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

Abstract

Intermediate-day plants (IDP) flower most rapidly and completely under intermediate photoperiods (e.g., 12-14 h of light), but few species have been identified and their flowering responses are not well understood. We identified Echinacea purpurea Moench as an IDP and, based on our results, propose a novel mechanism for flowering of IDP. Two genotypes of E. purpurea ('Bravado' and 'Magnus') flowered most completely (>/=79%) and rapidly and at the youngest physiological age under intermediate photoperiods of 13-15 h. Few (</=14%) plants flowered under 10- or 24-h photoperiods, indicating E. purpurea is a strongly quantitative IDP. Plants were also induced to flower when 15-h dark periods were interrupted with as few as 7.5 min of low-intensity lighting (night interruption, NI). Flowering was progressively earlier as the NI increased to 1 h, but was delayed when the NI was extended to 4 h. Stem length increased by >/=230% as the photoperiod or NI duration increased, until plants received a saturating duration (at 14 or 1 h, respectively). Flowering was inhibited when 16-h photoperiods were deficient in red (R, 600-700 nm) light, and was promoted when photoperiods were deficient in far-red (FR, 700-800 nm) light. Because of our results, we propose the flowering behavior of IDP such as E. purpurea is composed of two mechanisms: a light-dependent response operating through light-labile (type I) phytochrome in which flowering is inhibited by an LD, and a light-stable (type II) phytochrome (i.e., phyB, D and E) response in which flowering is promoted by a short-night.

Effect of different shading intensities on growth and yield of cherry tomato

“…The similar results were reported by Singh et al (2013). Runkle and Heins (2001) reported that far red (FR) -deficient environments effectively retard stem extension in many herbaceous plants, they can delay flower initiation in some long day plants.…”

Dual induction rather than intermediate daylength response of flowering in Echinacea purpurea

“…Although no flowering occurred in continuous SD or LD in the present experiments (Table 2), a small proportion (10–15%) of cv. Bravado plants flowered in 10‐h and 24‐h photoperiods in the experiments by Runkle et al (2001). This difference was attributed by the authors to the fact that the plants were raised in 14–16 h daylengths, conditions which are inductive to flowering in this plant (Runkle et al 2001).…”

“…Bravado plants flowered in 10‐h and 24‐h photoperiods in the experiments by Runkle et al (2001). This difference was attributed by the authors to the fact that the plants were raised in 14–16 h daylengths, conditions which are inductive to flowering in this plant (Runkle et al 2001). Partial induction could therefore have taken place before the experimental treatments were started.…”

“…Recently, Runkle et al (2001) reported that the ornamental perennial Echinacea purpurea cv. Bravado and Magnus flowered most completely and rapidly at intermediate photoperiods of 13–16 h. Accordingly, they classified the plant as a quantitative intermediate daylength plant.…”

Seasonal flowering and evolution: the heritage from Charles Darwin

“…Because the sequence of inductive conditions is crucial, dual induction photoperiodic plants will not flower in either constant SD or constant LD conditions and, hence, they are distinct from daylength neutral species (Heide 2004). Such a dual daylength response is also not to be confused with intermediate daylength responses where LD and SD inputs may be satisfied simultaneously (Runkle et al 2001).…”