Growth and Development of Horticultural Crops (1+1)

Mechanism of vernalization

Phasic development theory

• The main points in this theory advanced by Lysenko (1934) are the growth and development of an annual seed plant consists of series of phases which must occur in some predetermined sequence.
  
• Commencement will take place only when preceding phase is over.
  
• The phases require different external conditions for completion like light and temperature.
  
• Vernalization accelerates the thermophase.
Hormonal theories

• First hormonal theory was proposed by Lang and Melchers (1947) is schematically shown below



• According to the scheme, precursor A is converted into a thermolabile compound B during cold treatment.
  
• Under normal conditions, B changes into C which ultimately causes flowering. But at higher temperature B is converted into D and flowering does not take place (devernalization).