1. Fruits - Fruit Development

2. Objectives
To learn how fruits develop
Consider the factors that influence fruit
growth
Consider how horticulturists influence the
growth and development of fruits
Learn about “ripening” - final stage of fruit
development

3. 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

4. Flower structure that leads
to fruit structure
Ovary Position
Multiple Separate Ovaries Per Flower
Multiple Flowers

5. Ovary Position
Grape Apple

6. Superior (above)
Example:
Grape
results in a berry
fruit (primarily
ovary tissue)
Ovary Position

7. Inferior (below)
Example:
Apple
results in a
pome fruit
(primarily
receptacle
tissue)
Ovary Position

8. Multiple Ovaries per Flower
Whole
Flower
Cross Section Of Flower
Whole
Fruit
Multiple
Ovaries

9. Multiple Ovaries per Flower
Example:
Blackberry
results in an
Aggregate Fruit
Includes receptacle
tissue
(Raspberry does
not include
receptacle tissue)

10. Multiple Flowers
Pineapple
Inflorescence
Receptacle &
ovaries develop
into fruit
Flowers

11. Multiple Flowers
Example:
Pineapple
results in a
Multiple Fruit
(primarily
ovary tissue fused
together)
Individual Berry-like FruitsReceptacle &
ovaries develop
into fruit

12. 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)

13. Factors that affect fruit size
Number of cells per fruit
Number of leaves per fruit
Intra-plant competition for photosynthate
Seed formation

14. 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

15. Fruit Growth Pattern
Fruit
Fresh
Weight
Time
Pollination/
Fertilization
Cell
Division
Period
Cell Expansion Period Ripening Period
Maturity (Full sized fruit)

16. Fruit Growth Pattern
Cell Division
Sets potential for
ultimate size of fruit
Cell Expansion
Achieves mature size
Fruit
Fresh
Weight
Time
Pollination/
Fertilization
Cell
Division
Period
Cell Expansion Period
Ripening Period
After this point, there will not be any more cells in this fruit

17. 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

18. Factors that affect fruit size
Number of cells per fruit
Number of leaves per fruit
Intra-plant competition for photosynthate
Seed formation

19. 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!)

20. Leaves per Fruit Effect
Cultivar or Leaf:Fruit Leaf Area Fruit
Species Ratio (cm2
)/Fruit Volume (cm3
)
10 171 131.4
20 372 167.4
Golden Delicious Apple 30 585 225.5
40 812 227.2
50 965 228.3
10 438 68.7
20 877 89.8
Elberta Peach 30 1316 90.7
40 1754 110.1
50 2199 119.4
75 3300 133.8

21. Factors that affect fruit size
Number of cells per fruit
Number of leaves per fruit
Intra-plant competition for photosynthate
Seed formation

22. 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

23. 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?

24. 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!

25. Factors that affect fruit size
Number of cells per fruit
Number of leaves per fruit
Intra-plant competition for photosynthate
Seed formation

26. 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.

27. 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

28. Apple Seed No./Fruit Size

29. 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

30. 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

31. 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

32. A Horticultural Manipulation
Fruit thinning to increase fruit size

33. 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 growth
After cell division is complete, the ultimate
potential size of the fruit is set!

34. When to thin, When its too late
Fruit
Fresh
Weight
Time
Pollination/
Fertilization
Cell
Division
Period
Cell Expansion Period
Ripening Period
Maturity (Full sized fruit)
THIN HERE
TOO LATE

35. 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

36. 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!

37. 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.

38. 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

39. How is fruit thinning done?
Hormone sprays to trees shortly after
“petal fall”

40. Summary
Horticultural fruits are varied in structure.
Fruit development procedes in a definable
pattern
Several factors in that development
influence fruit size
Horticulturists use thinning in tree fruit
crops to influence the final size of fruits