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Description of Syzygium paniculatum Gaertn. `Verlaine' and its propagation by stem cuttings
Scientia Horticulturae 75 (1998) 103±111
Description of Syzygium paniculatum Gaertn. `Verlaine' and its propagation by stem cuttings A. Lebruna,*, A.N. Toussaintb,1, J. Roggemansc,2 b
a Hortiforum asbl, Rue Verlaine 9, B-5030, Gembloux, Belgium Unite d0 Horticulture GeÂneÂrale, .Faculte Universitaire des Sciences Agronomiques de Gembloux, Avenue de la Faculte d0 Agronomie 2, B-5030, Gembloux, Belgium c Laboratoire d0 Applications Phytotechniques, Haute Ecole de LieÁge-Verviers-Huy-Gembloux, Rue Verlaine 9, B-5030, Gembloux, Belgium
Accepted 10 February 1998
Abstract Expanding the market for house plants is linked to increasing the diversity on offer to consumers. Accordingly, experiments were done to introduce a new plant onto the market: the cultivar `Verlaine' derived from Syzygium paniculatum. This cultivar has a dense foliage and an attractive aspect. It presents interesting characteristics like annual flowering and colorful fruits. The best results of propagation by cuttings were obtained when using cuttings from the basal part of the mother plant, placed in a 1±1 or 2±1 peat±perlite substrate, with a bottom heat around 228C. Auxins do not affect rooting. The origin of the adventitious roots is endogenous. # 1998 Elsevier Science B.V. Keywords: Syzygium; Cutting; Cultivar
1. Introduction The market for ornamental plants is increasing rapidly in Europe as a result of the economics of their production and their diversity. * Corresponding author. Fax: +32 81 625638 1 Tel.: +32 81 622417; fax: +32 81 622427; e-mail: [email protected] 2 Tel.: +32 81 625613; fax: +32 81 611202; e-mail: [email protected] 0304-4238/98/$19.00 # 1998 Elsevier Science B.V. All rights reserved PII S 0 3 0 4 - 4 2 3 8 ( 9 8 ) 0 0 1 2 2 - 8
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With a view to increasing the range of foliage plants, we are studying the genus Syzygium (Myrtaceae). This genus includes numerous trees and shrubs grown for their foliage and ornamental berries or their edible fruits. In Germany, another research group is studying Syzygium oleosum, with the intention of exploiting it as a house plant (Von Hentig and Ehlers, 1992). The present study focuses on Syzygium paniculatum Gaertn., a species native to Australia. S. paniculatum was first described by the botanist Gaertner in 1789 who named it Eugenia paniculata. Subsequently, it was referred to under different names including Myrtus paniculata and Eugenia myrtifolia. This species is easily propagated by seed but the new cultivar, S.p. `Verlaine', can only be multiplied vegetatively. In this paper we describe this cultivar and determine the best conditions for ensuring the rooting of stem cuttings. Four experiments were performed: (i) to examine the effect of the nature of the substrate and bottom heating, (ii) to examine the influence of auxins on rooting of the cuttings, (iii) to examine the effect of the position of the cuttings on the mother plant, (iv) to examine the influence of the period of the year in which the cuttings were taken on rooting. 2. Materials and methods 2.1. Influence of different factors on rooting of cuttings Experiments were performed with softwood leafy lateral cuttings, taken on greenhouse-grown 2 year-old stock plants, pruned 3 months earlier. Except for the experiment relative to the position of the cuttings on the stock plant, cuttings were taken from the apical part. The cuttings were 10 cm long with 4 nodes. Batches of 30 cuttings were used for each treatment in each experiment. All experiments were conducted in a greenhouse, under mist and at an air temperature of 258C. The four experiments were performed 3 times and the results are the means of the 3 replicates. In all experiments, the batches of cuttings were distributed randomly and observed weekly over a 90-day period. The statistical analysis was based on one-way or two-way analysis of variance (ANOVA), for fixed and crossed patterns (Dagnelie, 1992) after the normality of the data had been confirmed. The means were compared by Student's t-test at P<0.05. 2.1.1. Influence of substrates and bottom heat The substrates most frequently used to root cuttings (Rein et al., 1991) were tested: peat±coarse sand in the ratio 1±1, 2±1, 3±1 and 4±1 (pH 4.1±4.2); vermiculite±perlite: 1±1 (pH 7.3), peat±perlite: 1±1, 2±1, 3±1 and 4±1 (pH 3.3±3.5). The experiment was conducted with or without a constant average bottom heat of 220.58C.
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2.1.2. Influence of auxins Indole-3-acetic acid (IAA) and naphthalene acetic acid (NAA) are the two growth regulators that best promote rooting (Hartmann et al., 1990; Smalley et al., 1991). Preliminary experiments showed that there was no interaction between substrates, growth regulators and rooting. In our experiment using IAA, concentrations of 500, 1000, 1500 and 2000 ppm were tested. The basal part of the cuttings was dipped in a freshly prepared solution for 5 s before striking in the 1±1 peat±perlite substrate. In the experiment with NAA, the lower 3 cm of the cuttings were coated with a preparation of 2% NAA in talc and the excess powder was then shaken off. Cuttings were struck in the same substrate. A bottom heat of 220.58C was maintained. 2.1.3. Influence of the position of the cuttings on the mother plant To determine the effect of the position of the cuttings on the mother plant, three positions were selected: the apical part of the stock plant, the median part and the basal part. The cuttings were struck in the 1±1 peat±perlite mixture. A bottom heat of 220.58C was maintained. 2.1.4. Influence of the period of the year in which the cuttings are taken Preliminary observations showed that the cv `Verlaine' could easily be propagated by cuttings in spring and summer. Indeed, softwood cuttings taken during spring and summer usually tend to root more easily than cuttings taken in the winter (Hartmann et al., 1990; Wilson, 1993). Furthermore, propagation by stem cuttings of Eugenia Smithii, a closely related species, is very good from June to September, but very poor in November (Toussaint et al., 1991). In order to determine the possibility to root cuttings in less favourable periods, every month, from September to April, experiments were conducted on a peat± perlite 1±1 mixture, with a bottom heat of 220.58C. 2.2. Microscopy To determine where the adventitious roots are initiated, basal parts of rooted cuttings were fixed, dehydrated, embedded in paraffin following Heinemann's technique (1980) and sectioned at 15±20 mm. Sections were stained with malachite green and congo red. 3. Results and discussion 3.1. Description of the cultivar `Verlaine' For about 15 years, seeds from a Syzygium paniculatum plant were harvested every year and sown. One of the resultant seedlings differed quite noticeably from
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Fig. 1. 18-month-old Syzygium paniculatum `Verlaine' (approximate height: 1 m).
the parental type, presenting stable characteristics: smaller leaves (4 to 6 cm long by 1.5 to 2 cm wide) and shorter internodes (Fig. 1). Table 1 lists the main features that distinguish cv `Verlaine' from the species (Curtis, 1969; Schmid, 1972; Hyland, 1983; Whistler, 1988). The main asset of this plant is its denser foliage, which is pale green when young, darker green when mature, while its young leaves and stems are tinged with red. The general appearance of the plant can be compared to that of Ficus benjamina `Exotica'. Another asset of S.p. `Verlaine' is its great propensity for flowering after 1 or 2 years of culture. The axillary peduncles that grow laterally or at the top of the shoots, develop at least 3 to 5 flowers in a loose trichotomous panicle. The fruits are magenta, globular or ovoid berries, 1.5 cm in diameter, topped by a persistent calyx. 3.2. Influence of different factors on rooting of cuttings 3.2.1. Influence of substrates and bottom heat The cuttings tested on non-heated substrates (average temperature 16.08C) failed to root. However, when the substrate was heated (average temperature of 220.58C), the mean rooting rate exceeded 75% on the best substrates.
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Table 1 Main characters distinguishing Syzygium paniculatum and S. p. `Verlaine' Distinctive criteria
Syzygium paniculatum
S. p. `Verlaine'
Shoots
Internodes
15 to 50 mm long
15 to 40 mm long
Leaves
Length Width Primary veins
45 to 90 mm 15 to 30 mm 16 to 22 pairs
25 to 65 mm 12 to 24 mm 10 to 16 pairs
Flowers
Inflorescences
Terminal and axillary towards the top; cymes and sometimes panicles with 3, 7 or 11 flowers
Most often terminal; 3 to 5 flowers per panicle
Fruits
Drupes
Ovoid, 16 to 26 mm in diameter
Globular to ovoid, 15 to 22 mm in diameter
The experiments concerning the nature of the substrates showed that the 1±1 vermiculite±perlite mixture was not suitable as it caused the loss of over 90% of the cuttings due to rot. The results of the experiment done on 8 different substrates based on peat, sand and perlite are given in Fig. 2. The rooting percentage and speed of root production were higher on peat±perlite 1±1, 2±1 and 3±1 mixtures than on peat±sand ones but the loss of cuttings by rotting was higher on the 3±1 peat±perlite mixture
Fig. 2. Average rooting speed of cuttings of Syzygium paniculatum `Verlaine' depending on the nature of the substrate.
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(18%) than on the 1±1 and 2±1 ones (5.6%). The good rooting rates observed on peat±perlite substrates can be attributed to a lower pH in these mixtures and/or to the increase in aeration in substrates containing perlite, favouring rhizogenesis (Hartmann et al., 1990). The rooting rate was low on peat±sand 2±1, 3±1 and 4±1 substrates. In peat±sand substrates with a high peat-content, the poorer rooting rate observed could be due to the compaction of peat by water, which consequently would prevent proper aeration of the mixture and lead to rot in the cuttings. This also occurred in the 3±1 and 4±1 peat±perlite substrates but to a lesser extent, thanks to the favourable effect of perlite. The greater length of the root system observed on the peat±perlite mixtures could be attributed to the earlier development of the roots and/or excellent substrate aeration. The ease with which cuttings can be removed from this medium is a distinct advantage. 3.2.2. Influence of auxins There was no significant difference between IAA and NAA in their affect on rooting. No exogenous input of the growth substance seemed to affect rooting of Syzygium cuttings except for the 2000 ppm treatment which caused the highest percentage of loss of cuttings by rotting (18% for the 2000 ppm treatment against an average 2% to 5% for the lower concentrations) and the lowest rooting percentage (52%). This high concentration added to the endogenous auxin of the plant, which itself increases as a consequence of taking cuttings (Favre, 1977) might have led to a level which disturbed the hormonal metabolism and inhibited rhizogenesis. 3.2.3. Influence of the position of the cuttings on the mother plant The rooting success of cuttings taken from the three positions on the stock plants are shown in Fig. 3. The proportion of cuttings that developed roots was significantly higher among those taken from the median and lower parts of the plant than from the apical part. Furthermore, roots developed earlier on cuttings originating from the basal and median parts of the stock plants than on those from the apex. Rooting was initiated as early as the third week on basal cuttings, in the fourth week on the median ones and in the sixth on the apical ones. Only 73% of the apical cuttings had rooted after 13 weeks whereas 99% of the basal ones had rooted after only 7 weeks. The natural accumulation of endogenous auxin, favourable to the development of roots, in the basal part of the stock plants (Wilson, 1993) along with the influence of the nearby root system which encourages juvenility (Chaperon, 1979; Bonga, 1982) are both likely to explain the results obtained. 3.2.4. Influence of the period of the year in which the cuttings are taken The rooting percentage and speed of production of roots were similar on cuttings of S.p. `Verlaine' at whatever time between September and April they
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Fig. 3. Average rooting speed for cuttings of Syzygium paniculatum `Verlaine' depending on the position of the cutting on the mother plant.
were struck. The percentage of rooted cuttings ranged from 64% to 71%. For November, the results are much better than those obtained for Eugenia Smithii (20±28% rooted cuttings), a closely related species (Toussaint et al., 1991). In other Myrtaceae like Chamaelaucium sp., the rooting of cuttings is unaffected by season (Curir et al., 1993). The fact that stock plants are grown in a greenhouse could favour rooting of cuttings (Macdonald, 1986; Marczynski and Joustra, 1993). Stoutemyer (1961) suggested that this could be due to increased air humidity and temperature or to the absence of UV rays in a greenhouse. 3.3. Microscopy Sections of the basal part of a rooted cutting exhibited the classical structure of a stem but with scar tissue consistent with a cutting, schizogenous spaces, tanniferous cells characteristic of the Myrtaceae, and cells with vacuoles containing much calcium oxalate. The sections showed that the adventitious roots originated endogenously in the young secondary phloem. 4. Conclusion The cultivar `Verlaine' of Syzygium paniculatum, originating from a seedling of Syzygium paniculatum has smaller leaves and shorter internodes than the parent
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species, resulting in dense foliage and a very attractive appearance. It offers additional interesting and original characteristics including annual flowering, colourful fruits and red colour of the young leaves. Rooting of cuttings of Syzygium paniculatum `Verlaine' ranged from fair to good depending on the technique applied. Several factors influence the rooting of cuttings: (i) bottom heat is needed (228C was found to be suitable); (ii) the nature of the substrate affects rooting of cuttings by its physical and/or chemical properties. An acid (pH value of about 3.5) well-aerated substrate was best. The results show the advantages of peat±perlite substrates (at 1±1 or 2±1 mixtures) over peat±sand mixtures. Considering the relatively high cost of perlite, it is advisable to choose the 2±1 peat±perlite mixture; (iii) the best position from which to take cuttings on stock plants in order to accelerate rooting is as close as possible to the root system. The addition of auxins does not affect rooting. Throughout the period from September to April, propagation by stem cuttings is successful. The histological study showed that root initiation is endogenous. Propagation by cuttings appears to be a reliable way of multiplication, but financial returns are likely to be modest because of the few shoots produced by each stock plant. Further work is needed to examine the influence of the age of stock plants on rooting of cuttings. In Eucalyptus sp., Jacobs (1977) noted that the rooting rate of cuttings from 3 year-old stock plants was less than of those from younger plants. Acknowledgements We thank the Ministry of the Walloon Region (Belgium) ± General Direction for Economy and Employment ± for its contribution to this research by PRIME projects. References Bonga, J.M., 1982. Vegetative propagation in relation to juvenility, maturity, and rejuvenation. In: Bonga, J.M., Durzan, D.J. (Eds.), Tissue Culture in Forestry. Martinus Nijhoff/Dr W. Junk Publishers, The Hague, Netherlands, pp. 387±412. Chaperon, H., 1979. Maturation et bouturage des arbres forestiers. In: AFOCEL (Ed.), Micropropagation d0 arbres forestiers. Etudes et Recherches, no. 12, 6/79, Nangis, France, pp. 19±31. Curir, P., Sulis, S., Mariani, F., Van Sumere, C.F., Marchesini, A., Dolci, M., 1993. Influence of endogenous phenols on rootability of Chamaelaucium uncinatum Schauer stem cuttings. Scientia Hortic. 55, 303±314. Curtis, A., 1969. Syzygium paniculatum. Curtis Bot. Mag. 177, 1. Dagnelie, P., 1992. TheÂorie et meÂthodes statistiques. Vols. 1 et 2. Les Presses Agronomiques de Gembloux, Gembloux, Belgique, 378 pp. et 472 pp.
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Favre, J.-M., 1977. La rhizogeneÁse. Annales de l0 Universite d0 Abidjan (SeÂrie C), Abidjan, CoÃte d'Ivoire, 100 pp. Hartmann, H.T., Dale, E.K., Davies, F.T., 1990. Plant propagation. Prentice-Hall, New Jersey, USA, 646 pp. Heinemann, P., 1980. Biologie veÂgeÂtale. Travaux Pratiques. Faculte Universitaire des Sciences Agronomiques de Gembloux, Gembloux, Belgique, 36 pp. Hyland, P.M., 1983. A revision of Syzygium and allied genera in Australia. Australian Journal of Botany 9, 1±164. Jacobs, R.M., 1977. Les Eucalyptus dans les reboisements. FA0, Rome, Italie, 75 pp. Macdonald, B., 1986. Practical woody plant propagation for nursery growers. Batsford, London, Great Britain, 669 pp. Marczynski, S., Joustra, M.K., 1993. Influence of daylength and irradiance on growth of the stock plants and subsequent rooting of cuttings of Betula utilis D. Don. and Corylus maxima Mill. cultivar `Purpurea'. Scientia Hortic. 55, 291±301. Rein, W.H., Wright, R.D., Seiler, J.E., 1991. Propagation medium moisture level influences adventitious rooting of woody stem cuttings. J. Amer. Soc. Hort. Sci. 116(4), 632±636. Schmid, R., 1972. Floral anatomy of Myrtaceae I. Syzygium. Bot. Jahrb. Syst. 92(4), 433±489. Smalley, T.J., Dirr, M.A., Armitage, A.M., 1991. Photosynthesis and leaf water, carbohydrate and hormone status during rooting of stem cuttings of Acer rubrum. J. Amer. Soc. Hort. Sci. 116(6), 1052±1057. Stoutemyer, V.T., 1961. Light and propagation. Comb. Proc. Int. Plant Prop. Soc. 11, 252±260. Toussaint, A.N., Lebrun, A., Roggemans, J., 1991. Cutting and in vitro propagation of Eugenia Smithii Poir. Acta Horticulturae 314, 77±83. Von Hentig, W.U., Ehlers, D., 1992. Syzygium-Arten GruÈnppflanzen fuÈr Wohnbereiche. Neue Zierpflanzen 5. Deutscher gartenbau 6, 8±9. Whistler, W.A., 1988. A revision of Syzygium (Myrtaceae) in Samoa. J. Arnold Arbor. 69, 167±192. Wilson, P.J., 1993. Propagation characteristics of Eucalyptus globulus Labill. ssp. globulus stem cuttings in relation to their original position in the parent shoot. Journal of Horticultural Science 68(5), 715±724.
Description of Syzygium paniculatum Gaertn. `Verlaine' and its propagation by stem cuttings A. Lebruna,*, A.N. Toussaintb,1, J. Roggemansc,2 b
a Hortiforum asbl, Rue Verlaine 9, B-5030, Gembloux, Belgium Unite d0 Horticulture GeÂneÂrale, .Faculte Universitaire des Sciences Agronomiques de Gembloux, Avenue de la Faculte d0 Agronomie 2, B-5030, Gembloux, Belgium c Laboratoire d0 Applications Phytotechniques, Haute Ecole de LieÁge-Verviers-Huy-Gembloux, Rue Verlaine 9, B-5030, Gembloux, Belgium
Accepted 10 February 1998
Abstract Expanding the market for house plants is linked to increasing the diversity on offer to consumers. Accordingly, experiments were done to introduce a new plant onto the market: the cultivar `Verlaine' derived from Syzygium paniculatum. This cultivar has a dense foliage and an attractive aspect. It presents interesting characteristics like annual flowering and colorful fruits. The best results of propagation by cuttings were obtained when using cuttings from the basal part of the mother plant, placed in a 1±1 or 2±1 peat±perlite substrate, with a bottom heat around 228C. Auxins do not affect rooting. The origin of the adventitious roots is endogenous. # 1998 Elsevier Science B.V. Keywords: Syzygium; Cutting; Cultivar
1. Introduction The market for ornamental plants is increasing rapidly in Europe as a result of the economics of their production and their diversity. * Corresponding author. Fax: +32 81 625638 1 Tel.: +32 81 622417; fax: +32 81 622427; e-mail: [email protected] 2 Tel.: +32 81 625613; fax: +32 81 611202; e-mail: [email protected] 0304-4238/98/$19.00 # 1998 Elsevier Science B.V. All rights reserved PII S 0 3 0 4 - 4 2 3 8 ( 9 8 ) 0 0 1 2 2 - 8
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A. Lebrun et al. / Scientia Horticulturae 75 (1998) 103±111
With a view to increasing the range of foliage plants, we are studying the genus Syzygium (Myrtaceae). This genus includes numerous trees and shrubs grown for their foliage and ornamental berries or their edible fruits. In Germany, another research group is studying Syzygium oleosum, with the intention of exploiting it as a house plant (Von Hentig and Ehlers, 1992). The present study focuses on Syzygium paniculatum Gaertn., a species native to Australia. S. paniculatum was first described by the botanist Gaertner in 1789 who named it Eugenia paniculata. Subsequently, it was referred to under different names including Myrtus paniculata and Eugenia myrtifolia. This species is easily propagated by seed but the new cultivar, S.p. `Verlaine', can only be multiplied vegetatively. In this paper we describe this cultivar and determine the best conditions for ensuring the rooting of stem cuttings. Four experiments were performed: (i) to examine the effect of the nature of the substrate and bottom heating, (ii) to examine the influence of auxins on rooting of the cuttings, (iii) to examine the effect of the position of the cuttings on the mother plant, (iv) to examine the influence of the period of the year in which the cuttings were taken on rooting. 2. Materials and methods 2.1. Influence of different factors on rooting of cuttings Experiments were performed with softwood leafy lateral cuttings, taken on greenhouse-grown 2 year-old stock plants, pruned 3 months earlier. Except for the experiment relative to the position of the cuttings on the stock plant, cuttings were taken from the apical part. The cuttings were 10 cm long with 4 nodes. Batches of 30 cuttings were used for each treatment in each experiment. All experiments were conducted in a greenhouse, under mist and at an air temperature of 258C. The four experiments were performed 3 times and the results are the means of the 3 replicates. In all experiments, the batches of cuttings were distributed randomly and observed weekly over a 90-day period. The statistical analysis was based on one-way or two-way analysis of variance (ANOVA), for fixed and crossed patterns (Dagnelie, 1992) after the normality of the data had been confirmed. The means were compared by Student's t-test at P<0.05. 2.1.1. Influence of substrates and bottom heat The substrates most frequently used to root cuttings (Rein et al., 1991) were tested: peat±coarse sand in the ratio 1±1, 2±1, 3±1 and 4±1 (pH 4.1±4.2); vermiculite±perlite: 1±1 (pH 7.3), peat±perlite: 1±1, 2±1, 3±1 and 4±1 (pH 3.3±3.5). The experiment was conducted with or without a constant average bottom heat of 220.58C.
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2.1.2. Influence of auxins Indole-3-acetic acid (IAA) and naphthalene acetic acid (NAA) are the two growth regulators that best promote rooting (Hartmann et al., 1990; Smalley et al., 1991). Preliminary experiments showed that there was no interaction between substrates, growth regulators and rooting. In our experiment using IAA, concentrations of 500, 1000, 1500 and 2000 ppm were tested. The basal part of the cuttings was dipped in a freshly prepared solution for 5 s before striking in the 1±1 peat±perlite substrate. In the experiment with NAA, the lower 3 cm of the cuttings were coated with a preparation of 2% NAA in talc and the excess powder was then shaken off. Cuttings were struck in the same substrate. A bottom heat of 220.58C was maintained. 2.1.3. Influence of the position of the cuttings on the mother plant To determine the effect of the position of the cuttings on the mother plant, three positions were selected: the apical part of the stock plant, the median part and the basal part. The cuttings were struck in the 1±1 peat±perlite mixture. A bottom heat of 220.58C was maintained. 2.1.4. Influence of the period of the year in which the cuttings are taken Preliminary observations showed that the cv `Verlaine' could easily be propagated by cuttings in spring and summer. Indeed, softwood cuttings taken during spring and summer usually tend to root more easily than cuttings taken in the winter (Hartmann et al., 1990; Wilson, 1993). Furthermore, propagation by stem cuttings of Eugenia Smithii, a closely related species, is very good from June to September, but very poor in November (Toussaint et al., 1991). In order to determine the possibility to root cuttings in less favourable periods, every month, from September to April, experiments were conducted on a peat± perlite 1±1 mixture, with a bottom heat of 220.58C. 2.2. Microscopy To determine where the adventitious roots are initiated, basal parts of rooted cuttings were fixed, dehydrated, embedded in paraffin following Heinemann's technique (1980) and sectioned at 15±20 mm. Sections were stained with malachite green and congo red. 3. Results and discussion 3.1. Description of the cultivar `Verlaine' For about 15 years, seeds from a Syzygium paniculatum plant were harvested every year and sown. One of the resultant seedlings differed quite noticeably from
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Fig. 1. 18-month-old Syzygium paniculatum `Verlaine' (approximate height: 1 m).
the parental type, presenting stable characteristics: smaller leaves (4 to 6 cm long by 1.5 to 2 cm wide) and shorter internodes (Fig. 1). Table 1 lists the main features that distinguish cv `Verlaine' from the species (Curtis, 1969; Schmid, 1972; Hyland, 1983; Whistler, 1988). The main asset of this plant is its denser foliage, which is pale green when young, darker green when mature, while its young leaves and stems are tinged with red. The general appearance of the plant can be compared to that of Ficus benjamina `Exotica'. Another asset of S.p. `Verlaine' is its great propensity for flowering after 1 or 2 years of culture. The axillary peduncles that grow laterally or at the top of the shoots, develop at least 3 to 5 flowers in a loose trichotomous panicle. The fruits are magenta, globular or ovoid berries, 1.5 cm in diameter, topped by a persistent calyx. 3.2. Influence of different factors on rooting of cuttings 3.2.1. Influence of substrates and bottom heat The cuttings tested on non-heated substrates (average temperature 16.08C) failed to root. However, when the substrate was heated (average temperature of 220.58C), the mean rooting rate exceeded 75% on the best substrates.
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Table 1 Main characters distinguishing Syzygium paniculatum and S. p. `Verlaine' Distinctive criteria
Syzygium paniculatum
S. p. `Verlaine'
Shoots
Internodes
15 to 50 mm long
15 to 40 mm long
Leaves
Length Width Primary veins
45 to 90 mm 15 to 30 mm 16 to 22 pairs
25 to 65 mm 12 to 24 mm 10 to 16 pairs
Flowers
Inflorescences
Terminal and axillary towards the top; cymes and sometimes panicles with 3, 7 or 11 flowers
Most often terminal; 3 to 5 flowers per panicle
Fruits
Drupes
Ovoid, 16 to 26 mm in diameter
Globular to ovoid, 15 to 22 mm in diameter
The experiments concerning the nature of the substrates showed that the 1±1 vermiculite±perlite mixture was not suitable as it caused the loss of over 90% of the cuttings due to rot. The results of the experiment done on 8 different substrates based on peat, sand and perlite are given in Fig. 2. The rooting percentage and speed of root production were higher on peat±perlite 1±1, 2±1 and 3±1 mixtures than on peat±sand ones but the loss of cuttings by rotting was higher on the 3±1 peat±perlite mixture
Fig. 2. Average rooting speed of cuttings of Syzygium paniculatum `Verlaine' depending on the nature of the substrate.
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(18%) than on the 1±1 and 2±1 ones (5.6%). The good rooting rates observed on peat±perlite substrates can be attributed to a lower pH in these mixtures and/or to the increase in aeration in substrates containing perlite, favouring rhizogenesis (Hartmann et al., 1990). The rooting rate was low on peat±sand 2±1, 3±1 and 4±1 substrates. In peat±sand substrates with a high peat-content, the poorer rooting rate observed could be due to the compaction of peat by water, which consequently would prevent proper aeration of the mixture and lead to rot in the cuttings. This also occurred in the 3±1 and 4±1 peat±perlite substrates but to a lesser extent, thanks to the favourable effect of perlite. The greater length of the root system observed on the peat±perlite mixtures could be attributed to the earlier development of the roots and/or excellent substrate aeration. The ease with which cuttings can be removed from this medium is a distinct advantage. 3.2.2. Influence of auxins There was no significant difference between IAA and NAA in their affect on rooting. No exogenous input of the growth substance seemed to affect rooting of Syzygium cuttings except for the 2000 ppm treatment which caused the highest percentage of loss of cuttings by rotting (18% for the 2000 ppm treatment against an average 2% to 5% for the lower concentrations) and the lowest rooting percentage (52%). This high concentration added to the endogenous auxin of the plant, which itself increases as a consequence of taking cuttings (Favre, 1977) might have led to a level which disturbed the hormonal metabolism and inhibited rhizogenesis. 3.2.3. Influence of the position of the cuttings on the mother plant The rooting success of cuttings taken from the three positions on the stock plants are shown in Fig. 3. The proportion of cuttings that developed roots was significantly higher among those taken from the median and lower parts of the plant than from the apical part. Furthermore, roots developed earlier on cuttings originating from the basal and median parts of the stock plants than on those from the apex. Rooting was initiated as early as the third week on basal cuttings, in the fourth week on the median ones and in the sixth on the apical ones. Only 73% of the apical cuttings had rooted after 13 weeks whereas 99% of the basal ones had rooted after only 7 weeks. The natural accumulation of endogenous auxin, favourable to the development of roots, in the basal part of the stock plants (Wilson, 1993) along with the influence of the nearby root system which encourages juvenility (Chaperon, 1979; Bonga, 1982) are both likely to explain the results obtained. 3.2.4. Influence of the period of the year in which the cuttings are taken The rooting percentage and speed of production of roots were similar on cuttings of S.p. `Verlaine' at whatever time between September and April they
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Fig. 3. Average rooting speed for cuttings of Syzygium paniculatum `Verlaine' depending on the position of the cutting on the mother plant.
were struck. The percentage of rooted cuttings ranged from 64% to 71%. For November, the results are much better than those obtained for Eugenia Smithii (20±28% rooted cuttings), a closely related species (Toussaint et al., 1991). In other Myrtaceae like Chamaelaucium sp., the rooting of cuttings is unaffected by season (Curir et al., 1993). The fact that stock plants are grown in a greenhouse could favour rooting of cuttings (Macdonald, 1986; Marczynski and Joustra, 1993). Stoutemyer (1961) suggested that this could be due to increased air humidity and temperature or to the absence of UV rays in a greenhouse. 3.3. Microscopy Sections of the basal part of a rooted cutting exhibited the classical structure of a stem but with scar tissue consistent with a cutting, schizogenous spaces, tanniferous cells characteristic of the Myrtaceae, and cells with vacuoles containing much calcium oxalate. The sections showed that the adventitious roots originated endogenously in the young secondary phloem. 4. Conclusion The cultivar `Verlaine' of Syzygium paniculatum, originating from a seedling of Syzygium paniculatum has smaller leaves and shorter internodes than the parent
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species, resulting in dense foliage and a very attractive appearance. It offers additional interesting and original characteristics including annual flowering, colourful fruits and red colour of the young leaves. Rooting of cuttings of Syzygium paniculatum `Verlaine' ranged from fair to good depending on the technique applied. Several factors influence the rooting of cuttings: (i) bottom heat is needed (228C was found to be suitable); (ii) the nature of the substrate affects rooting of cuttings by its physical and/or chemical properties. An acid (pH value of about 3.5) well-aerated substrate was best. The results show the advantages of peat±perlite substrates (at 1±1 or 2±1 mixtures) over peat±sand mixtures. Considering the relatively high cost of perlite, it is advisable to choose the 2±1 peat±perlite mixture; (iii) the best position from which to take cuttings on stock plants in order to accelerate rooting is as close as possible to the root system. The addition of auxins does not affect rooting. Throughout the period from September to April, propagation by stem cuttings is successful. The histological study showed that root initiation is endogenous. Propagation by cuttings appears to be a reliable way of multiplication, but financial returns are likely to be modest because of the few shoots produced by each stock plant. Further work is needed to examine the influence of the age of stock plants on rooting of cuttings. In Eucalyptus sp., Jacobs (1977) noted that the rooting rate of cuttings from 3 year-old stock plants was less than of those from younger plants. Acknowledgements We thank the Ministry of the Walloon Region (Belgium) ± General Direction for Economy and Employment ± for its contribution to this research by PRIME projects. References Bonga, J.M., 1982. Vegetative propagation in relation to juvenility, maturity, and rejuvenation. In: Bonga, J.M., Durzan, D.J. (Eds.), Tissue Culture in Forestry. Martinus Nijhoff/Dr W. Junk Publishers, The Hague, Netherlands, pp. 387±412. Chaperon, H., 1979. Maturation et bouturage des arbres forestiers. In: AFOCEL (Ed.), Micropropagation d0 arbres forestiers. Etudes et Recherches, no. 12, 6/79, Nangis, France, pp. 19±31. Curir, P., Sulis, S., Mariani, F., Van Sumere, C.F., Marchesini, A., Dolci, M., 1993. Influence of endogenous phenols on rootability of Chamaelaucium uncinatum Schauer stem cuttings. Scientia Hortic. 55, 303±314. Curtis, A., 1969. Syzygium paniculatum. Curtis Bot. Mag. 177, 1. Dagnelie, P., 1992. TheÂorie et meÂthodes statistiques. Vols. 1 et 2. Les Presses Agronomiques de Gembloux, Gembloux, Belgique, 378 pp. et 472 pp.
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Favre, J.-M., 1977. La rhizogeneÁse. Annales de l0 Universite d0 Abidjan (SeÂrie C), Abidjan, CoÃte d'Ivoire, 100 pp. Hartmann, H.T., Dale, E.K., Davies, F.T., 1990. Plant propagation. Prentice-Hall, New Jersey, USA, 646 pp. Heinemann, P., 1980. Biologie veÂgeÂtale. Travaux Pratiques. Faculte Universitaire des Sciences Agronomiques de Gembloux, Gembloux, Belgique, 36 pp. Hyland, P.M., 1983. A revision of Syzygium and allied genera in Australia. Australian Journal of Botany 9, 1±164. Jacobs, R.M., 1977. Les Eucalyptus dans les reboisements. FA0, Rome, Italie, 75 pp. Macdonald, B., 1986. Practical woody plant propagation for nursery growers. Batsford, London, Great Britain, 669 pp. Marczynski, S., Joustra, M.K., 1993. Influence of daylength and irradiance on growth of the stock plants and subsequent rooting of cuttings of Betula utilis D. Don. and Corylus maxima Mill. cultivar `Purpurea'. Scientia Hortic. 55, 291±301. Rein, W.H., Wright, R.D., Seiler, J.E., 1991. Propagation medium moisture level influences adventitious rooting of woody stem cuttings. J. Amer. Soc. Hort. Sci. 116(4), 632±636. Schmid, R., 1972. Floral anatomy of Myrtaceae I. Syzygium. Bot. Jahrb. Syst. 92(4), 433±489. Smalley, T.J., Dirr, M.A., Armitage, A.M., 1991. Photosynthesis and leaf water, carbohydrate and hormone status during rooting of stem cuttings of Acer rubrum. J. Amer. Soc. Hort. Sci. 116(6), 1052±1057. Stoutemyer, V.T., 1961. Light and propagation. Comb. Proc. Int. Plant Prop. Soc. 11, 252±260. Toussaint, A.N., Lebrun, A., Roggemans, J., 1991. Cutting and in vitro propagation of Eugenia Smithii Poir. Acta Horticulturae 314, 77±83. Von Hentig, W.U., Ehlers, D., 1992. Syzygium-Arten GruÈnppflanzen fuÈr Wohnbereiche. Neue Zierpflanzen 5. Deutscher gartenbau 6, 8±9. Whistler, W.A., 1988. A revision of Syzygium (Myrtaceae) in Samoa. J. Arnold Arbor. 69, 167±192. Wilson, P.J., 1993. Propagation characteristics of Eucalyptus globulus Labill. ssp. globulus stem cuttings in relation to their original position in the parent shoot. Journal of Horticultural Science 68(5), 715±724.