Pre Germination Treatments to Overcome Seed Dormancy
Authors- ^** Padmavati Gore, ^*Dr.Veena Gupta, ^*Dr. Anjali Kak koul
^**Scientist, ^*Principal scientist
ICAR- National Bureau of Plant Genetic Resources, New Delhi-110012.


A dormant seed (or other germination unit) is one that does not have the capacity to germinate in a specified period under any combination of normal physical environmental factors (temperature, light/dark, etc.) that otherwise is favorable for its germination, i.e. after the seed becomes non-dormant. (Baskin and Baskin, 2004). Seed dormancy breaks down naturally over time in some genera with time but other require some form of pre-treatment to facilitate seed germination. There are several methods used for specific genera.

Methods to Break the Dormancy:

Dormancy caused by an impermeable seed coat is known as physical dormancy. Puncturing or scarifying the seed coat by using different techniques like., piercing, nicking, chipping or filing with a knife, needle or sandpaper are preferred procedures to overcome seed-coat dormancy.

Pre-chilling: The ability of pre-chilling to release dormancy was probably due to various metabolisms that occur during these treatments, such as increasing the level and responsiveness of endogenous gibberellins but substantial decreasing in ABA level ( Bewley and Black, 1982 ). pre-chilling of the seeds by using the moist substratum at a temperature of 3°-5°C for 7 days (For more dormant seeds, the treatment may be extended to 14 days) improve germination in some seeds. e.g. Cabbage, Cauliflower, and Sunflower.

Preheating: high temperature frequently enhanced the degradation of the seed tissues. As a result, the energy supply to embryonic axis may increase and diffusion in and out of the seeds by such substances as water, oxygen, inhibitors and carbon dioxide, may be easier, and hence, it promotes germination ( Bewley and Black, 1982) . In Maize and Lettuce drying at 40˚C for seven days with free air circulation enhance germination.

Pre-washing: in some seeds naturally occurring substances act as inhibitors that affect the germination. Washing the seeds in the water before placing for germination removes substances that enhance germination. e.g. Sugar beet

Pre-soaking: Soaking treatment may have promoted the leaching of germination inhibitors on the seed coat ( Xia and Kermode, 2002 ) seeds with hard seed coat should be soaked in warm water for some period to enhance the process of imbibitions. e.g. Chillar, Subabul.

Scarification: Rubbing or puncturing of seed coat with pointed needle or rubbing them against rough surface enhances the germination in some seeds. Mechanical scarification is effective at any point on the seed coat, but the micropylar region should be avoided as it is the most sensitive part of the seed where the radicle is located. e.g. Coriander, Castor.

Application pressure: Hydraulic pressure of 2000 atmosphere at 18°C is also improves the seed germination. It may be due to increase in permeability of seed coat to water and O2. e.g.Medicago sativa

Exposure of seeds to light: It also helps to break the dormancy & increase the germination, depending on the species. When using constant temperatures for germination of species where light is required, the tests should be illuminated for at least eight hours of every 24-hour cycle. When alternating temperatures are used, any necessary application of light should coincide with the high temperature cycle. Light intensity should be 750-1250 lux from cool, white lamps.

Chemical treatments: Among various chemicals potassium nitrate (0.2%) and thio-urea (0.5 to 3%) are commonly used for breaking seed dormancy. Substratum (The material used for placing the seeds for germination) may be moistened with 2% solution of KNO3 (2g KNO3 + 100ml of water) in breaking seed dormancy in rice, tomato, chilies. Potato tubers are dipped in thio-urea solution (1%) for one hour when fresh harvested produce is to be used as seed material.

Gibberellic acid treatment : . Endogenous dormancy may be a result of proximity of Germination inhibitors. Use of low level of growth regulators (i.e., Gibberellins, Cytokinins and Ethylene, etc.) may break the seed dormancy. Among varipus growth regularors GA3 is most commonly used. Pre-soaking of seeds with GA3 at the conc. of 500 ppm have been used in many species for breaking seed dormancy. For prepare 500 ppm solution of GA3, weigh 500 mg of GA3 & dissolve in a few drops of alcohol and make up the final volume (1000 ml) by adding distilled water. The substratum used for germination may be moistened with 500 ppm solution of GA3 (co application of GA3) e.g. Wheat, Oat. Sorghum.

References:


1. Baskin JM and Baskin CCA, 2004 Classification System for Seed Dormancy, Seed Sci. Res 1:1-16.
2. Xia and Kermode, 2002 Dormancy of Yellow Cedar (Chamaecyparis nootkatensis) Seed is Effectively Terminated by Treatment With 1-Propanol or Nitrate in Combination With Warm Water Soaking Gibberellin and Moist Chilling, Seed Sci. Technol., 28:227-240.
3. Bewley and Black, 1982 Physiology and Biochemistry of Seeds in Relation to Germination, vol. 2,Springer-Verlag, Berlin.



About Author / Additional Info:
Working as Scientist at ICAR-NBPGR in the Division of Germplasm Conservation.