Effect of varying lengths of inductive and supplementary non-inductive photoperiods on vegetative growth and flowering of Impatiens balsamina

Abstract

The photoperiodic requirement for flowering in Impatiens balsamina changes with the length of the photoperiod. Floral buds were initiated with two 8 hr but with four 15 hr photoperiods and flowers opened with four 8 hr but twenty-eight 15 hr photoperiods. A part of the photoperiodic requirement for floral induction in this plant can be substituted by LDs containing 4 or more hours of darkness (10). It indicates the identical nature of the floral stimulus produced during the dark period, whether it forms a part of the inductive or non-inductive cycles. The effect of these supplementary non-inductive photoperiodic cycles in causing floral bud initiation also depends on the length of the first inductive obligatory cycle. More floral buds and flowers were produced on plants exposed to 15 hr than 8 hr photoperiods, probably due to the higher number of leaves that were produced under the former condition of weaker induction. The shorter the dark period in the photoperiodic cycle, the weaker the induction, the slower the rate of extension growth but the more differentiation of leaves.