response of plants to duration and
timings of light and dark periods
Plant in order to flower require a
particular day length or light
period called photoperiod and
response of plants in terms of
flowering is called
7. 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 .
8.
9. 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
10.
11. 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.
12.
13. 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
14. 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
15. 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
16. 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
17. 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)
18. 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
19. significance
Most importantly in flowering
Bud dormancy
Control vegetative trait
Tuberisation in plants
Bulb formation
More yield of fruit.
