Vernalisation

VERNALISATION

There are plants, in which flowering is qualitatively or quantitatively dependent on exposure of low temperature.

In annual plants growth usually starts in the spring, flowers are formed in the summer and fruits and seeds are produced in the fall.

Biennials on the other hand, remain vegetative in the first growing season and after prolonged exposure to cold winter temperature, flower in the following season.

Cold treatment during winters is essential for flowering for these plants.

If they do not get it, they either do not flower or their flowering is much reduced.

The effect of cold or chilling treatment that plants get during winters in the field can be given in the laboratory.

As a result of this artificial cold treatment, the biennials and many winter varieties of cereals can be made to flower in the same season.

This low temperature treatment is known as vernalization or yarovization (= making spring like).

The term vernalization was given by Russian scientist Lysenko.

Site of vernalisation : Shoot tip, embryo tip, root apex, as observed by Wellensiek.

Requirements of Vernalisation

1. Low temperature : 0º -5ºC

2. Period of low temperature : Few hours -few days

3. Actively dividing cells (Meristematic cells)

4. Water

5. Aerobic condition

6. Proper nourishment

In the process of low temperature treatment a hypothetical hormone called vernalin (by Melcher's) is produced.

It is now believed that vernalin is a gibberellin like substance, because vernalized plants have higher gibberellin levels than non vernalized plants.

Vernalization is beneficial in reducing the period between germination and flowering.

Thus, more than one crop can be obained during a year.