conditions.
    Precautions:
    • Scarification should not proceed to the point at which the seeds are injured and inner parts of seed are exposed.
    • The sand should be passed through coarse sieve mesh to separate bigger size gravels so as to avoid confusion between seed and gravels at the time of sowing.
    • Irrigation during stratification should be given at regular intervals to maintain adequate moisture level.
    • Seed should not sprout during stratification.
    • Mulching of seed beds after sowing is must to ensure uniform germination

Last modified: Thursday, 20 September 2012, 10:31 AM