Types of Dormancy

1. Innate (primary/ physiological) dormancy:

• The seeds that are incapable of germination just after ripening even under favorable conditions are said to have innate dormancy.
• The dormancy is present immediately after the new embryo ceases to grow when it is still attached to the parent plant or prevents the seed from germination after the ripe seed is shed or harvested.
• This dormancy may be due to the presence of some germination inhibitors, immature embryos, rudimentary embryos, and mechanically resistant seed coats preventing the entry of gases and water.
• Such dormancy prevents the seed from vivipary.

2. Induced (secondary) dormancy:

• Some seeds are capable of germinating under favorable conditions just after ripening but when these seeds are stored under unfavorable conditions even for a few days they become unable to germinate. This kind of dormancy is said to be induced or secondary dormancy.
• Dormancy develops within the seed when a non-dormant seed is exposed to certain external conditions and continues even after the conditions are changed or seeds are removed from them.
• A limited supply of O2 and a high concentration of CO2 has induced dormancy in the case of wild oat and Brassica nigra.

3. A special type of dormancy:

• Sometimes seeds germinate but the growth of the sprouts is found to be restricted because of a very poor development of root and coleoptiles. This kind of dormancy is known as a special type of dormancy.