Plant Propogation and Nursery Management

Methods of Breaking Dormancy

Several methods are used for breaking seed dormancy of horticultural crops. These are briefly described hereunder:
1. Softening seed coat and other seed coverings: This helps in better absorption of water and gases, which ultimately leads to better germination of the seeds. This can be achieved by scarification.

a) Scarification: Scarification is the process of breaking, scratching, mechanically altering or softening the seed covering to make it permeable to water and gases. Three types of treatments are commonly used as scarification treatments. These include mechanical, chemical and hot water treatments.

i) 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 a different size than the seed to facilitate subsequent separation.
• Scarification should not proceed to the point at which the seeds are injured and inner parts of seed are exposed.
ii) Acid scarification

• Dry seeds are placed in containers and covered with concentrated Sulphuric acid (H₂SO₄) or HCl in the ratio of one part of seed to two parts of 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 period, 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, brinjal and tomatoes are reported to respond simple sulphuric acid treatment.
iii) Hot water scarification

• Drop the seeds into 4-5 times their volume of hot water with temperature ranging from 77 to 100^oC.
• 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.
• The seed should be sown immediately after hot water treatment.
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.
• The hard seeds are planted in summer or early fall when the soil temperature is still higher, that usually facilitates germination.
• For instance the stone fruit including cherry, plum ,apricot 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.