Abstract
To assess photoperiod sensitive/insensitive phases of 3 long day plants (LDPs) viz., Pansy cv. Baby Bingo, Snapdragon cv. Coronette and Petunia cv. Dreams and one short days plant (SDP) viz., Cosmos cv. Sonata Pink a non-linear statistical model was used for its validation. Six plants of each cultivar were transferred from LD to SD and Vice versa at four days interval from emergence until first flower appearance. Plants at juvenile phase (initial phase of development) were insensitive to photoperiod in both inductive (LD for LDPs and SD for SDP) and non-inductive (SD for LDPs and LD for SDP) environment. After completing the juvenile phase when plants were transferred from LD to SD (Pansy, Snapdragon and Petunia) and SD to LD (Cosmos), they showed a coherent recognition of the stimulus carry forward from their respective inductive environment and induced flowering. However, plants transferred from non-inductive environment to inductive showed a continuous phase of photosensitivity. The duration of photoperiod sensitive phases varied with the cultivars. Hence, it is concluded that LDPs and SDP are not sensitive to photoperiod during their entire course of growth and development. Therefore, providing light during whole growing span is mere wastage of energy. These cultivars require 5-10 days of photoperiod at critical phase to flower that will minimize the production cost of cut flower industry.