Vernalization (Yarovization)

Temperature, besides light, is the other major environmental factor governing flowering; a plant's response to temperature is described by three cardinal points -- minimum, optimum and maximum. Vernalization is the term for a low-temperature (chilling) pretreatment that induces early flowering; the phenomenon was first noted by Klippart in 1918, and the term itself was coined in 1928 by T. D. Lysenko for the effect of low temperature on the flowering of plants. Chouard (1960) defined vernalization simply as the acceleration of a plant's ability to flower brought about by chilling.

Many plants -- cereals and crucifers among them -- require a period of cold treatment before they will flower; practically, this is done by pretreating seeds or seedlings at a low temperature of about 1-6 degrees C for four to six weeks. The site where vernalization is perceived is believed to be the shoot apical meristem, and in most annual plants vernalization is effective when applied at the seed stage. Like the photoperiodic stimulus, the vernalization stimulus is thought to be a transmissible chemical signal, hypothesised as 'vernalin', which Melchers (1939) showed could be transferred from a vernalized plant to a non-vernalized one by grafting.

Advantages of vernalization :

• Crop plants attain early flowering, by the shortening of the juvenile phase.
• Crops can be cultivated in regions where they do not grow naturally.