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Effects of apical growing point size and tuber weight on production in Sandersonia aurantiaca
Scientia Horticulturae 94 (2002) 323–332
Effects of apical growing point size and tuber weight on production in Sandersonia aurantiaca G.E. Clarka,*, G.K. Burgeb a
New Zealand Institute for Crop and Food Research Limited, Pukekohe Research Centre, Cronin Road, RD 1, Pukekohe, New Zealand b New Zealand Institute for Crop and Food Research Limited, Food Industry Science Centre, Private Bag 11 600, Palmerston North, New Zealand Accepted 7 December 2001
Abstract The size of apical growing points on four grades of sandersonia tuber (3–5, 5–7, 7–10 and >10 g) increased with increasing tuber weight (R2 ¼ 0:71). These tubers were divided in two separate experiments to provide weights of 16.7, 33 and 50% and 50, 75 and 100% of the original grade size weights. Tubers were grown in the main season under standard forcing conditions. Harvested stem length was significantly greater with increasing tuber size, but declined with increasing severity of cutting treatment. Similar results also occurred with stem weight, flower number and vase-life. Regression analysis of stem length versus planted tuber size for the combined data from both experiments produced a significant relationship (R2 ¼ 0:83), with the fitted line being: L ¼ 673:5 336:9 0:7626T (where L is the stem length, T the tuber planted weight and 673.5 is the upper asymptote). Stem size and flower number were influenced by tuber weight rather than by apical growing point size. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Sandersonia; Sandersonia aurantiaca; Tuber; Apical growing point; Weight; Flower production
1. Introduction Sandersonia aurantiaca (Hook.) is a tuberous ornamental crop grown for its cut flowers. In New Zealand, tubers are produced for both local and export markets. Tubers are forked or spherical with a single growing point on the end of each fork or on each side of the sphere (Brundell and Reyngoud, 1986) from which develops a single flowering stem. The critical tuber size or weight for flowering in sandersonia is unknown, but in a good growing season flowers have been reported on stems grown directly from seed. * Corresponding author. Tel.: þ64-9238-6414; fax: þ64-9238-6119. E-mail address: [email protected] (G.E. Clark).
0304-4238/02/$ – see front matter # 2002 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 4 2 3 8 ( 0 2 ) 0 0 0 1 1 - 0
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G.E. Clark, G.K. Burge / Scientia Horticulturae 94 (2002) 323–332
Halevy (1990) proposed that in some geophytes flower size may be controlled not just by storage organ size but by the size of the apical meristem. The size of the apical growing point of sandersonia and its relationship to tuber weight and flower production has not been studied. If the size of the apical growing point is an important factor that controls the size of the resultant flower stem there are implications for the production of quality tubers and the selection of tuber lines. This study examines the effect of the size of the apical growing point and tuber weight on sandersonia production to determine the main factor controlling stem size.
2. Materials and methods Tubers of four grade sizes, 3–5, 5–7, 7–10 and >10 g stored for 4–5 months at 4 8C were used in two separate experiments. Tubers were cut to specific sizes and dipped in a protective fungicide mixture of 0.5 g/l benomyl plus 2.0 g/l thiram for 10 min prior to planting into polystyrene trays (595 420 190 mm) containing commercial (Yates NZ) nitrogen stabilised composted radiata pine bark fines (0–8 mm) with incorporated fertilisers. At planting the water soluble nutrient content of the bark media was measured in a 1:1.5 media:water (v:v) extract using colorimetry and atomic absorption methods. Media nutrient levels were pH, 5.2–5.4; Ca, 39–96 ppm; K, 59–66 ppm; P, 16–24 ppm; Mg, 25–60 ppm and N, 69–71 ppm. Table 1 Weights and nutrient concentrations of sandersonia tuber pieces in Experiment 1 and weights in Experiment 2 for each grade size at planting (d:f: ¼ 9) Cutting treatment
Tuber grade size (g) 3–5
5–7
7–10
Mean
P-value
LSD0.05
10þ
Planted tuber weights (g) Experiment 1 50% 33% 16.7%
1.85 1.24 0.63
2.76 1.80 0.91
4.22 2.76 1.39
5.50 3.63 1.82
– – –
– – –
– – –
Experiment 2 100% 75% 50%
3.52 2.71 1.79
5.52 4.08 2.73
7.65 5.89 3.78
11.00 8.35 5.45
– – –
– – –
– – –
1.84 0.16 0.09 0.27 0.16 0.05 2.1
2.14 0.12 0.08 0.24 0.14 0.04 1.9
2.14 0.11 0.09 0.26 0.13 0.05 2.0
2.01 0.13 0.09 0.32 0.15 0.06 2.1
NSa <0.05 <0.001 <0.001 <0.05 <0.001 <0.01
– 0.03 0.012 0.05 0.023 0.013 0.14
Tuber nutrient concentration (%) N 1.94 Ca 0.15 Mg 0.13 P 0.51 S 0.16 Na 0.10 K 2.2 a
Not significant.
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Tubers were planted at a depth of 25 mm with 28 tubers/tray (one tray per plot) and four replicates (trays) per treatment, in a randomised block design. The trays were held in an unheated glasshouse that had forced air circulation and was ventilated at 20 8C. The trays were sprinkler-irrigated until emergence and then drip-irrigated twice daily at 2.5 l/m2. The crop was supported with netting. Stems were cut just above the second leaf node when the second flower on the stem had reached anthesis. Stem lengths, stem weights, flower number, harvest dates were recorded and vase-life determined. Vase-life was evaluated in distilled water under standard conditions at 20 8C with 20–25 mE/m2/s at bench height for 12 h days. Vase-life was deemed to be completed when greater than 50% of the flowers had senesced. All data were analysed by analysis of variance and regression analysis (Genstat 5). 2.1. Experiment 1—severe tuber cutting The size of the two apical growing points of 10 tubers from each grade size was measured. The outer protective cap or sheath that covers the growing point was removed and the growing point was measured across the basal plane using a calibrated ocular micrometer in a binocular microscope. The tubers were weighed, cut in half and then dried at 80 8C for 48 h prior to nutrient analysis. Table 2 Effect of tuber size and cutting treatments on sandersonia vase-life Cutting treatment
Vase-life for each weight grade (days) Tuber grade size (g)
Mean
3–5
5–7
7–10
10þ
15.8 15.4 14.9
15.4 15.0 14.7
15.3 15.1 14.9
16.0 15.4 14.9
15.4
15.0
15.1
15.4
P-value
LSD0.05
SED (d:f: ¼ 33)
Tuber size Cutting Tuber size cutting
<0.05 <0.001 NSa
0.28 0.25 –
0.14 0.12 –
Experiment 2 100% 75% 50%
15.4 14.6 14.7
14.9 15.0 14.0
16.0 15.6 15.2
16.2 15.6 15.7
14.9
14.7
15.6
15.8
P-value
LSD0.05
SED (d:f: ¼ 33)
<0.001 <0.05 NS
0.49 0.43 –
0.24 0.21 –
Experiment 1 50% 33% 16.7% Mean
Mean
Tuber size Cutting Tuber size cutting a
Not significant.
15.6 15.2 14.9
15.6 15.2 14.9
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Two hundred tubers in each of the four grade sizes were cut in half (based on weight) and placed in a 20 8C thermostatically controlled incubator on 15 October 1996 to pre-sprout (Clark, 1994). Tubers were divided at this stage to ensure equal development of the growing points as Brundell and Reyngoud (1986) had shown that one growing point could be dominant in undivided tubers. On 22 October 1996, the tubers were re-cut into pieces weighing 16.7, 33 and 50% of the original grade size weights (Table 1). 2.2. Experiment 2—moderate tuber cutting Sixty tubers of each grade size were cut in half (by weight) and placed together with a further 60 uncut tubers from each grade size in a 20 8C thermostatically controlled incubator on 22 September 1997 to pre-sprout (Clark, 1994). These tubers were divided to ensure equal development of both growing points, whereas from the remaining tubers only one growing point was required. On 2 October 1997 the tubers were cut into pieces weighting 50, 75 and 100% of the original grade size weights (Table 1). The tubers for the 100% treatment had one of the growing points excised.
Table 3 Effect of tuber size and cutting treatments on sandersonia stem length Cutting treatment
Stem length for each weight grade (mm) Tuber grade size (g)
Mean
3–5
5–7
7–10
10þ
532 488 373
521 497 374
564 510 405
606 551 459
464
464
493
583
P-value
LSD0.05
SED (d:f: ¼ 33)
Tuber size Cutting Tuber size cutting
<0.001 <0.001 NSa
15.8 13.7 –
7.78 6.74 –
Experiment 2 100% 75% 50%
542 501 463
601 549 518
654 589 513
664 632 589
502
556
585
628
P-value
LSD0.05
SED (d:f: ¼ 33)
<0.001 <0.001 NS
21.9 19.0 –
10.78 9.34 –
Experiment 1 50% 33% 16.7% Mean
Mean
Tuber size Cutting Tuber size cutting a
Not significant.
556 512 402
615 568 520
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3. Results and discussion In this study tuber nutrient levels were greater for most macro-nutrients in the two smaller grade sizes (Table 1) ðP < 0:05Þ. Nutritional studies on sandersonia have shown that tuber nutrient concentrations have little effect on stem size (Clark, 1997; Clark and Burge, 1999) and so differences in stem size found in this study are probably due to carbohydrate reserves in the tuber piece rather than the nutrient levels. The vase-life was slightly greater with the less severe tuber cutting treatments in both experiments and in Experiment 2 with the larger tuber grade sizes (Table 2). Previous studies have not found any effect of production techniques on the vase-life of sandersonia flower stems (Clark, 1997; Clark and Burge, 1999). The lower flowers on sandersonia stems open and senesce first. Vase-life is defined to be complete when more than 50% of the flowers have senesced. The larger tuber pieces have longer stems with more flowers and so the longer vase-life found in this study is probably due to the greater number of flowers. Harvested stem length was greater with increasing tuber size and declined with severity of cutting treatments in both experiments (Table 3) ðP < 0:001Þ. Similar results also occurred for both stem weight and flower numbers (Tables 4 and 5). Brundell and Reyngoud (1986) and Clark and Reyngoud (1997) both found that the number of Table 4 Effect of tuber size and cutting treatments on sandersonia stem weight Cutting treatment
Stem weight for each weight grade (g) Tuber grade size (g)
Mean
3–5
5–7
7–10
10þ
8.3 7.2 4.2
8.6 7.4 4.4
10.5 8.4 5.3
12.0 9.4 6.6
6.6
6.8
8.1
9.3
P-value
LSD0.05
SED (d:f: ¼ 33)
Tuber size Cutting Tuber size cutting
<0.001 <0.001 <0.05
0.43 0.37 0.75
0.21 0.18 0.37
Experiment 2 100% 75% 50%
9.9 9.7 7.2
11.8 9.9 9.1
14.6 12.6 8.9
14.8 14.0 12.7
8.9
10.3
12.0
13.8
P-value
LSD0.05
SED (d:f: ¼ 33)
<0.001 <0.001 NSa
1.23 1.06 –
0.60 0.52 –
Experiment 1 50% 33% 16.7% Mean
Mean
Tuber size Cutting Tuber size cutting a
Not significant.
9.9 8.1 5.1
12.7 11.6 9.5
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Table 5 Effect of tuber size and cutting treatment on sandersonia flower number Cutting treatment
Flower number for each weight grade Tuber grade size (g)
Experiment 1 50% 33% 16.7% Mean
Mean
3–5
5–7
7–10
10þ
6.8 5.9 3.5
7.4 6.9 4.2
9.4 8.2 5.8
10.3 9.0 6.9
5.4
6.2
7.8
8.7
P-value
LSD0.05
SED (d:f: ¼ 33)
Tuber size Cutting Tuber size cutting
<0.001 <0.001 NSa
0.24 0.21 –
0.12 0.10 –
Experiment 2 100% 75% 50%
8.7 8.0 6.9
9.7 9.0 8.2
10.7 9.9 7.9
10.8 10.5 9.6
7.9
9.0
9.5
10.3
Mean
Tuber size Cutting Tuber size cutting a
P-value
LSD0.05
SED (d:f: ¼ 33)
<0.001 <0.001 <0.05
0.39 0.34 0.68
0.19 0.17 0.34
8.5 7.5 5.1
10.0 9.3 8.2
Not significant.
sandersonia flowers and the size of stem were dependent on planted tuber weight. In gloriosa, a closely related species, Carow (1976) found that stem production was related to tuber size. Bulb size of many species is related to the ability to flower, or to the number or size of flowers (Rees, 1992; Le Nard and De Hertogh, 1993). The critical size for flowering varies between species and often within a cultivar as well as under different environmental conditions. For example, in narcissus it is 10 g, in tulips it ranges from 60 to 100 mm, iris 40–60 mm, gladiolus 30–60 mm, Eucrosia 21–27 g and Leucocoryne 0.1–0.2 g (Rees, 1986; Roh and Meerow, 1992; Le Nard and De Hertogh, 1993; Kim et al., 1998). Small iris and lily bulbs only produce leaves. Progress beyond this stage to the initiation of flowers is dependent on apex size, which is related to bulb size (Rees, 1992). Bulb size is correlated with apical meristem size in lilies (Kohl, 1967), iris (Doss and Christian, 1979) and brodiaea (Han et al., 1990). With some bulb crops the size of the apical meristem appears to be more important than bulb size in determining flowering ability (Halevy, 1990; Han et al., 1990). However, others have concluded that apical meristem size alone is not a good indicator of flowering potential as bulb treatments that increase flowering do not influence apical meristem size (Doss and Christian, 1979). The growing point increased in size with tuber weight (R2 ¼ 0:71) (Fig. 1). There was a significant relationship (P < 0:05) between planted tuber weight and stem length
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329
Fig. 1. Regression of growing point size on tuber weight.
(R2 ¼ 0:77, 0.83 and 0.83, respectively) in Experiments 1 and 2 and for the combined data. Exponential curves gave the best-fit to the data in both experiments (Figs. 2 and 3) and in the combined data (Fig. 4). The equation for the fitted regression to the combined data is given as: L ¼ 673:5 336:9 0:7626T (where L is the stem length, T the tuber planted weight and 673.5 is the upper asymptote). Sandersonia tubers can be easily divided, so it is possible to alter tuber size independently of growing point size. In this study, stem length was controlled by the weight of the tuber piece and not by the growing point size. Stems were not longer from tuber pieces of the same weight but with a larger growing point. The regression was a good fit for most of the data points, however, the stem lengths of the most severe cutting treatment (16.7%) in Experiment 1 were below the fitted line (Fig. 2). For planted tuber weights between 1.2 and 1.5 g and between 1.7 and 1.9 g the stem length of the most severe cutting treatment (16.7%) was less than that of the 33 and 50% cutting treatment (P < 0:05). While the weights of tubers were similar, those in the most severe cutting treatment (16.7%) had the larger growing points (Fig. 1). In Experiment 2 where planted tuber weights of treatments overlapped (3.5–4.2 and 5.6–6.1 g), there was no difference in stem length between the treatments (Fig. 3). One possible explanation for this is that the carbohydrate reserves in the tip of the tuber are less than in the rest of the tuber. This study shows that the performance of tubers is influenced by tuber weight rather than the size of the growing point. Therefore, production systems for sandersonia should focus on increasing tuber weight to optimise stem size.
330
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Fig. 2. Regression of planted tuber weights of the four grade sizes against stem length for Experiment 1.
Fig. 3. Regression of planted tuber weights of the four grade sizes against stem length for Experiment 2.
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331
Fig. 4. Regression of planted tuber weights of the four grade sizes against stem lengths for both experiments.
Acknowledgements We acknowledge Ian Brooking for his initial studies on sandersonia apical meristems and encouragement to carry out this study, and Fred Potter and Maaike Bendall for statistical analysis of the data. This research was funded by the Foundation for Research, Science and Technology.
References Brundell, D.J., Reyngoud, J.L., 1986. Observations on the development and culture of sandersonia. Acta Hortic. 177, 439–447. Carow, B., 1976. Gloriosa rothschildiana. Flower and tuber production. Acta Hortic. 64, 181–186. Clark, G.E., 1994. Assessment of storage and sprouting treatments for Sandersonia aurantiaca. New Zeal. J. Crop Hort. Sci. 22, 431–437. Clark, G.E., 1997. Effects of nitrogen and potassium nutrition on soil-grown Sandersonia aurantiaca stem and tuber production. New Zeal. J. Crop Hort. Sci. 25, 385–390. Clark, G.E., Burge, G.K., 1999. Effects of nitrogen nutrition on Sandersonia cut flower and tuber production in soil-less media. New Zeal. J. Crop Hort. Sci. 27, 145–152. Clark, G.E., Reyngoud, J.L., 1997. Effects of production methods on Sandersonia cut stem quality and daughter tuber size. Acta Hortic. 430, 731–735. Doss, R.P., Christian, J.K., 1979. Relationship between bulb size, apex size and flowering in bulbous iris cv. Ideal. Physiol. Plantarum 45, 215–218. Halevy, A.H., 1990. Recent advances in control of flowering and growth habit of geophytes. Acta Hortic. 266, 35–42.
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Han, S.S., Halevy, A.H., Sachs, R.M., Reid, M.S., 1990. Enhancement of growth and flowering of Triteleia laxa by ethylene. J. Am. Soc. Hort. Sci. 115, 482–486. Kim, H.H., Ohkawa, K., Nitta, E., 1998. Effects of bulb weight on the growth and flowering of Leucocoryne coquimbensis F. Phill. Acta Hortic. 454, 341–346. Kohl, H.C., 1967. Correlation between rate of initiation and apex diameter of Lilium longiflorum cultivar ‘Ace’. HortScience 2, 15–16. Le Nard, M., De Hertogh, A.A., 1993. Bulb growth and development and flowering. In: De Hertogh, A., Le Nard, M. (Eds.), The Physiology of Flower Bulbs. Elsevier, Amsterdam, pp. 29–43. Rees, A.R., 1986. Narcissus: flowers per tonne of bulbs. Acta Hortic. 177, 261–266. Rees, A.R., 1992. Ornamental Bulbs, Corms and Tubers. CAB International, Wallingford, pp. 71–72. Roh, M.S., Meerow, A.W., 1992. Flowering of Eucrosia influenced by bulb size and watering frequency. HortScience 27, 1227.
Effects of apical growing point size and tuber weight on production in Sandersonia aurantiaca G.E. Clarka,*, G.K. Burgeb a
New Zealand Institute for Crop and Food Research Limited, Pukekohe Research Centre, Cronin Road, RD 1, Pukekohe, New Zealand b New Zealand Institute for Crop and Food Research Limited, Food Industry Science Centre, Private Bag 11 600, Palmerston North, New Zealand Accepted 7 December 2001
Abstract The size of apical growing points on four grades of sandersonia tuber (3–5, 5–7, 7–10 and >10 g) increased with increasing tuber weight (R2 ¼ 0:71). These tubers were divided in two separate experiments to provide weights of 16.7, 33 and 50% and 50, 75 and 100% of the original grade size weights. Tubers were grown in the main season under standard forcing conditions. Harvested stem length was significantly greater with increasing tuber size, but declined with increasing severity of cutting treatment. Similar results also occurred with stem weight, flower number and vase-life. Regression analysis of stem length versus planted tuber size for the combined data from both experiments produced a significant relationship (R2 ¼ 0:83), with the fitted line being: L ¼ 673:5 336:9 0:7626T (where L is the stem length, T the tuber planted weight and 673.5 is the upper asymptote). Stem size and flower number were influenced by tuber weight rather than by apical growing point size. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Sandersonia; Sandersonia aurantiaca; Tuber; Apical growing point; Weight; Flower production
1. Introduction Sandersonia aurantiaca (Hook.) is a tuberous ornamental crop grown for its cut flowers. In New Zealand, tubers are produced for both local and export markets. Tubers are forked or spherical with a single growing point on the end of each fork or on each side of the sphere (Brundell and Reyngoud, 1986) from which develops a single flowering stem. The critical tuber size or weight for flowering in sandersonia is unknown, but in a good growing season flowers have been reported on stems grown directly from seed. * Corresponding author. Tel.: þ64-9238-6414; fax: þ64-9238-6119. E-mail address: [email protected] (G.E. Clark).
0304-4238/02/$ – see front matter # 2002 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 4 2 3 8 ( 0 2 ) 0 0 0 1 1 - 0
324
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Halevy (1990) proposed that in some geophytes flower size may be controlled not just by storage organ size but by the size of the apical meristem. The size of the apical growing point of sandersonia and its relationship to tuber weight and flower production has not been studied. If the size of the apical growing point is an important factor that controls the size of the resultant flower stem there are implications for the production of quality tubers and the selection of tuber lines. This study examines the effect of the size of the apical growing point and tuber weight on sandersonia production to determine the main factor controlling stem size.
2. Materials and methods Tubers of four grade sizes, 3–5, 5–7, 7–10 and >10 g stored for 4–5 months at 4 8C were used in two separate experiments. Tubers were cut to specific sizes and dipped in a protective fungicide mixture of 0.5 g/l benomyl plus 2.0 g/l thiram for 10 min prior to planting into polystyrene trays (595 420 190 mm) containing commercial (Yates NZ) nitrogen stabilised composted radiata pine bark fines (0–8 mm) with incorporated fertilisers. At planting the water soluble nutrient content of the bark media was measured in a 1:1.5 media:water (v:v) extract using colorimetry and atomic absorption methods. Media nutrient levels were pH, 5.2–5.4; Ca, 39–96 ppm; K, 59–66 ppm; P, 16–24 ppm; Mg, 25–60 ppm and N, 69–71 ppm. Table 1 Weights and nutrient concentrations of sandersonia tuber pieces in Experiment 1 and weights in Experiment 2 for each grade size at planting (d:f: ¼ 9) Cutting treatment
Tuber grade size (g) 3–5
5–7
7–10
Mean
P-value
LSD0.05
10þ
Planted tuber weights (g) Experiment 1 50% 33% 16.7%
1.85 1.24 0.63
2.76 1.80 0.91
4.22 2.76 1.39
5.50 3.63 1.82
– – –
– – –
– – –
Experiment 2 100% 75% 50%
3.52 2.71 1.79
5.52 4.08 2.73
7.65 5.89 3.78
11.00 8.35 5.45
– – –
– – –
– – –
1.84 0.16 0.09 0.27 0.16 0.05 2.1
2.14 0.12 0.08 0.24 0.14 0.04 1.9
2.14 0.11 0.09 0.26 0.13 0.05 2.0
2.01 0.13 0.09 0.32 0.15 0.06 2.1
NSa <0.05 <0.001 <0.001 <0.05 <0.001 <0.01
– 0.03 0.012 0.05 0.023 0.013 0.14
Tuber nutrient concentration (%) N 1.94 Ca 0.15 Mg 0.13 P 0.51 S 0.16 Na 0.10 K 2.2 a
Not significant.
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Tubers were planted at a depth of 25 mm with 28 tubers/tray (one tray per plot) and four replicates (trays) per treatment, in a randomised block design. The trays were held in an unheated glasshouse that had forced air circulation and was ventilated at 20 8C. The trays were sprinkler-irrigated until emergence and then drip-irrigated twice daily at 2.5 l/m2. The crop was supported with netting. Stems were cut just above the second leaf node when the second flower on the stem had reached anthesis. Stem lengths, stem weights, flower number, harvest dates were recorded and vase-life determined. Vase-life was evaluated in distilled water under standard conditions at 20 8C with 20–25 mE/m2/s at bench height for 12 h days. Vase-life was deemed to be completed when greater than 50% of the flowers had senesced. All data were analysed by analysis of variance and regression analysis (Genstat 5). 2.1. Experiment 1—severe tuber cutting The size of the two apical growing points of 10 tubers from each grade size was measured. The outer protective cap or sheath that covers the growing point was removed and the growing point was measured across the basal plane using a calibrated ocular micrometer in a binocular microscope. The tubers were weighed, cut in half and then dried at 80 8C for 48 h prior to nutrient analysis. Table 2 Effect of tuber size and cutting treatments on sandersonia vase-life Cutting treatment
Vase-life for each weight grade (days) Tuber grade size (g)
Mean
3–5
5–7
7–10
10þ
15.8 15.4 14.9
15.4 15.0 14.7
15.3 15.1 14.9
16.0 15.4 14.9
15.4
15.0
15.1
15.4
P-value
LSD0.05
SED (d:f: ¼ 33)
Tuber size Cutting Tuber size cutting
<0.05 <0.001 NSa
0.28 0.25 –
0.14 0.12 –
Experiment 2 100% 75% 50%
15.4 14.6 14.7
14.9 15.0 14.0
16.0 15.6 15.2
16.2 15.6 15.7
14.9
14.7
15.6
15.8
P-value
LSD0.05
SED (d:f: ¼ 33)
<0.001 <0.05 NS
0.49 0.43 –
0.24 0.21 –
Experiment 1 50% 33% 16.7% Mean
Mean
Tuber size Cutting Tuber size cutting a
Not significant.
15.6 15.2 14.9
15.6 15.2 14.9
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Two hundred tubers in each of the four grade sizes were cut in half (based on weight) and placed in a 20 8C thermostatically controlled incubator on 15 October 1996 to pre-sprout (Clark, 1994). Tubers were divided at this stage to ensure equal development of the growing points as Brundell and Reyngoud (1986) had shown that one growing point could be dominant in undivided tubers. On 22 October 1996, the tubers were re-cut into pieces weighing 16.7, 33 and 50% of the original grade size weights (Table 1). 2.2. Experiment 2—moderate tuber cutting Sixty tubers of each grade size were cut in half (by weight) and placed together with a further 60 uncut tubers from each grade size in a 20 8C thermostatically controlled incubator on 22 September 1997 to pre-sprout (Clark, 1994). These tubers were divided to ensure equal development of both growing points, whereas from the remaining tubers only one growing point was required. On 2 October 1997 the tubers were cut into pieces weighting 50, 75 and 100% of the original grade size weights (Table 1). The tubers for the 100% treatment had one of the growing points excised.
Table 3 Effect of tuber size and cutting treatments on sandersonia stem length Cutting treatment
Stem length for each weight grade (mm) Tuber grade size (g)
Mean
3–5
5–7
7–10
10þ
532 488 373
521 497 374
564 510 405
606 551 459
464
464
493
583
P-value
LSD0.05
SED (d:f: ¼ 33)
Tuber size Cutting Tuber size cutting
<0.001 <0.001 NSa
15.8 13.7 –
7.78 6.74 –
Experiment 2 100% 75% 50%
542 501 463
601 549 518
654 589 513
664 632 589
502
556
585
628
P-value
LSD0.05
SED (d:f: ¼ 33)
<0.001 <0.001 NS
21.9 19.0 –
10.78 9.34 –
Experiment 1 50% 33% 16.7% Mean
Mean
Tuber size Cutting Tuber size cutting a
Not significant.
556 512 402
615 568 520
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3. Results and discussion In this study tuber nutrient levels were greater for most macro-nutrients in the two smaller grade sizes (Table 1) ðP < 0:05Þ. Nutritional studies on sandersonia have shown that tuber nutrient concentrations have little effect on stem size (Clark, 1997; Clark and Burge, 1999) and so differences in stem size found in this study are probably due to carbohydrate reserves in the tuber piece rather than the nutrient levels. The vase-life was slightly greater with the less severe tuber cutting treatments in both experiments and in Experiment 2 with the larger tuber grade sizes (Table 2). Previous studies have not found any effect of production techniques on the vase-life of sandersonia flower stems (Clark, 1997; Clark and Burge, 1999). The lower flowers on sandersonia stems open and senesce first. Vase-life is defined to be complete when more than 50% of the flowers have senesced. The larger tuber pieces have longer stems with more flowers and so the longer vase-life found in this study is probably due to the greater number of flowers. Harvested stem length was greater with increasing tuber size and declined with severity of cutting treatments in both experiments (Table 3) ðP < 0:001Þ. Similar results also occurred for both stem weight and flower numbers (Tables 4 and 5). Brundell and Reyngoud (1986) and Clark and Reyngoud (1997) both found that the number of Table 4 Effect of tuber size and cutting treatments on sandersonia stem weight Cutting treatment
Stem weight for each weight grade (g) Tuber grade size (g)
Mean
3–5
5–7
7–10
10þ
8.3 7.2 4.2
8.6 7.4 4.4
10.5 8.4 5.3
12.0 9.4 6.6
6.6
6.8
8.1
9.3
P-value
LSD0.05
SED (d:f: ¼ 33)
Tuber size Cutting Tuber size cutting
<0.001 <0.001 <0.05
0.43 0.37 0.75
0.21 0.18 0.37
Experiment 2 100% 75% 50%
9.9 9.7 7.2
11.8 9.9 9.1
14.6 12.6 8.9
14.8 14.0 12.7
8.9
10.3
12.0
13.8
P-value
LSD0.05
SED (d:f: ¼ 33)
<0.001 <0.001 NSa
1.23 1.06 –
0.60 0.52 –
Experiment 1 50% 33% 16.7% Mean
Mean
Tuber size Cutting Tuber size cutting a
Not significant.
9.9 8.1 5.1
12.7 11.6 9.5
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Table 5 Effect of tuber size and cutting treatment on sandersonia flower number Cutting treatment
Flower number for each weight grade Tuber grade size (g)
Experiment 1 50% 33% 16.7% Mean
Mean
3–5
5–7
7–10
10þ
6.8 5.9 3.5
7.4 6.9 4.2
9.4 8.2 5.8
10.3 9.0 6.9
5.4
6.2
7.8
8.7
P-value
LSD0.05
SED (d:f: ¼ 33)
Tuber size Cutting Tuber size cutting
<0.001 <0.001 NSa
0.24 0.21 –
0.12 0.10 –
Experiment 2 100% 75% 50%
8.7 8.0 6.9
9.7 9.0 8.2
10.7 9.9 7.9
10.8 10.5 9.6
7.9
9.0
9.5
10.3
Mean
Tuber size Cutting Tuber size cutting a
P-value
LSD0.05
SED (d:f: ¼ 33)
<0.001 <0.001 <0.05
0.39 0.34 0.68
0.19 0.17 0.34
8.5 7.5 5.1
10.0 9.3 8.2
Not significant.
sandersonia flowers and the size of stem were dependent on planted tuber weight. In gloriosa, a closely related species, Carow (1976) found that stem production was related to tuber size. Bulb size of many species is related to the ability to flower, or to the number or size of flowers (Rees, 1992; Le Nard and De Hertogh, 1993). The critical size for flowering varies between species and often within a cultivar as well as under different environmental conditions. For example, in narcissus it is 10 g, in tulips it ranges from 60 to 100 mm, iris 40–60 mm, gladiolus 30–60 mm, Eucrosia 21–27 g and Leucocoryne 0.1–0.2 g (Rees, 1986; Roh and Meerow, 1992; Le Nard and De Hertogh, 1993; Kim et al., 1998). Small iris and lily bulbs only produce leaves. Progress beyond this stage to the initiation of flowers is dependent on apex size, which is related to bulb size (Rees, 1992). Bulb size is correlated with apical meristem size in lilies (Kohl, 1967), iris (Doss and Christian, 1979) and brodiaea (Han et al., 1990). With some bulb crops the size of the apical meristem appears to be more important than bulb size in determining flowering ability (Halevy, 1990; Han et al., 1990). However, others have concluded that apical meristem size alone is not a good indicator of flowering potential as bulb treatments that increase flowering do not influence apical meristem size (Doss and Christian, 1979). The growing point increased in size with tuber weight (R2 ¼ 0:71) (Fig. 1). There was a significant relationship (P < 0:05) between planted tuber weight and stem length
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Fig. 1. Regression of growing point size on tuber weight.
(R2 ¼ 0:77, 0.83 and 0.83, respectively) in Experiments 1 and 2 and for the combined data. Exponential curves gave the best-fit to the data in both experiments (Figs. 2 and 3) and in the combined data (Fig. 4). The equation for the fitted regression to the combined data is given as: L ¼ 673:5 336:9 0:7626T (where L is the stem length, T the tuber planted weight and 673.5 is the upper asymptote). Sandersonia tubers can be easily divided, so it is possible to alter tuber size independently of growing point size. In this study, stem length was controlled by the weight of the tuber piece and not by the growing point size. Stems were not longer from tuber pieces of the same weight but with a larger growing point. The regression was a good fit for most of the data points, however, the stem lengths of the most severe cutting treatment (16.7%) in Experiment 1 were below the fitted line (Fig. 2). For planted tuber weights between 1.2 and 1.5 g and between 1.7 and 1.9 g the stem length of the most severe cutting treatment (16.7%) was less than that of the 33 and 50% cutting treatment (P < 0:05). While the weights of tubers were similar, those in the most severe cutting treatment (16.7%) had the larger growing points (Fig. 1). In Experiment 2 where planted tuber weights of treatments overlapped (3.5–4.2 and 5.6–6.1 g), there was no difference in stem length between the treatments (Fig. 3). One possible explanation for this is that the carbohydrate reserves in the tip of the tuber are less than in the rest of the tuber. This study shows that the performance of tubers is influenced by tuber weight rather than the size of the growing point. Therefore, production systems for sandersonia should focus on increasing tuber weight to optimise stem size.
330
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Fig. 2. Regression of planted tuber weights of the four grade sizes against stem length for Experiment 1.
Fig. 3. Regression of planted tuber weights of the four grade sizes against stem length for Experiment 2.
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Fig. 4. Regression of planted tuber weights of the four grade sizes against stem lengths for both experiments.
Acknowledgements We acknowledge Ian Brooking for his initial studies on sandersonia apical meristems and encouragement to carry out this study, and Fred Potter and Maaike Bendall for statistical analysis of the data. This research was funded by the Foundation for Research, Science and Technology.
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