Growing Habits, Floral Development, and Temperature Requirements for Flowering in Lachenalia Unicolor (Liliaceae)

Growing Habits, Floral Development, and Temperature Requirements for Flowering in Lachenalia unicolor (Liliaceae)

Eiichi Kodaira1*,** and Seiichi Fukai2

1Kyoto Botanical Garden, Sakyo-ku, Kyoto 606-0823, Japan 2Faculty of Agriculture, Kagawa University, Miki-cho, Kagawa 761-0795, Japan

Inflorescence initiation of Lachenalia unicolor occurred in early September before planting. Flower primordia at the lowest position of the inflorescence formed perianth and stamen primordia in early October and pistil primordia in early November. They maintained the same stage until early January in a greenhouse without heating. Mature pollen was formed in mid-February, with subsequent flowering in mid-April. Additional inflorescences were formed at the axil of storage leaves in some bulbs. Bulbs grown in a growth chamber kept at 20°C showed deformed inflorescence, although bulbs grown at 15°C flowered normally. Bulbs grown at 25°C produced no scapes. Bulbs stored at 5, 10, 15, 20, 25, or 30°C for 8 weeks from 6 August showed inflorescence initiation at any temperature, except at 5°C. The optimum temperature for floral development was 20–25°C. After floral initiation at 20, 25 + 20, or 25°C, bulbs were cultured in a growth chamber in a temperature combination of 20°C and 15°C. Bulbs grown at 20°C failed in normal flowering with a high frequency of seriously deformed inflorescences. Once bulbs had been exposed to 15°C for at least 2 months, flowering was accelerated by transferring to 20°C. Growing temperature at a constant 15°C delayed anthesis because of the long period from budding to anthesis.

Key Words: flowering control, Lachenalia unicolor, temperature requirement.

no information related to the growth and flowering habits Introduction of L. unicolor has been available. To use this species as Lachenalia unicolor Jacq., which is endemic from a pot plant, flowering control is expected. Information Riebeek-Kasteel to Somerset West in South Africa, is a about the effects of temperature on flowering of horticulturally important species of the genus Lachenalia L. unicolor is essential for flowering control. (Duncan, 1988). Plants of L. unicolor have excellent pink In this study, bulbs of L. unicolor were grown in a flowers. They flower in late spring in south-west Japan. greenhouse without heating to reveal their growth and Lachenalia species bloom during different seasons in flowering habits. The effects of temperature on initiation an unheated greenhouse: L. rubida blooms in autumn, and development of flower buds were also investigated L. aloides in early spring, and L. unicolor in late spring to ascertain their temperature requirements for flowering. in Japan. The differences in flowering time are Materials and Methods attributable to the different temperature requirements for flower bud development and flowering among these Plant materials species. Effects of temperature on flowering in Bulbs of L. unicolor were lifted when their leaves had Lachenalia species have been reported in L. aloides died back; they were stored in plastic pans at room ‘Pearsonii’ (Roh, 2005; Roh et al., 1995, 1998), temperature until the start of each treatment. All bulbs L. aloides var. quadricolor (Kodaira and Fukai, 2004), were cloned; 2.5–5.0 g samples were selected for each L. rubida (Kodaira and Fukai, 2005), and L. ‘Ronina’ experiment. (Du Toit et al., 2001a, 2003, 2004); however, to date, Flower bud development in a greenhouse without heating (Exp. I) Received; December 17, 2007. Accepted; April 4, 2008. * Corresponding author (E-mail: [email protected]). Five bulbs were planted in 18-cm pots filled with a ** Present address: Kyoto Herbal Garden, Takeda Pharmaceutical medium comprising commercially available planting Company Ltd. medium (Metro-Mix 350, Sun Gro Horticulture Canada

426 J. Japan. Soc. Hort. Sci. 77 (4): 426–430. 2008. 427

Ltd., Canada), Masa (granite soil), and sand (1 : 1 : 1, Results (v/v)) on 2 October, 2002. They were cultured in a greenhouse without heating (ventilation at 25°C). Five Flower bud development in a greenhouse without heating bulbs were sampled twice a month from 2 June, 2002– (Exp. I) 17 April, 2003 to elucidate the time course of The vegetative shoot apex of the current axis produced inflorescence and floral development. Floral initiation two storage leaves, two sheath leaves and two foliage and flower bud development at the lowest position on leaves through mid-June (Fig. 1). Foliage leaves (L5, an inflorescence were observed under a binocular; pollen L6) formed storage leaves the following season by development was assessed using an optical microscope enlargement of their basal part. Floral initiation of with acetocarmine stain. Floral development was primary inflorescence occurred at the shoot apex in early classified into 12 developmental stages established in September (Fig. 2). In mid-September, flower primordia Hyacinthus (Beyer, 1942): I, vegetative shoot apices; formed continuously from lower to upper positions, II, shoot apices broaden (reproductive); III, flower resulting in inflorescence formation. After the formation primordia appear; IV, outer perianth primordia appear; of two or three flower primordia in the inflorescence, a V, inner perianth primordia appear; VI, outer stamen new growing point formed at the axil of the upper foliage primordia appear; VII, inner stamen primordia appear leaf (L6). Stamen and pistil primordia formed in mid- and six stamen primordia become visible; VIII, pistil October. After completion of flower organs in early primordia appear; IX, pollen mother cells appear; X, November, further development was suspended until microspores at the tetrad stage; XI, mature pollen stage; early January. Mature pollen formed in mid-February. XII, anthesis. The number of inflorescences per plant, The flowers bloomed in mid-April. Shortly after primary percent of flowered plants, date of anthesis of the first inflorescence formation, secondary and/or tertiary opened flower, the length of scape and number of flowers inflorescences formed at the axil of lower foliage leaf on an inflorescence were recorded. This experiment was in the last growing season (EL1) or upper storage leaf performed at the Kyoto Botanical Garden, Japan. in the current season (L2), respectively (Fig. 1). The new growing point that would develop the next axis was Effects on flowering of growing temperatures (Exp. II) formed by a sympodial branching system. On 28 September, 2005, four bulbs were planted in 15-cm pots filled with medium consisting of Masa and Effects on flowering of growing temperatures (Exp. II) manure (3 : 1 (v/v)). The bulbs were placed in growth Plants grown at 15°C or in an unheated greenhouse chambers at 15, 20, or 25°C and in an unheated showed normal anthesis (Table 1). Plants grown at 25°C greenhouse with natural day length, respectively. In each did not flower at all. Most plants grown at 20°C produced treatment, 12 bulbs (three pots) were used. This experiment was performed at the Faculty of Agriculture, Kagawa University, Japan.

Effects on flowering of temperatures during both storage and culture (Exp. III) First, to ascertain the effect of storage temperature on flower bud development, five bulbs were stored under dry conditions at 5, 10, 15, 20, 25, or 30°C for 8 weeks from 6 August, 2004, respectively. Floral initiation and bulb development were determined at the end of storage on 1 October, 2004. From 3 August, 2005, bulbs were stored either at 25°C for 8 weeks, at 25°C for 4 weeks followed by 20°C for 4 weeks, or at 20°C for 8 weeks. On 28 September, 2005, four bulbs of each treatment were planted in 15- cm pots filled with Masa and manure (3 : 1 (v/v)). The plants were grown in growth chambers using a combination of temperatures at 20°C and 15°C (Table 2). Each treatment had 17 bulbs: 12 were planted; 5 were dissected to determine flower bud development after storage. This experiment was performed at the Faculty Fig. 1. Illustration of the branching system through the growing of Agriculture, Kagawa University. season of L. unicolor. L1–L2, storage leaves; L3–L4, sheath leaves; L5–L6, foliage leaves; I1, primary inflorescence; I2, secondary inflorescence; I3, tertiary inflorescence; BR, bract; FL, flower; GP, growing point; EL1–EL2, ex-foliage leaves (thereafter becoming storage leaves). 428 E. Kodaira and S. Fukai

Fig. 2. Floral development of L. unicolor grown in an unheated greenhouse. Five plants were used for each observation. Filled and open circles show primary and secondary inflorescences, respectively. Both circles represent the numbers of plants. I, vegetative shoot apices; II, shoot apices broaden (reproductive); III, flower primordia appear; IV, outer perianth primordia appear; V, inner perianth primordia appear; VI, outer stamen primordia appear; VII, inner stamen primordia appear and six stamen primordia become visible; VIII, pistil primordia appear; IX, pollen mother cells appear; X, microspores at the tetrad stage; XI, mature pollen stage; XII, anthesis.

Table 1. Effect of growing temperatures on flowering of L. unicolor.

Percentage of plants Primary inflorescences Growing Percentage of Number of temperature flowered plants flowering with Date of Date of Days from Length of Number of deformity inflorescences (°C) (%) per plant budding anthesis budding to scape flowers (%) anthesis (cm) Controlz 100 0y 1.3 ax 21 Mar. c 20 Apr. c 29.9 a 7.7 b 48.2 a 15 100 0 1.6 a 16 Jan. a 14 Mar. a 57.1 b 12.8 a 59.2 a 20 75.0 88.8 1.3 a 5 Feb. b 15 Apr. b 69.1 c 7.5 b 28.3 b 250 — — —————

Bulbs were planted on 28 September, 2005 and cultured in a growth chamber at each condition after floral initiation at room-temperature storage. In each investigation, 12 bulbs were used. z Unheated greenhouse. y Percentage of plants having deformed inflorescence in flowered plants. x Mean separation within columns by Scheffe’s test at the 1% level.

Fig. 3. Deformed inflorescences of L. unicolor grown at 20°C. Thickened bracts (A) and ramification (B) on an inflorescence. White arrows indicate respective phenomena. deformed inflorescences having thickened large bracts Effects on flowering of temperatures during both storage at upper positions on the inflorescence or a ramification and culture (Exp. III) at the top of the inflorescence (Fig. 3). Plants grown in At the end of storage at 5, 10, 15, 20, 25, or 30°C for an unheated greenhouse needed a shorter period from 8 weeks from 6 August, floral initiation was observed budding to anthesis compared to those at 15°C. in all bulbs except those stored at 5°C. The optimum tem- J. Japan. Soc. Hort. Sci. 77 (4): 426–430. 2008. 429 perature for floral development was 20–25°C (Fig. 4). for 2 months followed by growth at 20°C (Table 2). The Despite the storage temperature regime combining 20 longer growing period at 15°C apparently delayed bloom- and 25°C, all bulbs showed the same developmental ing and lengthened the period from budding to anthesis. stage of flowering (VIII) after 8 weeks of storage. The Discussion bulbs were grown at five different temperature regimes. Analysis of variance showed that the storage temperature Flower-bud initiation in L. unicolor bulbs occurred of bulbs and growing temperatures affected flowering, between lifting and planting, as in L. aloides ‘Pearsonii’ respectively, but did not affected interactionally (data (Roh, 2005), L. aloidea var. quadricolor (Kodaira and not shown). All data were subjected to Scheffe’s test Fukai, 2004), L. rubida (Kodaira and Fukai, 2005), and (Table 2). Bulbs grown at 20°C flowered at only 33– the other six species of Lachenalia (Kodaira et al., 2006). 67% and most showed serious deformity. Bulbs grown The manner of plural inflorescence formation of at 15–20°C or 15°C succeeded in flowering normally. L. unicolor, in which secondary inflorescences were The earliest bloom was observed in bulbs grown at 15°C formed at the axil of storage leaves, resembles those of L. aloides var. quadricolor (Kodaira and Fukai, 2004) and L. rubida (Kodaira and Fukai, 2005), but not that of L. ‘Ronina’ (Du Toit et al., 2001b, 2002), in which secondary inflorescence was formed only by the sympodial branching system. The optimum temperatures (20–25°C) for early floral development of L. unicolor are almost the same as those for other Lachenalia species: 23–27°C in L. aloides ‘Pearsonii’ (Roh et al., 1995), 10–22°C in L. ‘Ronina’ (Du Toit et al., 2001a), 20°C in L. aloides var. quadricolor (Kodaira and Fukai, 2004), and 20°C in L. rubida (Kodaira and Fukai, 2005). In Exp. II, bulbs were planted on 28 September just after floral initiation. Plants grown at 15°C flowered normally, but bulbs ° L. unicolor grown at 20 or 25 C did not flower normally, although Fig. 4. Developmental stages of flower buds of stored at ° different temperatures. Filled and open circles represent the the temperature (20–25 C) was suitable for their early number of plants, respectively. Temperature treatment started floral development. Deformed flowers were observed at on 6 August, 2004; observations were completed on 1 October, the upper part of the inflorescence, suggesting that the 2004. See footnotes for Figure 2. temperature affected later stages of inflorescence

Table 2. Effect of growing temperatures of L. unicolor after bulb storage on flowering.

Temperature Percentage of Percentage of Primary inflorescences Growing Number of of bulb temperature flowered plants flowering Date of Date of Days from Length of Number of storage plants with deformity inflorescences ° (°C) per plant budding anthesis budding to scape flowers ( C) (%) (%) anthesis (cm) 25 20 33.3 75.0 1.0 az 18 Jan. b 7 Apr. d 79.5 c 6.0 b 34.0 b 25 15 (2 months) + 20 100 0 1.3 a 6 Jan. a 14 Feb. a 38.6 a 13.3 a 67.4 a 25 15 (3 months) + 20 100 0 1.7 a 9 Jan. ab 15 Feb. a 37.0 a 13.4 a 55.0 ab 25 15 (4 months) + 20 100 0 1.7 a 15 Jan. b 22 Feb. b 38.5 a 14.4 a 56.1 ab 25 15 100 0 1.7 a 11 Jan. ab 11 Mar. c 59.0 b 13.0 a 61.1 a 25 + 20 20 58.3 66.7 1.1 a 25 Jan. b 30 Mar. e 64.3 c 7.4 b 35.6 a 25 + 20 15 (2 months) + 20 100 0 1.6 a 4 Jan. a 4 Feb. a 30.7 a 12.8 a 52.3 a 25 + 20 15 (3 months) + 20 100 0 1.1 a 5 Jan. a 13 Feb. b 39.5 ab 12.5 a 50.4 a 25 + 20 15 (4 months) + 20 100. 0 1.4 a 9 Jan. a 19 Feb. c 40.3 b 12.8 a 48.4 a 25 + 20 15 100. 0 1.6 a 10 Jan. a 9 Mar. d 57.7 c 10.9 a 48.6 a 20 20 66.7 62.5 1.0 a 26 Jan. b 25 Mar. d 58.0 b 5.8 b 26.6 b 20 15 (2 months) + 20 100 0 1.4 a 5 Jan. a 5 Feb. a 30.2 a 12.0 a 60.1 a 20 15 (3 months) + 20 91.7 0 1.5 a 10 Jan. a 9 Feb. a 29.9 a 12.9 a 56.4 a 20 15 (4 months) + 20 100 0 1.7 a 19 Jan. ab 19 Feb. b 30.2 a 12.2 a 48.4 ab 20 15 90.9 0 1.8 a 10 Jan. a 5 Mar. c 54.2 b 11.2 a 47.3 ab

Bulbs were stored at a combination of 25°C and 20°C for 8 weeks from 3 August to 28 September, 2005. The bulbs were planted on 28 September after the floral initiation stage of inner stamen or pistil primordia. They were cultured in a growth chamber at a combination of 15°C and 20°C. In each investigation, 12 bulbs were used. z Mean separation within columns by Scheffe’s test at the 5% level. 430 E. Kodaira and S. Fukai development and that L. unicolor has special temperature bloembolgewassen. Meded. Landb Hogesch. Wageningen 46: requirements for inflorescence development and flow- 1–17 (In Dutch with English abstract). ering because bulbs grown at 15°C for various periods De Hertogh, A. A. 1974. Principles for forcing tulips, hyacinths, daffodils, Easter lilies and Dutch irises. Sci. Hort. 2: 313–355. and then moved to 20°C flowered normally. Duncan, G. D. 1988. The Lachenalia handbook. p. 64. In: J. N. Seasonal changes in temperature play an important Eloff (ed.). Ann. 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