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KITTUR RANI CHENNAMMA COLLEGE OF HORTICULTURE, ARABHAVI

GROWTH AND DEVELOPMENT OF FRUIT CROPS

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PRESENTED BY: Vijaylaxmi U K Jr. Msc

PHYSIOLOGY OF FLOWERING IN FRUIT CROPS

- PHOTOPERIODISM

UNIVERSITY OF HORTICULTURAL SCIENCES, BAGALKOT

The first step of sexual reproduction.

Most important in plant breeding.

One of the most dramatic events in the ontogeny of a plant.

Flowering leads to an exciting succession of events like anthesis, fruit set, fruit development, maturation and ripening.

Flowering

Flower MorphologyFlowerReproductive part of the plant. A flower is a metamorphosed shoot meant especially for the reproduction of the plant.

Floral parts1.Sepals2.Petals3.Stamen4.Pistil5.Receptacle

Diagram of a typical flower

Physiology Of Flowering

Flowering Transitional phase in the life cycle

of a plant.Immense importance for

perpetuation & origin of variability in the next generation.

Takes place by the transformation of vegetative apex into a reproductive structure.

The change from the vegetative state to the reproductive state.

Shoot meristem is reduced to develop sepals, petals, stamens, stigma etc.. . in case of leaves.

The plant must attain specific state of “Ripeness to response” before it flowers.

Once the stage is reached, then it can induce to flower.

a. Irreversible changes in which apical bud changes its vegetative phase to reproductive phase.

b. Improper conditions causing flower buds to abort are1. High temp2. Moisture stress

c. Flowering can be induced naturally or through PGR (plant growth regulators).

Flower Initiation and Development

Factors influencing the transformation of the juvenile phase into the mature phase:

1. Temperature – Vernalization2. Photoperiodism3. Drought stress4. Low fertility levels5. Hormonal balance.

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Flower ProductionFour genetically regulated

pathways to flowering have been identified.

1. The light-dependent pathway2. The temperature-dependent

pathway3. The gibberellin-dependent

pathway4. The autonomous pathway. Plants can rely primarily on

one pathway, but all four pathways can be present.

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Physiology of flowering It involves two steps.1. Events in the bud leading to flowering:a. Induction: -flowering stimulus is generated.-Influenced by water stress, chilling temperature or

photoperiod. b. Evocation: -shoot apical has received floral stimulus and

irreversibly committed to form flower bud primordia.

c. Initiation: -evoked bud becomes recognizable as a flower bud

and is thus committed to reproductive development.

-broadening and flattening of the growing points.

2. Differentiation of the growing points:

Increase in synthesis of DNA and RNA.

Frequency of cell division within the central zone of shoot apical meristems is increased.

Shoot meristem is induced to develop sepals, petals, stamens and carpals in case of leaves.

The flat apical meristem becomes domed.

The meristem becomes a block like structure.

The subsequent development of flower meristem is relatively rapid.

The plants in order to flower require a certain day length i.e., the relative length of day and night which is called as photoperiod. The response of plants to the photoperiod expressed in the form of flowering is called as photoperiodism.

Photoperiodism

1. Julien Tournois (1910) – 1st found about Long Day in flowering.

2. George Klebs (1918) – observe the function of Long Day in flowering.

3. Garner & Allard (1920) –found photoperiod ⇨relative duration of light and dark towards control flowering of certain crops.

eg: Tobacco – flowering once expose to short light period (SDP).

Hence it has been concluded that the relative length of the day is a prime factor in flowering of plants.

4. Hamner & Bonner (1938) – Dark time has more function in determining the reaction in photoperiod.

History of photoperiodism

Control of flowering

Flowering

“Florigen” hormone

Flower buds

Photoperiod mechanism in the leaves

Change in day length

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Depending upon the duration of the photoperiod, plants are classified into 3

categories.

18 hours

Short and Long Day Plants Flowering

1. Short Day Plants (SDP): These plants require a relatively short day light period (usually 8-10 hours) and a continuous dark period of about 14-16 hours for subsequent flowering. oThese plants are also known as long-night-plants.

Eg. Chrysanthemums, straw berry, coffee, pineapple etc…

o In short day plants the dark period is critical and must be continuous. If this dark period is interrupted even with a brief exposure of red light (660-665 nm wavelength), the short day plant will not flower.

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2. Long day plants (LDP):These plants require a longer day

light period (usually 14-16 hours) in a 24 hours cycle for subsequent flowering. Also called as short night plants. Eg: Apple, passion fruit etc.. In long day plants the light period is critical. The prolongation of the light period stimulates flowering in long day plants.

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3. Day neutral plant (DNP):Without critical day length, they can flower in any day length of 24hr cycle, if other conditions are satisfied.

eg. Banana, guava, tomato, brinjal etc…

Critical Day Period It is the duration of the photoperiod or the

dark period that ultimately determines whether the plant has to go through vegetative growth or to produce flowers. 

Referred as the day length of 24hr cycle - the shortest day length for LDP flower and the longest day length for SDP flower.

K. Hamner and J. Bonner in 1938

Long Short Day Plants: These are short day plants but must be exposed to long days during early periods of growth for subsequent flowering.Eg : species of Bryophyllum, night jasmine etc..Short-Long Day Plants: These are long day plants but must be exposed to short days during early periods of growth for subsequent flowering. gs: Wheat (Triticum), Rye (Secale),

perennial temperate grass etc…

Initiation of flowering in a plant after exposure of light for a required period of time. It is calculated for a 24hrs. The time of specific exposure to light within a day is called as photoinductive cycle. The number of these cycle may be 1 or 2 or more depending on plant species and together they are called photoinduction.

Photoperiodic induction

It is a biological, proteinaceous pigment that absorbs light.

It is a non photosynthetic, photoreceptor pigment.

Mature leaves are the site of production of these stimulus.

Two types : i) Red light absorbing form which is designated

as PR ii) Far-red absorbing form which is designated as

PFR.

Phytochrome

What Is Phytochrome ?Phytochrome is a pigment found in some plant cells that has been proven to control plant development. This pigment has two forms or “phases”. P-red light sensitive (Pr) and P –far red light sensitive (Pfr) forms. The actual plant response is very specific to each species and some plants do not respond at all.

When PR form of the pigment absorbs red light (660-665 nm), it is converted into PFR form.

When PFR form of the pigment absorbs far-red light (730-735 nm) converted in to PR form.

The PFR form of the pigment gradually changes into PR form in dark.

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H. A. Borthwick and S. B. Hendricks 1950

* Plants measure the ratio of Pfr/Pr.LDP would flower when the ratio is high.SDP would flower when the ratio is low.

Since Pfr is liable to change and is broken down at night it reverts back to Pr.

The longer the night, the lower the phytochrome (Pfr) content.

The relative amount of Pfr remaining at the end of the night would be an indication of the day length.

Flowering in SDP:◦ Short day plants flower when the night

period is long. ◦ In day light or red light, phytochrome red (Pr)

is converted to phytochrome far red (Pfr). The conversion actually only requires a brief exposure to white or red light.

◦ In the dark, Pfr is slowly converted back to Pr. ◦ A long night means that there is a long time

for the conversion. ◦ Under short day conditions (long night) at the

end of the night period the concentration of Pfr is low.

◦ In SDP, low Pfr concentration is the trigger for flowering.

(Fast)

Dark Reversion

Red Light740 nm660 nm

PrPfr

(Slow)

Far Red LightSynthesis Destruction

Vegetative(Non-

Flowering)

Reproductive(Flowering)

Mid-Summer Sunlight

Short-Day Plants Need Low Pfr to Bloom!

In the short-day plant

PFR PR builds upDarkness (slow)

Short-day plants

FLORIGENActivated

FLOWERING

Flowering in LDP:◦ Long day plants flower when the

night period is short.◦ In day light (white or red) the Pr is

converted to Pfr.◦ During periods when the day light

period is long but critically the dark period is short, Pfr does not have long to breakdown in the dark. There is a higher concentration of Pfr.

◦ In LDP, high Pfr concentration is the trigger for flowering.

(Fast)

Dark Reversion

Red Light740 nm660 nm

Pr Pfr

(Slow)

Far Red LightSynthesis

Destruction

Vegetative(Non-Flowering)

Reproductive(Flowering)

Mid-Summer Sunlight

Long-Day Plants NeedLow Pr to Bloom!

In the long-day plant

PFR builds up PR

SunlightRed light

Long-day plants

FLOWERING

FLORIGENActivated

◦ Dark period (length of night is called as Nycto period) more important in photoperiodism reaction because interruption during night will inhibit flowering in SDP but promote flowering in LDP.

◦ Dark interrupted by short exposure of light results in flowering in long day plants. But if light period is interrupted by dark exposure has no effect on flowering.

◦ In short day plants, Pr promotes flowering when Pfr suppresses it, when it is vice versa in long day plants.

Importance of photoperiodismAnnuals can be grown twice or

thrice in a year.Prevention of winter dormancy

and autumn leaf fall.Increased stolon formation

through long days in Strawberry.Plants like radish, carrot etc..can

be made to remain vegetative for longer period.

Yield can be increased.

Photoperiodism and flowering in fruit crops

Mango: Flower induction is caused by cool temperature and not by short photoperiods and flowering is inhibited by warm temperature and not by long photoperiods.

Strawberry: Flower formation is influenced by the duration of length of daily light period. Short days induce flower production.

Papaya: Long day and high temperature promote female flower production where as short day and low temperature promote male flower production.

Pineapple: Neither a diurnal temperature nor short days are necessary for natural flowering.

Guava: There is no quantitative involvement of photoperiod in flowering as it is a day neutral plant.

Passion fruit : Artificial light or long days increase the flowering but number of flowers are reduced in shaded treatment.

In fruit crops like peaches, plums and cherries, floral initiation appears to be unaffected by photoperiod.

Summary SunlightRed light

Darkness (slow)Far red light

(fast)

PFR builds up

Long-day plants

FLOWERING

FLORIGENActivated

PR builds up

Short-day plants

FLORIGENActivated

FLOWERING

References

Fruit Tree Physiology W S Dhillon, Z A Bhat

Physiology Of Crop Plants Franklin Gardener

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