HORT 101 Dormancy

The flower buds on many woody perennials are initiated in summer, over-winter, and bloom the following spring.

 

=> Why don't the buds continue development, and bloom in the fall?

 

=> What would happen if they did bloom in autumn rather than spring?

 

Such buds do not flower now because they are dormant.

 

- developmentally arrested

 

- yet metabolically active

 

 

1. Today's Objectives

 

a) To introduce the concept of dormancy as a adaptive mechanism.

 

b) To learn how dormancy is controlled and broken.

 

c) To learn how the phenomenon of dormancy influences different aspects of horticulture.

2. Dormancy as an adaptive mechanism.

 

a)

 

b)

 

c) Horticultural implications (3 examples)

 

- Relocation of plants outside their native range

 

(A common horticultural practice!)

 

- Seed propagation of plants which have a dormancy requirement.

 

- Control of weeds and "weed seed banks"

 

 

3. Seed dormancy

 

a) Viable seeds of many horticultural plants will not germinate when first placed in favorable environmental conditions.

 

b) Adaptive characteristic to improve seedling establishment.

 

 

 

 

 

4. Mechanisms of Seed Dormancy

 

a) Physical dormancy

 

 

 

scarification

 

b) physiological dormancy

 

 

 

 

=> Why don't seeds germinate within fruit?

 

viviparous seeds -

 

c) after-ripening

 

 

 

d) stratification

 

 

 

e) double dormancy

 

- two forms of dormancy active simultaneously

ex. red bud - has impervious seed coat requiring scarification & imbibed seeds require stratification

 

- generally 2 years to break dormancy

 

 

=> Almost all woody perennials exhibit some form of seed dormancy. Thus if propagated by seeds, requires consideration.

 

=> Most of our vegetable and flower seeds do not have a dormancy requirement. Likely selected against during domestication.

• Dormancy in weed seeds provides a stable seed bank for the continuous presence of weeds.

  5. Bud dormancy

   

  a) Several different types of bud dormancy

   

  b) Dormancy imposed on bud by another portion of the plant.

   

   

  c) Dormancy imposed by adverse environmental conditions

  ( ecodormancy, quiescence)

   

   

  d) Dormancy imposed by internal mechanisms

  (rest, endodormancy)

   

   

   

  chilling requirement

   

  6. Bud dormancy in woody perennials can be controlled by a combination of mechanisms.

   

  a) Buds are initially in rest. (endodormancy)

   

   

   

   

   

   

  b) Buds then kept "dormant" by low winter temperatures

   

   

   

   

   

  => Although buds are not developing in each instance, the different controlling mechanisms are significant to horticulturists.

  7. Dormancy in different climatic regions & native plants

   

  a) Northern temperate climate

   

   

   

   

  b) Temperate region

   

   

   

   

   

  c) Subtropical region

   

   

   

   

  d) Tropical region

   

   

   

   

   

  What is likely to happen, if hardy northern species are moved south?

   

   

   

   

  What happens when temperate species are moved to tropics and subtropics?

   

   

   

   

   

  8. Horticulturist have only limited ability to modify dormancy.

   

  a) sprinkler irrigation to delay bud break

   

  b) fall ethephon treatment to delay bud break

   

  c) chemical treatments to break dormancy

   

   

  9. Take Home Messages

   

  a) Dormancy is an adaptive mechanism which synchronizes plant development with seasonal changes in environment.

   

  b) Plants exhibit different mechanisms for controlling dormancy.

   

  c) Dormancy influences different aspects of horticulture.