Photoperiodism and Vernalisation

PHOTOPERIODISM:

Photoperiodism is the Physiological response of plants to relative length of light (day) and dark(night) periods.

W.W.Garner and H.A. Allard (America 1915-20) found that a newly developed tobacco mutant, Maryland Mammoth and soybeans (Glycine Max) had strange seasonal pattern in flowering.

The term 'photoperiodism' was coined by Garner and Allard (1920) 

They classified the plants into three groups according to their photoperiods

a) Short day plants : Such plants require to flower the day length less than the certain critical day length (for say 12 hours) Such plants are also called long night plants

Examples of short day plants are 

Maryland Mammoth , tobacco ,soybean , Chrysanthemum, rice , Chenopodium album , Xanthium strumarium

Generally kharif crops and many tropical plants .

b) 

Such plants which flower only when the day length is longer than a certain period 

That's why such plants are also called short night plants.Wheat , barley , oat , Sugarbeet , spinach , lettuce , castor generally rabi crops.

Day neutral plants:

Such plants are unaffected by the day length

e.g. Maize , tomato , sunflower, cotton , cucumber, balsam

Critical Period:

It is the photoperiod required to induced flowering e.g. M.M. tobacco  CDP is 12 hours

Vernalisation 

Firstly G.Gassner of Germany reported the effect of temperature on reproductive development.Vernal means spring

The term 'Vernalisation was coined by T.D. Lysenko (1920)

The Russian term 'Jarovizacija' means pre sowing treatment 

Vernalisation is the cold treatment to a plant bud or seedling in order to fulfil a specific low temperature requirement for accelerating the flowering.

Site of Vernalisation:

Growing point apical buds

Cause: The growth substance formed by low temp. Induction was named ' Vernalin' by G.Melchers(1939)

According to Mikhail Chailakhayan (1968) there were two substances responsible for Vernalisation :

1) Gibberellin or Gibberellin like substances 

2) Anthesin

Devernazation: If   the vernalized seed or plant is kept at high temperature just after Vernalisation , the effect of the low temp. Treatment is completely removed .This process is called devernalisation

Factors of Devernalisation:

a) High temp

b) Anaerobic condition 

Practical benefits:

1) To induce earlier flowering and earlier maturity of crop

2) To escape frost , drought and flood

3) To extend Cultivation to the region with very low temp 

Agricos 

Vaishnavi Nimkar 🌾🌱🌾