The conversion of winter variety of wheat into spring variety by low temperature or chilling treatment was termed as vernalisation by Lysenko. Acceleration of the ability to flower by a chilling treatment.
Mechanism of Vernalisation
There are two main theories regarding mechanism of vernalisation
(i) Phasic Development Theories: Vernalisation occurs mostly by chilling treatment or low temperature.
(ii) Hormonal Theory: The vernalisation involves the formation of a floral hormone called vernalin. Formation of floral hormone, which is transmitted to other parts of the plant.
Importance of Vernalisation
(a) Vernalisation increase the cold resist of plant.
(b) It helps in the crop-improvement.
(c) It increase the resistance of plants to fungal disease.
(d) To reduce the vegetative period and induce the flowering.
The plants in order to flower, require a certain day length is the relative length of day and night which is called as photoperiod.
The response of plants to the photoperiod expressed in the form of flowering is called as
photoperiodism. The phenomenon of photoperiodism was first discovered by Garner and Allard (1920, 22) with soyabean, tobacco, etc. Depending upon the duration of the photoperiod, they classified plants into three categories
(i) Short Day Plant: These plants require a relatively short day light period (usually 8-10 h) and a continuous dark period of about 14-16 h. For subsequent flowering, e.g., soyabean, rice, strawberry.
(ii) Long Day Plants: The plants requiring a photoperiod of more than 12 h are called long day plant like barley, Hibiscus syriacus, etc.
(iii) Day Neutral Plants: These plants flower in all photoperiod ranging from 5-24 h. Continuous exposure like tomato, cotton, sunflower, etc.
(iv) Intermediate Plants: The plants require a photoperiod of 12-15 h for flowering.
(v) Long-short Day Plants: These plants require first long photoperiod and then short photoperiod.
(vi) Short-long Day Plants: These plants require first short photoperiod and then long photoperiod for flowering.
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