Dormancy in seed

 

Dormancy in seed:

·      Seed dormancy refers to a state in which viable seeds fail to germinate when provided conditions normally favorable to germination i.e . adequate moisture, appropriate temperature.

Main two Types of seed dormancy:

1.seed coat  dormancy

2.Internal dormancy

·      Primary dormancy is when seeds are released from a plant this is a dormant state.

·      Secondary dormancy is when seeds are released from a plant that is in a non-dormant state, but later become dormant

Types of seed dormancy:

1.Physiological dormancy:

·      This is the most abundant of seed dormancy in angiosperms plants.

·      Physiological dormancy is divided into three levels: deep , intermediate And non-deep

2. Morphological dormancy:

·      This class of seed dormancy refers to seed with undeveloped  and differentiated embryos, this includes embryos in which the cotyledons and hypocotyls , radical axis are differentiated , but small in size.

·      These embryos do not have physiological dormancy and only require additional time to grow and germinate.

3.Morphophysiological dormancy:

·      In this class, seeds have embryos that are undeveloped and differentiated as well as a physiological component to their dormancy.

·      Thus to germinate , these  seeds require time for embryo growth and a dormancy breaking treatment.

·      Morphophysiological dormancy can be divided into eight levels with possible dormancy breaking treatments.

4.Physical dormancy:

·      This class of seed dormancy is caused by one or more water- impermeable layers of palisade cells in the seed coat that impede germination because the seed cannot complete inhibition.

·      Chemical or physical abrasion of these water impermeable layer can break physical seed dormancy.

5. Combinational dormancy:

·      This class groups seeds with simultaneous physiological and physical dormancy.

·      In this case , physiological dormancy Is generally characterized as non-deep.

·      A cold stratification treatment of seed after scarification to permit inhibition is  a common dormancy breaking treatment in this class of seeds.

Factors Causing dormancy of seeds:

Ø Hard seed coat

Ø Dormancy due to temperature

Ø Immature embryo

Ø Light sensitive seed

Ø Dormancy due to growth inhibitory chemicals

Ø Excessive salts

Ø Dormancy due to absence of light