Available online at www.sciencedirect.com South African Journal of Botany 77 (2011) 631–637 www.elsevier.com/locate/sajb Flowering of Watsonia laccata as influenced by corm storage and forcing temperatures ⁎ J.K. Suh a, , J.H. Kim a, A.K. Lee a, M.S. Roh b a Dankook University, College of Bio-Resources Science, Department of Environmental Horticulture, Cheonan, Chungnam 330-714, Republic of Korea b US Department of Agriculture, Agricultural Research Service, National Arboretum, Floral and Nursery Plants Research Unit, Beltsville MD 20705, USA Received 24 March 2010; received in revised form 28 November 2010; accepted 22 December 2010 Abstract The genus Watsonia, belonging to the family Iridaceae, is comprised of about 50 species including W. laccata (Jacquin) Ker Gawler that flowers from September to November following low temperature and winter rainfall. Therefore, we hypothesized that flowering would be favored by forcing at low greenhouse temperatures. Using clonal W. laccata corms, four experiments were designed to investigate the effect of temperatures during corm storage, forcing, and their interaction on growth and flowering. Corm formation is favored by growing plants at 18°– 20°/15°–17 °C and 21°–23°/18°–20 °C, day/night temperatures. Flowering was earliest with corms produced at 24°–26°/18°–20 °C and forced at 18°–20/15°–17 °C, and was significantly delayed when forced at 27°–29°/24°–26 °C. Flowering was, however, favored by 2 or 4 weeks of high temperatures (27°–29°/24°–26 °C) prior to forcing at low temperatures (18°–20°/15°–17 °C). The number of florets was not significantly affected by corm storage, forcing temperatures, or their interaction, although forcing at high temperatures tends to reduce the floret number. Burn symptom at the tips of leaves was frequently observed, and further studies are required to understand the cause of the tip burn and how to correct the symptom. © 2010 SAAB. Published by Elsevier B.V. All rights reserved. Keywords: Controlled flowering; Corms; Dormancy; Leaf-tip burn symptoms; New floral crops; Watsonia laccata 1. Introduction 20.5 °C and 9.9 °C (Ascough et al., 2007a,b). Growth and flowering of W. tabularis (Eck.) J. W. Mathews & L. Bolus was The endemic flora of the Cape area in South Africa includes influenced by paclobutrazol to produce a compact container germplasm of many geophytes such as Lachenalia (Duncan, plant (Thompson et al., 2005; Wulster and Ombrello, 2000). 1988), Ornithogalum (Du Plessis and Duncan, 1989), and However, cultural information related to corm production, Sparaxis and other Iridaceae (Ehrich et al., 2009) which have growth, and flowering of Watsonia, is not available. the potential to develop into new floral crops (Helme and Recently, information on seed germination and in vitro Trinder-Smith, 2006). One of these attractive genera, Watsonia, propagation of four winter-rainfall Watsonia Mill species that closely related to Gladiolus, is comprised of about 50 species included W. laccata (Ascough et al., 2007a,b), and leaf cutting (Goldblatt, 1999). Seeds of W. laccata, a species native to an propagation of Lachenalia aloides (L. F.) Engl. ‘Pearsonii’ and area with winter-rainfall area, germinated well at temperatures Ornithogalum dubium Houtt. hybrid that are endemic to South ranging 10°–20 °C, whereas germination was inhibited at Africa was reported (Roh and Lawson, 1992). Controlled temperatures ranging 25°–40 °C. The average maximum and flowering as influenced by temperatures during bulb storage minimum temperatures at the native sites were, respectively and greenhouse forcing of Lachenalia and Ornithogalum and four Iridaceae that include Freesia and Sparaxis (Ehrich et al., ⁎ Corresponding author. Tel.: +82 41 5503642; fax: +82 41 5633643. 2009) was investigated. Both storage of bulbs and forcing in the E-mail address: [email protected] (J.K. Suh). greenhouse require low temperatures around 10°–12.5 °C to 0254-6299/$ - see front matter © 2010 SAAB. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.sajb.2010.12.007 632 J.K. Suh et al. / South African Journal of Botany 77 (2011) 631–637 produce quality plants with optimum flower bud development greenhouses were maintained at 18°–20°/15°–17 °C, 21°–23°/ and inflorescence elongation (Roh, 2004; Roh et al., 1998; Roh 18°–20 °C, 24°–26°/21°–23 °C, and 27°–29°/24°–26 °C. Date and Hong, 2007). A protocol for year-round forcing of of flowering was recorded at anthesis of the first florets, scape Lachenalia hybrid was also developed (Roh et al., 1995). plus inflorescence length was measured, and the number of Flowering time of W. laccata in nature is from September to florets was counted. At anthesis, the presence of a second and November following low temperature and the winter-rainfall third inflorescence from each corm was recorded. On Apr. 3, all season. Forcing Ixia hybrids at 18 °C day/10 °C night in plants were moved to a greenhouse at 21°/15.6 °C and watered conjunction with paclobutrazol treatment produced attractive once a week until leaves were dried. Harvested corms were plants (Wulster and Ombrello, 2000). Flowering of Freezia laxa stored at a constant 20 °C until grading and used in other (Thunb.) Goldblatt & J.C. Manning and other South African experiments. There were 24 plants planted singly in 10-cm pot Iridaceae was mainly controlled by temperature at 13 °C at per treatment, each plant being treated as an experimental unit in night with day temperature at 17 °C or above, and dormancy a completely randomized design. could be maintained and flowering was delayed at temperature above 20 °C (Ehrich et al., 2009). Therefore, we hypothesized 2.3. Effect of temperature during corm enlargement before that flowering could be affected by temperatures ranging from harvest and during forcing (Expt. 2) 10° to 20 °C. However, no information on how temperatures affect these developments is in Watsonia available at present. Corms grown in greenhouses as described in Expt. 1 were Using corms of clonal W. laccata population, several experi- harvested following the schedule indicated (Table 1), and stored ments were planned to understand the effect of forcing at 20 °C until planting on Sept. 27, 1995. The size of corms was temperature on growth, flowering, and corm production, of 7–9 cm in circumference and the leaf length varied from b1cm temperature during corm enlargement before harvest and during (corms grown at 30°–32°/27°–29 °C) to 2–3 cm (corms grown forcing, of forcing temperature and the duration, of different at 21°–23°/18°–20 °C and 24°–26°/2°–23 °C). The depth of duration of forcing temperature, and of bulb storage after corm planting was about 2–3 cm. Following planting, pots were harvest and forcing temperature. placed in air conditioned greenhouses maintained at 18°–20°/ 15°–17 °C, 21°–23°/18°–20 °C, 24°–26°/21°–23 °C, and 2. Materials and methods 27°–29°/24°–26 °C. Experimental design was a 4 (tempera- tures during corm enlargement)×4 (temperatures during 2.1. Source of plant material and general culture forcing) factorial design with 24 plants per treatment. Date of leaf emergence was recorded, and at anthesis, length of leaves, Watsonia laccata corms collected from Bredasdorp, Cape scapes, and inflorescences, the number of florets, and the length Province, South Africa, were received from Missouri Botanical of leaf tip burn showing severe symptoms were recorded and tip Garden (Goldblatt 4855; St. Louis, MO) in 1987, and multiplied of leaves expressing burn symptoms were collected. When at the US Dept. of Agriculture, Agricultural Research Service, leaves were longer than 3 cm, the date of leaf emergence was Floral and Nursery Plants Research Unit, Beltsville, MD, USA counted from the potting date. until 1996. During the corm multiplication years, plants showing color break symptoms similar to the tulip color breaks 2.4. Effect of different duration of temperature treatment on at anthesis were removed. During the multiplication period for growth and flowering (Expt. 3) corms, greenhouse temperatures were maintained at 21 °C during the day (08:00 HR–16:00 HR) and 15.6 °C (21°/ Corms (5–6 cm in circumference) enlarged in a greenhouse 15.6 °C) during the night, although day temperatures during maintained at 21°–23°/18°–20 °C were used. Corms were summer exceeded 28°–32 °C. Three corms were potted per potted on Sept. 28, 1995, and received constant 18°–20°/15°– 15 cm pot in a growing medium (soil:perlite:peat moss, 1:1:1 by 17 °C or constant 27°–29°/24°–26 °C for 12 weeks. Some pots volume) and 0.8 grams of a slow release fertilizer 14N-6P-8.1K received 2, 4, 6, 8, and 10 weeks at 18°–20°/15°–17 °C and was applied at planting and supplemented with 200 ppm N from then were moved to a greenhouse maintained at 27°–29°/24°– a 20N-8.6P-11.7K water soluble fertilizer once a month. In all 26 °C for 10, 8, 6, 4, and 2 weeks, respectively, for a total of experiments, data was subjected to analysis of variance, and 12 weeks. Following temperature treatments, all corms were means were compared by Duncan's Multiple Range Test using forced in a greenhouse maintained at 21°–23°/18°–20 °C. SAS Software (Statistical Analysis System, 2002). The number of days to leaf emergence and flowering was counted from the Table 1 potting day. Forcing temperature and subsequent handling of plants for harvesting corms in 1994 (Expt. 1). 2.2. Effect of forcing temperature on growth, flowering, and Forcing temperature Beginning of Last watering Corm harvest corm production (Expt. 1) (°C) drying plants 21–23/18–20C Apr.