Transcript Horticulture Unit 5 GROWTH STIMULANTS, RETARDANTS AND ROOTING HORMONES Growth Regulating Substances  Called hormones: organic chemicals which act and interact to affect growth rate  Auxins: accelerate growth by.

Horticulture
Unit 5
GROWTH STIMULANTS,
RETARDANTS AND
ROOTING HORMONES
Growth Regulating
Substances
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Called hormones: organic chemicals which
act and interact to affect growth rate
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Auxins: accelerate growth by stimulating
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Gibberellins: stimulate growth in stem
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Cytokinins: stimulate cell division (only
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Inhibitors: inhibit seed germination,
cell enlargement
and leaf by cell elongation
works with auxins present)
stem elongation and hasten ripening of
fruit.
Growth Hormones
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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.
Apical Dominance
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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.
Major Discoveries
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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
Chemical Stimulants
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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
Natural Stimulants
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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
Chemical Retardants
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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)
Rooting Hormones
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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.
Rooting Hormones
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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.
Dwarfing Rootstock
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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.
Commercially Used
Plant Growth Regulators
Trade Name
Effect
Used on
A-Rest
Shortens stem length
Mums, lily, poin settia
B-Nine
Shortens stem length
Mum, hydrangea, petunia, azalea ,
poinsettia
Cycocel
Shortens stem on poinsettia,
induces heavier flower bud set on
azalea
Poinsettia , aza lea, geraniu m
Phosfon
Shortens stem length
Lily, mum
Florel
Induces basal breaks on roses,
retards growth on poinsettia ,
increases number of branches on
carnation, speeds ripening of
tomatoes, assists in faster rooting
Rose, poinsettia, carnation ,
tomato, cuttings
Bonzi
Shortens stem length
Sumagic
Shortens stem length
Poinsettia , geranium, petunia,
mum, impatiens, coleus, pansy,
snapdragon, celosia
Poinsettia , mum, ce losia , coleus,
marigold, periwinkle, petunia,
ageratum, dahlia
Student Activities
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Complete self-evaluation at the
end of this unit.
Using nursery catalogs and
books, make a list of available
dwarf fruit trees and details.