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Temperature regime during bulb production affects foliage and flower quality of Lachenalia cv. Ronina pot plants
Scientia Horticulturae 102 (2004) 441–448
Temperature regime during bulb production affects foliage and flower quality of Lachenalia cv. Ronina pot plants E.S. du Toit a,∗ , P.J. Robbertse a , J.G. Niederwieser b a
Department of Plant Production and Soil Science, Faculty of Natural and Agricultural Sciences, University of Pretoria, Pretoria 0002, South Africa b Roodeplaat Vegetable and Ornamental Plant Institute, Agricultural Research Council, Private Bag X293, Pretoria 0001, South Africa Accepted 14 June 2004
Abstract Flowering-sized bulbs of Lachenalia that developed under three different temperature regimes [S. Afr. J. Plant Soil 18 (1) (2001a) 28] were used to assess the quality of subsequent pot plants. Plants were grown in a growth cabinet at a 15/10 ◦ C day/night temperature regime. When the oldest flower of the inflorescences opened, the pot plants were transferred to a growth cabinet that provided a constant temperature of 22 ◦ C with lower lighting conditions to simulate office conditions. The flowering date, keeping ability as well as the morphology of the inflorescences were evaluated. After the senescence of the inflorescences, the plants were harvested and dissected into different plant parts for evaluation. The temperature pre-treatments had a major effect on the performance of the subsequent pot plants. Flowering occurred 8 weeks earlier compared to plants normally grown in outdoor conditions in the Pretoria region (summer rainfall area). Furthermore, the low temperature regime (LTR) treated bulbs produced inflorescences with the longest keeping ability and simultaneous flowering was noticed. The lower the temperature regime during the bulb production phase, the greater is the peduncle length, rachis length, floret number as well as the peduncle diameter of the primary, secondary and tertiary inflorescences. © 2004 Elsevier B.V. All rights reserved. Keywords: Lachenalia; Temperature; Plant morphology; Flower quality
∗
Corresponding author. Tel.: +27-12-420-3227; fax: +27-12-420-4120. E-mail address: [email protected] (E.S. du Toit). 0304-4238/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.scienta.2004.06.003
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E.S. du Toit et al. / Scientia Horticulturae 102 (2004) 441–448
1. Introduction Defining an attractive pot plant is not always easy, since it is a criterion that is difficult to measure or quantify and varies with each country (De Hertogh and Le Nard, 1993). Optimally bulbs used for producing forced potted plants should be able to produce plants with the following qualities: plant life in excess of 10 days at 20 ◦ C, minimal post-greenhouse growth of the flowering potted plant, dual purpose (home and garden), sensitivity to forcing at 13–16 ◦ C, not susceptible to flower abortion or abscission, available for year-round forcing and not requiring growth retardants (De Hertogh, 1990). Blaauw and his co-workers (Hartsema, 1961) found that temperature is the major external factor controlling growth, development and flowering in bulbous crops such as tulip, hyacinth and narcissus. Du Toit et al. (2001a, 2002) found differences in plant growth and bulb development between the high, moderate and low temperature regime treated Lachenalia bulbs. However, no research has yet been done to evaluate the effect of temperature during the production of Lachenalia bulbs on their subsequent flowering behaviour during growth as a pot plant. Therefore, the objectives in this paper were to determine if different temperature regimes during the bulb production phase would influence plant and flower quality during the pot plant phase. As mentioned in Du Toit et al. (2001a), this experiment was repeated for two consecutive seasons with very similar results and for uncomplicated reporting, only the second year’s results will be reported.
2. Materials and methods Lachenalia bulbs in South Africa are propagated by means of leaf cuttings taken in the winter, grown to a prescribed size and lifted in summer, selected and stored until the next season’s planting date, before they are used for commercial bulb production. These bulblets are then planted in autumn, grown in the field and are lifted during October–November after leaf senescence. Bulbs are then stored at ±25 ◦ C up to end-February–mid-March, and finally stored at 13 ◦ C for 2 weeks to improve inflorescence development. The bulbs that were used for this experiment had been produced in growth chambers under three temperature regimes: (1) high temperature regime (HTR); (2) moderate temperature regime (MTR); (3) low temperature regime (LTR). The HTR was 28/12 ◦ C day/night, the MTR was 22/12 ◦ C day/night and the LTR was 15/5 ◦ C day/night during the active growing season (Du Toit et al., 2001a). Bulbs were lifted on 15 November and thereafter stored dry at 25 ◦ C. During the 25 ◦ C storage, inflorescence bud development was monitored by taking samples of 10 bulbs at 5-day intervals and excising the inflorescence buds with the aid of a dissection microscope. When more than 50% of inflorescence buds of the 10 bulb sample had reached the G-phase (three carpel primordia in the oldest flower bud formed), the bulbs were subsequently stored dry at 13 ◦ C for 14 days before planting. The low temperature forcing treatment was recommended by Louw (1991) for further flower differentiation and elongation of the inflorescence inside the bulb, thus improving the quality of the inflorescence. As a result of the temperature regimes during bulb production, the bulbs from the three temperature pre-treatments reached the ready-for-planting stage on different dates (Du Toit
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443
et al., 2002). MTR and HTR-treated bulbs were therefore planted on 23 December and the LTR-treated bulbs on 15 January. At the date of planting the bulbs had a weight range of 5–10 g each and a circumference of 5 to ≥9 cm. One hundred bulbs each from the HTR, MTR and LTR treatments were planted singly into 9 cm plastic pots containing sterilised, composted bark. The pots were placed in the same growth cabinet and arranged in a randomised block design according to Steele and Torrie (1980). A 12 h photoperiod with a light intensity of 200 ± 10% mol m2 s−1 PAR at plant level was supplied with a 15/10 ◦ C day/night temperature regime. Lighting was provided by a combination of WHO fluorescent and incandescent globes. After opening of the oldest flower on the inflorescence, plants were transferred to a growth cabinet that provided a constant temperature of 22 ◦ C and a 12 h photoperiod with only fluorescent tubes (35 ± 10% mol m2 s−1 PAR) to simulate office conditions. The following parameters were used for evaluating pot plant quality: date of opening of oldest flower on inflorescence (flowering date); date when 100% of flowers on inflorescence opened (full-bloom); date when 50% of flowers on inflorescence wilted; number of inflorescences per pot; number of flowers per inflorescence; length of rachis; length of peduncle and diameter of the peduncle base; simultaneous flowering, expressed as date of full bloom minus date of first flower opening and inflorescence longevity, expressed in days by subtracting date of 50% wilted flowers from date of 100% wilted flowers per inflorescence. After plants had reached the 100% flower wilting stage, plants were dissected and the parameters leaf number per plant, leaf area (cm2 ), fresh mass (g) and dry mass (g) were determined. Data were analysed using the CORR (Pearson correlation) and GLM (general linear model) procedure in the SAS (Statistical Analysis Systems) program. Analysis of variance was also performed. Tukey’s studentized range test (Steele and Torrie, 1980) was applied to compare treatment means.
3. Results 3.1. Planting and flowering date As mentioned in Section 2, Lachenalia bulbs to be used for forcing were lifted, harvested from the three temperature regimes during October/November after leaf senescence, stored at 25 ◦ C to allow inflorescence bud development, held for 2 weeks at 13 ◦ C and re-planted towards end-February–mid-March. Observations by Du Toit et al. (2001a) indicated that inflorescence differentiation in temperature-treated ‘Ronina’ bulbs not only took place during the dormancy (storage) period, as reported by Louw (1991) in cultivar Romelia, but already started during the prior growing season before lifting. These bulbs had therefore been affected by the LTR, MTR and HTR treatments and were ready for planting 8 weeks earlier (from end-December to mid-January) than normally experienced with field grown bulbs. Despite the fact that the HTR and MTR bulbs were planted about 1 month earlier than the LTR bulbs, the date of first flowering of the LTR-treated bulbs was not notably later (Fig. 1). This implies that the suppressed inflorescence development of the LTR-treated bulbs (Du
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Fig. 1. Effect of high (HTR), moderate (MTR) and low (LTR) treatments during the bulb production phase on the time course of flowering of the primary inflorescence when subsequently forced at 15/10 ◦ C with a 12 h photoperiod.
Toit et al., 2002), was negated during the subsequent treatments. On the other hand, the flowering date of the pot plants grown from the HTR-treated bulbs were 2 weeks later. Pot plants grown from the LTR-treated bulbs flowered more uniformly than those grown from the MTR- and HTR-treated bulbs (Fig. 1), showing 100% anthesis within 3 weeks in the LTR plants compared to 6 weeks for MTR plants and 13 weeks for HTR plants. 3.2. Inflorescence and foliage quality The best quality inflorescences were found in plants grown from the LTR-treated bulbs. However, MTR-treated bulbs also produced good quality inflorescences (Fig. 2). There was a strong correlation between peduncle length, rachis length, flower number and peduncle cross-section (Table 1). The lower the temperature treatment during the bulb production phase, the better the inflorescence quality is during the pot plant phase in terms of the peduncle length, rachis length, flower number as well as the peduncle cross-section (firmness) Table 1 Relationship between different measurements conducted on the inflorescence Inflorescence type
Inflorescence measurement
Inflorescence measurement
Primary, secondary or tertiary
Rachis length
Peduncle length Floret number Peduncle cross-section
Peduncle length ∗∗
Significant correlation at the 1% (P ≤ 0.01) level.
R-value ∗∗ ∗∗ ∗∗
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Fig. 2. Effect of the high (HTR), moderate (MTR) and low (LTR) treatments during bulb production on the total length, peduncle length, rachis length, flower number and the peduncle cross-section of the primary, secondary and tertiary inflorescence (top to bottom, respectively) during the pot plant phase. Treatment means with letters in common are not significantly different at P ≤ 0.05.
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Table 2 Effect of high (HTR), moderate (MTR) and low (LTR) treatments given to Lachenalia plants during the bulb production phase on foliage and inflorescence qualities when plants are subsequently forced Treatment
Inflorescence no./plant
Keeping ability (days)
No. of leaves
Leaf area (cm2 )
Dry mass (g)
HTR MTR LTR
1.6 (a) 3.0 (b) 2.8 (b)
25 (a) 23 (a) 24 (a)
6.2 (a) 6.8 (a) 6.5 (a)
120 (a) 220 (b) 270 (b)
0.6 (a) 1.0 (b) 1.1 (b)
Means followed by different letters are significantly different at the 5% (P ≤ 0.05) level.
of the primary, secondary and tertiary inflorescences. In terms of the mentioned parameters, second and third order inflorescence were of poorer quality than first order inflorescences. Pot plants grown from MTR and LTR-treated bulbs each produced an average of 3 inflorescences compared to those of the 1.6 of the HTR-treated bulbs (Table 2). One growth module in Lachenalia cv. Ronina, consists of two cataphylls, two green leaves and an inflorescence (Du Toit et al., 2001b). Table 2 shows that, the HTR, MTR and LTR-treated bulbs at the end of the pot plant phase produced an average of six leaves per plant (two leaves/module). The leaf area as well as the dry mass of the LTR-treated plants was, however, higher compared to those of the MTR and HTR-treated plants (Table 2). The LTR-treated bulbs also produce broader leaves than those of the MTR and HTR (results not presented). 3.3. Inflorescence longevity In all three treatments the sum of the longevity of all three inflorescences (keeping ability) of the potted plants averaged 24 days (Table 2). In spite of significant differences between
Fig. 3. Effect of the high (HTR), moderate (MTR) and low (LTR) temperature regime during the bulb production phase on the longevity of the primary, secondary and tertiary inflorescence. Treatment means with letters in common are not significantly different at P ≤ 0.05.
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treatments, the time from first flower to full-bloom in all three treatments was very similar (Fig. 3). The major contribution towards longevity was, however, made by the duration of the period between full bloom and flower wilting (Fig. 3) where the LTR treatment excelled the other treatments by far.
4. Discussion 4.1. Planting and flowering date Flower initiation and differentiation in the LTR-treated bulbs were suppressed by the low growing temperature (Du Toit et al., 2002). However, it can be reasoned that during the pre-harvest temperature increase (35 ◦ C) and during storage (25 ◦ C) the rate of flower differentiation increased. The subsequent lower temperature (13 ◦ C during storage, 2 weeks before planting) and the low temperature (15/10 ◦ C day/night) after planting triggered scape elongation and thus accelerated flowering in LTR bulbs. Therefore, flower differentiation and scape elongation are two different processes requiring different optimal temperatures. This is in accordance with thermoperiodic responses in Tulipa as recorded by De Hertogh and Le Nard (1993), where flower differentiation takes place under a warm temperature climate (summer) and induction of scape elongation under cooler conditions (fall–winter). The delay in the flowering HTR bulbs are explained in Du Toit et al. (2001a, 2002), whereas the HTR during the bulb preparation phase had a negative effect on flower development. Although the MTR- and HTR-treated bulbs were planted 1 month later than the LTR bulbs, the extended period between planting and full bloom of the HTR plants can be mainly ascribed to later anthesis of the secondary and tertiary inflorescences. This again implies that the high temperature regime (HTR) during the bulb preparation phase retarded the inflorescence growth during the following year (Du Toit et al., 2001a, 2002). 4.2. Inflorescence and foliage quality Inflorescence quality assessment is mainly based on flower number (Louw, 1991). The temperature regime at which bulbs are grown during the bulb production phase, has a significant effect on flower emergence and number (Du Toit et al., 2001a). Low temperatures during the bulb production phase delayed flowering (Du Toit et al., 2001a), retarded the modular growth sequence of bulbs (Du Toit et al., 2002), and caused an increase in flower number per inflorescence. High temperatures during the bulb production phase produced inflorescences with a lower fresh mass, lower flower number and flower abortion during the pot plant phase (Du Toit et al., 2001a, 2002). Multiple inflorescences are very appealing for the consumer and low temperature regimes during the bulb production phase can therefore be recommended for inducing multiple inflorescences. A possible reason for the reduced number of inflorescences on the HTR bulbs can be ascribed to flower abortion (Du Toit et al., 2002). In Fig. 3 of this paper, the authors provide a schematic illustration showing how HTR enhanced module development, but on the other hand caused inflorescence abortion (blasting). A too high temperature exposure
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during the bulb production phase may, therefore, reduce the number of inflorescences of the treated bulbs during the pot plant phase, instead of promoting it. 4.3. Inflorescence longevity Inflorescence longevity is an important quality for a pot plant. Louw (1991) and Jansen van Vuuren (1990) found that the storage conditions before planting do not affect the keeping ability of the inflorescences of Lachenalia cv. Romelia, and Ornithogalum, respectively. Whereas, our data clearly illustrate that growth temperatures of the previous year can affect the keeping ability of the inflorescences (Fig. 3).
5. Conclusion The bulb production phase plays an important role in the quality of the final pot plant. It is therefore essential for the grower to consider the bulb’s history of the previous year before it is sold as a marketable size bulb for pot plant production. In this study it was shown that subjecting the plants to a low temperature regime during the bulb production phase shifted the flowering date 2 months earlier compared to bulbs that were produced under normal climatic conditions. The lower the temperature during bulb production, the more uniform was flowering during the pot plant phase. The LTR-treated bulbs rendered the highest quality inflorescences with a considerable keeping ability. The LTR treated bulbs also produced the most attractive leaves during the pot plant phase.
References De Hertogh, A.A., 1990. Basic criteria for selecting flower bulbs for North American markets—gardens, outdoor cut flowers, forced cut flowers and potted plants. North Carolina Horticultural Research Series No. 85, Raleigh. De Hertogh, A.A., Le Nard, M., 1993. The Physiology of Bulbs. Elsevier, Amsterdam. Du Toit, E.S., Robbertse, P.J., Niederwieser, J.G., 2001a. Effect of temperature on bulb size of Lachenalia cv. Ronina during the bulb preparation phase. S. Afr. J. Plant Soil 18 (1), 28–31. Du Toit, E.S., Robbertse, P.J., Niederwieser, J.G., 2001b. Evaluation of bulb growth and structure of Lachenalia cv. Ronina bulbs. S. Afr. J. Bot. 67, 667–670. Du Toit, E.S., Robbertse, P.J., Niederwieser, J.G., 2002. Effects of growth and storage temperature on Lachenalia cv. Ronina bulb morphology. Sci. Hortic. 94, 117–123. Hartsema, A.H., 1961. Influence of temperatures on flower formation and flowering of bulbous and tuberous plants. In: Ruhland, W. (Ed.), Handbuch der Pflanzenphysiologie. Springer-Verlag, Berlin, 16, pp. 123–167. Jansen van Vuuren, P.J., 1990. Die invloed van temperatuur op die ontogenie en bloeiwyse morfogenese van Ornithogalum thyrsoides Jacq. D.Sc. (Agric) Thesis. University of Pretoria, Pretoria, South Africa. Louw, E., 1991. The effect of temperature on inflorescence initiation and differentiation and development of Lachenalia cv. Romelia. M.Sc. (Agric) Dissertation. University of Pretoria, Pretoria, South Africa. Steele, G.D. Torrie, J.H., 1980. Principles and Procedures of Statistics, 2nd ed. McGraw Hill, New York.
Temperature regime during bulb production affects foliage and flower quality of Lachenalia cv. Ronina pot plants E.S. du Toit a,∗ , P.J. Robbertse a , J.G. Niederwieser b a
Department of Plant Production and Soil Science, Faculty of Natural and Agricultural Sciences, University of Pretoria, Pretoria 0002, South Africa b Roodeplaat Vegetable and Ornamental Plant Institute, Agricultural Research Council, Private Bag X293, Pretoria 0001, South Africa Accepted 14 June 2004
Abstract Flowering-sized bulbs of Lachenalia that developed under three different temperature regimes [S. Afr. J. Plant Soil 18 (1) (2001a) 28] were used to assess the quality of subsequent pot plants. Plants were grown in a growth cabinet at a 15/10 ◦ C day/night temperature regime. When the oldest flower of the inflorescences opened, the pot plants were transferred to a growth cabinet that provided a constant temperature of 22 ◦ C with lower lighting conditions to simulate office conditions. The flowering date, keeping ability as well as the morphology of the inflorescences were evaluated. After the senescence of the inflorescences, the plants were harvested and dissected into different plant parts for evaluation. The temperature pre-treatments had a major effect on the performance of the subsequent pot plants. Flowering occurred 8 weeks earlier compared to plants normally grown in outdoor conditions in the Pretoria region (summer rainfall area). Furthermore, the low temperature regime (LTR) treated bulbs produced inflorescences with the longest keeping ability and simultaneous flowering was noticed. The lower the temperature regime during the bulb production phase, the greater is the peduncle length, rachis length, floret number as well as the peduncle diameter of the primary, secondary and tertiary inflorescences. © 2004 Elsevier B.V. All rights reserved. Keywords: Lachenalia; Temperature; Plant morphology; Flower quality
∗
Corresponding author. Tel.: +27-12-420-3227; fax: +27-12-420-4120. E-mail address: [email protected] (E.S. du Toit). 0304-4238/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.scienta.2004.06.003
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E.S. du Toit et al. / Scientia Horticulturae 102 (2004) 441–448
1. Introduction Defining an attractive pot plant is not always easy, since it is a criterion that is difficult to measure or quantify and varies with each country (De Hertogh and Le Nard, 1993). Optimally bulbs used for producing forced potted plants should be able to produce plants with the following qualities: plant life in excess of 10 days at 20 ◦ C, minimal post-greenhouse growth of the flowering potted plant, dual purpose (home and garden), sensitivity to forcing at 13–16 ◦ C, not susceptible to flower abortion or abscission, available for year-round forcing and not requiring growth retardants (De Hertogh, 1990). Blaauw and his co-workers (Hartsema, 1961) found that temperature is the major external factor controlling growth, development and flowering in bulbous crops such as tulip, hyacinth and narcissus. Du Toit et al. (2001a, 2002) found differences in plant growth and bulb development between the high, moderate and low temperature regime treated Lachenalia bulbs. However, no research has yet been done to evaluate the effect of temperature during the production of Lachenalia bulbs on their subsequent flowering behaviour during growth as a pot plant. Therefore, the objectives in this paper were to determine if different temperature regimes during the bulb production phase would influence plant and flower quality during the pot plant phase. As mentioned in Du Toit et al. (2001a), this experiment was repeated for two consecutive seasons with very similar results and for uncomplicated reporting, only the second year’s results will be reported.
2. Materials and methods Lachenalia bulbs in South Africa are propagated by means of leaf cuttings taken in the winter, grown to a prescribed size and lifted in summer, selected and stored until the next season’s planting date, before they are used for commercial bulb production. These bulblets are then planted in autumn, grown in the field and are lifted during October–November after leaf senescence. Bulbs are then stored at ±25 ◦ C up to end-February–mid-March, and finally stored at 13 ◦ C for 2 weeks to improve inflorescence development. The bulbs that were used for this experiment had been produced in growth chambers under three temperature regimes: (1) high temperature regime (HTR); (2) moderate temperature regime (MTR); (3) low temperature regime (LTR). The HTR was 28/12 ◦ C day/night, the MTR was 22/12 ◦ C day/night and the LTR was 15/5 ◦ C day/night during the active growing season (Du Toit et al., 2001a). Bulbs were lifted on 15 November and thereafter stored dry at 25 ◦ C. During the 25 ◦ C storage, inflorescence bud development was monitored by taking samples of 10 bulbs at 5-day intervals and excising the inflorescence buds with the aid of a dissection microscope. When more than 50% of inflorescence buds of the 10 bulb sample had reached the G-phase (three carpel primordia in the oldest flower bud formed), the bulbs were subsequently stored dry at 13 ◦ C for 14 days before planting. The low temperature forcing treatment was recommended by Louw (1991) for further flower differentiation and elongation of the inflorescence inside the bulb, thus improving the quality of the inflorescence. As a result of the temperature regimes during bulb production, the bulbs from the three temperature pre-treatments reached the ready-for-planting stage on different dates (Du Toit
E.S. du Toit et al. / Scientia Horticulturae 102 (2004) 441–448
443
et al., 2002). MTR and HTR-treated bulbs were therefore planted on 23 December and the LTR-treated bulbs on 15 January. At the date of planting the bulbs had a weight range of 5–10 g each and a circumference of 5 to ≥9 cm. One hundred bulbs each from the HTR, MTR and LTR treatments were planted singly into 9 cm plastic pots containing sterilised, composted bark. The pots were placed in the same growth cabinet and arranged in a randomised block design according to Steele and Torrie (1980). A 12 h photoperiod with a light intensity of 200 ± 10% mol m2 s−1 PAR at plant level was supplied with a 15/10 ◦ C day/night temperature regime. Lighting was provided by a combination of WHO fluorescent and incandescent globes. After opening of the oldest flower on the inflorescence, plants were transferred to a growth cabinet that provided a constant temperature of 22 ◦ C and a 12 h photoperiod with only fluorescent tubes (35 ± 10% mol m2 s−1 PAR) to simulate office conditions. The following parameters were used for evaluating pot plant quality: date of opening of oldest flower on inflorescence (flowering date); date when 100% of flowers on inflorescence opened (full-bloom); date when 50% of flowers on inflorescence wilted; number of inflorescences per pot; number of flowers per inflorescence; length of rachis; length of peduncle and diameter of the peduncle base; simultaneous flowering, expressed as date of full bloom minus date of first flower opening and inflorescence longevity, expressed in days by subtracting date of 50% wilted flowers from date of 100% wilted flowers per inflorescence. After plants had reached the 100% flower wilting stage, plants were dissected and the parameters leaf number per plant, leaf area (cm2 ), fresh mass (g) and dry mass (g) were determined. Data were analysed using the CORR (Pearson correlation) and GLM (general linear model) procedure in the SAS (Statistical Analysis Systems) program. Analysis of variance was also performed. Tukey’s studentized range test (Steele and Torrie, 1980) was applied to compare treatment means.
3. Results 3.1. Planting and flowering date As mentioned in Section 2, Lachenalia bulbs to be used for forcing were lifted, harvested from the three temperature regimes during October/November after leaf senescence, stored at 25 ◦ C to allow inflorescence bud development, held for 2 weeks at 13 ◦ C and re-planted towards end-February–mid-March. Observations by Du Toit et al. (2001a) indicated that inflorescence differentiation in temperature-treated ‘Ronina’ bulbs not only took place during the dormancy (storage) period, as reported by Louw (1991) in cultivar Romelia, but already started during the prior growing season before lifting. These bulbs had therefore been affected by the LTR, MTR and HTR treatments and were ready for planting 8 weeks earlier (from end-December to mid-January) than normally experienced with field grown bulbs. Despite the fact that the HTR and MTR bulbs were planted about 1 month earlier than the LTR bulbs, the date of first flowering of the LTR-treated bulbs was not notably later (Fig. 1). This implies that the suppressed inflorescence development of the LTR-treated bulbs (Du
444
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Fig. 1. Effect of high (HTR), moderate (MTR) and low (LTR) treatments during the bulb production phase on the time course of flowering of the primary inflorescence when subsequently forced at 15/10 ◦ C with a 12 h photoperiod.
Toit et al., 2002), was negated during the subsequent treatments. On the other hand, the flowering date of the pot plants grown from the HTR-treated bulbs were 2 weeks later. Pot plants grown from the LTR-treated bulbs flowered more uniformly than those grown from the MTR- and HTR-treated bulbs (Fig. 1), showing 100% anthesis within 3 weeks in the LTR plants compared to 6 weeks for MTR plants and 13 weeks for HTR plants. 3.2. Inflorescence and foliage quality The best quality inflorescences were found in plants grown from the LTR-treated bulbs. However, MTR-treated bulbs also produced good quality inflorescences (Fig. 2). There was a strong correlation between peduncle length, rachis length, flower number and peduncle cross-section (Table 1). The lower the temperature treatment during the bulb production phase, the better the inflorescence quality is during the pot plant phase in terms of the peduncle length, rachis length, flower number as well as the peduncle cross-section (firmness) Table 1 Relationship between different measurements conducted on the inflorescence Inflorescence type
Inflorescence measurement
Inflorescence measurement
Primary, secondary or tertiary
Rachis length
Peduncle length Floret number Peduncle cross-section
Peduncle length ∗∗
Significant correlation at the 1% (P ≤ 0.01) level.
R-value ∗∗ ∗∗ ∗∗
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Fig. 2. Effect of the high (HTR), moderate (MTR) and low (LTR) treatments during bulb production on the total length, peduncle length, rachis length, flower number and the peduncle cross-section of the primary, secondary and tertiary inflorescence (top to bottom, respectively) during the pot plant phase. Treatment means with letters in common are not significantly different at P ≤ 0.05.
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Table 2 Effect of high (HTR), moderate (MTR) and low (LTR) treatments given to Lachenalia plants during the bulb production phase on foliage and inflorescence qualities when plants are subsequently forced Treatment
Inflorescence no./plant
Keeping ability (days)
No. of leaves
Leaf area (cm2 )
Dry mass (g)
HTR MTR LTR
1.6 (a) 3.0 (b) 2.8 (b)
25 (a) 23 (a) 24 (a)
6.2 (a) 6.8 (a) 6.5 (a)
120 (a) 220 (b) 270 (b)
0.6 (a) 1.0 (b) 1.1 (b)
Means followed by different letters are significantly different at the 5% (P ≤ 0.05) level.
of the primary, secondary and tertiary inflorescences. In terms of the mentioned parameters, second and third order inflorescence were of poorer quality than first order inflorescences. Pot plants grown from MTR and LTR-treated bulbs each produced an average of 3 inflorescences compared to those of the 1.6 of the HTR-treated bulbs (Table 2). One growth module in Lachenalia cv. Ronina, consists of two cataphylls, two green leaves and an inflorescence (Du Toit et al., 2001b). Table 2 shows that, the HTR, MTR and LTR-treated bulbs at the end of the pot plant phase produced an average of six leaves per plant (two leaves/module). The leaf area as well as the dry mass of the LTR-treated plants was, however, higher compared to those of the MTR and HTR-treated plants (Table 2). The LTR-treated bulbs also produce broader leaves than those of the MTR and HTR (results not presented). 3.3. Inflorescence longevity In all three treatments the sum of the longevity of all three inflorescences (keeping ability) of the potted plants averaged 24 days (Table 2). In spite of significant differences between
Fig. 3. Effect of the high (HTR), moderate (MTR) and low (LTR) temperature regime during the bulb production phase on the longevity of the primary, secondary and tertiary inflorescence. Treatment means with letters in common are not significantly different at P ≤ 0.05.
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treatments, the time from first flower to full-bloom in all three treatments was very similar (Fig. 3). The major contribution towards longevity was, however, made by the duration of the period between full bloom and flower wilting (Fig. 3) where the LTR treatment excelled the other treatments by far.
4. Discussion 4.1. Planting and flowering date Flower initiation and differentiation in the LTR-treated bulbs were suppressed by the low growing temperature (Du Toit et al., 2002). However, it can be reasoned that during the pre-harvest temperature increase (35 ◦ C) and during storage (25 ◦ C) the rate of flower differentiation increased. The subsequent lower temperature (13 ◦ C during storage, 2 weeks before planting) and the low temperature (15/10 ◦ C day/night) after planting triggered scape elongation and thus accelerated flowering in LTR bulbs. Therefore, flower differentiation and scape elongation are two different processes requiring different optimal temperatures. This is in accordance with thermoperiodic responses in Tulipa as recorded by De Hertogh and Le Nard (1993), where flower differentiation takes place under a warm temperature climate (summer) and induction of scape elongation under cooler conditions (fall–winter). The delay in the flowering HTR bulbs are explained in Du Toit et al. (2001a, 2002), whereas the HTR during the bulb preparation phase had a negative effect on flower development. Although the MTR- and HTR-treated bulbs were planted 1 month later than the LTR bulbs, the extended period between planting and full bloom of the HTR plants can be mainly ascribed to later anthesis of the secondary and tertiary inflorescences. This again implies that the high temperature regime (HTR) during the bulb preparation phase retarded the inflorescence growth during the following year (Du Toit et al., 2001a, 2002). 4.2. Inflorescence and foliage quality Inflorescence quality assessment is mainly based on flower number (Louw, 1991). The temperature regime at which bulbs are grown during the bulb production phase, has a significant effect on flower emergence and number (Du Toit et al., 2001a). Low temperatures during the bulb production phase delayed flowering (Du Toit et al., 2001a), retarded the modular growth sequence of bulbs (Du Toit et al., 2002), and caused an increase in flower number per inflorescence. High temperatures during the bulb production phase produced inflorescences with a lower fresh mass, lower flower number and flower abortion during the pot plant phase (Du Toit et al., 2001a, 2002). Multiple inflorescences are very appealing for the consumer and low temperature regimes during the bulb production phase can therefore be recommended for inducing multiple inflorescences. A possible reason for the reduced number of inflorescences on the HTR bulbs can be ascribed to flower abortion (Du Toit et al., 2002). In Fig. 3 of this paper, the authors provide a schematic illustration showing how HTR enhanced module development, but on the other hand caused inflorescence abortion (blasting). A too high temperature exposure
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during the bulb production phase may, therefore, reduce the number of inflorescences of the treated bulbs during the pot plant phase, instead of promoting it. 4.3. Inflorescence longevity Inflorescence longevity is an important quality for a pot plant. Louw (1991) and Jansen van Vuuren (1990) found that the storage conditions before planting do not affect the keeping ability of the inflorescences of Lachenalia cv. Romelia, and Ornithogalum, respectively. Whereas, our data clearly illustrate that growth temperatures of the previous year can affect the keeping ability of the inflorescences (Fig. 3).
5. Conclusion The bulb production phase plays an important role in the quality of the final pot plant. It is therefore essential for the grower to consider the bulb’s history of the previous year before it is sold as a marketable size bulb for pot plant production. In this study it was shown that subjecting the plants to a low temperature regime during the bulb production phase shifted the flowering date 2 months earlier compared to bulbs that were produced under normal climatic conditions. The lower the temperature during bulb production, the more uniform was flowering during the pot plant phase. The LTR-treated bulbs rendered the highest quality inflorescences with a considerable keeping ability. The LTR treated bulbs also produced the most attractive leaves during the pot plant phase.
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