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  • Author or Editor: Will Healy x
  • Journal of the American Society for Horticultural Science x
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Shoot emergence of cold-treated Liatris spicata Willd. corms was inhibited by SC soil, delayed at 10 or 15C (7 and 5 days, respectively), and promoted at 20, 25, or 30C. Within 15 days after planting, soil at 20C promoted the highest percentage of shoot emergence (81%). Plants were grown during the first 35 days after emergence under a combination of temperature and long or short days. Flowering shoot length was increased by either short days (8 hours; SD) at 13 or 15C or a 4-hour incandescent night interruption (NI) at 18C. When planted in May, a NI at 15 or 18C decreased the time to harvest by up to 14 days, whereas in November increasing the temperature to 18C, regardless of photoperiod, decreased the days to harvest by 16 days. Plants grown during the first 35 days after emergence under natural days at 15C then placed at 13, 15, or 18C under NI until harvest did not respond to the increasing temperature. Temperature and photoperiod influence Liatris development primarily during the first 35 days of development.

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The increase in photosynthetic photon flux (PPF) and plant temperature associated with supplemental high pressure sodium (HPS) irradiation were investigated during Petunia × hybrids Villm. `Red Flash' seedling development. Seedlings were treated for 14 days following emergence or 5 days after the first true leaf had expanded to 1 mm. Treatments consisted of continuous infrared (IR) radiation (Ambient + IR), ambient conditions with spill-over radiation from adjacent treatments (Ambient - IR), root zone heating to 19.5C (RZ Heat), continuous HPS irradiation at 167 μmol·s-1.m-2 PPF (HPS + IR) or continuous HPS irradiation at 167 μmol-1·m-2 PPF filtered through a water bath to remove IR (HPS - IR). Linear regression of natural log-transformed fresh weights indicated that increasing ambient PPF 53% and elevating plant temperature 4.3C (HPS + IR) increased seedling relative growth rate (RGR) by 45% compared with the control (Ambient - IR). Elevating plant temperature with + IR by 4.8C without supplementing PPF (Ambient + IR) increased RGR by 31% but failed to increase fresh weight (FW) above controls and resulted in etiolated plants that were unsuitable for transplanting. Once plants were removed from supplemental treatment and returned to ambient conditions, RGR for all treatments was similar. The increased FW promoted by IR and HPS treatments was maintained for up to 7 days after treatment. Therefore, the increased seedling growth responses observed with HPS treatment were due primarily to an increase in RGR during HPS treatment that is not sustained beyond treatment.

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Petunia × hybrida Villm. `Red Flash' plants received either 10 or 20 mol·day-1 photosynthetic photon flux (PPF) in growth chambers at: 175 μmol·m-2·s-1 for 16 hours, 350 μmol·m-2·s-1 for 8 or 16 hours, or 350 μmol·m-2 s-1 for 8 hours plus 8 hours of incandescent photoperiod extension (5 μmol·m-2·s-1 PPF). The irradiation components of peak, total, and duration were examined. Doubling total PPF increased total carbohydrate (CHO) production by 60%, seedling dry weight (DW) by 30%, rate of seedling growth by 25%, and acid invertase activity by 50% compared to the other treatments, once the seedlings had reached the two-leaf stage. Seedlings receiving 20 mol·day-1 PPF partitioned 14% more CHO into ethanol soluble sugars rather than starch, which may explain the increase in relative growth rate observed with supplemental irradiance treatments. Extending the photoperiod for 8 hours with 5 μmol·m-2·s-1 PPF reduced total CHO production by 50% compared to the same treatment without photoperiodic lighting. Treatment with 350 μmol·m-2·s-1 for 8 hours resulted in the highest O2 evolution (8.8 μmol O2/min per dm2). Increasing the photoperiod from 8 to 16 hours gave the lowest rate of O2 evolution (4.5 μmol O2/min per dm2). Previous reports of the importance of photosynthetic period in controlling partitioning between starch and sugars may have simply observed a decreasing rate of starch accumulation due to increased total PPF.

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Stock plants of Aeschynanthus `Koral' were grown with irradiances of 120 or 240 μmol·s-1·m-2 at 18/17, 24/17, or 30/17C (day/night) under 12-hour thermo- and photoperiods. Tip cuttings from stock plants grown at 18/17C flowered earlier than those from stock plants grown at 24/17 or 30/17C when cuttings were forced in a glasshouse under natural days (23/18 C). No cuttings from stock plants grown at 30/17C reached the visible bud stage after 86 days, while 93% of the cuttings forced at 18/17C did reach the visible bud stage. A. `Koral' plants were grown at 18, 24, or 30C in a factorial combination of temperatures at 12-hour thermo- and photoperiods (100 μmol·s-1·m-2). After 8 weeks, only plants grown at 18/18C had visible buds. After 18 weeks, plants grown at 24/24 or 24/18C had visible buds after having unfolded =2.5 times as many leaves as plants grown at 18/18C. Rapid flowering of A. `Koral' is promoted by constant 18C under a 12-hour photoperiod.

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