Grape_Physiology_7_horones
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Transcript Grape_Physiology_7_horones
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Plant Growth Regulators are substances
synthesized by the plant to act as messengers
They are produced at one site and generally
transported in the xylem or phloem to another
to induce a physiological reaction (eg growth)
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Very small amounts of hormone are required
to cause an action
They may act either alone or interact with
other hormones
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They may also cause different effects in
different parts of the grape vine
These reactions are complex and not always
fully understood
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There are five main groups of hormones in
plants
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Source of production
New vegetative growth
Young leaves
Seeds
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Actions
Attracts sugar and nutrients to site of
production
Stimulates cell growth in young tissue
Inhibits lateral budburst further down the
shoot ie apical dominance
Promotes growth towards light
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Source of production
Young growing shoot and leaves
Root tips
Actions
Suppresses flower bud initiation and fruitfulness in cool
weather/poor light
Promotes growth and cell elongation
Example
GA-3 is sprayed on seedless grapes to increase grape size
and yield
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Source of production
Root tips
Actions
Promotes cell multiplication in differentiating
tissues at apices
Attracts auxin and gibberellin, sugars, nutrients
Promotes even budburst
Promotes lateral branching
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Promotes development of leaves, fruit
structures, fruit set with gibberellins to
balance fruitfulness of lateral buds
Delays senescence
Promotes berry as a sink
Involved in anthocyanin and flavour formation
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Source of production
Mature leaves
Seeds, roots
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Action
Generally counteracts effects of auxin, gibberellin
and cytokinin
Induces stomatal closure in response to water
stress
Reduces growth in response to water stress, cold
and short days
Possibly promotes ripening as auxin production
reduces in seeds
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Source of production
Mature leaves and other parts of vine
Action
Affects many types of growth, not all of which are
clearly defined
Promotes ripening and berry colour
Promotes abscission zone development
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In general terms, auxins and gibberillins
complement each other, promoting growth
Cytokinin induces fruit and ripening when
weather conditions and other factors are suitable
for fruit to ripen
Absissic acid and ethylene promotes ripening and
prepares the vine for dormancy
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Table 7.2: factors affecting hormone
production
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Auxin is produced in the growing tips and
travels downwards
To prevent uneven budburst and end point
principle, where the end bud bursts first, canes
are arched during pruning to slow the
movement of auxin along the cane
Spur pruning is not subject to uneven
budburst
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Removal of the growing tip will promote
lateral growth, as the site of auxin inhibition of
budburst is removed
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Shaded shoots tend to grow long and spindly
with long internodes until they reach light,
where growth becomes normal
Buds also tend to be less fruitful in shaded
vines, due to the actions of gibberellin
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Berry size is related to the number of seeds
(developed embryos) due partly to hormone
production, increasing the berry as a sink
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Warm, well drained soils during budbreak
improve the evenness of budburst due in part
to cytokinins produced from increased root
growth promoted due to the warmer
conditions
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Fruitfulness
The number of clusters is increased with
warmer temperatures due to cytokinin
production
Whereas in shaded or cool situations
gibberellins tends to promote tendril
formation
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As vegetative growth slows close to ripening,
less auxin and gibberellins are produced
Less auxin is produced as the seed ripens in
stage 2
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Abscissic acid increases in proportion
inducing véraison and the berry becomes a
major sink
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Cytokinin also increases, attracting sugar to
the berry, abscissic acid and perhaps having an
effect on berry colour and flavour
Continuing ripening during cool climates may
depend partially on warmer soil temperatures
favouring cytokinin production
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Ethylene is used as a growth regulator
Ethephon liberates ethylene
Depending on timing of application it may:
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Increase berry colour and enhance maturation
Slow vegetative growth
Enhance budbreak
Cause cluster abscission
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Researchers have found that irrigating one side
of a plant can produce the same crop with half
the water
It can also increase colour and flavour
production by up to 30%
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As one half of the vine's root system is watered,
the other half begins to dry out
This stimulates the production of abscissic acid
This causes the leaves to partly close their
stomata and the shoot growth to uniformly slow
down, thereby conserving water
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If this situation is maintained, shoot function
will eventually recover
However, at about the time that recovery
starts the other side of the root system is
watered
This leaves the first side to dry out which
ensures one side is constantly in a 'dry phase'
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Hormones are synthesized within the vine control
the initiation and development of inflorescence
primordia within the bud
They do not act in isolation
Relative proportions of determine what is formed
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The number size of inflorescences is the first
indication of yield
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Yield
Yield
per vine
Vines
per hectare
Bunches
per vine
Inflorescences
per shoot
Bunch
weight
Shoots
per vine
Nodes
per vine
Berry
number
Percent
bud break
Florets per
inflorescence
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Percentage
fruit set
Berry
size
Berry
abscision
Fecundity
› the potential reproductive capacity of an organism or
population
Fruitfulness
› The presence of inflorescence primordia in latent buds
› Mean bunch number per shoot
› Three step process:
Formation of an uncommitted primordium
Development into inflorescence primordium
Formation of flowers
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The grapevine buds develop in the axil of the
leaf and the shoot, that is, at the node.
There are various types of grapevine buds:
Prompt bud
Compound bud
Latent bud
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The lateral shoot arises from the lateral or
prompt bud
It is formed between the primary or new
season’s shoot and the leaf arising from it, that
is, in the leaf axil
It may be also referred to as the true axillary
bud
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The prompt bud can burst in the current
season to produce short shoot known as the
lateral
However, lateral shoots will form only under
certain conditions
Vigorous vines or if topping occurs early in the
season
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Lateral shoots are generally unfruitful but
bunches may grow on the lateral shoot
If they do they are usually small and ripen
after those carried on the primary shoot
These bunches are referred to as 'second set'
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The compound bud is formed after the prompt
bud and develops more slowly
These buds also develop in the leaf axil at the
node.
It consists of three true buds
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The compound bud does not burst until the
season after its development
Generally only the middle, or primary, bud
bursts to develop the primary (main) shoot
If this is damaged (wind, frost, etc) then the
secondary or tertiary buds may burst
However, these buds are generally less fruitful,
that is they have fewer bunches per shoot
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The number of potential bunches per bud
develops in the previous season before bud
burst
Those at the base of the shoot will be more
developed than those close to the apical tip.
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Environmental factors during bud
development influence the potential crop in 18
months time
A major influence is light interception at the
bud and the temperature; increased light and
temperature has been shown to result in
greater fruitfulness.
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These are buds that may be any type of bud
that do not burst in the season that they are
formed
Instead they remain dormant and viable and at
some later stage may burst. Latent buds may
take several seasons to burst, often as a result
of vine damage or heavy pruning
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Buds undergo differentiation
That is, primordial structures within the bud
change depending on plant growth regulators
that these structures receive
The level of plant growth regulators that the bud
receives is dependant on climatic conditions
during differentiation
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Differentiation coincides with flowering
And the slowing down of vegetative growth
Very sensitive to water stress
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Anlagen is a primordia that can become
Inflorescences
› Repeated branching
Tendrils
› Few branches
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Enhance initiation of anlagen
Encourage tendril formation as opposed to
inflorescence formation
Recall…
Promote cell elongation so
Possibly a mechanism to promote vegetative
growth over reproductive?
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Enhance initiation of anlagen
Encourage inflorescence formation as opposed
to tendril formation
Recall…
Promote cell division
Produced in warm conditions
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Discourage the initiation of anlagen
Recall…
Produced by the roots in response to water
stress
The process is very sensitive to water stress
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