Flowering of Herbaceous Perennials under Various Night Interruption and Cyclic Lighting Treatments

Abstract

<jats:p>Six long-day species of herbaceous perennials were grown under six night-interruption (NI) photoperiod treatments to determine their relative effectiveness at inducing flowering. Photoperiods were 9-hour natural days with NI provided by incandescent lamps during the middle of the dark period for the following durations: 0.5, 1, 2, or 4 hours; 6 minutes on, 54 minutes off for 4 hours (10% or 6/54 cyclic lighting); or 6 minutes on, 24 minutes off for 4 hours (20% or 6/24 cyclic lighting). For five species, the experiment was repeated with more mature plants; for the sixth, <jats:italic>Rudbeckia fulgida</jats:italic> Ait. `Goldsturm', following a cold treatment of 8 weeks at 5 °C. The species generally showed a quantitative flowering response to the NI duration until a saturation duration was reached; as the length of the uninterrupted night break increased, flowering percentage, uniformity, and number and plant height increased and time to flower decreased. Minimum saturation durations of NI were 1 hour for <jats:italic>Coreopsis grandiflora</jats:italic> Hogg ex Sweet `Early Sunrise' and <jats:italic>Hibiscus moscheutos</jats:italic> L. `Disco Belle Mixed', 2 hours for <jats:italic>Campanula carpatica</jats:italic> Jacq. `Blue Clips' and <jats:italic>Coreopsis verticillata</jats:italic> L. `Moonbeam', and 4 hours for unchilled <jats:italic>R. fulgida</jats:italic> `Goldsturm'. <jats:italic>Echinacea purpurea</jats:italic> Moench `Bravado' flowered similarly across all lighting treatments. The 6/24 cyclic lighting regimen induced flowering comparable to that under a continual 4-hour NI for four of the six species and the cold-treated <jats:italic>R. fulgida</jats:italic> `Goldsturm'. Flowering under the 6/54 regimen was generally incomplete, nonuniform, and delayed compared to that under saturation duration treatments. Three of five species flowered earlier when more mature plants were placed under the NI treatments. Cold-treated <jats:italic>R. fulgida</jats:italic> `Goldsturm' flowered more rapidly than unchilled plants and the saturation duration of NI decreased to 1 hour.</jats:p>

Photoperiod and Cold Treatment Regulate Flowering of Rudbeckia fulgida `Goldsturm'

“…This phenomenon has also been reported with other species (Grossin and Mathon, 1961;Lang, 1965). Similarly, Runkle et al (1998a) found that the saturation duration of NI for 'Goldsturm' decreased from 4 to 1 h following 8 weeks of cold. A cyclic lighting regimen, 6 min on and 24 min off for 4 h (20% or 6/24 cyclic lighting), was as effective as a continual 4-h NI for cooled plants, but not for noncooled plants (Runkle et al, 1998a).…”

“…In agreement with Yuan (1995) and Runkle et al (1998a), but not Nau (1996), a cold treatment was not required for flowering of 'Goldsturm' but did hasten time to flower by ≈35%. Application of a cold treatment also reduced the number of new nodes developed below the first inflorescence.…”

“…In addition, Yuan (1995) recommended that, to overcome juvenility, plants have at least 10 nodes before inductive long days (LD) are provided. Four hours of lighting during the middle of 15-h nights were sufficient to induce flowering of 'Goldsturm'; shorter night interruption (NI) durations or cyclic lighting regimens were ineffective or delayed flowering for noncooled plants (Runkle et al, 1998a).…”

Photocontrol of flowering and stem extension of the intermediate‐day plant Echinacea purpurea

“…We reported the sensitivity of E . purpurea ‘Bravado’ to short (30 min) durations of NI (Runkle et al 1998). To our knowledge, no NI studies have been performed on any other IDP.…”

“…The FR response is supported by many studies in which NI and day‐extension (DE) lighting containing R and FR more effectively induce flowering (i.e., flowering is more complete and rapid) than light deficient in FR. Some exceptions exist: Whitman et al (1998) found that lamps with various R:FR (from 0.7 to 8.8) induced flowering similarly in 3 species that Runkle et al (1998) found were light‐dominant LDP. Nevertheless, in many LDP, FR light simultaneously promotes flowering (through light‐labile phytochrome) and stem extension (through light‐stable phytochrome).…”