. Soc. Hort. Sci. 121 694 698 Davis, T.D. Andersen, A.S. 1989 Growth retardants as aids in adapting new floricultural crops to pot culture Acta Hort. 252 77 85 Downs, R.J. Thomas, J.F. 1982 Phytochrome regulation of flowering in the long-day plant
Fumiko Kohyama, Catherine Whitman, and Erik S. Runkle
Ki Sun Kim, Art Cameron, and Erik S. Runkle
Echinacea purpurea Moench., or purple coneflower, has been classified both as an intermediate-day plant and a short-day/long-day plant by different research groups. We performed experiments to determine at what developmental stage Echinacea`Magnus' became sensitive to inductive photoperiods, and identified photoperiods that induced the most rapid flowering. Seedlings were raised under continuous light in 128-cell plug trays, then were transplanted into 11.4-cm plastic pots. Plants were transferred to 10-hour short days (sd) once seedlings developed 3, 4, 5, 6, 7, or 8 true leaves. After 4 or 6 weeks of sd treatment (primary induction), plants were moved to 16- or 24-hour photoperiods until flowering (secondary induction). Plants were also grown under continuous 10-, 14-, and 24-hour photoperiods to serve as controls. At least 4 leaves were required for flower induction; flowering was delayed and the percentage was low when plants had 3 leaves at the beginning of primary induction. Plants under continuous 14-hour photoperiods had the highest flower percentage (100%) and flowered earliest (87 days). Plants under continuous 10- and 24-hour photoperiods did not flower. Four weeks of sd followed by 16-hour photoperiods induced complete flowering and in an average of 95 days. However, 6 weeks sd was required for 100% flowering when the final photoperiod was 24 hours.
Erik S. Runkle and Royal D. Heins
Plastics that selectively reduce the transmission of far-red light (FR, 700 to 800 nm) reduce extension growth of many floricultural crops. However, FR-deficient (FRd) environments delay flowering in some long-day plants (LDPs), including `Crystal Bowl Yellow' pansy (Viola ×wittrockiana Gams). Our objective was to determine if FR light could be added to an otherwise FRd environment to facilitate flowering with minimal extension growth. In one experiment, plants were grown under a 16-hour FRd photoperiod, and FR-rich light was added during portions of the day or night. For comparison, plants were also grown with a 9-hour photoperiod [short-day (SD) control] or under a neutral (N) filter with a 16-hour photoperiod (long day control). Flowering was promoted most (i.e., percent of plants that flowered increased and time to flower decreased) when FR-rich light was added during the entire 16-hour photoperiod, during the last 4 hours of the photoperiod, or during the first or second 4 hours after the end of the photoperiod. In a separate experiment, pansy was grown under an FRd or N filter with a 9-hour photoperiod plus 0, 0.5, 1, 2, or 4 hours of night interruption (NI) lighting that delivered a red (R, 600 to 700 nm) to FR ratio of 0.56 (low), 1.28 (moderate), or 7.29 (high). Under the N filter, the minimum NI duration that increased percent flowering was 2 hours with a moderate or low R:FR and 4 hours with a high R:FR. Under the FRd filter, 2 or 4 hours of NI lighting with a moderate or low R:FR, respectively, was required to increase percent flowering, but a 4-hour NI with a high R:FR failed to promote flowering. Pansy appears to be day-neutral with respect to flower initiation and a quantitative LDP with respect to flower development. The promotion of reproductive development was related linearly to the promotion of extension growth. Therefore, it appears that in LDPs such as pansy, light duration and quality concomitantly promote extension growth and flowering, and cannot readily be separated with lighting strategies.
Matthew G. Blanchard and Erik S. Runkle
Kent State Univ. Press Kent, OH Blanchard, M.G. Runkle, E.S. 2009 Effects of a new cyclical lighting system on flower induction in long-day plants: A preliminary investigation Acta Hort. 813 623 630
Erik S. Runkle and Royal D. Heins
For many long-day plants (LDP), adding far red light (FR, 700 to 800 nm) to red light (R, 600 to 700 nm) to extend the day or interrupt the night promotes extension growth and flowering. Blue light (B, 400 to 500 nm) independently inhibits extension growth, but its effect on flowering is not well described. Here, we determined how R-, FR-, or B-deficient (Rd, FRd, or Bd, respectively) photoperiods influenced stem extension and flowering in five LDP species: Campanula carpatica Jacq., Coreopsi ×grandiflora Hogg ex Sweet, Lobelia ×speciosa Sweet, Pisum sativum L., and Viola ×wittrockiana Gams. Plants were exposed to Rd, FRd, Bd, or normal (control) 16-hour photoperiods, each of which had a similar photosynthetic (400 to 700 nm) photon flux. Compared with that of the control, the Rd environment promoted extension growth in C. carpatica (by 65%), C. ×grandiflora (by 26%), P. sativum (by 23%), and V. ×wittrockiana (by 31%). The FRd environment suppressed extension growth in C. ×grandiflora (by 21%), P. sativum (by 17%), and V. ×wittrockiana (by 14%). Independent of the R: FR ratio, the Bd environment promoted stem extension (by 10% to 100%) in all species, but there was little or no effect on flowering percentage and time to flower. Extension growth was generally linearly related to the incident wide band (100 nm) R: FR ratio or estimated phytochrome photoequilibrium except when B light was specifically reduced. A high R: FR ratio (i.e., under the FRd filter) delayed flower initiation (but not development) in C. carpatica and C.×grandiflora and inhibited flower development (but not initiation) in V.×wittrockiana. Therefore, B light and the R: FR ratio independently regulate extension growth by varying magnitudes in LDP, and in some species, an FRd environment can suppress flower initiation or development.
Richard L. Harkess and Robert E. Lyons
A study was undertaken to determine the rate of floral initiation in Rudbeckia hirta. R. hirta plants were grown to maturity, 14-16 leaves, under short days (SD). Paired controls were established by placing half of the plants under long days (LD) with the remainder left under SD. Beginning at the start of LD (day 0), five plants were harvested daily from each photoperiod group for twenty days. Harvested meristems were fixed in 2% paraformaldehyde - 2.5% glutaraldehyde in 0.1 M sodium cacodylate buffer (pH 7.0) for 24 hrs, dehydrated in an ethanol series, embedded in paraffin and sectioned at 8 μm. Serial sections were stained with Methyl-green Pyronin, with adjacent sections treated with RNase for nucleic acid comparison. All events of floral initiation were identified, The results of limited inductive photoperiod indicate that 16-18 LD were required for flowering.
Yi-Lu Jiang, Yuan-Yin Liao, Tzong-Shyan Lin, Ching-Lung Lee, Chung-Ruey Yen, and Wen-Ju Yang
chlorohydrin, KNO 3 , and CaC 2 , have been tested but did not promote winter flowering of pitaya ( Chang, 2003 ; Khaimov and Mizrahi, 2006 ; Yen and Chang, 1997 ). Pitaya is generally known as a long-day plant, which flowers in several flushes between May
Yi-Lu Jiang, Yuan-Yin Liao, Meng-Tzu Lin, and Wen-Ju Yang
commonly grown red pitaya varieties are selected from crosses between Hylocereus undatus and Hylocereus sp. Pitaya is a long-day plant, which flowers in several flushes between May and October in the northern hemisphere ( Luders and McMahon, 2006 ). The
Chin Chin Lee, Ted E. Bilderback, and Judith F. Thomas
Photoperiod treatments of 10, 12, 14, and 16 hours and a field control were used to determine the photoperiodic response of Heptacodium miconioides Rehd. The F values for vegetative growth responses under various photoperiods exhibited a highly significant linear effect. Leaf count, area, and weight, shoot length, and stem weight were lower for plants exposed to the 10- or 12-hour photoperiod than those of plants grown under the 14- or 16-hour photoperiod or in the field. Plants under the 10- or 12-hour photoperiod became dormant after 5 weeks of treatment. The growth responses for the 10- and 12-hour photoperiods were similar. There also were no differences in growth responses of plants from the 14- and 16-hour photoperiods or from the field. A favorable photoperiod for growth of Heptacodium must exceed 12 hours; thus, it can be classified as a long-day plant in reference to vegetative growth. Leaf tissues under the 10- and 12-hour photoperiods were significantly thicker than those under the 14- and 16-hour periods or under field conditions due to longer cells of the palisade mesophyll layer. Plants grown in the field and under the 14- or 16-hour photoperiods were the only ones that initiated inflorescences. With days at 30C, leaf and stem dimensions were larger than those at 22C. Nights at 18C resulted in a larger leaf area, leaf weight, and stem weight than at 26C. There was a significant effect on total leaf thickness due to day × night temperature interaction.
Peter R. Hicklenton, Suzie M. Newman, and Lindsay J. Davies
The effects of night temperature (NT) and photosynthetic photon flux (PPF) on time to flower and flower yield in `Bristol Fairy' and `Bridal Veil' Gypsophila paniculata L. (perennial baby's breath) were studied in controlled environments. Plants were grown with nights at 8, 12, 16, and 20C and 450 or 710 μmol·s-1·m-2 photosynthetic photon flux (PPF). Days were at 20C. In both cultivars, the times from the start of treatments to visible bud and from visible bud to anthesis were delayed at the lower PPF and at an NT <20C. The delays in `Bristol Fairy' were greater than those in `Bridal Veil'. Failure of `Bristol Fairy' plants to reach anthesis was common at SC NT and either 450 or 710 μmol·s-1·m-2 PPF; whereas in `Bridal Veil', nearly all plants flowered, regardless of environmental conditions. Flower yield (measured as fresh weight of inflorescences) decreased with NT in `Bristol Fairy' but was highest at 8 or 12C in `Bridal Veil'. In a second experiment using the same cultivars, the effect of curtailing long-day (LD) conditions at various stages on stem elongation and flower yield was investigated. `Bristol Fairy' required more LD cycles (>56) than `Bridal Veil' for maximum stem elongation and flower yield. Terminating LD conditions before the start of inflorescence expansion resulted in lower yields and shorter plants in both cultivars.