American Journal of Plant Sciences, 2011, 2, 776-780
doi:10.4236/ajps.2011.26092 Published Online December 2011 (
Copyright © 2011 SciRes. AJPS
Adaptability of Mor in ga ol eif er a Lam.
(Horseradish) Tree Seedlings to Three
Temperature Regimes
Quintin E. Muhl, Elsa S. du Toit, Petrus J. Robbertse
Department of Plant Production and Soil Science, University of Pretoria, Pretoria, South Africa.
Received August 12th, 2011; revised September 22nd, 2011; accepted October 24th, 2011.
Moringa oleifera trees are naturally found in tropical climates around the world, while the extent of their adaptability
to cooler climates was the main ob jective of this stud y. A total of 264 trees, made up of an equal number hardened and
non-hardened seedlings were randomly assigned to three temperature-controlled greenhouses each with a different
fluctuating night/day temperature regime (TR) namely; 10/20˚C ± 2˚C, 15/25˚C ± 2˚C and 20/30˚C ± 2˚C. During the
32-week trial period, biweekly measurements of tree height, stem diameter and leaf area estimates of each individual
tree within all three temperature regimes (TRS) were taken. The 20/30˚C TR was the most favorable towards overall
tree growth, as the highest values were obtained across most measured parameters. The increase in temperature re-
sulted in growth rate increases of over 650% between the 10/20˚C and 20/30˚C and over 250% between the 10/20˚C
and 15/25˚C night/day TRS. The hardening-off pre-treatment increased both final tree height and stem diameter, re-
sulting in increases of 3.09 × (10/20˚C), 1.44 × (15/25˚C) and 1.23 × (20/30˚C) compared to their non-hardened off
counterparts. Although the average leaf area increased with the increase in TR and remained higher for the duration of
the trial, cycles of regular leaf drop and renewed flushes were prevalent at both the 15/25˚C and 20/30˚C temperature
Keywords: Hardening - Off, Biodiesel, Growth Rate
1. Introduction
Moringa oleifera Lam. also known as Horseradish tree is
one of 14 different species belonging to the family Mor-
ingaceae. Although indigenous to the sub-Himalayan re-
gions in northwestern India, it is currently found in nu-
merous countries situated in the tropical and sub-tropical
regions across Africa, South East Asia and South Ame-
rica (Jahn, 1988) [1]. M. oleifera is a fast growing, small
to medium sized tree ranging between 5 to 12 m in
height. The tree is evergreen in tropical, while deciduous
in sub-tropical climates. The tree canopy has an umbrella
shaped crown with bi-(tri-)pinnate leaves, while the indi-
vidual leaflets have a leaf area of one to two cm2. Flo-
wers are white to cream colored and zygomorphic. The
tree bears 20 to 30 cm long fruit that once mature,
change colour from green to brown revealing numerous
round or triangular seeds with three papery wings (Fol-
kard, et al., 1999) [2]. Amongst the most common uses
for M. o leifera such as animal forage, nutrition, medicine
and water purification, the seed also contains a multi-
purpose, non-drying oil. One of the uses for this oil is the
production of biofuel, in the form of biodiesel (Rashid et
al., 2008) [3]. Biodiesel is a renewable fuel source that is
obtained through the process of transesterification where
natural plant oils are transformed into a fuel, which can
be used in conventional diesel engines (Poeet, 2006) [4].
Since M. oleifera plantations of 3270 trees/ha can yield
anything between 991 - 3303 liters of oil per hectare, de-
pending on the soil and environmental conditions, it can
effortlessly compete with several other oil crops in terms
of liters of oil per hectare (Fuglie, 2001) [5]. Although M.
oleifera is grown throughout numerous African countries,
no evidence of large-scale commercial plantings have
been reported, possibly as a result of the limited scien-
tific data that is currently available on both the propaga-
tion and cultivation of the tree.
Adaptability of Moringa oleifera Lam. (Horseradish) Tree Seedlings to Three Temperature Regimes777
2. Materials and Methods
Growth performance trials were conducted at Phytotron
Section on the Experimental Farm of the University of
Pretoria (25˚45S, 28˚16E) at an altitude of 1372 m
above sea level.
Trees for the purpose of this trial were grown from
seeds sourced from wild M. oleifera trees in Malawi.
Seeds were planted and germinated in seedling trays con-
taining Hygromix™, a sterile, soilless growing medium
for seedlings, manufactured by Hygrotech Seed (Pty) Ltd.
After germinating seed under favorable green-house con-
ditions between 20˚C - 25˚C for one week, half the seed-
lings were left in the greenhouse, while the other half
was hardened-off by placing them outside where the av-
erage minimum/maximum temperatures fluctuated be-
tween 15/30˚C. Both treatments were irrigated to field-
capacity every second day. Equal numbers of hardened-
off (132) and non-hardened-off (132) seedling-trees were
randomly selected and transplanted into 10 liter black
plastic bags, five weeks after seed was planted into seed-
ling trays. These bags were filled with a commercial bark
potting medium manufactured by Braaks (Pty) Ltd. Trees
were placed onto benches inside temperature-controlled
greenhouses. The abovementioned 264 trees were equally
divided and randomly assigned to three different tem-
perature regimes TRS namely, 10/20˚C ± 2˚C, 15/25˚C ±
2˚C and 20/30˚C ± 2˚C, simulating night/day tempera-
ture fluctuations and exposed to natural daylight. The
average photosynthetic active radiation (PAR) at 12:00
in the afternoon on a clear day, inside the temperature-
controlled greenhouses was measured at 1350 µmol·m–2·s–1.
To adjust nitrogen deficiencies evident from soil analysis
results, 20 g of LAN (28) fertilizer was applied to each tree,
16 weeks after trial commencement. Irrigation was manu-
ally applied three times a week until field-capacity was
reached, as the excess water was able to drain from bags.
Bi-weekly measurements of tree height (mm), meas-
ured with a measuring tape and stem diameter (mm),
measured at soil level with a calliper were made of each
tree for the duration of the 32-week trial.
The total leaf area estimates of each tree were calcu-
lated according to a non-destructive method of leaf area
index (LAI) calculation described by Siegfried et al.
(2007) [6]. Firstly, the number of tripinnate leaves as
well as the number of leaflets on the youngest mature
leaf of each tree was counted. Secondly, the number of
leaflets per leaf was multiplied with the number of leaves
per tree to provide an estimate for the number of leaflets
per tree. Then, leaflets were randomly sampled from the
three temperature treatments and measured with a LI-
3100, Licor leaf area meter to provide an estimated leaf
area (cm2) of the individual leaflets. Finally the average
leaf area of a single leaflet was multiplied with the esti-
mated number of leaves per tree to provide an approxi-
mate leaf area per tree.
Data collected over the 32-week trial period were sta-
tistically analyzed using the Statistical Analysis System
(SAS Version 9.1) program for Microsoft Windows, by
the Statistics Department at the University of Pretoria.
The Analysis of Variance (ANOVA) was performed, to-
gether with F-test (Steele and Torrie, 1980) [7] to en-
able the comparison between treatment means.
3. Results and Discussion
The difference in average tree height and stem diameter
of both hardened-off (HO) and non-hardened-off (NHO)
trees within each temperature regime (TR) for the 32-
week trial duration is illustrated in Figure 1. Amongst
the three TRS investigated in this trial, the 20/30˚C TR
clearly was the most favorable for tree growth, with a
final average tree height of 1970 mm and stem diameter
of 28.4 mm. Growth at the 15/25˚C TR was significantly
less with a final average tree height and stem diameter of
1100 mm and 16.1 mm respectively. The 10/20˚C regime
was certainly not conducive to M. oleifera growth as
hardly any noticeable growth occurred throughout the
32-week period. This TR limited the average final tree
height to 480 mm and stem diameter to 8.8 mm. The
effect of the fertilizer application during week 16 was
responsible for the sudden change in growth line gradient.
It is also noticeable how fertilizer use efficiency varied
between the three TRS, while the increase in growth rate
was highest at the 20/30˚C regime, the 10/20˚C regime
revealed only a slight increase in response to the fertil-
izer application (Figure 1).
The final growth between the HO and NHO seedlings
at all three TRS for both the tree height as well as the
stem diameter was not significantly different (Figure 1).
However, the growth rates between the HO and NHO
seedlings for both these parameters differed among and
within the three TRS as illustrated in Table 1. In addition
the percentage increase in growth rate, increased with a
decrease in TR, exemplifying the importance of harden-
ing off seedlings especially if seedlings are to be trans-
planted into a cooler climate. Regardless of the final
growing climate, the HO seedlings are at an advantage
and therefore the hardening-off process is highly rec-
ommended for M. oleifera trees.
The hardening-off process involves several complex
processes that have an effect on numerous morphological
and physiological mechanisms enhancing plant growth
under unfavorable environmental conditions (Villar-
Salvador et al., 1999) [8]. Amongst numerous other
plants, the effect of hardening seedlings prior to trans-
planting were studied on Rosmarinus officinalis and Ne-
rium oleander by Sánchez-Blanco et al. (2004) [9] and
Copyright © 2011 SciRes. AJPS
Adaptability of Moringa oleifera Lam. (Horseradish) Tree Seedlings to Three Temperature Regimes
Copyright © 2011 SciRes. AJPS
Figure 1. Differences in average tree height (cm) and stem diameter (mm) of Moringa oleifera cultivated from both hard-
ened-off and non-hardened-off seedlings at various temperature regimes over a 32-week period. Vertical bars represent LSD.
NHO—non-hardened-off, HO—hardened-off, TH—tree height and SD—stem diameter.
Table 1. Differences in average growth rate (mm/week) between the temperature regimes and hardening-off treatments over
the 32-week trial period. Different letters indicate significant differences at P 0.05 according to the F-test. NHO—non-hard-
ened-off, HO—hardened-off.
Growth rate (mm/week)
Pre-treatment 10/20˚C 15/25˚C 20/30˚C
Tree height Stem diameter Tree height Stem diameter Tree height Stem diameter
NHO 4.33a 0.11g 18.86c 0.28i 52.94e 0.63k
HO 13.36b 0.21h 27.12d 0.33j 65.08f 0.73l
Average 8.85ab 0.16gh 22.99cd 0.30ij 59.01m 0.68n
Adaptability of Moringa oleifera Lam. (Horseradish) Tree Seedlings to Three Temperature Regimes779
Bañon et al. (2006) [10] respectively. Both these papers
reported the superiority of the hardened (HO) plants over
their non-hardened (NHO) counterparts upon the expo-
sure to unfavorable environmental growing conditions
(Sánchez-Blanco et al. 2004 [9]; Bañon et al. 2006 [10]).
The growth rates between the various TRS, as shown
in Table 1, were significantly different (P 0.05), in
which a 10˚C increase between the 10/20˚C and 20/30˚C
in the night/day TR caused a tree growth rate increase of
over 650% in tree height and 400% in stem diameter.
While the 5˚C difference between the 10/20˚C and 15/
25˚C TR resulted in a tree height and stem diameter
growth rate increases of over 250% and 200% respec-
tively. The increase in vegetative growth of M. oleifera
trees brought about by the increase in TR agrees with
similar observations made in several other tropical and
subtropical trees (Menzel and Paxton, 1985 [11]; Troc-
houlias and Lahav, 1983 [12]; George and Nissen, 1987
[13]; Utsunomiya, 1992 [14]), such as mango (Whiley et
al., 1989 [15]), macadamia (Lahav and Trochoulias, 1982
[16]) and lychee (Menzel and Paxton, 1985 [11]).
According to Downs and Hellermers (1975) [17], tem-
perature affects both physical and metabolic processes
within plants, by altering the reaction rates of enzyme
systems, since the optimum temperatures for enzymatic
reactions are enzyme specific, and only vary between
enzymatic systems. The highest growth rates are only
achieved once the environmental temperature coincides
with the requirements of these enzymatic reactions. As
the enzymatic reactions responsible for the processing of
photosynthates are temperature sensitive, growth and de-
velopment are a function of the growing temperature.
Temperature extremes would therefore lead to atypical
and reduced growth.
The optimum TR for the purposes of this study evi-
dently is the 20/30˚C TR, as it produced the highest
growth across all measured parameters. However, ac-
cording to Downs and Hellermers (1975) [17], tropical
trees that reach their maximum cardinal temperature,
often manifest this through rapid stem elongation, thin
leaves and reduced dry matter production at the expense
of reproductive development. Observations of the above
symptoms under the 20/30˚C TR, suggest that any fur-
ther increases in temperature would most likely decrease
growth. Compared to the 20/30˚C TR, growth was sig-
nificantly reduced at the 15/25˚C TR, while hardly any
growth was observed at the low 10/20˚C TR. It can
therefore be assumed that the threshold temperature for
growth of M. oleifera trees is within the 10˚C - 20˚C
range. This not only verifies the fact that M. oleifera fa-
vors tropical growing environments as stated by Morton
(1991) [18] and Mughal et al. (1999) [19], but also de-
monstrates the reluctance of M. oleifera to acclimatize
and generate satisfactory growth under cooler climates.
Similarly to the temperature effect on both tree height
and stem diameter, the average leaf area (cm2) increased
with an increase in TR (Figure 2). However, the increase
in leaf area was less steady, as fluctuations in leaf area
occurred due to repeated cycles of leaf drop followed by
renewed flushes. The extent of these fluctuating leaf area
measurements intensified with an increase in TR and was
the most volatile under the 20/30˚C regime. The 15/25˚C
treatment also showed volatility, but to a lesser extent
than the 20/30˚C treatment. The 10/20˚C was the most
stable, showing a slight but constant increase of leaf area
over the 32-week trial period.
4. Conclusions
Growth of M. oleifera is evidently favoured by high
growing temperature of >25˚C, confirming the prefer-
Figure 2. Increase in average tree leaf area (cm2) of Moringa oleifera trees at three temperature regimes over a 32-week pe-
riod. Treatment means with letters in common are not significantly different at P 0.05. Vertical bars represent LSD.
Copyright © 2011 SciRes. AJPS
Adaptability of Moringa oleifera Lam. (Horseradish) Tree Seedlings to Three Temperature Regimes
ence of M. oleifera towards tropical growing environ-
ments. This was confirmed by the temperature treatment
results, where trees at the 20/30˚C TR revealed the high-
est growth rates for both tree height and stem thickening.
In addition, the 20/30˚C temperature treatment, although
variable, consistently had the highest leaf area over the
entire trial period. As the effect of additional, higher TRS
were not investigated in this study, the possibility of im-
proved growth at even higher temperatures cannot be
excluded. Tropical climates are therefore ideal for the
cultivation of M. oleifera, however satisfactory growth
during the hot summer months in sub-tropical climates is
achievable, if the winters are mild, as trees are frost ten-
der. The hardening-off of the seedlings prior to trans-
planting has proven to increase the growth rate of both
tree height and stem diameter across all three TRS. The
hardening off process is highly recommended for M.
oleifera trees, especially if intended cultivation is in be-
low optimal temperature environments.
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