PHOTOPERIODISM
Photoperiodism is the phenomenon of physiological changes that occur in plants in response to relative length of day and night (i.e. photoperiod). ¢ The response of the plants to the photoperiod, expressed in the form of flowering is also called as photoperiodism. ¢ The phenomenon of photoperiodism was first discovered by Garner and Allard (1920). TYPES OF PHOTOPERIODISM Depending upon the duration of photoperiod, the plants are classified into three categories. 1. Short day plants (SDP) 2. Long day plants (LDP) 3. Day neutral plants (DNP) 1. SHORT DAY PLANTS These plants require a relatively short daylight period (usually 8-10 hours) and a continuous dark period of about 14-16 hours for subsequent flowering. These plants are also known as long-night plants. ¢ E.g. Rice, coffee, soybean, tobacco and chrysanthemum ¢ In short day plants, the dark period is critical and must be continuous. If this dark period is interrupted with a b...