CHAPTER: 14(C)
Vernalization
Vernalization:
•
The
term vernalization was coined by T.D. Lysenko in 1920s. Other important scientists
who have contributed to the study on vernalization were F.G. Gregory and O.N.
Purvis (1961).
•
In
many plants the flowering is influenced not only by the correct photoperiod but
also by temperature.
•
The
cold (low temperature) treatment to a plant bud or seedling in order to fulfil
a specific low temperature requirement for accelerating flowering is called
vernalization or Yarovisation.
•
Chourad
(1960) has defined vernalization as the “Acquisition of the ability to flower
by a chilling treatment.
•
This
type of agricultural practices results in shortening of the interval between
sowing and flowering.
•
Vernalization
method can be successfully applied in a no. of plants, mostly belonging to
families Graminae (oat, Wheat), leguminaceae (Pea, Clover), Cruciferae
(Cabbage) etc.
•
Vernalization
does not occur in dry seed. The seed should be semi-germinated and should have
an active embryo.
•
The
cold treatment (low temperature) to a plant bud seedling in order to fulfill
specific low temperature requirements for accelerating flowering is called vernalization.
•
Klippart in 1857, while working with two
varieties of wheat the winter and spring wheat, noticed the low temperature
requirement for flowering.
•
The
winter wheat is shown in winter and produces flower in summer. And spring wheat
is shown in the spring season and produces flower in summer.
•
He
observed that if the germinated seeds of winter wheat are treated with a low
temperature these can behave as spring wheat. He concluded that the winter
wheat require low temperature (O0C to 50C) for subsequent
flowering.
•
Lysenko
(1929-30) observed that, if seeds of winter wheat are germinated in an ice box
and subjected to suitable light, moisture, these can be shown in spring season
and will flower with spring varieties of wheat.
•
He
gave the name of this phenomenon as “transformation of winter forms in to
spring forms or vernalization”.
•
Vernalization
may be defined as “the method of inducing early flowering in plants by treatment
of their seeds at very low temperature”.
Site
of Vernalization:
•
Root
and shoot apices, apical buds, leaves, and embryos are the plant parts may be
the potential site of vernalization.
Requirement
of Vernalization:
- Low
temperature, (Perception of cold stimulus).
- Presence
of floral hormone i.e., Vernalin
- Active
embryo or shoot (age of plant)
- Oxygen
- Water
- Growth
activators are required to express the effect of vernalization.
Mechanism
of Vernalization:
Ø The mechanism of
vernalization can be discussed by two theory:
- Phasic
development theory
- Hormonal
Theory
- Phasic
development theory:
•
Lysenko
gave a two phasic theory, according to which growth and development of a plant
are two distinct phenomena.
•
Growth
is an increase in the size of a plant without any profound qualitative change
in the growing parts.
•
During
development the plant enters a new phase qualitatively differing from the
preceding phase and bringing it nearer to its final phase of life, i.e., fruit
bearing.
•
Exposure
to low temperature is necessary for the change over from growth phase to
development phase.
•
Starting
of any of these phases will take only when the previous phase has been
completed
•
The
phase requires different external condition for completion such as light &
temperature.
•
Since
vernalization process is dependent on a sequence of biochemical reactions,
water, oxygen are indispensable in the vernalization process.
•
Purvis
stated that seed must contain at least 90% water of their absolute dry weight
for adequate vernalization.
•
Vernalization
of dry seed is not possible. It is also not possible to vernalize seeds kept in
an atmosphere of nitrogen in spite of provision of adequate quantities of
water.
•
The
oxygen requirement is though low but absolute. The respiratory energy is
necessary. If respiratory inhibitors are used the response to vernalization
decreases.
Importance
of Vernalization:
•
Crops
can be produced earlier and crops can be grown in the region where they do not
grow naturally.
•
Plant
breeding can be accelerated by the application of vernalization technique.
•
It
increase the cold and drought resistance power of the plant.
•
Helps
to reduce incidence of diseases in several plants .
•
Enhance
the yield of crops.
•
Vernalization
is required to break dormancy and induce growth.
•
Off
season vegetables and crops and flowers can be produced by vernalization.
•
May
help to resolve the adverse condition during the period of development of
crops.
•
Devernalization
helps in the control of flowering of onion, garlic, potato, and other no. of
plants.
•
It
shortens the vegetative period and hasten flowering period which will make a
benefit to the farmer.
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