Growth Stimulants, Retardants, and Rooting Hormones

1
Growth Stimulants, Retardants, and Rooting
Hormones

• Unit 5

2
Objectives

• List 1 example of a substance used to stimulate
  plant growth
• Explain why chemical retardants are applied to
  floral crops and name 2 commonly used retardants
• Explain the use of rooting hormones on cuttings
  and list several rooting hormones
• Describe orally the source of 1 plant growth
  stimulant
• Demonstrate the proper application of a rooting
  hormone to cuttings
• Explain how rootstock is used in dwarfing fruit
  trees
• Define biostimulants

3
Hormones

• Growth regulating substances in plants
• Hormones are organic chemicals that act and
  interact to affect growth rate
• Auxins (to increase) accelerate growth by
  stimulating cell enlargement
• Gibberellins stimulate growth in stem and leaf
  by cell elongation
• Also stimulate premature flowering, growth of
  young fruits, and breaking of dormancy

4
Hormones (cont)

• Cytokinins stimulate cell division
• Work along w/ auxins
• Will not work w/o auxins present
• Inhibitors (abscisic acid) inhibit seed
  germination, stem elongation, and hasten ripening
  of fruit
• Chemicals react w/ one another in complex systems
  in the plant

5
Apical Dominance

• Terminal Bud secretes chemicals that inhibit or
  prevent growth of auxiliary buds
• Causes the plant to grow tall rather than send
  out side branches (p. 51 fig. 5-1)
• Helps in competition with other plants
• Methods other than pruning have been researched
  to control plant growth rate, size and shape

6
Stimulants

• Enable plants to grow taller (p. 52 fig. 5-2)
• Causes the stems to stretch out
• Nodes are further apart
• Example
• Gibberellic Acid may be natural or artificial

7
Chemical retardants

• Cause plants to be shorter and more compact (p.
  53 fig. 5-4)
• Used on lawn grasses (Limit)
• Interrupts cell division, stem elongation, and
  seed head formation
• Roots continue to grow
• May reduce the natural Gibberellic acid

8
Rooting Hormones

• Used when propagating plants from cuttings
• Large percent of plants root and root quickly
• Usually mixed w/ talc and used as powders or
  dissolved in liquid and used as a wet dip
• All rooting hormones should contain a fungicide
  to prevent fungi from rotting of the cutting
• (p. 54 fig. 5-7)

9
Dwarfing Rootstocks

• Developed to decrease labor costs in orchards
• Rootstock Root or piece of root used for
  grafting
• Malling Rootstock made it possible to control
  the size and rate of growth of apple trees by
  selecting the proper rooting stock

10
Plant Biostimulants

• Natural and Organic Product (from living
  organisms)
• Work to stimulate soil microbial activity,
  stimulate plant growth and promote disease
  resistance
• Humic acid (byproduct of Humus) is an example
• Methanol blocks photorespiration so plants use
  water for growth rather than transpiring it into
  the air

11
Allelopathy

• The production of a chemical compound by 1 plant
  that slows down or stops the growth of another
  plant
• Naturally used to stop competition from other
  plants
• Some green manure or cover crops have this effect
  on weeds

12
Objectives

• List 1 example of a substance used to stimulate
  plant growth
• Explain why chemical retardants are applied to
  floral crops and name 2 commonly used retardants
• Explain the use of rooting hormones on cuttings
  and list several rooting hormones
• Describe orally the source of 1 plant growth
  stimulant
• Demonstrate the proper application of a rooting
  hormone to cuttings
• Explain how rootstock is used in dwarfing fruit
  trees
• Define biostimulants