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Horticulture Unit 5

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Inhibitors: inhibit seed germination, stem elongation and hasten ripening of fruit. ... Using nursery catalogs and books, make a list of available dwarf fruit ... – PowerPoint PPT presentation

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Title: Horticulture Unit 5


1
HorticultureUnit 5
  • GROWTH STIMULANTS, RETARDANTS AND ROOTING HORMONES

Original Power Point Created by Rebecca
Johnson Modified by Georgia Agricultural
Education Curriculum Office June 2002
2
Growth Regulating Substances
  • Called hormones organic chemicals which act and
    interact to affect growth rate
  • Auxins accelerate growth by stimulating cell
    enlargement
  • Gibberellins stimulate growth in stem and leaf
    by cell elongation
  • Cytokinins stimulate cell division (only works
    with auxins present)
  • Inhibitors inhibit seed germination, stem
    elongation and hasten ripening of fruit.

3
Growth Hormones
  • Organic chemicals principally produced by
    actively growing plant tissue such as short tips
    and young leaves.
  • They move throughout the plant and can be found
    in many parts.
  • They react with one another.

4
Apical Dominance
  • The terminal bud secrets chemicals which inhibit
    or prevent growth of lateral buds.
  • This causes the plant to grow tall and not send
    out side branches.
  • Seems to be a genetic program directing the plant
    to grow above competing plants.
  • Once the plant reaches flowering age, the
    terminal bud becomes a flower bud and the
    chemicals are no longer secreted.
  • Pinching the terminal bud has the same effect and
    side branching occurs sooner.

5
Major Discoveries
  • Chemical and natural stimulants that cause plants
    to grow taller or faster
  • Chemical retardants that cause plants to grow
    slower
  • Hormones that cause plants to root faster
  • Dwarfing rootstock for fruit trees

6
Chemical Stimulants
  • Enables plants to grow taller.
  • Most common is gibberellic acid
  • Gibberellic acid causes the stems of plants to
    stretch out
  • The nodes (the joints at which bulbs, leaves and
    branches) are further apart

7
Natural Stimulants
  • Chemical known as alcohol Triacontanol
  • Found in alfalfa and has been known to nursery
    men for 30 years.
  • Stimulation is brought about by mulching with
    alfalfa hay or by watering plants with an alfalfa
    tea

8
Chemical Retardants
  • Used to retard the growth of plants making them
    shorter and more compact and therefore more
    attractive.
  • One of the newest applications for growth
    retardants is on lawns, a chemical called Limit
    is used new and it restricts grass growth for 6
    to 8 weeks.
  • A new plant regulator called Sumagic reduces
    the height of plants by inhibiting production of
    the hormone Gibberellic acid. (which cause stems
    to elongate)

9
Rooting Hormones
  • When propagating plants from cuttings, it is very
    important that they root as quickly as possible
  • Indoleacetic acid (IAA) is a natural plant
    hormone that causes roots to form
  • Chemical hormones, indolebutyric acid (IBA) or
    naphaleneacetic acid (NAA) are the most common
    used today.

10
Rooting Hormones
  • Rooting hormones are either mixed with talc and
    used as powders or mixed with liquid and used as
    a wet dip
  • All rooting hormones should contain a fungicide.

11
Dwarfing Rootstock
  • As the cost of labor has increased, growers are
    looking for smaller trees.
  • Discovered trees from certain types of roots, do
    not grow as large and bear fruit earlier.
  • A complete series of rootstock known as malling
    rootstock was developed.

12
Commercially Used Plant Growth Regulators
13
Student Activities
  • Complete self-evaluation at the end of this unit.
  • Using nursery catalogs and books, make a list of
    available dwarf fruit trees and details.
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