Factors affecting rooting ability of Coleonema aspalathoides

SClENTIA HORTICULTUR~ ELSEVIER

Scientia Horticulturae 58 (1994) 335-341

Factors affecting rooting ability of Coleonema aspalathoides A. Heller, A. Borochov, A.H.

Halevy*

The Kennedy Leigh Centre for Horticultural Research, Faculty of Agriculture, The Hebrew University of Jerusalem, PO Box 12, Rehovot 76100, Israel

(Accepted 17 January 1994)

Abstract

Rooting of Coleonema aspalathoides was found to be affected by the cutting type (soft or semi-woody), concentration ofindolebutyric acid (IBA) solution in which cutting bases are immersed prior to rooting, duration of the immersion, as well as the photoperiod and shading of stock plants. The most successful rooting was obtained with soft cuttings pretreated for 4 h with 250 ppm IBA. Shading of stock plants also improved rooting ability. The rooting ability is seasonal and was found to decline during the plant's natural flowering season. Under controlled environmental conditions, rooting ability declined as the plant approached peak flowering. Cuttings taken from stock plants exposed to fully inductive conditions (short days, 12:17 °C night/day) exhibited lower rooting ability than those taken from stock plants grown under semi-inductive conditions (long day, 12:17 °C night/ day). Keywords: Coleonema aspalathoides; Rooting

1. Introduction

Coleonema aspalathoides (Rutaceae), commonly known as Diosma (Williams, 1981 ), was studied to examine the possibility of adapting it as a new flowering pot plant (Heller et al., 1994). One of the prerequisites for such adaptation is the ability to continuously produce plants on a large scale. Growers who have attempted to propagate the plant by cuttings reported conflicting results. The aim of this work was to determine the optimal conditions for the rooting *Corresponding author. Abbreviations: 1BA= indolebutyric acid; LD = long day; SD = short day 0304-4238/94/$07.00 © 1994 Elsevier Science B.V. All rights reserved SSDI 0304-4238 ( 94 )00637-U

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A. Heller et al. / Scientia Horticulturae 58 (1994) 335-341

of Coleonema cuttings and, accordingly, to develop suitable techniques for its vegetative propagation.

2. Materials and methods

In most of the experiments, 2-year-old Coleonema stock plants were used. The plants were grown from cuttings in pots containing volcanic gravel and kept in a net-house ( 15% shade) under prevailing conditions of temperature and photoperiod. Apical cuttings (7 cm long) were taken and defined as soft (42% dry weight ) or semi-woody (43.3% dry weight ). The cuttings (20 replicates per treatment) were dipped for different time periods in solutions containing various concentration of indolebutyric acid (IBA; Sigma). During IBA treatment, environmental conditions were controlled at 21 °C, 55 + 5% relative humidity, and light intensity of 12 gmol m -2 s-1 (provided by cool white fluorescent and incandescent lamps). Upon termination of treatment the cuttings were transferred to trays containing a peat/granular polystyrene mix (3: l, v/v). During the rooting process cuttings were watered for 20 s at 30-min intervals in winter (November to April) or for 10 s every 10 rain in summer (May to October). The rooting bed was warmed to 22°C and light intensity at the level of the cuttings was 83 gmol m -2 s- ~at midday. After 42 days the number of roots per cutting was recorded and the percentage of rooting (cuttings that exhibited roots) determined. Phytosanitary measures applied during rooting consisted of the addition of the fungicides Marpean (0.2%) and Benlate (0.1%) to the rooting solution, drenching of rooting medium with Dinon (0.25%) (Alon Israel Chemicals), and spraying of the cuttings once or twice a week with Mancidan (0.25 % ) to prevent foliar diseases. The influence of different photoperiods on rooting ability was examined in 1year-old stock plants grown from cuttings in 15-cm pots. The bedding mixture contained peat and volcanic gravel (l: 1, v/v) with Osmocote granules (NPK 14: 14: 14 ) (0.03%). The stock plants were kept in a phytotron at night/day temperatures of 12: 17 ° C under either long day (LD) ( 16 h light ) or short day (SD) ( 8 h light ) conditions (see accompanying paper, Heller et al., 1994, for details). Semi-woody cuttings were taken and treated as described above. The experiments of Figs. 1 and 4 were repeated three times and those of Figs. 2 and 3 were repeated in two additional growing seasons with similar results. 3. Results and discussion

Preliminary tests showed that the rooting ability of woody cuttings (taken from the base of the branch, 55% dry weight) was very low. The percentage of rooting increased with increasing softness of the cutting (Table 1 ). All subsequent experiments were therefore carried out on soft or semi-woody cuttings. Immersion of the base of the cuttings in IBA prior to rooting improved its root-

A. Heller et al. / Scientia Horticulturae 58 (1994) 335-341

337

Table 1 Effect of cutting type on rooting ability. Cutting bases were immersed in IBA (250 ppm) solution for 4 h before being transferred to the rooting bed. Parameters were evaluated 42 days after transfer. Values are means of 20 replications_+ SE Cutting type

Dry weight (%)

Rooting (%)

Roots per rooted cutting

Soft Semi-woody Woody

42.1 + 1.7 43,3 _+0.3 54.9 _+2.0

55 10 5

1.5_+0.8 7.5 + 0,6 3.0 + 0.4

10090 J 80

0 0 ¢F

60 50 40 3020 10 0

1

25 ppm 24 h

250 ppm 4h

X X x x X X x X x X x x x

I X x X X X x X x X X x x X X X x X X X x X x X x

70 E~ (-

500 pprn 3.5 h

I 0 0 0 ppm 4000 I~om 5000 ppm 2h

SOLUTION

1==

1==

H:

0.4 Z

0.8X

IBA

1 •

1 •

"RME

POWDER

Fig. 1. Effect of treatment with IBA powder or different combinations oflBA solution concentrations and durations of immersion on rooting percentage of semi-woody cuttings. Values are means of 20 replications.

ing ability. Optimal treatment conditions were found to be a concentration of 250 ppm IBA (Fig. 1 ) and immersion for 4 h or more (data not shown). Immersing the cuttings in IBA solution under these conditions was more effective than using higher IBA concentrations or a rooting powder (Fig. 1 ). Auxins are known to be the main factors encouraging rooting in most plants (Audus, 1959; Jarvis, 1986 ). Although IBA treatment improved rooting of Coleonema cuttings throughout the year, its effect was greater during the winter months (Figs. 1 and 2 ). Since flowering also occurs during this time, there may be a connection between the two

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A. Heller et aL / Scientia Horticulturae 58 (1994) 335-341

100908070(-

o o r~

6050403020e e WATER o--o IBA

100

6,11 17.12 13.1 4.2

1987

25.2 17.3

28.4

2S.5 | , 6

w 4.7 18.7 15,6 31,6 27.9 16.10 I).11 27.11~L$2 8.I 2.2

1988

1989

Date Fig. 2. Effect of IBA treatment (250 ppm, 4 h dip) on the rooting percentage of semi-woody cuttings at different times of the year. Values are means of 20 replications.

processes in Coleonema. Such a connection has been found before in several plants, e.g. Dahlia (Biran and Halevy, 1973). In a number of plants, such as Chenopodium rubrum (Teltscherova et al., 1976), Begonia (Heide, 1967), tobacco and Rudbeckia (Bernier et al., 1981 ), a drop in auxin level was found upon induction of flowering. In Coleonema, the SD photoperiod which enhanced flowering (Heller et al., 1994) also reduced the percentage of rooting (Figs. 3 and 4). A year-round evaluation of the rooting ability of cuttings, not treated with IBA, revealed distinct seasonal fluctuations. The lowest rooting percentages were recorded during the winter months: November to March for semi-woody cuttings (Fig. 2) and October to February for soft cuttings (Fig. 3 ). Seasonal effects were less pronounced with respect to the number of roots per cutting (data not shown) this was true for both types of cuttings. Although IBA treatment greatly improved rooting ability, it did not totally eliminate seasonal fluctuations in semi-woody cuttings (Fig. 2). Since the rooting percentage increased with a decrease in the cutting's percent dry weight (Table 1 ), we examined the effects of shading treatments on the percentage of rooting. Growing stock plants for 11 weeks under different shade levels reduced the cutting's dry weight and consequently enhanced its rooting ability (Table 2). Optimal rooting was observed in cuttings from plants grown in 50% shade, with a decline in rooting at higher shade levels.

339

A. Heller et al. / Scientia Horticulturae 58 (1994) 335-341

1009080 70 o o n,"

60 50 4-0 30 2O 10

H

0 4.2 "~.2 17.3

~W.4 ~

II.I; 4.7 16.7 18,11 ~ I J

27.9 16.10 6-11 27.11 22.12 6.1

1988

w 2.2

WATER

o-o 18A

•

1989

Date Fig. 3. Effect oflBA treatment (250 ppm, 4 h dip) on the rooting percentage of soft cuttings at different times of the year. Values are means of 20 replications.

100

O

90 80

70

g 0 0 ft.

60 50 40 30 20 10 |

0 0

2O

40

60

80

100

120

140

Time (days) --e--

IBA, LD

--©--

ControI, LD

--v--

IBA, SD

Fig. 4. Effect of photoperiod during stock plant growth and IBA treatment (250 ppm, 4 h dip) on rooting percentage of semi-woody cuttings. All stock plants were maintained under 12: 17 ° C (night / day) temperature regime. Values arc means of 20 replications.

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A. Heller et al. / Scientia Horticulturae 58 (1994) 335-341

Table 2 Effect of shading of stock plants on rooting percentage of cuttings. Stock plants were shaded from the beginningof June until the end of August ( 11 weeks), when cuttings were collected. (Cuttings taken from the control plants were soft). Cuttings were dipped in water for 4 h prior to transfer to the rooting bed. Maximum light intensity was 54 klux; shading levels are indicated as percentages of this value. Values are means of 20 replications± SE Shade (%)

Dry weight (%)

Rooting (%)

Roots per rooted cutting

0 50 75 87.5

40.9±0.7 36.6±0.5 35.4±0.5 34.2±1.9

30 90 40 65

1.7±0.4 3.4±0.4 2.6±0.3 1.3±0.1

It might be expected that the development of different root systems would influence the subsequent plant's growth rate. However, no differences were found in the growth increments of plants rooted by IBA treatments or without (data not shown). In both cases, maximum growth was achieved in 5-10 weeks after termination of rooting (data not shown). In addition, no differences were found in growth rates of plants originating from soft cuttings and from semi-woody cuttings (data not shown). The seasonality of rooting ability (Figs. 2 and 3) was found to be correlated with changes in natural photoperiod, with a decrease in rooting ability during winter when day length is short. The influence of photoperiod on flowering was examined under controlled conditions in the phytotron, where flowering was found to be improved and advanced in plants grown under SD as compared with LD conditions (Heller et al., 1994). Cuttings taken from stock plants grown under LD conditions usually exhibited higher rooting percentages than those taken from SD-grown stock plants (Fig. 4), but the number of roots per cutting was similar (data not shown). Treatment with IBA improved the rooting ability of cuttings harvested from stock plants grown under both photoperiods, but did not alter the relative trends of the results. With both treatments (IBA and water) rooting ability declined from Day 112 onward, reaching a minimum on Day 126 (time of peak of flowering in both treatments; Fig. 4). In summary, the results of this study show that rooting of Coleonema cuttings is influenced by several factors. (a) Type of cutting: the softer the cutting, the higher its percentage of rooting. (b) Concentration of IBA solution in which cuttings are immersed and duration of the treatment: a concentration of 250 ppm was found to be optimal and lower or higher concentrations resulted in a lower rooting ability. Immersion of cuttings in the IBA treatment solution for at least 1 h was needed in order to improve their rooting ability and maximum rooting percentages were achieved in cuttings immersed for 4 h.

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(c) Photoperiod. Cuttings from stock plants grown under LD conditions rooted better in terms of rooting percentage than those from SD-grown stock plants. (d) Shading. Moderate shading of stock plants improved the rooting ability of their cuttings, with optimal results at 50% shading. The decline in rooting at higher shading levels may result from the lower carbohydrate content of the cuttings.

Acknowledgements This study was supported by the Pearlstein Family Fund for Research in Ornamental Horticulture at the Hebrew University. We are very grateful to the donors for their support.

References Audus, L.J., 1959. Plant Growth Substances. Leonard Hill, London. pp. 145-149, 421-427. Bernier, G., Kinet, J.M. and Sachs, R.M., 1981. The Physiology of Flowering. Vol 2. CRC Press, Boca Raton, FL, pp. 137-139. Biran, I. and Halevy, A.H., 1973. The relationship between rooting of dahlia cuttings and the presence and type of bud. Physiol. Plant., 28: 244-247. Heide, O.M., 1967. The auxin level of begonia leaves in relation to their regeneration ability. Physiol. Plant., 20: 886-902. Heller A., Borochov, A. and Halevy, A.H., 1994. Factors affecting growth and flowering of Coleonema aspalathoides. Sci. Hortic., 58: 325-334. Jarvis, B.C., 1986. Endogenous control of adventitious rooting in non-woody cuttings. In: M.B. Jackson (Editor), New Root Formation in Plants and Cuttings. Martinus Nij hoff, Dordrecht, pp. 191 222. Teltscherova, L., Pavlova, L. and Pleskutova, D., 1976. Changes in the content of endogenous auxins in apical buds of Chenopodium rubrum L. induced with respect to the endogenous rhythm in capacity to flower. Biol. Plant., 19:205-211. Williams, I., 1981. Studies in the genera Diosmeae, Rutaceae. 9. A revision of the genus Coleonema. J. S. Afr. Bot., 47: 63-102.