Journal
Journal of Applied Horticulture, 19(3): 226-229, 2017
Appl
Effective rhododendron propagation through stem cuttings
P. Ferus*, J. Konôpková, D. Bošiaková and P. Hoťka
Mlyňany Arboretum, Institute of Forest Ecology SAS, Vieska nad Žitavou 178, 95152 Slepčany, Slovakia.
*E-mail: peter.ferus@savba.sk
Abstract
Rhododendrons represent the most attractive element of the Mlyňany Arboretum IFE SAS for visitors at the season opening time.
Because of necessity of the old collection renewal and re-evaluation of general rules in the area of rhododendron vegetative propagation,
in this work we tested the effect of genotype, cutting collection time, auxin treatment and cultivation substrate on the rooting success
of annual stem cuttings from Rhododendron impeditum ´Purple Pillow´, R. keleticum ´Robert Seleger´, R. makinoi, R. catawbiense,
R. fortunei, R. smirnowii, R. x hybridum ´Cunningham´s White´ and R. x hybridum ´Nova Zembla´. Despite the only one statistically
significant effect of genotype, better rooting results were observed after cuttings were treated by indolyl-butyric acid (IBA) and cultivated
in substrate composed from peat and perlite (1:1), compared to other auxin formulas (indolyl-acetic acid (IAA) and naphthyl-acetic
acid (NAA) and TS 1 substrate. Cutting collection time is recommended to adapt to the mother shrub developmental stage/fitness.
Exceptions from this general propagation procedure can occur among cultivars.
Key words: Rhododendron, propagation, cuttings, genotype, collection time, substrate, auxin
Introduction
Rhododendrons, as one of the most decorative shrub group with
wide diversity of habitual characteristic, leaf size as well as
flower richness and colour, represent one of the most important
collections in numerous botanical gardens, arboretums and parks.
Their natural distribution area comprises particularly middle
China, Tibet and Japan, North America and high-mountain
regions of Europe and Indonesia (Krüssmann, 1962).
Presently, The American Rhododendron Society (http://www.
rhododendron.org/rhododendronA-Z.htm) lists 316 botanical
species and 1125 cultivars of rhododendron. Flowering
rhododendron shrubs, especially attractive for public, are
traditionally associated with the visitor season opening in
Mlyňany Arboretum IFE SAS. According to the last inventory
carried out in 2012, in this arboretum almost 200 many-decadesold rhododendron individuals, taxonomically classified into 19
species and 18 cultivars (Hoťka and Barta, 2012), are growing.
Rhododendron fortunei Lindl. and R. x hybridum Cunningham´s
White are among the most abundant genotypes belonging to the
species.
One of the shortest ways to produce sufficient amount of
phenotypically stable rhododendron plantlets to cover growing
market demand is the rooting of stem cuttings. During the
past century, the methodology of this way of propagation was
elaborated (Wells, 1982). The large-scale production require
proper timing for stem cutting collection, best type of cuttings for
successful rooting, cutting adjustment before starting the rooting
process, effective hormone treatment, choice of cultivation
medium, necessity of the bottom heat input as well as light
intensity, air temperature and humidity set up.
In the own adventitious rooting, following three phases
are recognized: induction, initiation and expression. The
induction phase is devoid of visible cell division and involves
reprogramming of target cells to the following establishment
of meristemoids. During initiation phase, root primordia form
and the expression phase corresponds to their growth through
the stem tissues and establishment of the vascular connections
between the newly formed root and the original stem cutting (da
Costa et al., 2013).
Present research deals also with early detection of rhododendron
rooting success through metabolic markers. For instance, Merge
et al. (2011) tested dynamics of cutting peroxidase activity
and starch concentration in the course of rooting phases. They
found that opposite to stable starch content, peroxidase activity
decreased in the induction phase, increased in the initiation phase
and fell again in the expression phase, thus having potential
candidate for such a marker. Chlorophyll fluorescence parameters
(Fv/Fm, RC/ABS and PI) also tightly corresponded with changes
associated with rhododendron grafting and adventitious root
formation (Dokane et al., 2013). During the first 4 days they
decreased possibly due to wounding and water stress in early
stages of the grafting process, then rose and fell again till day
13, when callus bridges in graft region were observed, and finally
fluctuated what was ascribed to the root formation.
The aim of our work was to standardize the rooting procedure
for the most threatened rhododendron genotypes in Mlyňany
Arboretum IFE SAS as well as their perspective alternates, and
thus to re-evaluate the general view on the rooting methodology.
Material and methods
Laboratory experiment 2014: Potted rhododendron individuals
(Rhododendron impeditum Balf. f. & W.W. Sm., cv. Purple Pillow
and R. keleticum Balf. f. & Forrest, cv. Robert Seleger) as well
as older individual of R. makinoi Tagg grown in a plant nursery
cold frame of Mlyňany Arboretum IFE SAS with peat substrate
were used as source material for annual shoot cutting collection
in August 2014 (Wells, 1982; for more details on cultivation
Journal of Applied Horticulture (www.horticultureresearch.net)
Effective rhododendron propagation through stem cuttings
227
Table 1. Rhododendron species collection for rooting tests with characterization of mother shrub locations in the Mlyňany Arboretum IFE SAS,
cultivation conditions and sampling terms
Genotype
GPS
Light conditions
Cutting collection date
22nd August 2014
22nd August 2014
R. impeditum ´Purple Pillow´
N48.322087, E18.367352
R. keleticum ´Robert Seleger´
N48.322087, E18.367352
Light-Shadow
Light-Shadow
R. makinoi
N48.322087, E18.367352
Shadow
22nd August 2014
R. catawbiense
N48.320439, E18.369609
Shadow-Light
14th June 2016
R. fortunei
N48.320251, E18.369761
Half-Shadow
23rd May 2016
R. smirnowii
N48.319453, E18.369293
Shadow-Light
15th June 2016
R. x hybridum ´Cunningham´s White´
N48.32006, E18.370015
Half-Shadow
14th June 2016
R. x hybridum ´Nova Zembla´
N48.31941, E18.369334
Shadow-Light
15th June 2016
conditions see Table 1 and Fig. 1A).
Five centimetre long apical part of 5-8 annual shoots with 5 leaves
(in R. impeditum ´Purple Pillow´ 10 leaflets, in R. makinoi
with reduced area to one third) were cut angle-wise at the bottom
using grafting knife, wounded part was submerged into 1 %
indolyl-acetic acid (IAA) or 1 % indolyl-butyric acid (IBA) talc
(Rhizopon A or Rhizopon AA, Rhizopon, Netherland) and shaken
off from the powder rests. Cuttings were then placed into 9 cm
plastic pots with TS 1 substrate (Klasmann-Deilmann GmbH,
Germany; pH 6.4) or peat moss (Bora s.r.o., Slovakia) combined
with perlite (LBK Perlit s.r.o., Slovakia) in the ratio 1:1 (v/v) of
final pH 5.5 and substrate pressed. Whole pots were enclosed
into plastic bags and placed under artificial light source of 100
μmol.m-2.s-1 and photoperiod 16/8 hours. The cultivation room
was air conditioned to 21°C. Once a week, leaves and substrate
were sprayed by distilled water. After 5 months, rooting success
was recorded.
Laboratory experiment 2016: Older rhododendron individuals
located in old Ambrozy´s park of the Mlyňany Arboretum IFE
SAS, namely R. catawbiense Michx., R. fortunei Lindl., R.
smirnowii Trautv., R. hybridum cv. Cunningham´s White and
R. hybridum cv. Nova Zembla, were sampled for 10 cuttings of
semi-matured annual shoots in May-June 2016 (Walter, 2011; for
more details see Table 1 and Fig. 1B).
Whole annual shoot with 5 reduced (to one third) upper leaves
were cut angle-wise at the bottom, wounded part submerged
into 0.5% indolyl-butyric acid (IBA; Rhizopon AA, Rhizopon,
Netherland) or 0.5% naphthyl-acetic acid (NAA; Bioplant KFT.,
Hungary) talc and shaken off from the powder rests. Cuttings
were placed into 9 cm plastic pots with peat moss (Bora s.r.o.,
Slovakia) combined with perlite (LBK Perlit s.r.o., Slovakia)
in the ratio 1:1 (v/v) and enclosed into plastic bags. Cultivation
was carried out in the same light, temperature and hydration
conditions for 6 months.
Statistical analysis: Percentage of rooting and percentage of
callus formation as well as cumulative new shoot length of
rooted cuttings in R. keleticum ´Robert Seleger´ were subjucted
to statistical analysis of variance (ANOVA). Comparison among
means was performed using LSD multiple range test. The symbols
*, ** and *** indicate significant differences at P ≤ 0.05, 0.01 and
0.001, respectively, and the letters imply significant differences
at P ≤ 0.05.
Results and discussion
In the first experiment, only cuttings from potted rhododendron
species rooted (Table 2). The most successful (100%) was R.
keleticum ´Robert Seleger´, which rooted in any substrate and
under any auxin treatment. On the other hand, R. impeditum
´Purple Pillow´ could form roots only in peat-perlite substrate
after stimulation by IAA (67%). R. makinoi usually formed callus
and root appeared occasionally only in the same combination of
substrate and stimulator formula. Among rooted cuttings of R.
keleticum ´Robert Seleger´, significantly larger cumulative new
shoot length was observed when peat-perlite substrate with IBA
preparation was applied (ca. 8 cm in average, Fig. 2).
Lab experiment in 2016 revealed the best rooting (80 %) in R.
Fig. 1. Monthly minimal (Tmin) and maximal (Tmax) air temperature as well as precipitation (P) dynamics in Mlyňany Arboretum IFE
SAS in year 2014 (A) and 2016 (B).
Journal of Applied Horticulture (www.horticultureresearch.net)
228
Effective rhododendron propagation through stem cuttings
Table 2. Rooting success of rhododendron cuttings as influenced by substrate and
stimulator formula. The symbols *, ** and *** indicate significant differences at
confidence levels of P ≤ 0.05, 0.01 and 0.001, respectively
Genotype
Substrate
Auxin
Rooting
Callus
(%) formation (%)
67
Peat + Perlite
IAA
0
R. impeditum ´Purple Pillow´
IBA
0
0
0
0
TS 1 substrate
IAA
IBA
0
0
100
0
Peat + Perlite
IAA
R. keleticum ´Robert Seleger´
IBA
100
0
100
0
TS 1 substrate
IAA
IBA
100
0
33
0
Peat + Perlite
IAA
R. makinoi
IBA
0
67
0
TS 1 substrate
IAA
60
IBA
0
0
Peat + Perlite
IBA
R. catawbiense
60
20
NAA
40
30
Peat + Perlite
IBA
R. fortunei
80
0
NAA
50
20
Peat + Perlite
IBA
R. smirnowii
50
40
NAA
80
0
Peat + Perlite
IBA
80
0
R. x hybridum ´Cunningham´s
20
NAA
0
White´
Peat + Perlite
IBA
R. x hybridum ´Nova Zembla´
50
0
NAA
20
30
Callus formation %
Rooting %
Factor
P
% Variance
P
% Variance
Genotype
Sampling Time
Substrate
Auxin
**
n.s.
n.s.
n.s.
67.21
0
0
32.59
n.s.
n.s.
n.s.
n.s.
fortunei, R. smirnowii and R. hybridum ´Cunningham´s White´
(Table 2). Except for R. smirnowii, rooting was attained when
IBA was applied. Generally, much more cuttings from any tested
rhododendron genotype rooted in this stimulator than in NAA.
On the other hand, naphthyl-acetic acid caused more extended
formation of callus in R. catawbiense (30 %), R. fortunei (20 %)
and R. hybridum ´Nova Zembla´ (30 %).
Statistical analysis of variance revealed that only genotype had
significant (P ≤ 0.01) effect on rooting percentage. However,
auxin treatment also contributed to the rooting portion variability
Fig. 2. Cumulative new shoot length of rooted cuttings of R. keleticum
´Robert Seleger´ in different substrate and auxin stimulator. Letters
indicate significant differences at confidence levels of P ≤ 0.05.
by almost 33 %. Opposite situation was observed in the
callus formation percentage with 95 % of variability
ascribed to auxin treatment and almost 5 % associated
with genotype. Among both experiments no factor had
significant effect on callus formation percentage.
Study of Nawrocka-Grześkowiak (2004) showed that
IBA application at higher concentration (4 or 2 %) had the
best effect on cutting rooting success in R. catawbiense
´Grandiflorum´, R. hybridum ´Cunningham´s White´ R.
yakushimanum Nakai and other decorative botanical
rhododendron species. Similar results were reported
by Hieke (1988) from the Institute of Ornamental
Gardening in former Czechoslovakia. However, in R.
catawbiense ´Album´, good results with NAA were
observed (Harrington, 1990). In our experiments,
cuttings generally repoduced better to IBA than IAA
or NAA but some species preferred one of the latter
auxins (for instance R. smirnowii). NAA particularly
stimulated callus formation.
Beel and Piens (1980) observed larger rooting success
of R. hybridum ´Nova Zembla´ in peat substrate with
lower CaCO3 load. Hence, substrate reaction can play
an important role in the rooting process. Chen et al.
(2003) presented research on the effect of compost
composition on pothos (Epipremnum aureum), maranta
(Maranta leuconeura) and shefflera (Schefflera
arboricola) cuttings rooting. They found that five
substrates formulated from composted municipal
4.77
solid waste with biosolids (max. 20%) or composted
0
yard trimmings (max. 50%) as well as equal volumes
0
of sphagnum peat and pine bark, with optimal bulk
95.33
density, porosity, low electrical conductivity and pH,
markedly improved root growth. Sufficient substrate hydration
is also essential for rooting success, as described by Rein et al.
(1991) studying moisture level in relation to R. hybridum ´HinoCrimson´ rooting percentage. Substrates used in our experiments
differed in pH and most probably also in bulk density and porosity.
Despite insignificant effect detected by statistical analysis, more
acidic and more porous substrate composed from peat and perlite
seems to be more suitable for rhododendron cuttings rooting than
the TS 1 substrate. This is in accordance with the rhododendron
cultivation manual of Böhm (2004).
Since the only one factor significantly influencing the rooting
result was the genotype, regardless of the cutting collection time,
we can state that R. makinoi belongs to difficult-to-root genotypes
of rhododendrons (Wu and Barnes, 1981). Nevertheless, cutting
tightness should be taken into account because half-mature
annual shoots are highly recommended (Walter, 2011). Thus, for
deciding collection period, genotype and site specific approach
should be applied. Except this, mother plant fitness is important
for the cutting rooting process (da Costa, 2013). Early drought
and high air temperatures cause growth inhibitor accumulation
hampering the rooting process. But this was not in our case,
as there was no temperature extreme and water stresss (Fig.
1) before the cutting collection, which could affect the mother
rhododendron individuals.
The study revealed that the cutting collection time, genotype
and site characteristics should be taken into consideration for
Journal of Applied Horticulture (www.horticultureresearch.net)
Effective rhododendron propagation through stem cuttings
maximizing rooting. For rooting of the rhododendron cuttings
prefer substrate composed from peat and perlite. Most of the
tested rhododendron genotypes showed better rooting response
to IBA. Differences among genotypes, concerning this general
rooting procedure may occur.
Acknowledgement
This work was supported by the Scientific Grant Agency under
project VEGA 2/0183/14. Thanks to Mr. Tomáš Bibeň for
technical support.
References
Beel, E. and G. Piens, 1980. Propagating rhododendron hybrids by
cuttings. Verbondsnieuws voor de Belgische Sierteelt, 24: 431-434.
Böhm, Č. 2004. Vše o rododendronech [All about rhododendrons].
Praha: Květ.
Chen, J., D.B. McConnell, C.A. Robinson, R.D. Caldwell and Y.
Huang, 2003. Rooting foliage plant cuttings in compost formulated
substrates. HortTech., 13: 110-114.
da Costa, C., M.R. de Almeida, C.M. Ruedell, J. Schwambach, F.S.
Marashin and A.G. Fett-Neto, 2013. When stress and development
go hand in hand: main hormonal controls of adventitious rooting in
cuttings. Front. Plant Sci., 4: 133.
Dokane, K., L. Mertena, D. Merge and U.Kondratovics, 2013. Changes
in photosynthetic parameters during graft union and adventitious root
formation in cutting grafts of Rhododendron subg. Hymenanthes.
Acta Hort., 990: 59.
229
Harrington, J. 1990. Rhododendron propagation. J. Am. Rhod. Soc., 44(3)
Hieke, K. 1988. Propagation by cuttings of evergreen rhododendrons at
Průhonice. J. Am. Rhod. Soc., 42(1).
Hoťka, P. and M. Barta, 2012. Dreviny Arboréta Mlyňany SAV [Inventory
of the living collections of the Mlyňany Arboretum SAS], Bratislava:
Veda.
Krüssmann, G. 1962. Handbuch der Laubgehölze. Berlin: Paul Parey.
Merge, D., K. Dokane and U. Kondratovics, 2011. Can changes in starch
content and peroxidase activity be used as rooting phase markers for
rhododendron leaf bud cuttings? Acta Biol. Cracov. Bot., 53: 74-79.
Nawrocka-Grześkowiak, U. 2004. Effect of growth substances on the
rooting of cuttings of rhododendron species. Folia Hort., 16: 115123.
Rein, W.H. R.D. Wright and J.R. Seiler, 1991. Propagation medium
moisture level influences adventitious rooting of woody stem
cuttings. J. Amer. Soc. Hort. Sci., 116: 632-636.
Wells, J.S. 1982. The propagation of hybrid rhododendrons from stem
cuttings – an historical review. J. Am. Rhod. Soc., 36(4).
Walter, V. 2011. Rozmnožovaní okrasných stromů a keřů [Propagation
of the ornamental trees and shrubs]. Praha: Brázda.
Wu, F.T. and M.F. Barnes, 1981. The hormone levels in stem cuttings of
difficult-to-root and easy-to-root rhododendrons. Biochem. Physiol.
Pflanzen, 176: 13-22.
Received: November, 2016; Revised: January, 2017; Accepted: February, 2017
Journal of Applied Horticulture (www.horticultureresearch.net)