Flowering of Aeschynanthus 'Koral' at Fluctuating and Constant Temperatures

Autor: Mark Roh, Brooks Whitton, Will Healy
Rok vydání: 1990
Předmět:
Zdroj: Journal of the American Society for Horticultural Science. 115:906-909
ISSN: 2327-9788
0003-1062
Popis: Stock plants of Aeschynanthus ‘Koral’ were grown with irradiances of 120 or 240 μmol·s·m at 18/17, 24/17, or 30/17C (day/night) under 12-hour thermoand photoperiods. Tip cuttings from stock plants grown at 18/ 7C 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 thermoand photoperiods (100 μmol·s·m). 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. Aeschynanthus are valued for their brilliant red or orange flowers that form in leaf axil or in a terminal cluster (Liberty Hyde Bailey Hortorium, 1976). Saylor (1973) began a breeding program in the late 1960s to develop compact hybrids. These new hybrids and upright species have attracted new interest in Aeschynunthus as a potted floral crop in the greenhouse industry (Christensen, 1988; Paludin, 1985). A. 'Koral’ (syn. Schlatter’s Koral) is a hybrid of unknown lineage that was provided by the U.S. Dept. of Agriculture Florist and Nursery Crops Laboratory. This cultivar may have resulted from crosses between A. speciosus and A. hildebrandii in Denmark (Lentjes, 1985). ‘Koral’ was chosen for this project because it is compact and it flowers prolifically, producing brilliant red flowers with maroon stripes. The foliage is not glossy, unlike that of some other cultivars. The effect of temperature on flowering of Aeschynanthus has not been thoroughly studied. Past research has focused on whether flowering was promoted by either increasing irradiance, temperature, or by photoperiod. Zimmer (1972) grew A. speciosus in a 12-hr photoperiod (incandescent lamps; 3700 lux) at 14, 17, 20, or 23C nights and 23C days. After 145 days, vegetative growth increased with increasing night temperature. Only plants at a constant 23C flowered, but only 20% of these plants reached anthesis. Zimmer did not consider whether absolute temperature or relative difference between night and day temperatures was involved in the flowering response. Flowering may have been triggered by constant temperatures. Zimmer also found that light quantity was more effective than daylength in promoting early flowering. He concluded that for A. speciosus to flower, high light and high temperature were required. Welander (1984) tested night temperatures of 12, 15, 18, or 21C (day temperatures maximally 4C higher) and found that days to anthesis of A. speciosus increased with increasing temperature. In a preliminary study, plants of A. ‘Koral’ grown in growth for publication 29 Jan. 1990. Scientific Article no. A-6039, Contri8200 of the Maryland Agricultural Experiment Station. We acknowlland Sea Grant College for computer support and the USDA Florist ry Crops Laboratory for graduate assistance and plant material. The blishing this paper was defrayed in part by the payment of page nder postal regulations, this paper therefore must be hereby marked ent solely to indicate this fact. student. Professor. chambers at 18/17C day/night initiated flowers before plants grown at 24/17 or 30/17C. These results coincided with Christensen’s (1988) remarks that vegetative growth of A. hildebrandii takes place at 21C or above, while flowering occurs at 17 to 18C. Low temperature seemed to be the primary factor triggering rapid flowering of Aeschynanthus. The objectives of this research were to determine: 1) the flowering response of A. ‘Koral’ to a range of temperatures; 2) whether constant or fluctuating temperatures promote rapid flowering; and 3) whether the light or dark period temperature was critical. Materials and Methods Stock plant treatments (expt. 1). On 23 Nov. 1987, plants of A. ‘Koral’ were placed in growth chambers at 18/17, 24/17, or 30/17C ( ± lC;day/night) under 12-hr thermoand photoperiods. Irradiance levels of 120 or 240 μmol·s·m -2 were supplied with cool-white fluorescent plus incandescent lamps. Nitrogen at 200 mg·liter (20N-8.6P-16.6K) was applied weekly. On 13 Jan., fifteen 5-cm tip cuttings were harvested from each chamber. Three cuttings were directly rooted per 0.75-liter pot containing Premix Bx medium (Premier, Pointe Her Pere, Quebec, Canada) under natural photoperiod in a glasshouse (21/18C day/night minimum air temperature). After cuttings rooted, fertilization was resumed. Number of leaves and shoot length were recorded at anthesis of the first flower in the terminal cluster. On 4 Apr. (after 81 days), a floral rating was assigned and the number of leaves and shoot length were recorded on all plants not at anthesis. Floral ratings were assigned as follows: O = vegetative shoots; 1 = visible bud present; 1.5 = bud >1 cm long; 2 = anthesis; and 3 = post-anthesis. Stock plants grown at 18/17C were discarded due to prolific flowering and lack of vegetative growth. Cuttings from the 24/ 17 and 30/17C chambers were harvested on 9 Mar., 1 Apr., or 23 May. Three cuttings were directly rooted per 0.75 -liter container and grown under natural days in a glasshouse as before. Floral ratings of cuttings were recorded on 1 or 24 June (April and May harvest), at which time cuttings were flowering. Floral rating was analyzed using SAS GLM procedure (SAS Institute, Cary, N.C.). Stock plant and cutting treatments (expt. 2). On 9 Mar., fifteen 5-cm cuttings were harvested from stock plants grown at J. Amer. Soc. Hort. Sci. 115(6):906-909. 1990. Table 2. Floral stage of plants that originated from stock plants grown at 30/17 or 24/17C with 12-hr thermoand photoperiods. Cuttings were harvested on 9 Mar., 1 Apr., or 23 May and floral ratings were assigned 81, 86, or 30 days later, respectively. Plants were grown in a greenhouse at 21/18C after the cuttings were harvested (expt. 1). Stock plant day/night temperature Date of cutting harvest (“c) March April May ‘Floral rating (O = vegetative, 1 = visible bud, 1.5 = bud >1 cm, 2 = anthesis, 3 = post-anthesis). **Significant at P = 0.01. 30/17 or 24/17C (240 μmol·s ·m) and directly rooted in pots placed into 18/17, 24/17, or 30/17C chambers, thus resulting in six treatments. Number of leaves, leaf number of lowest bud, and floral rating were recorded on 3 June, after 86 days, at which time plants were flowering. Constant vs. fluctuating temperatures (expt. 3). Plants were grown in growth chambers at 18, 24, or 30C (± 2C) during a 12-hr light period, then plants were transferred to 18, 24, or 30C for a 12-hr dark period resulting in nine treatment combinations. Irradiance was suppIied with daylight fluorescent lamps at 100 μmol·s·m -2 at canopy level. Six plants of A. ‘Koral’ (pruned to three shoots each) were placed in treatments on 12 Jan. A replicate in time began 13 Mar. Fifteen apices from shoots similar to the three left on the pruned plants were dissected and determined to be vegetative at the start of treatment. Number of leaves >1.5 cm (from leaf tip to base) were recorded, and the top leaf was notched to allow successive growth measurement. Data were collected after 18 weeks from the start of treatment. The following data were recorded: number of leaves unfolded >1.5 cm; node at which the first flower bud appeared (from notched leaf); number of flower buds; and length of longest flower bud. Data were analyzed using SAS GLM procedure.
Databáze: OpenAIRE
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