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Adenium obesum (Forssk.), Roem. & Schult., commonly known as desert rose, is a high-value, container-grown ornamental plant produced worldwide for its bright floral display and striking sculptural caudex. Little scientific-based information exists regarding the effect of light intensity and nutritional levels on Adenium growth and flowering. In this study, A. obesum ‘Red’ and ‘Ice Pink’ were grown under full sun [with a measured maximum photosynthetically active radiation (PAR) of 1850 mmol·m·s], 30% shade (1255 mmol·m·s), or 50% shade (943 mmol·m·s) in 1.25-L pots topdressed with controlled-release fertilizer Nutricote Plus (18N–2.6P–6.6K) at rates to provide 0.4, 0.9, or 1.4 g of nitrogen (N) per pot. Canopy height and width, flower number, and visual quality ratings (based on plant size and form, foliage color, and flowering) were highest after 16 weeks of growth for both cultivars when fertilized with 1.4 g of N per pot. A 30% shade level resulted in plants with the highest flower numbers and quality ratings. Plants grown at 50% shade had the greatest canopy heights and widths, but flower numbers and quality ratings were low. In full sun, plants were smaller overall. In a second experiment, A. obesum ‘Red’ produced the highest shoot dry weight when grown 20 weeks at 30% or 50% shade with 1.4 g of N per pot. Root formation is an important measure of aesthetic value for this crop. As plants mature, roots enlarge dramatically and are often washed to expose sculptural forms. The highest root dry weights were measured at 1.4 g of N under both full sun and 30% shade. The genus Adenium is a member of the family Apocynaceae and originates from Africa, south of the Sahara from Senegal to Sudan and Kenya, and through Saudi Arabia, Oman, and Yemen (Oyen, 2008; Plaizier, 1980). Commonly known as desert rose, the genus is prized for its attractive floral array atop a swollen, sculptural caudex (Rowley, 1987). As roots mature they swell and enlarge along with the caudex and add an important sculptural element that compliments the flowers; therefore, root formation is an important measure of aesthetic value for this crop (Dimmitt et al., 2009). Adenium plants in a wide range of architectural forms, growth habits, and flower colors are available for sale globally. However, there is no scientific literature regarding Adenium cultural requirements. Production of Adenium species under a minimum PAR of 1000 to 1600 mmol·m·s and a temperature range of 30 to 35 C (85 to 95 F) with high humidity during the growing season has been suggested (Dimmitt, 1998). It also was reported that Adenium responded well to a balanced fertilizer such as 20N– 20P205–20 K20 plus micronutrients at a concentration of 200 mg·L N (Dimmitt, 1998); however, no data were presented. A limited number of nutritional studies on other herbaceous genera within the family Apocynaceae has been published. Plumeria rubra grown in pure silica sand in 4-L containers were treated with a low and high nutrient level (2.4 g and 24.0 g, respectively, of 14N–14P–14K of Osmocote ) in a glasshouse for 60 d during August and September (Huante et al., 1995). In that study, more biomass was produced under high nutrient supply, whereas more biomass was allocated to the roots in low nutrient supply. Mandevilla Vogue varieties were shown to be moderate feeders, responding best to use of a balanced fertilizer at a rate of 100 to 200 mg·L and it was recommended that a low to medium rate of a standard slowrelease fertilizer should be added at planting (Mart, 2012). In a study testing the effects of Sumagic (uniconazole) on the growth and flowering of Mandevilla ‘Alice Du Pont’, Deneke et al. (1992) chose 8.3 kg of Osmocote (18N–6P–12K) per cubic meter of potting medium. Plants were also liquid fertilized weekly with 300 mg·L N from 20N– 4.3P–16.6K (20–10–20). In an experiment conducted with Dipladenia sanderi L. (Plaza et al., 2009), fertigation was applied in a nutrient solution containing with a pH of 7.2 and an electrical conductivity of 1.2 dS·m. Established landscape plants of Allamanda cathartica ‘Hendersonii’ were used in an experiment testing four different fertilizers on growth and quality (Broschat et al., 2008). The authors concluded that Allamanda in the landscape may not benefit greatly from increasing fertilization. Vinca (Catharanthus roseus L.) seedlings benefitted from high concentrations of N (up to 32 mM) in the fertilizer, whereas only low concentrations of phosphorus and potassium (0.25 mM) were needed (van Iersel et al., 1999). Kessler (1998) indicated that pluggrown Vinca seedlings should be fertilized once or twice a week with 50 to 75 mg·L N. Nitrogen levels could be increased to 100 to 150 mg·L once true leaves develop. To determine the cultural requirements for producing good-quality desert rose plants in containers, the following study was conducted to determine effects of light and nutritional levels on growth and flowering of Adenium obesum ‘Red’ and ‘Ice Pink’, two cultivars that are in commercial production in Florida. Materials and Methods Expt. 1. Established liners from vegetative stem cuttings (10 to 15 cm in height) in 72-cell trays of A. obesum ‘Red’ and ‘Ice Pink’ were obtained from a commercial propagator (Oglesby Plants International, Inc., Altha, FL). Fifty-four plants of each cultivar were potted into green 1.25-L (15.2 cm diameter) azalea pots with Fafard 2 Mix substrate (65% peat, 20% perlite, 15% vermiculite; Conrad Fafard Inc., Agawam, MA). After potting, all plants were trimmed to 5.0 to 7.5 cm in height and Nutricote Plus (18N– 2.6P–6.6K; 140-d formulation) controlledrelease fertilizer (Chisso-Asahi Fertilizer Co., Ltd., Tokyo, Japan) was applied to the substrate surface at 2.5, 5.0, or 7.5 g per pot (equivalent to 0.4, 0.9, and 1.4 g N per pot). One month after planting, flower buds were removed to promote shoot growth. Fertilizer treatments were reapplied 12 weeks after the initial potting. Pots were placed onto groundcover beds outdoors under natural daylength and temperature conditions 22 Apr. 2010 at MidFlorida Research and Education Center (MREC), Apopka, FL. Different light intensity treatments were obtained by attaching 1.5-m wide sections of black woven polypropylene shadecloth to a 1.2-m high steel pipe (1.4 cm diameter) structure spaced to cover individual growing areas 1.2 m wide · 1.5 m long (Fig. 1). There were 18 individual blocks that were 1.2 m high, 1.2 m wide, and 1.5 m long laid out in north-by-south orientation. Six blocks were covered with woven polypropylene shadecloth at 30% or 50% shade rating and six blocks were left unshaded. One plant of each cultivar received each fertilizer treatment under each light level for a total of 54 plants. The use of no shadecloth (i.e., full sun), 30% or 50% shadecloth resulted in maximum PAR levels Received for publication 21 Nov. 2013. Accepted for publication 27 Jan. 2014. Graduate Student. Professor of Environmental Horticulture. Biological Scientist. To whom reprint requests should be addressed; e-mail hennyrjz@ufl.edu. 430 HORTSCIENCE VOL. 49(4) APRIL 2014 of 1850, 1255, or 943 mmol·m·s, respectively, in individual growing areas. Light levels were measured biweekly with a LICOR Quantum Radiometer Photometer (Model No. LI-185B; Lincoln, NE). In addition, total solar radiation (W·m) was measured throughout each experiment using a LI-COR Model LI-200 pyranometer (LICOR Biosciences, Lincoln, NE). Plants were hand-watered as needed for the first 4 weeks after which they received daily irrigation from overhead 20.3-cm spinner sprinklers for 15 min unless it rained. To prevent blowover or knocking over, potted plants in each block were placed in Dillen CTA66 pocket azalea trays (48 cm · 32 cm) (Myers Industries, Middlefield, OH). Final plant canopy height and width, leaf length and width of the first fully expanded leaf on the dominate stem, and visual plant quality were recorded after 16 weeks of growth. The number of open flowers on each plant was recorded weekly. Visual quality rating was based on evaluations and rankings by four observers of overall plant form, foliage quality, and appearance and flower number on the following scale: 1 = poor; 2 = fair; 3 = saleable; 4 = good; 5 = excellent. Expt. 2. Fifty-four liners of A. obesum ‘Red’ (7 to 9 cm in height) were potted from 72-cell trays into 1.25-L (15.2 cm diameter) containers filled with Fafard 2 Mix. To promote lateral branching, plants were trimmed to 5.0 to 7.5 cm in height. The same fertilizer and application rates as in Expt. 1 were used and pots were placed on groundcover beds outdoors on 25 July 2011 under natural daylength and temperature conditions at MREC, Apopka, FL, using the same growth structures and watering regime as in Expt. 1. Fertilizer treatments were reapplied 12 weeks after initial potting and light treatments consisted of the same 0%, 30%, or 50% shade as in Expt. 1. Twelve weeks after initiation of the experiment, open flowers were first observed and weekly flower counts began and ended 8 weeks later at which time final measurements of canopy height and width and flower counts were made and plants were rated for visual quality using the same scale as in the first experiment. Plants were then cut off at the soil line and the tops bagged in brown paper bags. Roots were removed from pots and excess soil was washed away; roots were allowed to air-dry for 3 to 4 h and then were placed in paper bags. The bagged tops and roots were dried in a TD Vac Dryer (Heat Pipe Technology, Gainesville, FL) at 73 C (165 F) for 2 weeks. Dry weights were recorded using a Scout Pro scale (Model No. SPE2001; Ohaus Corporation, Pine Brook, NJ). Data were analyzed using analysis of variance procedures of the SAS program (SAS Institute Inc., Cary, NC).

Effect of Light Intensity and Nutrition Level on Growth and Flowering of Adenium obesum ‘Red’ and ‘Ice Pink’