African Journal of Biotechnology Vol. 8 (6), pp. 1078-1081, 20, March 2009
Available online at http://www.academicjournals.org/AJB
ISSN 1684–5315 © 2009 Academic Journals
Full Length Research Paper
Effects of pre-chilling and temperature on seed
germination of Corchorus olitorius L. (Tiliaceae) (Jew’s
Mallow), a wild leafy vegetable
M. Nkomo and L. Kambizi1*
Biological Sciences Department, Walter Sisulu University, P/Bag X1 Mthatha 5117, South Africa.
Accepted 10 November, 2008
The wild leafy vegetable, Corchorus olitorius L, has a potential for development as a crop. Self
propagation of this species is by seed. In an attempt to improve the length of time of its availability, the
effects of pre-chilling and temperature on germination of its seeds were investigated. Although it had a
o
seed viability of 90.1% (using the tetrazolium technique), seed subjected to a temperature of 25 C for
o
both pre-chilled and unchilled seeds showed no germination. Seeds subjected to a temperature of 35 C
did germinate with a maximum of 88% germination from seeds that had been pre-chilled for 3 ½ days
compared to those which were unchilled, pre-chilled for a day or pre-chilled for 7 days. Pre-chilling
o
followed by exposure to a temperature higher than 30 C encourages germination of C. olitorius seeds.
Nursery establishment under such conditions may improve its length of availability.
Key words: Corchorus olitorius, germination, temperature, pre-chilling, wild vegetable.
INTRODUCTION
In South Africa, the use of leafy vegetables is as old as
the history of modern man (Jansen van Rensburg et al.,
2007). Collection and cultivation of these vegetables continues to be widespread among black South Africans
(Bhat and Rubuluza, 2002; Jansen van Rensburg et al.,
2004, Husselman and Sizane, 2006; Modi et al., 2006).
In the Eastern Cape Province, the use of wild vegetables continues to be relatively high, which is compounded by the marginal socio-economic status of most of the
population. Quantitatively, the consumption of leafy vegetables collected from the wild or as weeds tends to be
inversely proportional to household income (Vorster et
al., 2002). Poor households tend to use these types of
leafy vegetables more than wealthier counterparts, because they lack the financial means to purchase vegetables and the wherewithal to produce their own (Vorster
et al., 2002). The use of wild food forms part of a safety
devise that rural people use to cope with poverty, disaster
and livelihood stress (Rose and Guillarmod, 1974; Rubaihayo, 1997; Shackleton et al., 2000).
*Corresponding author. E-mail: Lkambizi@wsu.ac.za. Tel:
+27475022274. Fax: +27866586969.
The collection of leafy vegetables and the knowledge
associated with this practice was a female domain among
both the Koisan (Fox and Young, 1982; Parsons, 1993)
and the Bantu-speaking tribes (Jansen van Rensburg et
al., 2004). In some rural areas of the Eastern Cape, this
practice continues to be associated with women. However, available evidence indicates that once a particular
plant species becomes domesticated and is grown as a
crop, men become involved, especially when its production is commercialized (Van Averbeke and Juma, 2006a).
These wild vegetables tend to be regarded as a female
food, but gender distinctions in terms of their consumption are less universal than in terms of their collection
(Whitbread, 1986; Hart and Vorster, 2006).
C. olitorius is an exotic annual dicotyledonous herb that
has been cultivated in India since ancient times. Commonly known as Jew’s mallow or wild okra (English), Wild
jute in Afrikaans; thelele and ligusha in Xitsonga and
Shangaan (Fox and Norwood, 1982; Bromilow, 1995;
Van Wyk and Gericke, 2000, Vorster et al., 2002) it is one
of the wild leafy vegetables used in the Eastern Cape in
South Africa. C. olitorius belongs to the Tiliaceae family
and is an erect annual herb that varies from 20 cm to
approximately 1.5 m in height depending on the cultivar.
The stems are angular with simple oblong to lanceolate
Nkomo and Kambizi
leaves that have serrated margins and distinct hair-like
teeth at the base. The bright yellow flowers are small and
the fruit is an angular capsule. Corchorus seeds show a
high degree of dormancy which can be broken by means
of hot water treatment (Schippers et al., 2002a). It has
been recorded to establish naturally from seeds and tolerates a wide range of soils and climates (Oladiran, 1986).
In Botswana, attempts to encourage farmers to cultivate
this plant have remained fruitless due to poor germination
(Velempini et al., 2003).
In South Africa, C. olitorius is only harvested from the
wild, but it has the potential for development as a crop,
particularly in the north and eastern parts of the country.
Okra on the other hand is a cultivated crop, albeit on a
limited scale (Khuvutlu and Laker, 1993). Many of the
vegetable species including C. olitorius, especially those
that grow as weeds or in the wild, are seasonal and
highly perisha-ble. To extend the period during which
they are available, different ways of preserving these
vegetables have been developed. These mostly are the
sun-drying of fresh leaves and the sun-drying of blanched
or cooked leaves. Both these methods transform the
leafy vegetables into dry products that have prolonged
shelf life (Vorster et al., 2005). However, this still falls
short in meeting the dem-and for fresh leaves of C.
olitorius. Moreover, some nutri-ents may be lost during
the preservation process.
In the study area natural germination of this plant begins towards the end of spring and grows throughout summer. In this experiment, C. olitorius seeds were germinated and seedlings were established in winter well before
the onset of spring. This was done in an attempt to ensure availability of fresh leaves of the vegetable for more
than one season. In the advent of recent challenges in
food security, enhancing germination of C. olitorius for
possible domestication in the study area may provide an
economic and nutritious option.
MATERIALS AND METHODS
Plant collection
Seeds of C. olitorius were harvested from the wild within OR Tambo
Municipality in the Eastern Cape. The seeds were collected within 3
weeks of their production whilst flowering was still occurring on the
other branches of the plant. Plant identification was done at the Kei
herbarium at Walter Sisulu University.
Tetrazolium chloride test
In ensuring that seeds utilized for the experiment were viable, a
seed viability test using the tetrazolium technique (Grabe, 1970)
was conducted. Three replicates of 50 seeds each were used.
Using the procedure by Peters (2000), the seeds were imbibed for
24 h in water, cut along the margin without damaging the embryo
and soaked in colourless 0.1% solution of 2,3,5-triphenyltetrazolium
chloride (TTC) solution for 18 h at 25oC in the dark (Kambizi et al,
2006). The seeds were removed from TTC solution and washed
with distilled water. The seeds were then viewed under a light
microscope to observe the stained embryos. Whole embryos of viable seeds appeared bright red in colour.
1079
Germination experiment
Germination testing was done in 9-cm sterile Petri dishes lined with
two Whatman No. 1 filter papers. These were moistened using distilled water, each treatment having three replicates of 50 seeds each.
Prior to exposure to these conditions seeds were also subjected to
prechilling for 1, 3 ½ and 7 days pre-chilling at 6oC. The effect of
temperature on germination was investigated by placing the Petri
dishes in incubators set at 25 and 35oC. Seeds were moistened
with distilled water via Whitman’s filter paper discs and exposed to
continuous illumination from white fluorescent tubes. The Petri dishes were examined daily and seed was considered germinated
when the radicle was visible. Data collected were subjected to
analysis of variance with temperature and pre-chilling as treatments
using Microsoft excel 2007.
RESULTS AND DISCUSSION
C. olitorius seeds utilized in the tetrazolium test yielded
90.1% viability. In many germination experiments the
tetrazolium chloride test has been shown to be in close
agreement with germination test results and has been
mentioned for over 650 plant species (Moore, 1985; Leist
and Krämer, 2003). This high percentage could be attributed to the fact that the seeds were harvested and the
germination trials conducted within three weeks. To further support the high percentage obtained, it is possibly
due to the use of seeds harvested and tested during the
same season.
After the analysis of variance on the results, it was
observed that there were significant differences between
the treatments as well as the interaction between the
treatments as shown by Table 1. Seeds placed at a temo
perature of 25 C showed no signs of germination. On the
o
other hand those placed at 35 C did germinate, with the
percentages ranging from 2 to 88% being the highest
across all the replicates. Table 2 shows germination of C.
olitorius seeds at two different temperatures and three
different pre-chilling conditions.
Germination did not occur in any of the seeds placed at
o
a temperature of 25 C in the control and all the prechilled seeds. While those placed at a temperature of
o
35 C showed signs of germination; this may possibly be
due to the fact that C. olitorius grows well mostly when
o
day temperatures average 30 C and above. Further looking at the differences found within the seeds placed at a
o
temperature of 35 C as shown on Table 2, there is a
significant difference between seeds pre-chilled for 3 ½
days and the rest. Contrary to the study that Corchorus
seeds show a high degree of dormancy which can be
broken by means of hot water treatment (Schippers et al.,
2002a), in this experiment seeds subjected to pre-chilling
o
conditions of approximately 6 C showed germination.
Pre-chilling has also been reported to cause lethal effects
on viable seeds (Ren and Tao, 2004) while other studies
have implicated cold stratification to break dormancy of
viable seeds and enhance germination in many species
(Baskin et al., 2001). This may have been the case with
C. olitorius in this investigation. Results showed that
seeds pre-chilled for a day and seven days had lower
1080
Afr. J. Biotechnol.
Table 1. Analysis of variance of seed germination in Corchorus olitorius.
Source of variation
Temperature
Pre-chilling
Interaction
Within
Total
SS
2562.667
5984
5984
290.667
14821.333
df
1
3
3
16
23
MS
2562.667
1994.667
1994.667
18.167
Comp F
141.0642
109.798
109.798
F at 1%
8.530
5.292
5.292
F at 5%
4.494
3.239
3.239
*Significant at (P> 0.01).
Table 2. Germination of Corchorus olitorius seeds at two different temperatures and three different pre-chilling conditions.
Pre-chilling treatment
Untreated (Control)
Pre-chilled for 1 day
Pre-chilled for 3 ½ days
Pre-chilled for 7 days
Temperature
o
o
25 C
35 C
b
0
3.33
(4.163)
b
0
1.33
(1.154)
a
0
75.33 (11.101)
b
0
0.67
(1.154 )
Each value represents mean percentage germination with
standard deviation in parenthesis. Means followed by the same
superscript do not differ significantly (P>0.01).
germination percentages as compared to those pre-chilled for three and a half days. The trend observed shows
a low percentage from one day followed by a sharp
percentage spike or exponential increase for those prechilled for 3 ½ days, followed by a sharp decrease as the
number of days increased.
However, several other experiments involving pre-chilling of seeds for plant species that grow mostly in summer
have revealed that seeds pre-chilled for usually approximately 7 days have the highest germination percentages
(Baskin et al., 2001). This was not the case in this experiment as the highest was observed in seeds pre-chilled for
3 ½ days. This may probably be that the pre-chilling plays
a pivotal role in the number of days that will result in the
highest percentage germination. If the temperature was
o
considerably lower than 6 C then the peak percentage
germination may probably be observed on different prechilling days than 3½. The pre-chilling treatment conditions may actually be simulating the events that occur
during the winter season just before the onset of summer.
The highest average percentage germination of 75.3%
is not excessively far-off the viability of 90.1% obtained
from the TTC test. This may also explain the high natural
regeneration, as the dormancy will be as low as 14.8%
using the high germination of 75.3% and a viability of
90.1%. Nursery establishment of C. olitorius under the
conditions investigated in this experiment may be utilized
to ensure availability of its seedlings well before the onset
of summer thereby lengthening the period of usage during each year and to reinforce efforts to domesticate it in
the Eastern Cape, South Africa.
ACKNOWLEDGEMENT
This research was supported by Walter Sisulu University
and the National Research Foundation of South Africa.
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