Flowering of Watsonia Laccata As Influenced by Corm Storage and Forcing Temperatures ⁎ J.K

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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 (temperatures 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. 3 May 2 May 16 Corms were planted, one corm (8–10 cm in circumference) 24–26/21–23C Apr. 3 May 16 May 30 per 10 cm pot, on Sept. 20, 1994. Temperature treatments 27–29/24–26C Apr. 3 May 31 June 13 – – started on Sept. 22. Greenhouse temperatures in air-conditioned 30 32/27 29C Apr. 23 July 14 July 14 J.K. Suh et al. / South African Journal of Botany 77 (2011) 631–637 633

Table 2 Growth and flowering response of W. laccata as influenced by forcing temperatures. Forcing Temperature (°C) Days to flower Flowering percentage Inflore-scence length (cm) No. of florets Presence of second, third inflorescence 18–20/15–17 107 d z) 24/24 54 b 18 b 24/24, 15/24 21–23/18–20 121 c 24/24 66 a 21 a 17/24, 5/24 24–26/21–23 185 b 13/24 56 b 20 a 0/24, 0/24 27–29/24–26 259 a 20/24 49 c 17 b 0/24, 0/25 Level of significance 11.0 5.8 2.6 z)Mean separation within columns by DMRT at 5% level. Means with the same letter in the same column are not significantly different.

There were 18 plants per treatment. Date of flowering, the corms were produced per corm when forced at 18°–20°/15°– length of leaf, scape, and inflorescence, and total number of 17 °C (data not presented, Fig. 1). florets were recorded. Three to 5 plants grown in a 18°–20°/15°–17 °C greenhouse 3.2. Effect of temperature during corm enlargement before were sampled to observe the development of inflorescences and harvest and during forcing development of the new bulb unit under a stereoscope and a scanning electronic scope (SEM) as described (Roh et al., 1998) Leaf emergence was in 32 days when corms were enlarged at on Nov. 8, 17, and 24 and on Dec. 20. 21°–23°/18°–20 °C and forced at 18°–20°/15°–17 °C and emergence was significantly earlier than when corms were formed at 24°–26°/21°–23 °C which took 6 to 9 days, 2.5. Effect of different forcing temperature (Expt. 4) depending on the forcing temperatures (Table 3). Flowering was the earliest when corms were produced at 21°–23°/18°– Bulbs grown and harvested as described in Expt. 3 were used, and after potting on Oct. 6, they were placed in a greenhouse maintained at 18°–20°/15°–17 °C (low) or at 27°– 29°/24°–26 °C (high). Treatment details are shown in Table 5. On Jan. 8, 1996, all plants were moved to a 21°/18 °C greenhouse until data collection at anthesis, as described in Expt. 3.

3. Results

3.1. Effect of forcing temperature on growth, flowering, and corm production

Plants forced at 18°–20°/15°–17 °C were the earliest flowering in 107 days from all plants forced (Table 2). As forcing temperatures were increased, flowering was significantly delayed, particularly when forced at 24°–26°/21°–23 °C. No plants forced at 24°–26°/21°–23 °C flowered during forcing, but flowered in 259 days only after they were moved to a 21°/15.6 °C greenhouse on Apr. 3. Plants forced at 21°– 23°/18°–20 °C produced the longest leaves (66.0 cm). The number of florets was significantly higher when forced at 21°– 23°/18°–20 °C (21 florets) and 24°–26°/21°–23 °C (20 florets) as compared with the number of florets when plants were forced at either lower or higher temperatures. Plants that were forced at 18°–20°/15°–17 °C produced the second inflorescence from all plants and third inflorescences from 15 plants out of 24 plants. However, plants forced at 24°–26°/21°–23 °C or higher did not produce any second or third inflorescences. The general appearance of plants on April 3 is shown in Fig. 1. Formation of corms was accelerated when forcing Fig. 1. Appearance of plants as influenced by forcing temperatures (A). Burn – – symptom is observed at the tip of the leaves. Corm development is shown at the temperatures were lower than 24° 26°/21° 23 °C and when time of drying of plants (B). Plants were grown in air-conditioned greenhouses harvested on July 12. Poor corm formation could be due to a maintained at (1) 18°–20°/15°–17 °C, (2) 21°–23°/18°–20 °C, (3) 24°–26°/ short period between flowering and corm harvest. Three to eight 21°–23 °C, and (4) 27°–29°/24°–26 °C. 634 J.K. Suh et al. / South African Journal of Botany 77 (2011) 631–637

Table 3 Effect of temperature during corm formation before harvest and during forcing on growth and flowering of W. laccata. Temperature (°C) No. of days to Length (cm) of No. of Floret corm multiplication greenhouse forcing leaf emergence flower leaf Scape inflore-scence leaf burn 21–23/18–20 18–20/15–17 32 144 40 28 16 0.03 23 21–23/18–20 43 152 45 25 17 0.11 22 24–26/21–23 43 170 47 31 22 0.19 25 27–29/24–26 32 184 43 32 21 0.13 21 24–26/21–23 18–20/15–17 6 147 40 30 18 0.14 23 21–23/18–20 9 161 40 29 18 0.05 23 24–26/21–23 8 175 40 29 22 0.03 24 27–29/24–26 6 186 40 32 20 0.31 23 27–29/24–26 18–20/15–17 12 151 38 29 19 0.04 24 21–23/18–20 12 153 38 28 20 0.04 23 24–26/21–23 22 183 35 27 20 0.13 21 27–29/24–26 20 189 33 32 18 0.45 19 30–32/27–29 18–20/15–17 21 137 35 30 21 0.01 24 21–23/18–20 21 157 36 28 24 0.01 24 24–26/21–23 19 173 34 30 24 0.04 23 27–29/24–26 18 184 34 34 20 0.88 23 Least significant difference 3.8 12 3.7 4.4 4.2 0.31 2.7 Corm multiplication (CM) *** z) *** *** * *** NS ** Greenhouse forcing (GF) * *** *** *** *** *** *** CM×GF *** NS *** NS ** *** *** z)NS, *, **, ***: Non-significant or significant at p≤0.05, 0.01 or 0.001, respectively.

20 °C and were forced at 18°–20°/15°–17 °C or at 21°–23°/ tion and 21°–23/18°–20 °C forcing temperature) to 24.1 cm 18°–20 °C, which took 144 and 152 days, respectively. (30°–32°/27°–29 °C corm production and 24°–26°/21°–23 °C Flowering was significantly delayed when corms were forced forcing temperature). The incidence of leaf tip burning was at 27°–29°/24°–26 °C. Flowering was significantly delayed as affected significantly by forcing temperatures and also by corm production and forcing temperatures were increased. interaction with corm production temperatures, showing longer There was a 30-day difference in flowering between corms tip burn at higher forcing temperatures. The number of florets produced at 21°–23°/18°–20 °C and forced at 18°–20°/15°– was significantly affected by both corm production and forcing 17 °C vs. corms produced at 30°–32°/27°–29 °C forced at 27°– temperatures, ranging from 19 to 25. 29°/24°–26 °C. When corms were produced at 30°–32°/27°–29 °C, average 3.3. Effect of different duration of temperature treatment on leaf length decreased to 34 cm from 36 cm, but length was not growth and flowering significantly affected by forcing temperatures (Table 3). The effect of temperatures during forcing on the scape length was Flowering was earliest at 127 days when plants received profound as compared with those during corm production. 10 weeks at 18°–20°/15°–17 °C followed by 2 weeks at 27°– Scape length was increased significantly as forcing tempera- 29°/24°–26 °C. As the duration at 18°–20°/15°–17 °C in- tures increased from 18°–20°/15°–17 °C to 27°–29°/24°– creased, flowering was accelerated (Table 4). Less than 26 °C. There was no interaction between temperatures during 134 days were required to flower when forced at18°–20°/ corm production and forcing for scape length. The inflorescence 15°–17 °C for 8 weeks or longer durations. The length of leaf, length varied from 16.8 cm (21°–23°/18°–20 °C corm produc- scape, and inflorescence was significantly shorter when forcing

Table 4 Effect of different durations of temperature treatment on growth and flowering of W. laccata. No. of weeks at (°C) No. of days to flowering Length (cm) No. of florets 18–20/15–17 27–29/24–26 Leaf scape Inflore-scence 0 12 175 a 33.5 b z) 33.8 a 14.7 b 22.3 a 2 10 177 a 38.0 a 34.3 a 18.2 a 20.6 ab 4 8 167 b 36.9 a 34.9 a 18.0 a 19.6 b 6 6 143 c 39.1 a 22.5 d 14.1 b 22.1 a 8 4 134 d 34.5 b 26.1 c 15.2 b 22.0 a 10 2 127 e 30.6 c 30.7 b 17. 0 a 21.9 a 12 0 134 d 38.6 a 36.0 a 18.4 a 19.9 b Least significant difference 4.60 3.09 4.46 2.63 2.32 z)Mean separation within columns by DMRT at 5% level. Means with the same letter in the same column are not significantly different. J.K. Suh et al. / South African Journal of Botany 77 (2011) 631–637 635

compared with forcing at high temperature, which took 187 days (Table 5). Although flowering was not accelerated by a 2 or 4 weeks of low temperature given at the beginning of the forcing period (184 or 164 days to flower, respectively), flowering was accelerated by a 2 or 4 weeks of high temperature treatment (142 or 150 days to flower, respectively). As the durations of low or high temperature treatment increased, flowering was accelerated or delayed, respectively. Accelera- tion of flowering by low temperature treatment was not observed when low temperature treatment was given for 8 weeks or longer. Flowering acceleration by low temperatures given prior to a high temperature treatment period was more significant than by low temperatures following a high temperature treatment period. However, extended high temper- Fig. 2. Development of the inflorescence showing flower buds (FB 1; terminal, FB2, and FB3), bracts (B1, B2, and B3) sustaining flower buds, and tepal (*, **) ature treatments for 6 weeks or longer prior to low temperature photographed in December 20. treatments did not accelerate flowering, but rather delayed flowering. Leaf length was increased to 37 or 38 cm, as the durations of at 18°–20°/15°–17° for 6 to 8 weeks than when forcing for high temperature exceeded 10 or 8 weeks following 2 or other durations. Although the number of florets was affected by 4 weeks of low temperature, respectively. In general, the scape treatments, the significant difference was only 2.7 florets (a was longer when forced at high temperature, but was the range of 22.3 florets to 19.6 florets). shortest (16 cm) when forced at 6 weeks each of low followed No evident scape elongation was observed 41 days after by high temperature. Following 12 weeks of low temperature potting when 5 plants grown at 18°–20°/15°–17 °C were treatment, scape length became longer (35 cm), but did not observed under a dissecting stereoscope. An inflorescence with differ from those that received only 2 weeks of low temperature 2–5 florets was observed 50 days after potting, and 4–6 layers at the beginning of forcing (37 cm). No significant differences of florets were evident with shoot apices of the daughter corms were found in inflorescence length that ranged from 14 to 20 cm visible. Scape and inflorescence was about 1.8 and 0.9 cm long, when plants were forced initially at low temperatures regardless respectively, with clear enlargement of daughter corms visible of the duration. The number of florets was significantly 83 days after potting. Formation of terminal florets with bracts, increased as the duration of low temperature treatment was and tepal was evident in a scanning electron microscope increased from 2 weeks (18 florets) to 12 weeks (24 florets). photograph (Fig. 2). Forcing at high temperatures longer than 10 weeks reduced the number of florets. 3.4. Effect of different 2-week of temperature during forcing 4. Discussion When forced at 18°–20°/15°–17 °C (low; L) or at 27°–29°/ 24°–26 °C (high; H) for 12 weeks, flowering was the earliest Very limited information on the requirement of temperature when forced at low temperature, which took 134 days, as during various growth and developmental stages of Watsonia is

Table 5 Treatment details and growth and flowering responses of W. laccata. Temperature treatment z) (2-wk interval) No. of days to flower Length (cm) of No. of florets 0–22–44–66–88–10 10–12 leaf scape Inflore-scence LHHHH H 184ay) 37ab 37 a 18 bcf 18 d L L H H H H 164 c 38 a 24 d 20 abdef 21 c LLLHH H 148ef 35bc16e14f21c LLLLH H 138gh 33c22d15ef21c LLLLL H 140gh 33c29c16def22bc LLLLL L 134h 30d35ab17def24a HLLLL L 142fg 31d33ab17cde23abc H H L L L L 150 e 33 c 32 bc 20 abc 24 ab HHHLL L 156d 33c35ab20ab23abc HHHHL L 163c 33c31bc22a21abc HHHHH L 174b 34c35ab17cde21c HHHHH H 187a 35bc35ab16def18d Least significant difference 8.0 2.96 5.01 3.20 2.63 z)Low temperature: (L: 18°–20°/15°–17 °C) or high temperature: (H: 27°–29°/24°–26 °C). y)Mean separation within columns by DMRT at 5% level. Means with the same letters in each column are not significantly different. 636 J.K. Suh et al. / South African Journal of Botany 77 (2011) 631–637 available: however, the use of Paclobutrazol inhibits growth of 20°/15°–17 °C). Storing corms at high temperatures (27°–29°/ W. tabularis (Thompson et al., 2005) and smoke treatment 24°–26 °C) for 2 or 4 weeks may not induce dormancy of fresh- promotes flowering of W. borbonica (Pourret) Goldblatt (Light harvested corms and it is most likely that Watsonia corms do not et al., 2007). However, to our knowledge, flowering of require dormancy breaking temperature at low temperature. Watsonia, occurring typically from August to November in More frequent sampling and observation using SEM will nature has not been studied with regard to an optimum determine when florets are initiated. Longer than 6 weeks of temperature requirement during bulb storage and forcing. either low or high temperatures upon potting affects flowering Temperatures around Cape Town, South Africa average around time significantly. Therefore, to accelerate or delay flowering, 12 °C with 105 mm rainfall in June and July, and W. laccata plants should be forced either at low or high temperatures, flowers naturally following this period, and therefore is respectively, for 8 weeks. considered a species occurring in the winter-rainfall regions. The number of florets was not significantly affected by corm storage, forcing temperatures, or their interaction, although 4.1. Early flowering by forcing at 18°–20°/15°–17 °C forcing at high temperatures tend to reduce the number. Although the number of florets when forced for 12 weeks at Plants forced at 18°–20°/15°–17 °C flowered earliest in all low and high temperatures was affected significantly by experiments. This is close to the maximum temperature 20.5 °C treatments, the difference which was only 2.7 florets (22.3 (Ascough et al., 2007a) at the native site. It is not known florets by forcing at high temperature vs. 19.6 florets by forcing whether flowering can be accelerated if corms are stored at low at low temperature) may not be significant horticulturally. It is temperatures and forced at temperatures lower than 18°–20°/ evident that, in a similar repeated experiment, the number of 15°–17 °C. However, Watsonia is considered a cool season florets is increased by forcing at low temperature (18 vs. 24 crop for early forcing. Flowering of Lachenalia aloides Engl. florets and also 23 vs. 18 florets). ‘Pearsonii’ is also accelerated by storing at low temperature and The reduction may result from a premature termination of forcing at high temperature (Roh et al., 1995). Temperatures floral initiation, or from a malformation such as floret abortion higher than 21°–23°/18°–20 °C during the entire forcing period which was also reported in Iridaceae (Ehrich et al., 2009. should be avoided to assure 100% flowering (Expt. 1) and to Inflorescence blast in Lachenalia aloides occurs when bulbs have the second and third inflorescence formed. This clearly stored at 10°–15 °C are forced at 26°/24 °C (Roh et al., 1995; suggests that flower formation is favored at low temperatures Roh et al., 1998). We conclude that the initiation and and flowering is delayed at temperatures above 20 °C when development of W. laccata florets is not influenced by corm dormant corms are supplied from South Africa to Germany are storage and forcing temperatures. It is not known whether forced (Ehrich et al., 2009) and in vitro induced corms of W. flower malformations such as abortion or blast could be induced vanderspuyiae when maintained in greenhouse maintained at by low irradiance as reported with four Iridaceae plants that temperatures of 16°–24 °C (Ascough et al., 2008). include Freesia laxa under the European conditions (Ehrich et Flowering time of W. laccata is also affected by the al., 2009). environment during corm production in the greenhouse conditions which may be useful information to select corm 4.3. Leaf tip burn incidence production sites other than the Cape area with similar environments for in the field. It seems that producing corms The incidence of tip burn occurring on leaves is a concern if at temperatures higher than 24°–26°/21°–23 °C may delay leaf W. laccata is to be considered for pot plant production even emergence, but not flowering after leaf emergence. Therefore, though the symptom is less than 0.5 cm. Forcing at different corms can be produced at high temperatures and forced at low temperatures did not affect symptom incidence. It is not known temperature (18°–20°/15°–17 °C). It is, therefore, that flower- whether there are other Watsonia species that do not show tip ing of W. laccata is favored at low temperatures and may not burn symptoms nor is the cause of the symptom known. require cold treatment before planting corms as summarized in Nutrient analysis of growing medium and tissues during leaf Freesia (Rees, 1992). Since temperatures lower than 18°–20°/ development should be performed to determine if symptom 15°–17 °C, i.e., at 10° to 13 °C, were not tested, the critical expression is related to a deficiency or toxicity of nutrient limit of low temperatures favoring the floral initiation and elements. Preferential accumulation of boron and manganese at development in W. laccata is unknown. the tips of old Curcuma hybrid, ‘Chiangmai Pride’ was reported (Roh and Lawson, 2009). 4.2. Further flowering acceleration by forcing for 2 or 4 weeks of 27°–29°/24°–26 °C followed by forcing at −20°/15°–17 °C 5. Conclusion

For early flowering, plants could be forced longer than Flowering of W. laccata is accelerated and promoted by 8 weeks at 18°–20°/15°–17 °C. During this period, flower bud forcing at low temperatures around 18°–20°/15°–17 °C for initiation, development, and anthesis is completed, but it is not 8 weeks followed by 2 to 4 weeks of 27°–29°/24°–26 °C. Corm known how long it takes to initiate flower buds. Flower bud formation is favored at low temperatures, resulting from an initiation may be favored by 2 or 4 weeks of high temperatures early initiation of daughter corms following flowering. No (27°–29°/24°–26 °C) prior to forcing at low temperatures (18°– malformation of florets was found when plants were forced at J.K. Suh et al. / South African Journal of Botany 77 (2011) 631–637 637 high temperatures, and the length of scape and inflorescence Helme, N.A., Trinder-Smith, T.H., 2006. The endemic flora of the Cape – was not affected significantly by forcing temperature. Further Peninsula, South Africa. South African Journal of Botany 72, 205 210. Light, M.E., Kulkarni, M.G., Ascough, G.D., Van Staden, J., 2007. Improved studies are required to understand the cause of the tip burn flowering of a South African Watsonia with smoke treatments. South incidence and how to correct tip burn if it is related to the African Journal of Botany 73, 298 (Abstracts). nutritional status of the leaves. Plessis, N.D., Duncan, G., 1989. Bulbous plants of Southern Africa. Tabelberg Publishers Ltd., Cape Town, Republic of South Africa. 192p. Acknowledgements Rees, A.R., 1992. Ornamental bulbs, corms and tubers. C.A.B international. Redwood Press, Ltd., Melksham, UK. Roh, M.S., 2004. Flowering and inflorescence development of Lachenalia We thank Dr. Peter Goldblatt, Missouri Botanical Gardens, aloides 'Pearsonii' as influenced by bulb storage and forcing temperature. St. Louis, MO, USA who provided corms used in these Scientia Horticulturae 104, 305–323. experiments. Critical review of this manuscript and revising the Roh, M.S., Grassotti, A., Guglieri, L., 1998. Storage and forcing temperatures manuscript to improve the readability by G. Wulster, R. affect inflorescence initiation, flowering, and floral blast of Lachenalia aloides 'Pearsonii'. Acta Horticulturae 454, 213–221. Anderson, and L. Stephens, and R. Lawson and comments from Roh, M.S., Hong, D.-K., 2007. Inflorescence development and flowering of anonymous reviewer is greatly appreciated. Ornithogalum thyrsoides hybrids as affected by temperature manipulation during bulb storage. Scientia Horticulturae 113, 60–69. References Roh, M.S., Lawson, R.H., 1992. Propagation and transplant production technology of new floral crops. In: Kurata, K., Kaoze, T. (Eds.), Transplant Ascough, G.D., Erwin, J.E., Van Staden, J., 2007a. Temperature-dependent seed Production Systems. Kluwer Academic Publishers, Dordrecht, The – germination in Watsonia species related to geographic distribution. South Netherlands, pp. 1 20. Roh, M.S., Lawson, R.H., 2009. Source of boron in Curcuma for burn African Journal of Botany 73, 650–653. – Ascough, G.D., Erwin, J., Van Staden, J., 2007b. In Vitro propagation of four symptoms at leaf margins. J. Plant Nutrition 32, 798 808. Watsonia species. Plant Cell, Tissue and Organ Culture 88, 135–145. Roh, M.S., Lawson, R.H., Song, C.-Y., Louw, E., 1995. Forcing Lachenalia as – Ascough, G.D., Erwin, J.E., Van Staden, J., 2008. Reduced temperature, potted plant. Acta Horticulturae 397, 147 153. Statistical Analysis System, 2002. SAS Proprietary Software Version 9.00. SAS elevated sucrose, continuous Light and gibberellic acid promote corm formation in Watsonia vanderspuyiae. Plant Cell, Tissue and Organ Culture Institute Inc., Cary, NC, USA. 95, 275–283. Thompson, D.I., Anderson, N.O., Van Staden, J., 2005. Watsonias as container Duncan, G., 1988. The Lachenalia Handbook. Annals of Kristenbosh Botanic plants: using paclobruazol for flowering and height control. South African Journal of Botany 71, 426–431. Gardens, Vol. 17. National Botanical Gardens. 71p. Ehrich, L., Ulrichs, C., Grüneberg, H., 2009. Factors influencing flowering of Wulster, G.J., Ombrello, T.M., 2000. Control of height and flowering of Ixia – different South African Iridaceae. HortScience 44, 1792–1795. hybrids as container plants. HortScience 35, 1087 1088. Goldblatt, P., 1999. The Genus Watsonia. National Botanical Gardens, Kirstenbosch, Republic of South Africa.

Edited by J Van Staden