Euphorbia abyssinica latex promotes rooting of Boswellia
cuttings
Aklilu Negussie Æ Raf Aerts Æ Kindeya Gebrehiwot Æ Els Prinsen Æ Bart Muys
Received: 10 April 2008 / Accepted: 21 July 2008 / Published online: 5 August 2008

Springer Science+Business Media B.V. 2008
Abstract Traditional knowledge in northern Ethiopia points towards the root-stimulating
properties of the latex found in Euphorbia abyssinica (EAG). Stem cuttings of EAG as
well as cuttings of other species treated with EAG latex reportedly root easily in dry soil.
This could be attributable to endogenous auxins contained in the latex. We screened EAG
latex for auxins and precursor molecules using analytical LC-MS/MS, and tested the effect
of EAG latex on the rooting of woody cuttings of Boswellia papyrifera, a threatened
multipurpose tree. The EAG latex contained indole acetic acid (IAA) (0.06 lg/g latex), an
auxin controlling apical dominance and lateral rooting, as well as IAA metabolites and
conjugates. Boswellia cuttings treated with EAG latex rooted significantly sooner and
showed higher survival ratios than untreated controls. EAG is widely available and its latex
easy to obtain. Therefore it is a promising source of a natural plant growth regulator which
may be used for improving low technology vegetative propagation of woody species in
East and Northeast Africa, including the threatened Boswellia tree.
Keywords Auxins
Ethiopia
Indole acetic acid (IAA)
Rooting response

Traditional knowledge
Introduction
Vegetative propagation of trees is an invaluable tool for reliable and cost-effective pro-
duction of planting material for reforestation. The most common method of vegetative
A. Negussie
K. Gebrehiwot
Land Resources Management and Environmental Protection Department, Mekelle University,
P.O. Box 231, Mekelle, Ethiopia
R. Aerts (&)
B. Muys
Division Forest, Nature and Landscape, Katholieke Universiteit Leuven, Celestijnenlaan 200E-2411,
3001 Leuven, Belgium
e-mail: raf.aerts@ees.kuleuven.be
E. Prinsen
Department of Biology, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerpen, Belgium
123
New Forests (2009) 37:35–42
DOI 10.1007/s11056-008-9106-7

propagation for nursery stock production is the rooted cutting (Romero 2004). The method
often involves treating the cuttings with synthetic plant growth regulators (PGRs), typically
the auxins indole butyric acid (IBA) and naphthalene acetic acid (NAA) (e.g. Swamy et al.
2002; Tchoundjeu et al. 2002; Husen and Pal 2007). Alternative techniques to stimulate
adventitious root formation in cuttings include the inoculation of the rooting media with
ectomycorrhizal fungi or rhizobacteria that are able to produce PGRs (Niemi et al. 2002;
Teixeira et al. 2007), and the use of commercial concentrates of marine algae which are
rich in auxins (Crouch et al. 1992; Crouch and Vanstaden 1993).
On the other hand also wild or cultivated plants may be used as PGR sources. In particular
root tips, apical buds and young leaves but also cotyledons and expanding leaves are rich in
the natural auxin indole acetic acid (IAA) (Ljung et al. 2001, 2005). Extracts from these plant
tissues could therefore be used as substitutes for synthetic PGRs and improve the estab-
lishment of plants. In Mexico, for example, crude leaf-extracts of the Creosote bush (Larrea
tridentata Coville) have been shown to stimulate germination and growth of barley seedlings
(De la Rosa-Ibarra and Villareal 2000). For rural communities in developing countries, such
low technology propagation techniques would be much cheaper, more practical and thus far
more effective than the application of synthetic PGRs or micro-organisms.
In northern Ethiopia, traditional knowledge points towards Desert candle (Euphorbia
abyssinica J.F. Gmel.) (EAG) as a potential source of natural PGRs. This succulent tree of
dry deciduous and evergreen montane forest, woodland and shrub savanna is easily
propagated from untreated mature branch cuttings. It is therefore widely used as a live
fence and in hedge rows to control soil erosion (Fichtl and Admasu 1994). Farmers
attribute the ability of large EAG branches to regenerate with ease in dry soil to the milky
latex produced in all parts of the plants. As a consequence, it is local (but far from
widespread) practice to treat branch cuttings from other tree species with EAG latex to
stimulate root formation. The technique is said to be most successful at the end of the dry
season. If EAG latex indeed promotes root formation in woody cuttings, it may be related
to natural plant growth regulator hormones such as IAA contained in the latex, or to other
compounds preventing infection or decay of the cutting. Until now only rubber, certain
waxes and resins were identified as its major constituents (Uzabakiliho et al. 1987).
Therefore, the aim of this study was to screen EAG latex for endogenous auxins, and to
test the effect of the latex on the rooting ability of woody cuttings of the Frankincense tree
(Boswellia papyrifera Hochst.), a multipurpose tree that co-occurs with EAG in northeast
Africa and that is threatened due to human pressure and environmental degradation (Ge-
brehiwot et al. 2003; Negussie et al. 2008).
Materials and methods
Analysis of endogenous IAA, IAA intermediates and IAA conjugates
EAG latex was collected from three locations in Tigray, northern Ethiopia (Jijike, Hagere
Selam and Mekelle), and transported in waterproof, dark containers (designed to carry
photographic film) to the University of Antwerp (Antwerp, Belgium) for biochemical
analysis. Indole acetic acid (IAA), indole-3-ethanol (IEt), indole-3-lactate (ILA) and IAA
conjugates were purified from 1 g latex by a combined solid phase extraction procedure
following Prinsen et al. (1997). One hundred nanogram
13
C
6
-IAA (Cambridge Isotope
Laboratories Inc., Andover, Massachusetts, USA) was used for isotope dilution purposes.
The organic acids IAA and ILA in the extract were methylated.
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