1.
INTRODUCTION

2.
What is
photoperiodism?

3.
7 photoperiodic classes of
plants

4.
1.Critical day length
In both short day and long day plants there is a
specific light period which imposes a restriction
on flowering called critical day length .
2.Critical night length
Critical night lengths is that continuous dark
period which must not exceed in long day
plants and should always be exceeded in short
day plants .

5.
1.Short day plants (SDP)
Short day plants flower when day
length is shorter than certain
critical period.
Photoperiod below critical day length –
flowering
Photoperiod above critical day length –no
flowering
Short day plants=long night plants

6.
2.Long day plants (LDP)
Long day plants flower when day length is
longer than a certain critical day length.
Photoperiod below critical length – no flowering .
Photoperiod above critical length – flowering.
Long day plants =short night plants
Ex.spinacea oleracea,beta vulgaris,oat plant etc.

7.
Short -long day plant(SLDP)
 Short long day plant actually long day plants but
in their early life they need short day conditions.
 They will flower only if a certain no.of short days
are followed by certain no. of long days
 Ex. trifolium repens
 Canterbury bells

8.
Long- short day plants(LSDP)
 Long short day plants are short day plants but
require long day condition initially
 These plants flower when long photoperiods are
followed by short photoperiods.
 Example. Bryophyllum

9.
Day- neutral plants
 These plants flower in any photoperiod .
 They are insensitive to day length.
 Ex. Tomato , Phaseolus vulgaris etc.
plants can only flower within a definite
range of light hours .above and below the
range no flowering occurs.
Ex.sugarcane,kidney bean

10.
Amphiphotoperiodic plant
 They are reverse of the intermediate plants .
flowering both above and below an intermediate
day length .
 The plants remain vegetative in intermediate
day length .
 Ex.media elegans

11.
Night break phenomenon
 Plants with critical night length ,a short flash of light
in middle of night could make the plant behave as if
it has been exposed to long day.
 As a result no flowering will occur in (SDP)

12.
Photoperiodic induction
 An important photoperiod in 24 hours cycles
constitutes one inductive cycle .
 Plant may require one more inductive cycles for
flowering.
 i.e. soy bean -2cycles (SDP)
 Plantago-25 cycles(LDP)
 Continuous inductive cycle-early flowering
 Discontinuous inductive cycle –late flowering

13.
significance
 Most importantly in flowering
 Bud dormancy
 Control vegetative trait
 Tuberisation in plants
 Bulb formation
 More yield of fruit.