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