Write a note on vernalization.

Explanation

1. Certain plants require a low temperatue expousre in their earlier stages for flowering.
2. Many species of biennials and perennials are induced to flower by low temperature exposure `(0^(@)C to 5^(@)C)`. This process is called vernalization.
3. The term vernalization wa first used by T. D. Lysenko (1938).
Mechanism of Vernalization:
Two main theories to explain the mechanism of vernalization are:
1. Hypothesis of phasic development Hypothesis of hormonal involvement
Hypothesis of phasic development:
1. According to Lysenko, development of an annual seed plant consists of 2 phases.
2. First phase is thermo stage, which is v egetative phase requiring low temperature and suitable moisture.
3. Second phase is photo stage which requires high temperature for synthesis of florigen (flowering hormone).
Hypothesis of hormonal involvement:
1. According to Purvis (1961), formation of a substance A from its precusor, is converted into B after chiling.
2. The substance B is unstable. At suitable temperature B is converted stable compound D called Vernalin.
3. Vernalin is converted to F (Florigen). Florigen induces flower formation.
At high temperature B is converted to C and devernalization occurs.
Techiqune of Vernalization:
1. The seeds are first soaked in water and allowed to germinate at `10^d(@)C to 12^(@)C`.
Then seeds are transferred to low temperature `(3^(@)C to 5^(@)C)`.
3. Germinated seeds after this treatment are allowed to dry and then sown.
4. The plants will show quick flowering when compared to untreated control plants.
Devernalization: Reversal of the effect of vernalization is called devernalization.
Practical applications:
1. Vernalization shortens the vegetative period and induces the plant to flower earlier.
2. It increases the cold resistance of the plants.
It increases the resistance of plants to fungal disease.
5. Plant breeding can be accelerated.