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Fruits - Fruit Development
Objectives
To learn how fruits developConsider the factors that influence fruit
growthConsider how horticulturists influence the
growth and development of fruitsLearn about “ripening” - final stage of fruit
development
What is a fruit?
Botanically, a fruit is : one or more mature ovaries together with
accessory tissues
Horticulturally, a fruit is: one or more mature ovaries together with
accessory tissues that is relatively high in sugar content and, functionally, is usually eaten during the dessert portion of a meal, or as a sweet salad or snack
Flower structure that leads to fruit structure
Ovary PositionMultiple Separate Ovaries Per FlowerMultiple Flowers
Ovary Position
Grape Apple
Superior (above) Example:
Graperesults in a berry
fruit (primarily ovary tissue)
Ovary Position
Inferior (below) Example:
Appleresults in a
pome fruit (primarily receptacle tissue)
Ovary Position
Multiple Ovaries per Flower
WholeFlower
Cross Section Of Flower
WholeFruit
MultipleOvariesMultipleOvaries
Multiple Ovaries per Flower
Example: Blackberry results in an
Aggregate Fruit Includes receptacle
tissue
(Raspberry does not include receptacle tissue)
Multiple Flowers
Pineapple
Inflorescence
Receptacle & ovaries develop into fruit
Flowers
Multiple Flowers
Example: Pineapple results in a
Multiple Fruit (primarily ovary tissue fused together)
Individual Berry-like FruitsReceptacle & ovaries develop into fruit
Ovary Wall Structure
Pericarp Exocarp (outer layer) Mesocarp (middle layer) Endocarp (inner layer)
Examples: All 3 fleshy - berry Endocarp stony - drupe All 3 hard - nut
Seed(s)
Factors that affect fruit size
Number of cells per fruitNumber of leaves per fruitIntra-plant competition for photosynthateSeed formation
Fruit Growth Stages (after pollination & fertilization)
Cell Division (to increase the number of cells in the fruit)
Cell Expansion (to increase the fruit to mature size)
Ripening
Fruit Growth Pattern
FruitFreshWeight
Time
Pollination/Fertilization
CellDivisionPeriod
Cell Expansion Period Ripening Period
Maturity (Full sized fruit)
Fruit Growth Pattern
Cell Division Sets potential for
ultimate size of fruit
Cell Expansion Achieves mature size
FruitFreshWeight
Time
Pollination/Fertilization
CellDivisionPeriod
Cell Expansion PeriodRipening Period
After this point, there will not be any more cells in this fruit
Number of Cells per Fruit
Cell Division
4 cells
9 cells
Limits the Potential for Fruit Size
1 cell
1 cell
this
or this
Each cell can only get so big, so how many cells matters!
Each single cell from mitosis Only has the potential to get to a specific maximum size
Factors that affect fruit size
Number of cells per fruitNumber of leaves per fruitIntra-plant competition for photosynthateSeed formation
Number of Leaves per Fruit
Leaves are the sources of photosynthate (fixed carbon), developing fruits are the sinks for photosynthate Source = supplier Sink = user
More leaves per fruit means larger fruit (up to a point!)
Leaves per Fruit Effect
Cultivar or Leaf:Fruit Leaf Area FruitSpecies Ratio (cm2)/Fruit Volume (cm3)
10 171 131.420 372 167.4
Golden Delicious Apple 30 585 225.540 812 227.250 965 228.3
10 438 68.720 877 89.8
Elberta Peach 30 1316 90.740 1754 110.150 2199 119.475 3300 133.8
Factors that affect fruit size
Number of cells per fruitNumber of leaves per fruitIntra-plant competition for photosynthateSeed formation
Intra-plant Competition
A whole-plant view of not enough leaves per fruit
Overall, too many fruits and too few leaves
Removing some fruits very early in their development can allow those that remain to increase in size
How far can you go with reducing competition?
In apple, can you remove all but one fruit and grow that one remaining apple to be as big as, say, a watermelon?
NO!
The basic genetics of the species will prevent it!
So, way too many leaves per fruit is a waste!
You reach a point of diminishing return!
Factors that affect fruit size
Number of cells per fruitNumber of leaves per fruitIntra-plant competition for photosynthateSeed formation
Seed Formation
Seed number & distribution (in multi-seeded fruits) affect fruit size.
Each developing seed sends a hormonal signal (auxin) that stimulates pericarp and/or receptacle development around or near it.
If few seeds develop, fruit will be mis-shapen; if too few develop, fruit will abort.
Hormonal effect of seeds
In apple, each part of the ovary has two seeds. Their growth stimulates the receptacle and ovary tissue to develop. No seeds, little development
Cross-section
Longitudinal section
Absence of seed development
Absence of seed development
Seed develop-ment
Seed develop-ment
Apple Seed No./Fruit Size
Hormonal effect of seeds
In strawberry, each achene has one seed and stimulates the receptacle tissue to develop below it. Few achenes result in mis-shapen fruit!
Normal, dozens of achenes
One achene
Three achenes
The Exception!
Fruit can develop without any pollination or fertilization or seed development!
Called parthenocarpy From: parthenos (Gr., maiden)
carpic (Gr., fruit)
Examples: bananas, navel oranges, seedless grapes
Other Hormone Effects
Fruit shape and size can be altered by application of hormones Auxin or gibberellic acid (GAx)
Examples: Thompson Seedless grapes (green) - larger Red Delicious apples - more lobed
A Horticultural Manipulation
Fruit thinning to increase fruit size
Thinning the crop
Horticulturists thin (remove some young fruit) to increase leaf:fruit ratio and reduce intra-plant competition.
Timing of thinning is critical!Thinning, to be effective, must be done
early in the cell division phase of growthAfter cell division is complete, the ultimate
potential size of the fruit is set!
When to thin, When its too late
FruitFreshWeight
Time
Pollination/Fertilization
CellDivisionPeriod
Cell Expansion PeriodRipening Period
Maturity (Full sized fruit)
THIN HERE
TOO LATE
Why thin before cell division?
Assume a branch of an apple tree with 10 flowers
Assume enough leaves on that branch to support cell division in the developing ovaries (fruits) to total10,000 cells on the branch
If all 10 fruits remain on the branch and go through cell division, each fruit will have 1000 cells
If fruit thinning (remove 5 apples = 1/2 of the fruit) occurs then (after cell division is done) the 5 remaining apples will each have only 1000 cells!
If the number of flowers begins at 10, but fruit number is thinned to 5 just as cell division begins, and then cell division procedes to its maximum of 10,000 cells total, each fruit will have 2000 cells!
So, Thinning: after cell division: 5 fruits@1000 cells ea. before cell division: 5 fruits@2000 cells ea.
Number of Cells per Fruit
Cell Division
4 cells
9 cells
Limits the Potential for Fruit Size
1 cell
1 cell
Each cell can only get so big, so how many cells matters!
Each single cell from mitosis Only has the potential to get to a specific maximum size
How is fruit thinning done?
Hormone sprays to trees shortly after “petal fall”
Summary
Horticultural fruits are varied in structure.Fruit development procedes in a definable
patternSeveral factors in that development
influence fruit sizeHorticulturists use thinning in tree fruit
crops to influence the final size of fruits