Breaking seed dormancy

1. Scarification:

• The process of rupturing or weakening of the seed coats by mechanical or other means is called as scarification.
• Dormancy can be broken by rupturing, piercing and pricking the seed coat or pericarp near the embryo.
• Piercing in the outer layers of pericarp or integuments with sharp needles increases the germination in case of sorghum.
• Concentrated sulfuric acid, hydrochloric acid scarification for 3 minutes gave highest germination in case of blackgram.

2. Temperature treatment:

a. Low temperature treatment:

• Low temperature treatment (5-100C) for 5-30 days is found more effective in case of cool season crops like barley, oat, and hot season crop sorghum.
• For example; in case of apple, peach and rose, to break the seed dormancy, the seeds are treated in moist medium at low temperature (5-100C) for sufficient period and this process is called stratification.
• Artificial stratification is done by altering the layers of seeds with layers of wet sphagnum (peat moss), sand or some other suitable materials and keeping them in low temperature.

b. High temperature treatment

• Seeds of oil palm require as high as 50-600C to break their dormancy.
• Nut grass (Cyperus rotundus) seeds have to be heated at 400C on moist media for 3-6 weeks to break dormancy, otherwise would have lasted for 7-8 years.

c. Alternating temperature treatment

• An alteration of low and high temperature (the difference of the two being not more than 10-200C) greatly improves the germination of seeds in certain plants such as Poa pratensis, Chinese red pine (Pinus densiflora) and Japanese black pine (Pinus thimbergii).

3. Light treatment

• The dormancy of positively photoblastic seeds can be broken by exposing them to red light (most effective near 670 nm).
• The promotion of germination by red light and inhibition by far-red light (>700 nm) probably involves the operation of a proteinaceous pigment called as phyllochrome.
• The germination responses of seeds like tobacco (Nicotiana tabaccum) and some varieties of lettuce (Lactuca sativa) are promoted by light (positively photoblastic) while others such as onion are inhibited by light (negatively photoblastic).

4. Chemical treatment

• Chemicals like potassium nitrate, thiourea, acetone, mercury chloride, hydrogen peroxide, carbon monoxide, methylene blue, gibberellic acid, kinetin and ethylene can be used for breaking the dormancy in many crop seeds.

5. Application of pressure to seeds

• In certain plants like sweet clover (Melilotus alba) and alfalfa (Medicago sativa), the germination of seeds can be improved by 50- 200% if the seeds are subjected to hydraulic pressure of 2000 atmosphere at 180C for about 5-20 minutes.
• This effect of pressure on germination results due to changes in permeability of the testa to water and oxygen.