Journal of
AGROBIOLOGY
J Agrobiol 30(2): 83–88, 2013
DOI 10.2478/agro-2013-0008
ISSN 1803-4403 (printed)
ISSN 1804-2686 (on-line)
http://joa.zf.jcu.cz; http://versita.com/science/agriculture/joa
ORIGINAL ARTICLE
An evaluation of Johnson grass (Sorghum halepense L.) seed
hardness removing methods
Gholamreza Mohammadi, Negin Noroozi, Iraj Nosratti
Faculty of Agriculture and Natural Resources, Razi University, Kermanshah, Iran
Received: 26th August 2013
Revised: 17th February 2014
Published online: 30th March 2015
Abstract
Johnsongrass is one of the ten most dangerous weeds in the world affecting about 30 crops in
many countries. One of the tools for Johnsongrass propagation is a seed which commonly has
a primary dormancy mainly due to an impermeable seed coat. This dormancy is an important
problem especially when the Johnsongrass control strategies are studied in the laboratory
or in greenhouse experiments. The present study was conducted to evaluate methods for
removing the hardness of Johnsongrass seed. The two-factorial experiment was based on a
completely randomized design with four replications. The first factor was a seed hardness
removing method involving glume removal, seed pre-treatment with sulphuric acid, hydrogen
peroxide or sodium hypochlorite and control (without seed pre-treatment). The second factor
was seed treatment with distilled water or potassium nitrate solution during the experiment.
The results indicated that seed pre-treatment with sulphuric acid or glume removal along with
the treatment with distilled water during the experiment led to a higher mean germination
rate and higher germination percentage.
Key words: Johnson grass; Sorghum halepense; seed hardness removing; sulphuric acid;
hydrogen peroxide; sodium hypochlorite
1992). Seed dormancy, which denotes a relatively
inactive or resting condition, slows down or stops
weed seed germination. The dormant seeds in
the soil allow weeds to escape or avoid exposure
to control practices that target emerging and
emerged weed seedlings (Radosevich et al. 1996).
It is due to the seed coat being impermeable to
water or oxygen or both, hard seed coat, immature
embryo, embryos that require an “after-ripening
period” or as a result of endogenous chemical
germination inhibitors (Wareing and Phillips
1981). A condition of hard seededness, which is
prevalent in many species of plant families such
as Leguminosae, Malvaceae and Liliaceae, is one
INTRODUCTION
Seed dormancy can be defined as the failure of
seeds to germinate owing to factors associated
with their seed coat or embryo (Aiazzi and Arguello
Gholamreza Mohammadi, Dept. of Crop Production and Breeding, Faculty of Agriculture
and Natural Resources, Razi University,
Kermanshah, Iran
[email protected]
83
Journal of Agrobiology, 30(2): 83–88, 2013
methods of removing weeds involving seed
dormancy.
Acid treatments are often used to break
down dormancy especially in the species with
thick impermeable seed coats. Chemicals such
as sulphuric acid (H2SO4) (Nadjafi et al. 2006,
Rahnama-Ghahfarokhi and Tavakol-Afshari
2007) and mechanical scarification (Hermansen
et al. 1999) have been recommended to break
dormancy and enhance germination. Dormant
seeds that exhibit seed coat imposed dormancy
will germinate following damage or removal of
the seed coat. Some species require scarification
with either sulfuric acid or fire for dormancy
release (Finkelstein et al. 2008). Sixtus et
al. (2003) found that sulfuric acid and sand
paper treatment increased germination of Ulex
europaeus seeds, while hot water treatment
did not affect seed germination. Aliero (2004)
reported that use of hot water, sulfuric acid and
sand paper scarification affected the breaking
of Parkia biglobosa seed dormancy. According
to Ren and Tao (2004) the speed and percent
germination of Calligonum species can be greatly
increased by mechanical scarification or acid
treatments. Generally, concentrated sulphuric
acid treatment has been widely used to improve
seed germination of several hard seed coat species
(Tigabu and Oden 2001). Mechanical scarification
is a technique for overcoming the effect of an
impermeable seed coat. Mechanical scarification
can be done by rubbing seeds between two pieces
of sand paper or using a file, a pin or a knife to
rupture the seed coat, cracking with hammer or
a vice so that water can enter and germination
can begin (Hartmann et al. 2002). In order to
accelerate this method, it can be combined with
some treatments such as chemical applications or
mechanical seed coat removal (Martinez-Gomez
and Dicenta 2001).
Some studies on the role of sodium hypochlorite
(NaOCl) in releasing seed dormancy (Hsiao
and Quick 1984, 1985, Huang and Hsiao 1987)
indicated that germination, in general, increased
with increasing exposure of the weed seeds to
NaOCl. Muhammad et al. (2006) and Yushi et
al. (2008) reported a stimulation of germination
when seeds are treated with hydrogen peroxide.
Oxidant treatments such as hydrogen peroxide
appear to improve germination, providing
oxygen to the embryo. In fact hydrogen peroxide
acts primarily by oxidizing phenolic compounds
which suddenly can no longer bind oxygen after
treatment (Kouakou et al. 2009). Huang and
Hsiao (1987) suggested that NaOCl, H2O2 and
form of seed dormancy that is caused by both
genetic and environmental factors (Copeland
and McDonald 2001). The relationship between
seed dormancy and the success of a plant as a
weed is significant. Weed seeds vary extensively
with respect to degree, duration, and basis of
dormancy. The existence of a large population
of weed seeds with varying degrees and states of
dormancy is the main reason for many problems
with weed species (Ali et al. 2012).
Phytohormones can play important roles in
seed dormancy and germination. A crucial role
for abscisic acid (ABA) has been identified in
inducing seed dormancy. Factors determining
spatial and temporal ABA content and sensitivity
patterns in seeds positively regulate induction
of dormancy and probably its maintenance,
and negatively regulate dormancy release and
germination (Kucera et al. 2005).
Gibberellins [e.g., gibberellic acid (GA)] are
known to have stimulated seed germination in a
wide range of plant species (Thomas et al. 2005).
Gibberellins stimulate germination by inducing
hydrolytic enzymes that weaken barrier tissue
such as that of the endosperm or seed coat,
inducing mobilization of seed storage reserves
and stimulating expansion of the embryo
(Bewley and Black 1994). GA releases dormancy,
promotes germination and counteracts inhibitory
ABA effects, directly or indirectly. GA is required
for embryo cell elongation, for overcoming coat
restrictions to germination of non-dormant and
dormant seeds, and for inducing endosperm
weakening (Kucera et al. 2005).
Johnson grass [Sorghum halepense (L.)
Pers.] is a perennial weed spreading by seeds
and by long creeping rhizomes. It occurs in all
major agricultural areas of the world and was
listed by Holm (1969) and Holm et al. (1977) as
one of the world’s worst weeds. Johnsongrass is
a very prolific weed and seeds are its principal
means of dissemination (Holm et al. 1977).
After maturity, the seeds shatter readily from
spikelets. The majority of freshly harvested seeds
are highly dormant (Taylorson and McWhorter
1969, Taylorson 1975). Johnsongrass seeds can
remain viable after 25 years in the soil (Egley and
Chandler 1978) mainly due to their dormancy.
This can be a severe problem when Johnsongrass
control practices are applied in cropping
systems. In addition, seed dormancy is an
important obstacle in laboratory and greenhouse
experiments where weed seed germination and
seedling establishments are studied. Therefore,
several studies have been carried out to evaluate
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Journal of Agrobiology, 30(2): 83–88, 2013
H2SO4 acted in the termination of Johnson grass
primary dormancy by a modification of the hull
or seed coat membrane and also by supplying
additional oxygen to the seed. According to
Shanmugavalli et al. (2007) potassium nitrate
has been used since the 1980s to stimulate
germination with positive results.
In general, the study of seed hardness
removing methods is important especially when
the post-emergence weed control tools are studied
in laboratory and greenhouse experiments,
where weed seed germination and seedling
establishments are necessary. The objective of
this study was to compare several seed hardness
removing methods including glume removal
and different chemical seed pre-treatments to
stimulate the Johnson grass seed germination. In
addition to distilled water, the efficiency of KNO3
solution as a seed treatment agent during the
experiment was also evaluated.
Seed germination was recorded daily up
to day 18 after the start of the experiment. A
seed was considered germinated when a radicle
emerged of about 2 mm in length. Then the mean
germination rate was calculated according to the
following equation (Ellis and Roberts 1980):
MGR= ∑n / ∑Dn,
where MGR is the mean germination rate, n is
the number of seeds germinated on day and D is
the number of days from the start of test.
The seed germination percentage (SGP)
was determined at the end of the test. For
experimental data, an analysis of variance and a
means comparison (LSD test at the 0.05 level of
probability) were carried out using SAS software
(SAS Institute 2003).
RESULTS AND DISCUSSION
MATERIALS AND METHODS
Analysis of variance (Table 1) showed that both
germination percentage and mean germination
rate were significantly influenced by different
seed pre-treatments and treatments (P≤0.01).
Moreover, there was a significant two-way
interaction (seed treatment × seed pre-treatment)
for the traits under study (Table 1).
The present study was conducted at the Seed
Research Laboratory of the Faculty of Agriculture
and Natural Resources of Razi University,
Kermanshah, Western Iran. The experiment was
two-factorial based on a completely randomized
design with four replications. The first factor was
the seed hardness removing method including
glume removal, seed pre-treatment with H2SO4,
H2O2 or NaOCl and control (without seed pretreatment). The second factor was seed treatment
with distilled water or KNO3 solution (0.51%)
during the experiment.
Johnson grass seeds were collected from the
Agricultural Research Farm of Razi University.
For H2SO4 pre-treatment, seeds were immersed
in 98% sulphuric acid for 30 min. For H2O2
pre-treatment, seeds were immersed in 3.06%
hydrogen peroxide for 72 h. For NaOCl pretreatment, seeds were immersed in 4.09% sodium
hypochlorite for 10 h. Thereafter, all pre-treated
seeds were rinsed with distilled water. For glume
removal, the glume of the seeds was removed by
a tweezer. All seeds were placed in glass petri
dishes of 9 cm diameter on a layer of filter paper
(whatman #41). Ten seeds were placed in each
of the petri dishes. The seeds were moistened
with distilled water or a KNO3 solution during
the experiment (at 3–4-day intervals). The petri
dishes were placed in darkness in a germinator
at the alternate temperatures of 35 and 20 °C for
16 and 8 h, respectively.
Table 1. Analysis of variance of the traits under study
Mean Square
Source of variance
Germination
percentage
Mean
germination rate
Seed treatment (a)
38.02**
0.0154**
Seed pre-treatment (b)
32.08**
0.0842**
a*b
6.46**
0.0037**
Error
1.19
0.0007
CV (%)
29.3
14.3
** Significant at the 0.01 level of probability.
When the seeds were treated with distilled
water during the experiment, all seed pretreatments significantly increased the germination percentage of Johnson grass seeds as
compared with the control (no seed pre-treatment)
(Fig. 1). However, in the case of KNO3 application
during the germination period, only the seed pretreatment with H2SO4 and glume removal resulted
in significant improvement (50 and 42.5%,
respectively) in Johnson grass sed germination
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Journal of Agrobiology, 30(2): 83–88, 2013
percentage (Fig. 1). The highest seed germination
percentage occurred when the seeds were pretreated with H2SO4 and treated with distilled
water during the experiment (82.5%) (Fig. 1). The
H2SO4 pre-treatment enhanced seed germination
percentage by 686 and 400% for distilled water
and KNO3 treatments, respectively as compared
with the control variant. Similar results were
obtained in experiments with African locust
bean (Parkia biglobosa [Jacq.] Benth.) seeds
(Aliero 2004) in which seeds were soaked in 50%
to concentrated H2SO4 for 1 to 5 min; European
milkvetch (Astragalus hamosus L.) and blackdisk
medick [Medicago orbicularis (L.) Bartal.] (Patane
and Gresta 2006) and morong [Enterolobium
contortisiliquum (Vell.)] (Malavasi and Malavasi
2004) seeds, in which seed dormancy was broken
by soaking seeds in H2SO4 for 30, 60, 120 and 180
min. The concentrated sulphuric acid treatment
has been widely used to improve seed germination
of several hard seed coat species (Tigabu and
Oden 2001). Farhoudi et al. (2007) also reported
that the highest germination percentage of Rubia
tinctorum was observed in a treatment of 90%
sulfuric acid applied for 15 minutes. Tao (1982)
reported that sulphuric acid destroys the seed
coat and the seed gets more oxygen. According
to Huang and Hsiao (1987) during immersion of
seeds in concentrated sulphuric acid, oxidation
may be occurring via SO2–. Therefore, in addition
to seed coat removal, sulphuric acid provides
more oxygen and consequently can increase seed
germination.
Control
Glum
H2SO4
In control and glume removal conditions,
there was no significant difference between the
two seed treatments (distilled water and KNO3
solution) for germination percentage, but in
other seed pre-treatments, the seeds treated with
distilled water during the experiment performed
better in terms of this trait (Fig. 1). The lowest
mean germination rates (0.08 and 0.06 per
day for distilled water and KNO3 treatments,
respectively) were observed when Johnsongrass
seeds were not pre-treated (control). Although,
there was no significant difference between
control and the variant in which seeds were
pre-treated with NaOCl and treated with KNO3
during the experiment (Fig. 2). In general, the
traits under study were not notably influenced by
NaOCl pre-treatment (Figs 1 and 2). Hsiao and
Quick (1984) showed that before glume removal
the seeds soaked in NaOCl cannot use fully the
oxygen that NaOCl provides. The role of NaOCl
on seed germination is supplying oxygen to the
seed embryo, but it does not remove the shell
casing.
Glume removal along with the seed treatment
with distilled water during the experiment
led to the highest mean germination rate of
Johnsongrass seeds (0.36 per day) (Fig. 2). In
general, glume removal increased the mean
germination rate by 341 and 348% for distilled
water and KNO3 treatments, respectively, as
compared with the control (Fig. 2). According to
Hsiao and Quick (1984), glume removal provides
more oxygen to the seed and increases seed
Distilled water
Distilled water
KNO3
KNO3
H2O2
NAOCl
Control
Seed pre-treatment
Fig. 1. Johnsongrass seed germination percentage
in response to different seed pre-treatments and
treatments
86
Glum
H2SO4
H2O2
Removal
Seed pre-treatment
NAOCl
Fig. 2. Johnsongrass mean germination rate in
response to different seed pre-treatments and
treatments
Journal of Agrobiology, 30(2): 83–88, 2013
germination due to an increase in the transfer
of oxygen to the seed embryo. After the glume
removed seeds, the seeds pre-treated with H2SO4
showed the higher mean germination rates
(0.26 and 0.27 per day for distilled water and
KNO3 treatments, respectively) as compared
to the other seed pre-treatments (Fig. 2). The
improving effect of H2SO4 on dormant and hard
seed performance has been documented by other
workers (Hermansen et al. 2000, Nadjafi et
al. 2006, Rahnama-Ghahfarokhi and TavakolAfshari 2007). In most cases, the seeds treated
with distilled water during the experiment
performed better than those treated with KNO3
solution (Figs 1 and 2). This is in contrast with
the findings of Bewley and Black (1994) who
reported that KNO3 raises the ambient oxygen
levels by making less oxygen available for citric
acid cycle, thus improving the seed performance.
According to Taylorson and McWhorter (1969),
KNO3 increased Johnson grass germination by
12–17% in the presence of light. However, our
experiment was carried out in dark conditions
and this may be a reason for the lower efficiency
of KNO3.
This study revealed that both H2SO4 pretreatment and glume removal were efficient
methods for overcoming the Johnsongrass seed
hardness under laboratory conditions. Moreover,
the use of distilled water for seed treatment during
the experiment had a higher improving effect on
Johnsongrass seed performance as compared
with KNO3 solution. In general, these findings
could be helpful to workers who study different
post-emergence Johnsongass control methods in
laboratory and greenhouse conditions, where the
germination and seedling establishment of this
hard-seed weed are necessary.
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