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Describe grapevine reproductive morphology and grapevine varietal differencesRange: inflorescence primordial, buds, flowers, berries, clusters
Describe the 18-month reproductive cycle of a grapevine
Inflorescence initiationThe potential yield of a vine is determined
approximately 16 months before harvest
Inflorescence initiationInflorescence initiation starts in the buds as
they develop and continue to develop for 8-12 weeks
Therefore the basal buds have potentially the most time to develop
Inflorescence initiationInflorescence primordia and tendril
primordia develop from the same initial structures, called anlagen, which are undifferentiated tissue
Environmental conditions and the interaction of hormones determines whether the anlagen will develop into inflorescence primordia or tendril primordia
Inflorescence initiationInflorescence initiation occurs at about the
same time as floweringTherefore conditions at flowering also affect
inflorescence initiationIn good conditions vines usually form two
inflorescence primordia, but may form up to four
Inflorescence initiationInflorescence initiation is favoured by:Warm conditions
Inflorescence initiationLightIncreased light to buds and leaves increases
fruitfulness
(Source: winker, et al, (1974))
Inflorescence initiationOptimum nutrient levelsNitrogen, potassium and phosphorous
deficiencies all affect fruitfulness
Inflorescence initiationCarbohydrate levelsHigh vigour or drought can reduce the
carbohydrate levels reducing inflorescence initiation
Inflorescence initiationThe location of the budGenerally the primary bud has larger and
more inflorescence primordia as it is the most well developed
Buds located at nodes 4-10 potentially tend to have more inflorescence due mainly to the temperatures and time of development
Figure 5.2: fruitfulness along a cane
Inflorescence initiationThese factors have implications for pruningFor example, particularly in cooler climates
cane pruning is favoured to achieve maximum fruitful buds
Inflorescence initiationWhere low crops are desired, for example in
premium cabernet sauvignon spur pruning may be favoured
Canes that have grown in sunlight are generally selected, as they have many potentially fruitful buds
Flowering and Fertilisation
Figure 5.3: bloom sequence of grape flower: (a) calyptra attached, (b) calyptra separating, (c) open flower (after Babo and mach,
1909)(Source: weaver, 1976)
Flowering and Fertilisation
Figure 5.4: flower types: (a) hermaphrodite, (b) female, (c) male(After Babo and mach, 1909)
(Source: weaver, 1976)
Flowering and FertilisationV. Vinifera varieties generally have perfect or
hermaphrodite flowersThese flowers have functional pistil and
stamens so they are capable of self pollination
Flowering and Fertilisationflower development As buds swell in the spring the
inflorescence primordia which developed the year before, begin to differentiate into flowers
Flowering usually occurs 6-10 weeks after the beginning of shoot growth
The flower is fully developed when the pollen is mature in the anthers.
Flowering and FertilisationPollination and fertilisationDefinitions:Pollination:The transfer of pollen from the anther to the
stigma
Flowering and FertilisationFertilisation:The union of male nuclei from the pollen to
the female nuclei in the ovary
Flowering and FertilisationThe first visual indication that pollination is
occurring is when Capfall occursThe pollen is released from the mature
anthers this is termed cap fall and flowering is generally determined as when 80% cap fall occurs
Flowering and FertilisationThe pollen falls onto the stigma, then
develops a tube which grows down the style to the ovary for fertilisation to take place
Fertilisation occurs 2-3 days after pollination
Flowering and FertilisationThe embryo and berry development begin The embryo forms the seeds and the ovary
becomes the berry
Flowering and FertilisationFruit setFruit set is the transformation of flowers to
fruitUp to 70-80% of the flowers may fail to setThe size of the berry is largely determined by
the number of seeds it contains
Flowering and FertilisationThe more seeds the larger the fruitA berry may contain up to four seeds,
although two or less is usual in the wine grape varieties
Berries with pistils that have not been fertilised will abscise from the cluster
This is termed shatter
Flowering and FertilisationThe timing and the duration of flowering
are influenced by: Climate influencesIn warm climates, flowering will begin
when the mean daily temperature reaches 20oC
In cool climates, flowering can last several weeks, and increasing day length is thought to stimulate flowering
Flowering and FertilisationWarm, sunny, dry conditions favour pollen
dispersalCold, wet days prevent cap fall reducing
the level of fertilizationThe growth of the pollen tube is also
temperature sensitive Pollen tube growth is slowed in cooler
weather, leading to a reduction in fertilization
The changes in berry developmentThe green stage (Stage I).
This is a period of rapid cell division leading to increased berry size.
The berry remains hard and green
Stage I Stage II Stage III
Anthesis
Time
Veraison
Ripeness
Ber
ry v
olum
e
Fruitset
The resting stage (Stage II)is a period of slow physical growth, but is the
time seed development occurs.
Stage I Stage II Stage III
Anthesis
Time
Veraison
Ripeness
Ber
ry v
olum
e
Fruitset
The ripening stage (Stage III)The beginning of the ripening period is
signalled by veraison. The berry begins to soften and the colour of
the berry changes due to colour pigment synthesis denoting the start of ripening.
Stage I Stage II Stage III
Anthesis
Time
Veraison
Ripeness
Ber
ry v
olum
e
Fruitset
The ripening stage (Stage III)It is characterised by increasing berry size, but,
sugar begins to increase (increasing Brix), acids decrease, and colour and flavour develop.
The berries become softer to touch and translucent in appearance.
AcidsThe rate of decline of malic acid may
depend on:TemperatureIn hot climates, malic acid is metabolised
more rapidly than in cool climatesAs a rough rule of thumb, reaction rates
for many reactions double or triple for every 10 degrees
AcidsCultivar Some varieties, eg Cabernet franc, Chenin
blanc, Syrah and Pinot noir, have proportionally higher malic acid
Riesling, Semillon, merlot, Grenache have higher tartaric acid content
AcidsThe total amount of tartaric acid in the berry
reduces slowly as the berry ripensHowever, tartaric acid levels decline
compared to berry volume due to a dilution effect of increased in sugars and fluid in the cells
PotassiumPotassium (K+) increases after veraison in the
skin although the mechanism of uptake is not well understood
Potassium uptake increases the pH
Phenolic CompoundsPhenolic compounds give colour, flavour,
aroma and aging properties to wines, especially red wines
Phenolics are found in the seeds and skin, but are generally extracted from the skin during wine making
Anthocyanins are the specific phenols that produce colour in the berry skin
Phenolic CompoundsPhenols are thought to be produced in the
berry itselfThey are not transported from other parts of
the vine
Phenolic CompoundsAnthocyanin synthesis depends ono Temperatureo Sugar accumulationo Hereditary factors
Nitrogen CompoundsDuring ripening the total nitrogen content of
the berry increases due to an increase in ammonia cations, amino acids and proteins
Aromatic CompoundsAroma compounds develop late in berry
development and many are found close to the skin
Ripeness and sun exposure have effects on these compounds
Cultural and Climatic Influences on Berry MaturationYieldAchieving a balance between yield, quality
and vine health is essentialYields have been increased by using:
Improved clonal materialDisease free materialFertilisation, irrigation and pest control
However, increasing yield can reduce the vines ability to mature the fruit
YieldOvercroppingDelays fruit maturityRetains acidityRetards anthocyanin synthesisReduces sugar accumulation and flavour
development Suppresses subsequent yieldsMay shorten vine life
YieldAchieving an ideal yield depends onThe varietySoil characteristicsWeatherThe desired end product
YieldUndercropping Will not necessarily improve vine quality
eitherIt can result in:
YieldProlonged shoot growth and leaf
production Increased shadingDepressed fruit acidityUnbalanced berry nitrogen and inorganic
nutrient concentrationReduced yield can also lead to larger
berries
Sunlight
The proportion of far red light increases within the canopy
Increased proportions of far red is thought to:
Delay anthocyanin synthesis & decrease sugar concentration
Increase ammonia and nitrate content in fruit
Increase the total [email protected]
SunlightSunlight increases anthocyanin synthesisShaded fruit may have higher titratable
acidity and concentrations of tartaric and malic acids and a lower pH
SunlightThis may be a reflection of potassium
accumulation and lower pHMagnesium and potassium can also be
increased by shadingBerry size increases with shadingGrape aroma is also enhanced with
increasing sunlight
TemperatureSunlight directly and indirectly increases
berry temperaturesDarker coloured fruit has increased
temperatures, and tightly clustered fruit will have increased temperature
The Effect of Climatic and Viticultural Variable on Berry TemperatureVariable Effect on Berry Temperature
Sunlight Intensity
Berry temperature increases with increasing sunlight intensity.
Wind speed Berry temperature more closely approaches air temperature with high wind speed.
Fruit exposure Berry temperature is increased with exposure to sunlight and decreased with exposure to clear skies at night.Cluster
compactnessBerry temperature increases with more compact clusters, less wind penetration. Temperature is more rapidly conducted berry to berry across tight clusters.Berry size Large berries are heated in sunlight more than small ones.
Berry colour Dark berries are heated in sunlight more than white ones.
Sugar content Immature berries will be heated more in sunlight than mature.
TemperatureMalic acid metabolismAnthocyanin synthesisSugar accumulationAmino acid contentPotassium accumulationImproved aromas
TemperatureHowever this is varietal dependent and also
dependent on the temperature and duration of temperature
TemperatureIncreased temperature decreases:Flavour and aromaFruit development if high temperatures occur
after pollination, reducing berry size due to vine stress
NutrientsNitrogen directly affects canopy growth and
shadingThis impacts indirectly on fruit qualityLow soil nitrogen may increase anthocyanin
synthesis High potassium levels can reduce berry pH,
lowering fruit colour and colour stability in red wines
WaterWater affects the vine vigourA balance should be achieved to ensure
fruit maturesExcess water leads to canopy shading
which indirectly affects ripeningExcess water can also lead to a dilution
effect in the berry, and in some varieties berry splitting occurs, resulting in quality loss
