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Influence of cutting position and stem length on rooting of leaf-bud cuttings of Schefflera arboricola
Scientia Horticulturae, 28 (1986) 177--186 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands
177
I N F L U E N C E O F C U T T I N G P O S I T I O N A N D STEM L E N G T H ON ROOTING OF LEAF-BUD CUTTINGS OF SCHEFFLERA ARBORICOLA
JI]RGEN HANSEN Institute of Glasshouse Crops, Research Centre for Horticulture, Kirstinebjergvej 10, DK-5792 .~rslev (Denmark) (Accepted for publication 13 September 1985 )
ABSTRACT Hansen, J., 1986. Influence of cutting position and stem length on rooting of leaf-bud cuttings of Schefflera arboricola. Scientia Hortic., 28: 177--186. The influence on rooting, axillary bud break and shoot growth of the cutting position on the stock plant and the stem length of leaf-bud cuttings were investigated in Schefflera arboricola Hayata. Seedlings were grown under controlled greenhouse conditions for 13 weeks. Eight cuttings from the sub-apical to basal region were excised from each stock plant. The stem length above the node was the same for all cuttings, while the stem length below the node was cut to different lengths, ranging from 0.5 to 3.0 cm. Cuttings from sub-apical positions rooted more slowly, produced fewer roots and had a lower rooting percentage than cuttings from the more basal regions. Furthermore, the number of roots and rooting percentage increased with the length of the stem below the node. The subsequent axillary bud break and shoot growth was improved considerably in cuttings from sub-apical to basal positions, and by increasing the length of the stem below the node. Keywords: adventitious root formation; axillary bud break; cutting position; propagation;Schefflera arboricola; shoot growth;stem length.
INTRODUCTION The p o s i t i o n o f the. c u t t i n g o n the s t o c k p l a n t and t h e length o f the stem piece b e l o w the n o d e o f leaf-bud cuttings are t w o i m p o r t a n t f a c t o r s f o r a d v e n t i t i o u s r o o t f o r m a t i o n . The influence o f c u t t i n g position, s o m e t i m e s referred t o as t h e influence o f t o p o p h y s i s , has b e e n r e p o r t e d for several w o o d y species ( L o r e t i a n d H a r t m a n n , 1 9 6 4 ; R o u l u n d , 1 9 7 3 ; H a r t m a n n and Kester, 1 9 8 3 ) . I n f o r m a t i o n c o n c e r n i n g s o f t w o o d and h e r b a c e o u s plants, h o w e v e r , is very limited, even t h o u g h vegetative p r o p a g a t i o n o f such plants is o f great i m p o r t a n c e in h o r t i c u l t u r e . T h e influence o f c u t t i n g p o s i t i o n o n r o o t i n g has been investigated in
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178 'Baccara' roses (Jensen, 1967) and Hedera helix (Poulsen and Andersen, 1980). Generally, the ability to form roots increased with distance from the apex. However, differences in the degree of maturation along the shoot could affect root formation (Jensen, 1967). Furthermore, Leakey (1983) recently reported a sequential decrease in rooting percentage from apical to basal cutting positions in Triplochiton scleroxylon. In the mung bean rooting system, Fernqvist (1966} found a proportional increase in root number with length of the hypocotyl. Comparable results were obtained with the pea rooting system. In this system, Hansen and Eriksen (1974) found that the increase in number of roots per cutting was associated with the length of the third internode which formed the basis of the cutting. Furthermore, Veierskov (1978) demonstrated that the number of roots was dependent on the length of that part of the third internode that remained after cutting the stem at different distances from the node. The number of roots per cutting increased with stem length (Veierskov, 1978). For single-node cuttings of Hedera helix with a stem length equal to the internode length, Poulsen and Andersen (1980) also reported an increase in root number with increasing stem length. In a similar experiment with Triplochiton scleroxylon, Leakey (1983) found a drastic increase in rooting percentage with increasing stem (internode) length. The effects of cutting position and stem length on axillary bud break and shoot growth have only been investigated in a few experiments. In roses, bud break and shoot growth were closely related to the root-forming ability of the apical and sub-apical positions (Jensen, 1967). Cuttings from the basal positions, however, had a reduced bud break and shoot growth. The effect of position seems to be species-dependent, since no effect of position on subsequent shoot growth was observed in Hedera canariensis (Christensen, 1976). The influence of stem length on axillary bud break and subsequent shoot growth also appears to be dependent on the plant species. In roses, Jensen (1967) found a gradual improvement in bud break and shoot growth at increasing stem length of the cutting. The inverse relationship was reported for Hedera canariensis (Christensen, 1976). The purpose of the present investigation was to study the effects of cutting position and stem length in Schefflera arboricola and to develop a propagation technique to obtain fast and uniform r o o t formation. MATERIALS AND METHODS Plant material and stock-plant growing conditions. -- Seedlings of Schefflera arboricola Hayata were bought from E. Friis Andersen A/S, Denmark. The seedlings were potted on 11 May 1983 in 9-cm plastic pots in a growing medium of fertilized peat (Pindstrup 3, Pindstrup Mosebrug, Denmark) with the addition of 1.5 kg m -3 of ground limestone.
179 T h e g r o w i n g c o n d i t i o n s w e r e as follows: m i n i m u m air t e m p e r a t u r e 1 8 ° C ; v e n t i l a t i o n at 2 4 ° C ; shading w h e n necessary. Plants w e r e fertilized w i t h a 1.2 g 1-1 s o l u t i o n o f a c o m p l e t e fertilizer w i t h o u t a m m o n i u m n i t r o g e n and w i t h a low c o n t e n t o f iron a n d m a n g a n e s e . N o CO2 was supplied during t h e e x p e r i m e n t . All t h e e x p e r i m e n t a l p l a n t s w e r e s u r r o u n d e d b y shelter plants.
Preparation o f cuttings and rooting conditions. -- A f t e r 13 w e e k s o f g r o w t h , u n i f o r m single-stem s t o c k p l a n t s w e r e c u t i n t o single-node leaf-bud cuttings. T h e i m m a t u r e apical p a r t w a s discarded. Eight c u t t i n g s , n u m b e r e d f r o m t o p to basis, w e r e o b t a i n e d f r o m each s t o c k plant. T h e u p p e r m o s t p o s i t i o n c o m p r i s e d t h e first m a t u r e and fully d e v e l o p e d leaf. T h e c u t t i n g s w e r e excised j u s t a b o v e t h e n o d e . B e l o w the n o d e t h e excision o c c u r r e d at diff e r e n t d i s t a n c e s f r o m t h e n o d e , as s h o w n in T a b l e I. F o r each cutting, t h e l e n g t h o f s t e m b e l o w t h e n o d e was less t h a n the length of t h e i n t e r n o d e f r o m w h i c h t h e c u t t i n g was excised. T h e r e m a i n i n g p a r t o f t h e s t o c k p l a n t had a variable n u m b e r o f n o d e s and the i n t e r n o d e s w e r e short. TABLE I Plan for excision of cuttings with respect to cutting position on stock plant and length of stem below the node. Cutting positions were numbered from top to basis. The 16 stock plants per replicate were divided into 4 groups. In each group, the cuttings were excised according to the respective column Position of leaf-bud cutting
Length of stem below the node (cm) Group 1 Group 2 Group 3 Group 4
l(top) 2 3 4 5 6 7 8(basis)
0.5 1.0 2.0 3.0 0.5 1.0 2.0 3.0
1.0 2.0 3.0 0.5 1.0 2.0 3.0 0.5
2.0 3.0 0.5 1.0 2.0 3.0 0.5 1.0
3.0 0.5 1.0 2.0 3.0 0.5 1.0 2.0
All c u t t i n g s w e r e ~ o o t e d individually in 9-cm plastic p o t s . T h e r o o t i n g m e d i u m was t h e s a m e as t h e o n e used f o r t h e s t o c k plants. T h e p o t s w e r e p l a c e d s y s t e m a t i c a l l y o n t a b l e s u n d e r p o l y e t h y l e n e c o v e r in a heavily s h a d e d greenhouse. T h e t a b l e s w e r e e q u i p p e d w i t h electric b o t t o m - h e a t cables t o k e e p a m i n i m u m t e m p e r a t u r e o f 23 _+ 0 . 5 ° C in t h e r o o t i n g m e d i u m . C u t t i n g s w e r e watered with tap water only during propagation. The experimental cuttings w e r e s u r r o u n d e d b y a line o f shelter cuttings. A f t e r 21 d a y s o f r o o t i n g , t h e n u m b e r o f r o o t s longer t h a n 1 m m was
180
counted and the average number of roots per cutting {based on all cuttings in the treatment) and rooting percentage were calculated. Growth o f rooted cuttings. -- A parallel experiment was performed in which axillary bud break and shoot growth were measured. After 21 days of rooting the plants were gradually hardened over 1 week and then transferred to the greenhouse used to grow the stock plants. Axillary bud break and subsequent shoot growth of the cuttings were measured after 5, 8 and 11 weeks from excision and planting. Only released buds longer than 0.5 cm were recorded. Experimental design and statistics. -- Three replicates of each of the experiments were performed. Each replicate comprised 16 stock plants. The total number of stock plants per experiment thus comprised 48 uniform plants. In order to get precise information on the interaction between cutting position and stem length, each replicate of 16 plants was randomly divided into 4 groups and prepared according to Table I. With this experimental design, it was possible to evaluate statistically the effect of cutting position and stem length using the small number of stock plants. Analyses of variances were performed on all variables according to the split-plot design. The calculations of the LSD values at the 95% level of significance were based on this analysis of variance. ,-
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181 RESULTS
Effect of cutting position on root formation, axillary bud break and shoot growth. -- Rooting was affected by the position of the leaf-bud cutting on the stock plant. An increase in root number and rooting percentage was observed with distance from the apex (Fig. 1). The mean root number reached 'the highest value at positions 5--7 {Fig. 1A), whereas the rooting percentage reached the highest level at positions 3--7 (Fig. 1B). The effect of cutting position on axillary bud break 5, 8 and 11 weeks after the planting of cuttings is shown in Fig. 2. Five weeks after planting, there was a strong effect of the cutting position on the percentage of bud break. With increasing position number, up to position 7, bud break was increased from 3% to approximately 50%. The effect of cutting position ,
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Fig. 2. Effect on axillary bud break of position of the leaf-bud cutting on the stock plant. Bud break (measured as released buds longer than 0.5 cm) was recorded (A) 5, (B) 8 and (C) 11 weeks after excision and planting of the cuttings. Fig. 3. Effect on plant height of position of the leaf-bud cutting on the stock plant. Plant height (measured from pot rim to apex) was recorded (A) 5, (B) 8 and (C) 11 weeks after excision and planting of the cuttings.
182
was still present 8 weeks after planting, but at that time bud break was only reduced at the uppermost position. After a further 3-week period, no significant effect of cutting position on the percentage of bud break could be recorded. The subsequent growth of the lateral shoot was also measured 5, 8 and 11 weeks after the excision and planting of the cutting. The results (Fig. 3) demonstrate that the effect of cutting position on rooting and axillary bud break also affects the subsequent growth of the shoot. After 11 weeks from planting, plants originating from positions 1, 2 and 8 were significantly shorter than those from the other positions. Effect of length o f stem below the node on root formation, axillary bud break and shoot growth. -- Rooting was strongly influenced by the length of the stem below the node of the leaf-bud cutting (Fig. 4). Cuttings having only 0.5 cm of stem below the node had very few roots. Only 3.5 roots per cutting were recorded, and the rooting percentage was as low as 50. With increasing stem length the number of roots per cutting was increased. The rooting percentage increased also, and reached the highest level when the stem length approached 2 cm. The detailed results in Table II show that the increase in root number with stem length, with only a few exceptions, was found for all cutting positions. Axillary bud break was also influenced by the length of the stem below the node (Fig. 5). Five weeks after excision and planting hardly any cuttings with a 0.5-cm stem length had sprouted, whereas 50% of the cuttings with
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183
a 3-cm stem length had sprouted. The percentage of cuttings with axillary bud break approached the maximal value gradually, and after 11 weeks from excision approximately all cuttings had developed an actively growing shoot. T A B L E II N u m b e r of r o o t s per c u t t i n g as a f u n c t i o n of c u t t i n g p o s i t i o n o n t h e s t o c k p l a n t a n d o f s t e m l e n g t h b e l o w t h e n o d e . E a c h value r e p r e s e n t s t h e m e a n n u m b e r o f r o o t s per c u t t i n g o f 12 c u t t i n g s f r o m d i f f e r e n t stock p l a n t s Cutting position
Stem length (cm)
1 (top) 2 3 4 5 6 7 8 (basis)
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Fig. 5. E f f e c t o n axillary b u d b r e a k o f s t e m l e n g t h b e l o w t h e n o d e o f t h e leaf-bud cutting. B u d b r e a k was r e c o r d e d (A - - A) 5, (= - - =) 8 a n d (o - - o) 11 w e e k s a f t e r excision a n d p l a n t i n g o f t h e cuttings. Fig. 6. E f f e c t o n p l a n t h e i g h t o f s t e m l e n g t h b e l o w t h e n o d e o f t h e leaf-bud c u t t i n g . P l a n t h e i g h t was r e c o r d e d (A - - A) 5, (= - - =) 8 a n d (e - - o) 11 w e e k s a f t e r e x c i s i o n a n d p l a n t i n g o f t h e cuttings.
184 Plant height after 5, 8 and 11 weeks from excision is shown in Fig. 6. Plants from cuttings having a stem length of 0.5 cm were shorter than plants from cuttings with longer stem lengths. DISCUSSION Influence o f cutting position. -- The positional differences in root formation in Schefflera arboricola are in agreement with the general statement by Hartmann and Kester (1983) that the best rooting of cuttings is usually found in cuttings from the basal portions of a shoot. The increasing number of roots per cutting with the distance from the apex is in agreement with the findings for Hedera helix reported by Poulsen and Andersen (1980). The increase in rooting percentage, however, differs from the results reported for other species. For Hedera helix all cuttings were able to root (Poulsen and Andersen, 1980), while for Triplochiton scleroxylon a gradual reduction in rooting percentage was recorded with distance from apex (Leakey, 1983). The stimulation of rooting in more basal internodes could be due to the phase changes that gradually occur along the stem of a plant (Hartmann and Kester, 1983). Another explanation could be that the reduction in irradiance associated with an increase in distance from top to basis through a plant canopy causes an increase in root number. Stock plant irradiance effects on subsequent root formation have been investigated in a range of plant species. The majority of species investigated, including ScheffIera arboricola (J. Hansen, unpublished results, 1984), responded b y producing more roots at decreasing irradiance (Biran and Halevy, 1973; Hansen and Eriksen, 1974; Poulsen and Andersen, 1980; Hansen and Ernstsen, 1982). The uniform and nearly complete axillary bud break, which was observed 11 weeks after excision and planting of the cutting {Fig. 5), imply that the final rooting percentage for all cutting positions had gradually increased to over 90%. The differences in rooting percentage (Fig. 1) that were recorded after 3 weeks of rooting thus indicate differences in the rate of root formation in cuttings with different positional origin. The influence of cutting position on axi!lary bud break suggests that it is the onset of bud break rather than the capacity for this process that is affected. The present results are not in agreement with those reported by Jensen (1967) for 'Baccara' roses, where a decrease in bud break was observed at more basal positions. Consequently, cutting position influenced the subsequent shoot growth. Differences in plant height measured 11 weeks after planting were mainly a result of the different shoot growth periods from bud break to measurement of plant height. This effect differs from the results for the related species Hedera canariensis (Christensen, 1976). In that investigation there was no significant relationship between cutting position and subsequent shoot growth.
185
Influence of stem length. -- The increase in number of roots per cutting with increasing stem length below the node of the leaf-bud cutting is in agreement with the results for Pisum sativum (Veierskov, 1978). The present results with Schefflera arboricola show, however, that this effect was not only valid for a particular internode, as was reported for Pisum sativum (Veierskov, 1978), but was obtained for all the cutting positions investigated (Table II). Supporting results were reported for Hedera helix (Poulsen and Andersen, 1980), although in this experiment the different stem lengths were represented by the entire internode length. Veierskov (1978) suggested that the effect of stem or internode length was related to carbohydrates accumulated at the basis of the cutting, and that the carbohydrate amount was more optimal for root formation in a cutting with a long basal internode or stem compared to a cutting with a short internode or stem. This theory could explain the results with Schefflera arboricola, although the participation of other controlling factors cannot be excluded. A recent investigation by Veierskov et al. (1982) on the role of carbohydrates in the regulation of root formation in pea cuttings, however, does not support the carbohydrate theory. The effect of stem length on the rooting percentage was similar to the effect reported b y Jensen (1967) for 'Baccara' roses. The detailed investigation with Triplochiton cuttings (Leakey, 1983) also provides supporting results. Axillary bud break is also affected by the stem length of the cutting. The results, however, show that only the time of bud break is affected. The capacity for bud break is the same regardless of the stem length. The effect of stem length on final plant height is mainly a consequence of the influence of the time of axillary bud break. For Schefflera arboricola, it can be concluded that in order to obtain plants of uniform size it is necessary to standardize the cutting material for propagation. The uppermost, soft leaf-bud cuttings should be avoided and the stem length below the node should be approximately 2 cm. Due to early axillary bud break, such an optimization will also give a reduction of 2--3 weeks in total production time. This may be of importance in commercial propagation. ACKNOWLEDGEMENTS
The statistical analyses were made by Dr. Kristian Kristensen, Biometric Section, Lyngby. The skilful technical assistance of Messrs. Poul Mose, Ebbe E. Andersen and Gunnar Pedersen is greatly appreciated. REFERENCES Biran, I. and Halevy, A.H., 1973. Stock plant shading and rooting of dahlia cuttings. Scientia Hortic., 1 : 125--131.
186 Christensen, O.V., 1976. The growth rate and the variation in growth in relation to the stock plant of Hedera canariensis WiUd. 'Gloire de Marengo'. Scientia Hortic., 4: 377--385. Fernqvist, I., 1966. Studies on factors in adventitious root formation. Lantbrukshoeg~ kolans Ann., 32 : 109--244. Hansen, J. and Eriksen, E.N., 1974. Root formation of pea cuttings in relation to the irradiance of the stock plants. Physiol. Plant., 32: 170--173. Hansen, J. and Ernstsen, A., 1982. Seasonal changes in adventitious root formation in hypocotyl cuttings of Pinus sylvestris: Influence of photoperiod during stock plant growth and of indolebutyric acid treatment of cuttings. Physiol. Plant., 54: 99--106. Hartmann, H.T. and Kester, D.E., 1983. Plant Propagation. Principles and Practices. Prentice-Hall, Englewood Cliffs, NJ, 727 pp. Jensen, H.E.K., 1967. Stiklingeformering af v~eksthusroser. Thesis. Royal Veterinary and Agricultural University, Copenhagen, 57 pp. Leakey, R.R.B., 1983. Stockplant factors affecting root initiation in cuttings of Triplochiton scleroxylon K. Schum., an indigenous hardwood of West Africa. J. Hortic. Sci., 58: 277--290. Loreti, F. and Hartmann, H.T., 1964. Propagation of olive trees by rooting leafy cuttings under mist. Proc. Am. Soc. Hortic. Sci., 85 : 257--264. Poulsen, A. and Andersen, A.S., 1980. Propagation of Hedera helix: Influence of irradiance to stock plants, length of internode and topophysis of cutting. Physiol. Plant., 49 : 359--365. Roulund, H., 1973. The effect of cyclophysis and topophysis on the rooting ability of Norway spruce cuttings. For. Tree Improv., 5: 21--41. Veierskov, B., 1978. A relationship between length of basis and adventitious root formation in pea cuttings. Physiol. Plant., 42 : 146--150. Veierskov, B., Andersen, A.S. and Eriksen, E.N., 1982. Dynamics of extractable carbohydrates in Pisum sativum. I. Carbohydrate and nitrogen content in pea plants and cuttings grown at two different irradiances. Physiol. Plant., 55: 167--173.
177
I N F L U E N C E O F C U T T I N G P O S I T I O N A N D STEM L E N G T H ON ROOTING OF LEAF-BUD CUTTINGS OF SCHEFFLERA ARBORICOLA
JI]RGEN HANSEN Institute of Glasshouse Crops, Research Centre for Horticulture, Kirstinebjergvej 10, DK-5792 .~rslev (Denmark) (Accepted for publication 13 September 1985 )
ABSTRACT Hansen, J., 1986. Influence of cutting position and stem length on rooting of leaf-bud cuttings of Schefflera arboricola. Scientia Hortic., 28: 177--186. The influence on rooting, axillary bud break and shoot growth of the cutting position on the stock plant and the stem length of leaf-bud cuttings were investigated in Schefflera arboricola Hayata. Seedlings were grown under controlled greenhouse conditions for 13 weeks. Eight cuttings from the sub-apical to basal region were excised from each stock plant. The stem length above the node was the same for all cuttings, while the stem length below the node was cut to different lengths, ranging from 0.5 to 3.0 cm. Cuttings from sub-apical positions rooted more slowly, produced fewer roots and had a lower rooting percentage than cuttings from the more basal regions. Furthermore, the number of roots and rooting percentage increased with the length of the stem below the node. The subsequent axillary bud break and shoot growth was improved considerably in cuttings from sub-apical to basal positions, and by increasing the length of the stem below the node. Keywords: adventitious root formation; axillary bud break; cutting position; propagation;Schefflera arboricola; shoot growth;stem length.
INTRODUCTION The p o s i t i o n o f the. c u t t i n g o n the s t o c k p l a n t and t h e length o f the stem piece b e l o w the n o d e o f leaf-bud cuttings are t w o i m p o r t a n t f a c t o r s f o r a d v e n t i t i o u s r o o t f o r m a t i o n . The influence o f c u t t i n g position, s o m e t i m e s referred t o as t h e influence o f t o p o p h y s i s , has b e e n r e p o r t e d for several w o o d y species ( L o r e t i a n d H a r t m a n n , 1 9 6 4 ; R o u l u n d , 1 9 7 3 ; H a r t m a n n and Kester, 1 9 8 3 ) . I n f o r m a t i o n c o n c e r n i n g s o f t w o o d and h e r b a c e o u s plants, h o w e v e r , is very limited, even t h o u g h vegetative p r o p a g a t i o n o f such plants is o f great i m p o r t a n c e in h o r t i c u l t u r e . T h e influence o f c u t t i n g p o s i t i o n o n r o o t i n g has been investigated in
0304-4238/86/$03.50
© 1986 Elsevier Science Publishers B.V.
178 'Baccara' roses (Jensen, 1967) and Hedera helix (Poulsen and Andersen, 1980). Generally, the ability to form roots increased with distance from the apex. However, differences in the degree of maturation along the shoot could affect root formation (Jensen, 1967). Furthermore, Leakey (1983) recently reported a sequential decrease in rooting percentage from apical to basal cutting positions in Triplochiton scleroxylon. In the mung bean rooting system, Fernqvist (1966} found a proportional increase in root number with length of the hypocotyl. Comparable results were obtained with the pea rooting system. In this system, Hansen and Eriksen (1974) found that the increase in number of roots per cutting was associated with the length of the third internode which formed the basis of the cutting. Furthermore, Veierskov (1978) demonstrated that the number of roots was dependent on the length of that part of the third internode that remained after cutting the stem at different distances from the node. The number of roots per cutting increased with stem length (Veierskov, 1978). For single-node cuttings of Hedera helix with a stem length equal to the internode length, Poulsen and Andersen (1980) also reported an increase in root number with increasing stem length. In a similar experiment with Triplochiton scleroxylon, Leakey (1983) found a drastic increase in rooting percentage with increasing stem (internode) length. The effects of cutting position and stem length on axillary bud break and shoot growth have only been investigated in a few experiments. In roses, bud break and shoot growth were closely related to the root-forming ability of the apical and sub-apical positions (Jensen, 1967). Cuttings from the basal positions, however, had a reduced bud break and shoot growth. The effect of position seems to be species-dependent, since no effect of position on subsequent shoot growth was observed in Hedera canariensis (Christensen, 1976). The influence of stem length on axillary bud break and subsequent shoot growth also appears to be dependent on the plant species. In roses, Jensen (1967) found a gradual improvement in bud break and shoot growth at increasing stem length of the cutting. The inverse relationship was reported for Hedera canariensis (Christensen, 1976). The purpose of the present investigation was to study the effects of cutting position and stem length in Schefflera arboricola and to develop a propagation technique to obtain fast and uniform r o o t formation. MATERIALS AND METHODS Plant material and stock-plant growing conditions. -- Seedlings of Schefflera arboricola Hayata were bought from E. Friis Andersen A/S, Denmark. The seedlings were potted on 11 May 1983 in 9-cm plastic pots in a growing medium of fertilized peat (Pindstrup 3, Pindstrup Mosebrug, Denmark) with the addition of 1.5 kg m -3 of ground limestone.
179 T h e g r o w i n g c o n d i t i o n s w e r e as follows: m i n i m u m air t e m p e r a t u r e 1 8 ° C ; v e n t i l a t i o n at 2 4 ° C ; shading w h e n necessary. Plants w e r e fertilized w i t h a 1.2 g 1-1 s o l u t i o n o f a c o m p l e t e fertilizer w i t h o u t a m m o n i u m n i t r o g e n and w i t h a low c o n t e n t o f iron a n d m a n g a n e s e . N o CO2 was supplied during t h e e x p e r i m e n t . All t h e e x p e r i m e n t a l p l a n t s w e r e s u r r o u n d e d b y shelter plants.
Preparation o f cuttings and rooting conditions. -- A f t e r 13 w e e k s o f g r o w t h , u n i f o r m single-stem s t o c k p l a n t s w e r e c u t i n t o single-node leaf-bud cuttings. T h e i m m a t u r e apical p a r t w a s discarded. Eight c u t t i n g s , n u m b e r e d f r o m t o p to basis, w e r e o b t a i n e d f r o m each s t o c k plant. T h e u p p e r m o s t p o s i t i o n c o m p r i s e d t h e first m a t u r e and fully d e v e l o p e d leaf. T h e c u t t i n g s w e r e excised j u s t a b o v e t h e n o d e . B e l o w the n o d e t h e excision o c c u r r e d at diff e r e n t d i s t a n c e s f r o m t h e n o d e , as s h o w n in T a b l e I. F o r each cutting, t h e l e n g t h o f s t e m b e l o w t h e n o d e was less t h a n the length of t h e i n t e r n o d e f r o m w h i c h t h e c u t t i n g was excised. T h e r e m a i n i n g p a r t o f t h e s t o c k p l a n t had a variable n u m b e r o f n o d e s and the i n t e r n o d e s w e r e short. TABLE I Plan for excision of cuttings with respect to cutting position on stock plant and length of stem below the node. Cutting positions were numbered from top to basis. The 16 stock plants per replicate were divided into 4 groups. In each group, the cuttings were excised according to the respective column Position of leaf-bud cutting
Length of stem below the node (cm) Group 1 Group 2 Group 3 Group 4
l(top) 2 3 4 5 6 7 8(basis)
0.5 1.0 2.0 3.0 0.5 1.0 2.0 3.0
1.0 2.0 3.0 0.5 1.0 2.0 3.0 0.5
2.0 3.0 0.5 1.0 2.0 3.0 0.5 1.0
3.0 0.5 1.0 2.0 3.0 0.5 1.0 2.0
All c u t t i n g s w e r e ~ o o t e d individually in 9-cm plastic p o t s . T h e r o o t i n g m e d i u m was t h e s a m e as t h e o n e used f o r t h e s t o c k plants. T h e p o t s w e r e p l a c e d s y s t e m a t i c a l l y o n t a b l e s u n d e r p o l y e t h y l e n e c o v e r in a heavily s h a d e d greenhouse. T h e t a b l e s w e r e e q u i p p e d w i t h electric b o t t o m - h e a t cables t o k e e p a m i n i m u m t e m p e r a t u r e o f 23 _+ 0 . 5 ° C in t h e r o o t i n g m e d i u m . C u t t i n g s w e r e watered with tap water only during propagation. The experimental cuttings w e r e s u r r o u n d e d b y a line o f shelter cuttings. A f t e r 21 d a y s o f r o o t i n g , t h e n u m b e r o f r o o t s longer t h a n 1 m m was
180
counted and the average number of roots per cutting {based on all cuttings in the treatment) and rooting percentage were calculated. Growth o f rooted cuttings. -- A parallel experiment was performed in which axillary bud break and shoot growth were measured. After 21 days of rooting the plants were gradually hardened over 1 week and then transferred to the greenhouse used to grow the stock plants. Axillary bud break and subsequent shoot growth of the cuttings were measured after 5, 8 and 11 weeks from excision and planting. Only released buds longer than 0.5 cm were recorded. Experimental design and statistics. -- Three replicates of each of the experiments were performed. Each replicate comprised 16 stock plants. The total number of stock plants per experiment thus comprised 48 uniform plants. In order to get precise information on the interaction between cutting position and stem length, each replicate of 16 plants was randomly divided into 4 groups and prepared according to Table I. With this experimental design, it was possible to evaluate statistically the effect of cutting position and stem length using the small number of stock plants. Analyses of variances were performed on all variables according to the split-plot design. The calculations of the LSD values at the 95% level of significance were based on this analysis of variance. ,-
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181 RESULTS
Effect of cutting position on root formation, axillary bud break and shoot growth. -- Rooting was affected by the position of the leaf-bud cutting on the stock plant. An increase in root number and rooting percentage was observed with distance from the apex (Fig. 1). The mean root number reached 'the highest value at positions 5--7 {Fig. 1A), whereas the rooting percentage reached the highest level at positions 3--7 (Fig. 1B). The effect of cutting position on axillary bud break 5, 8 and 11 weeks after the planting of cuttings is shown in Fig. 2. Five weeks after planting, there was a strong effect of the cutting position on the percentage of bud break. With increasing position number, up to position 7, bud break was increased from 3% to approximately 50%. The effect of cutting position ,
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Fig. 2. Effect on axillary bud break of position of the leaf-bud cutting on the stock plant. Bud break (measured as released buds longer than 0.5 cm) was recorded (A) 5, (B) 8 and (C) 11 weeks after excision and planting of the cuttings. Fig. 3. Effect on plant height of position of the leaf-bud cutting on the stock plant. Plant height (measured from pot rim to apex) was recorded (A) 5, (B) 8 and (C) 11 weeks after excision and planting of the cuttings.
182
was still present 8 weeks after planting, but at that time bud break was only reduced at the uppermost position. After a further 3-week period, no significant effect of cutting position on the percentage of bud break could be recorded. The subsequent growth of the lateral shoot was also measured 5, 8 and 11 weeks after the excision and planting of the cutting. The results (Fig. 3) demonstrate that the effect of cutting position on rooting and axillary bud break also affects the subsequent growth of the shoot. After 11 weeks from planting, plants originating from positions 1, 2 and 8 were significantly shorter than those from the other positions. Effect of length o f stem below the node on root formation, axillary bud break and shoot growth. -- Rooting was strongly influenced by the length of the stem below the node of the leaf-bud cutting (Fig. 4). Cuttings having only 0.5 cm of stem below the node had very few roots. Only 3.5 roots per cutting were recorded, and the rooting percentage was as low as 50. With increasing stem length the number of roots per cutting was increased. The rooting percentage increased also, and reached the highest level when the stem length approached 2 cm. The detailed results in Table II show that the increase in root number with stem length, with only a few exceptions, was found for all cutting positions. Axillary bud break was also influenced by the length of the stem below the node (Fig. 5). Five weeks after excision and planting hardly any cuttings with a 0.5-cm stem length had sprouted, whereas 50% of the cuttings with
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183
a 3-cm stem length had sprouted. The percentage of cuttings with axillary bud break approached the maximal value gradually, and after 11 weeks from excision approximately all cuttings had developed an actively growing shoot. T A B L E II N u m b e r of r o o t s per c u t t i n g as a f u n c t i o n of c u t t i n g p o s i t i o n o n t h e s t o c k p l a n t a n d o f s t e m l e n g t h b e l o w t h e n o d e . E a c h value r e p r e s e n t s t h e m e a n n u m b e r o f r o o t s per c u t t i n g o f 12 c u t t i n g s f r o m d i f f e r e n t stock p l a n t s Cutting position
Stem length (cm)
1 (top) 2 3 4 5 6 7 8 (basis)
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Fig. 5. E f f e c t o n axillary b u d b r e a k o f s t e m l e n g t h b e l o w t h e n o d e o f t h e leaf-bud cutting. B u d b r e a k was r e c o r d e d (A - - A) 5, (= - - =) 8 a n d (o - - o) 11 w e e k s a f t e r excision a n d p l a n t i n g o f t h e cuttings. Fig. 6. E f f e c t o n p l a n t h e i g h t o f s t e m l e n g t h b e l o w t h e n o d e o f t h e leaf-bud c u t t i n g . P l a n t h e i g h t was r e c o r d e d (A - - A) 5, (= - - =) 8 a n d (e - - o) 11 w e e k s a f t e r e x c i s i o n a n d p l a n t i n g o f t h e cuttings.
184 Plant height after 5, 8 and 11 weeks from excision is shown in Fig. 6. Plants from cuttings having a stem length of 0.5 cm were shorter than plants from cuttings with longer stem lengths. DISCUSSION Influence o f cutting position. -- The positional differences in root formation in Schefflera arboricola are in agreement with the general statement by Hartmann and Kester (1983) that the best rooting of cuttings is usually found in cuttings from the basal portions of a shoot. The increasing number of roots per cutting with the distance from the apex is in agreement with the findings for Hedera helix reported by Poulsen and Andersen (1980). The increase in rooting percentage, however, differs from the results reported for other species. For Hedera helix all cuttings were able to root (Poulsen and Andersen, 1980), while for Triplochiton scleroxylon a gradual reduction in rooting percentage was recorded with distance from apex (Leakey, 1983). The stimulation of rooting in more basal internodes could be due to the phase changes that gradually occur along the stem of a plant (Hartmann and Kester, 1983). Another explanation could be that the reduction in irradiance associated with an increase in distance from top to basis through a plant canopy causes an increase in root number. Stock plant irradiance effects on subsequent root formation have been investigated in a range of plant species. The majority of species investigated, including ScheffIera arboricola (J. Hansen, unpublished results, 1984), responded b y producing more roots at decreasing irradiance (Biran and Halevy, 1973; Hansen and Eriksen, 1974; Poulsen and Andersen, 1980; Hansen and Ernstsen, 1982). The uniform and nearly complete axillary bud break, which was observed 11 weeks after excision and planting of the cutting {Fig. 5), imply that the final rooting percentage for all cutting positions had gradually increased to over 90%. The differences in rooting percentage (Fig. 1) that were recorded after 3 weeks of rooting thus indicate differences in the rate of root formation in cuttings with different positional origin. The influence of cutting position on axi!lary bud break suggests that it is the onset of bud break rather than the capacity for this process that is affected. The present results are not in agreement with those reported by Jensen (1967) for 'Baccara' roses, where a decrease in bud break was observed at more basal positions. Consequently, cutting position influenced the subsequent shoot growth. Differences in plant height measured 11 weeks after planting were mainly a result of the different shoot growth periods from bud break to measurement of plant height. This effect differs from the results for the related species Hedera canariensis (Christensen, 1976). In that investigation there was no significant relationship between cutting position and subsequent shoot growth.
185
Influence of stem length. -- The increase in number of roots per cutting with increasing stem length below the node of the leaf-bud cutting is in agreement with the results for Pisum sativum (Veierskov, 1978). The present results with Schefflera arboricola show, however, that this effect was not only valid for a particular internode, as was reported for Pisum sativum (Veierskov, 1978), but was obtained for all the cutting positions investigated (Table II). Supporting results were reported for Hedera helix (Poulsen and Andersen, 1980), although in this experiment the different stem lengths were represented by the entire internode length. Veierskov (1978) suggested that the effect of stem or internode length was related to carbohydrates accumulated at the basis of the cutting, and that the carbohydrate amount was more optimal for root formation in a cutting with a long basal internode or stem compared to a cutting with a short internode or stem. This theory could explain the results with Schefflera arboricola, although the participation of other controlling factors cannot be excluded. A recent investigation by Veierskov et al. (1982) on the role of carbohydrates in the regulation of root formation in pea cuttings, however, does not support the carbohydrate theory. The effect of stem length on the rooting percentage was similar to the effect reported b y Jensen (1967) for 'Baccara' roses. The detailed investigation with Triplochiton cuttings (Leakey, 1983) also provides supporting results. Axillary bud break is also affected by the stem length of the cutting. The results, however, show that only the time of bud break is affected. The capacity for bud break is the same regardless of the stem length. The effect of stem length on final plant height is mainly a consequence of the influence of the time of axillary bud break. For Schefflera arboricola, it can be concluded that in order to obtain plants of uniform size it is necessary to standardize the cutting material for propagation. The uppermost, soft leaf-bud cuttings should be avoided and the stem length below the node should be approximately 2 cm. Due to early axillary bud break, such an optimization will also give a reduction of 2--3 weeks in total production time. This may be of importance in commercial propagation. ACKNOWLEDGEMENTS
The statistical analyses were made by Dr. Kristian Kristensen, Biometric Section, Lyngby. The skilful technical assistance of Messrs. Poul Mose, Ebbe E. Andersen and Gunnar Pedersen is greatly appreciated. REFERENCES Biran, I. and Halevy, A.H., 1973. Stock plant shading and rooting of dahlia cuttings. Scientia Hortic., 1 : 125--131.
186 Christensen, O.V., 1976. The growth rate and the variation in growth in relation to the stock plant of Hedera canariensis WiUd. 'Gloire de Marengo'. Scientia Hortic., 4: 377--385. Fernqvist, I., 1966. Studies on factors in adventitious root formation. Lantbrukshoeg~ kolans Ann., 32 : 109--244. Hansen, J. and Eriksen, E.N., 1974. Root formation of pea cuttings in relation to the irradiance of the stock plants. Physiol. Plant., 32: 170--173. Hansen, J. and Ernstsen, A., 1982. Seasonal changes in adventitious root formation in hypocotyl cuttings of Pinus sylvestris: Influence of photoperiod during stock plant growth and of indolebutyric acid treatment of cuttings. Physiol. Plant., 54: 99--106. Hartmann, H.T. and Kester, D.E., 1983. Plant Propagation. Principles and Practices. Prentice-Hall, Englewood Cliffs, NJ, 727 pp. Jensen, H.E.K., 1967. Stiklingeformering af v~eksthusroser. Thesis. Royal Veterinary and Agricultural University, Copenhagen, 57 pp. Leakey, R.R.B., 1983. Stockplant factors affecting root initiation in cuttings of Triplochiton scleroxylon K. Schum., an indigenous hardwood of West Africa. J. Hortic. Sci., 58: 277--290. Loreti, F. and Hartmann, H.T., 1964. Propagation of olive trees by rooting leafy cuttings under mist. Proc. Am. Soc. Hortic. Sci., 85 : 257--264. Poulsen, A. and Andersen, A.S., 1980. Propagation of Hedera helix: Influence of irradiance to stock plants, length of internode and topophysis of cutting. Physiol. Plant., 49 : 359--365. Roulund, H., 1973. The effect of cyclophysis and topophysis on the rooting ability of Norway spruce cuttings. For. Tree Improv., 5: 21--41. Veierskov, B., 1978. A relationship between length of basis and adventitious root formation in pea cuttings. Physiol. Plant., 42 : 146--150. Veierskov, B., Andersen, A.S. and Eriksen, E.N., 1982. Dynamics of extractable carbohydrates in Pisum sativum. I. Carbohydrate and nitrogen content in pea plants and cuttings grown at two different irradiances. Physiol. Plant., 55: 167--173.