ISSN 0367-6315 (Print) / ISSN 2288-2162 (Online)
Korean J. Soil Sci. Fert. 49(5), 608-613 (2016)
http://dx.doi.org/10.7745/KJSSF.2016.49.5.608
Article
Trap Culture Technique for Propagation of Arbuscular Mycorrhizal Fungi using
Different Host Plants
Gopal Selvakumar1,2, Kiyoon Kim1, Denver Walitang1, Mak Chanratana1, Yeongyeong Kang1,
Bongnam Chung2, and Tongmin Sa1*
1
Department of Environmental and Biological Chemistry, Chungbuk National University, Cheongju, Chungbuk 26844, Republic of Korea
2
Horticultural and Herbal Crop Environment Division, National Institute of Horticultural and Herbal Science,
Rural Development Administration, Wanju 55365, Republic of Korea
(Received: August 23 2016, Revised: September 17 2016, Accepted: October 27 2016)
Arbuscular mycorrhizal fungi (AMF) spore propagation and long term maintenance is still a complicated
technique for farmers. The use of AMF for their ability to promote plant growth and protect plants against
pathogen attack and environmental stresses demands AMF propagation for large scale application. This study
aimed to propagate AMF spores by trap culture technique and assess their ability to propagate with different
host plants in a continuous plant cycle. Mycorrhizal inoculation by trap culture in maize resulted in longer
shoots and roots than sudangrass plants. Increase in dry weight with higher percentage also was observed for
maize plants. After first and second plant cycle, maize plants had the higher percentage of mycorrhizal
response in terms of colonization and arbuscules than sudangrass. Maximum in spore count also achieved in
the pots of maize plants. The results show that maize plant is more suitable host plant for AMF spore
propagation and trap culture technique can be used effectively to maintain the AMF culture for long time.
Key words: Arbuscular mycorrhizal fungi, Trap culture, Maize, Sudangrass, Spore propagation
Mycorrhizal response to different host plants after two plant cycle. (A) and (D) AMF spore count; (B) and (E) mycorrhizal
colonization; (C) and (F) arbuscules abundance.
1)
*Corresponding author: Phone: +82432612561, Fax: +82432715921, E-mail: tomsa@chungbuk.ac.kr
Acknowledgement: This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF)
funded by the Ministry of Education, Science and Technology (2015R1A2A1A05001885) and “Cooperative Research Program for Agriculture
Science & Technology Development (Project No. PJ01018001)” Rural Development Administration, Republic of Korea.
§
Gopal Selvakumar, Kiyoon Kim, Denver Walitang, Mak Chanratana, Yeongyeong Kang, Bongnam Chung, and Tongmin Sa
Introduction
Fertilizers are instant nutrient suppliers used to improve
plant growth in agriculture. Most of the countries utilize
chemical fertilizers and only few countries practice organic
farming. Among the organic fertilizers, bio-fertilizers received
a great interest among the farmers as it is ecofriendly.
Arbuscular mycorrhizal fungi (AMF) are wide spread soilborne fungi and form symbiotic and mutualistic interaction
with most of the plant species (Smith and Read 2008). AMF
has been shown to improve plant growth even at adverse
environmental conditions against biotic and abiotic stresses.
The use of AMF is increasing in agriculture, forestry and
environmental reclamation, to improve crop yield and soil
health (Johansson et al., 2004). The obligate biotrophic nature
of this fungi limits large scale production in a cost-efficient
way. However, the conventional method like trap culturing
can be a useful tool to propagate this fungi for plant growth
and land reclamation purposes in small scale cost-efficient
way (Guar and Adholeya, 2002).
AMF culture has been obtained through different methods
of propagation technique using different host plants. The
most widely used method is substrate-based, however, the
spores produced through this method are contaminated with
other microbes (Douds et al., 2006). The in vitro culture
method provide pure cultures of AMF propagules, however,
the production of AMF for large scale application is still in its
infancy. Guar and Adholeya (2002) reported that the efficiency
of mycorrhizal propagation varies depending on the host
plant used. In addition, there is no proper procedure for
long-term storage of this propagated AMF. Trejo-Aguilar et
al. (2013) reported that long-term subculturing reduced the
diversity of AMF spores in trap culture when a single host
was used. During continuous propagation cycle, dilution of
this trap culture inoculum may favor the diverse AMF species
than the field (Wang et al., 2008). A trap culture contains
609
spores, hyphae and colonized root bits as an inoculum and can
promote diverse AMF species. In contrast, Schalamuk and
Cabello (2010) reported that trap culture inoculum favored
higher propagation of Glomeraceae family while lower
number of spores was obtained from other families. Therefore,
we replace it to hypothesize that suitable host plants with
periodic rotation may reduce the loss of AMF diversity in trap
culture.
The present study aimed to assess the efficiency of trap
culture inoculum on plant growth and the effectiveness of
AMF propagation by trap culture using different host plants.
Materials and Methods
Study area and soil sample collection Saemangeum
is one of the world’s largest reclamation sites adding about
400 km2 to South Korea’s total geographical area. A total of
six rhizosphere soil samples (SS1 –SS6) were collected from
different plant species of Saemangeum reclamation land to
obtain different AMF isolates. Each rhizosphere soil sample
was collected in sterilized polyvinyl chloride bags along with
roots and was transported immediately to the laboratory in
icebox and kept at 4°C until use. Initial spore count of the
samples were assessed using wet sieving and decanting
method as described in Daniels and Skipper (1982) followed
by sucrose centrifugation method as described in Utobo et al.
(2011).
Pot preparation and application of fertilizer and compost
Soil samples were collected from rice field and were
consecutively sterilized for five days at 121°C for 15 min.
The sterilized soil was placed in 4 kg pots. Urea (nitrogen
content 46%), fused superphosphate (phosphate content 20%)
and potassium chloride (potassium content 60%) were used as
N, P, K fertilizer. Fertilizer application rate was determined
based on the recommended basal application rate for maize
Table 1. Inocula used in this study and initial spore count of the cultures.
Inoculum
Initial spore count
Maize
---- (per 100 g) ----
Sorghum-sudangrass
---------- (Inoculum g) ----------
CON
0
0
0
REF
50.67±2.03
250
250
SS1
32.33±2.73
250
250
SS2
19.67±2.19
250
250
SS3
17.33±0.88
250
250
SS4
12.33±0.88
250
250
SS5
66.67±5.78
250
250
SS6
32.00±2.08
250
250
CON – control, REF – reference spore (Claroideoglomus etunicatum), SS1 to SS6 – trap cultures collected from the rhizosphere of different
plant species in Saemangeum reclaimed land.
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Trap Culture Technique for Propagation of Arbuscular Mycorrhizal Fungi using Different Host Plants
(N : P : K = 17.4 : 3.0 : 6.9, kg 10 a-1) and sorghum- sudangrass
hybrid (N : P : K = 20.0 : 15.0 : 15.0, kg 10 a-1). Compost
(60% chicken dung, 20% bark and 20% saw dust) was added
-1
at 20.0 g kg of soil. Fertilizer and compost were mixed with
the soil before pot filling.
Greenhouse experiment and treatments Soil samples
collected from Saemangeum reclaimed land were used as
inoculants. The reference spore, Claroideoglomus etunicatum
was obtained from the Forest department, Chungbuk National
University and used as a positive control for mycorrhizal
culture. The culture was maintained in 5 kg sterilized arable
soil with sorghum-sudangrass hybrid as a host plant. The
inoculum and initial spore count were given in Table 1. Two
hundred fifty grams of Saemangeum rhizosphere soil sample
was used as inoculum in each 4 kg pot. Inoculants contain
active propagules of AMF spores, hyphae and colonized root
pits. Three to five day old seedlings of maize and sorghumsudangrass were used as host plants. Maize seeds were
surface sterilized by immersing in 70% ethanol for 1 min and
6% NaOCl for 5 min, followed by thorough rinsing with
sterile distilled water for 7-10 times. Sorghum-sudangrass
hybrid seeds were surface sterilized by immersing in 70%
ethanol for 2 min and 1% NaOCl for 3 min and thoroughly
rinsed with sterile distilled water for 7-10 times. Surface
sterilized maize and sorghum-sudangrass hybrid seeds were
sown in seedling trays and allowed to germinate for 5 days.
The germinated seedlings were transplanted to pots containing
trap culture inoculum. After 120 days, the plants were
harvested and the pot contents were mixed thoroughly. Soil
and root samples were collected and analyzed for spore count
and mycorrhizal colonization. New seedlings were planted in
the respective pots and maintained again for 120 days. Soil
and root samples were collected again for spore count and
mycorrhizal colonization analysis. During the experiment,
each pot received 100 ml of modified Hoagland’s nutrient
solution (pH 6.2) every week.
Root staining and colonization measurement
The
roots of maize and sorghum-sudangrass were harvested after
120 days of planting. The plant roots were washed with tab
water and cut into 1 cm fragments. Five ml of 10% (w/v)
KOH was added to the fragments in test tubes and incubated
at 90°C for 15 min. After incubation, KOH was decanted;
washed with tap water and 2% HCl was added and again
incubated at room temperature for 10 min to soften the root.
HCl was decanted and 5 ml of staining solution (0.05% of
trypan blue in lactoglycerol) was added and incubated at
90°C for 10 min. Staining solution was decanted and washed
with tap water then the root fragments were destained by the
addition of 5 ml of lactoglycerol (Phillips and Hayman, 1970).
Stained root fragments were arranged in glass slides and
observed under the microscope for the presence of hyphae,
vesicles and arbuscules. Scoring was done based on the
intensity of colonization (0 to 5) and based on the arbuscule
intensity (A0 to A3) as described by Trouvelot et al. (1986). A
total of 30 root fragments were observed for each treatment.
The intensity of the mycorrhizal root colonization was
estimated as the amount of cortex cell that was colonized by
mycorrhiza relative to the whole root system (M%) and to the
root fragments (m%). Abundance of arbuscule was estimated
as the arbuscule richness in the whole root system (A%) and
in the mycorrhizal parts of the root fragments (a%). The
Mycocalc software was used to determine the M%, m%, A%
and a%.
Plant growth parameters
After 120 days of plant
growth, plant shoot length, root length and fresh weight were
measured. After drying the samples in oven for 72 h at 70°C,
the dry weight was measured for maize and sorghum-sudangrass
plants.
Results and Discussion
Arbuscular mycorrhizal fungi is well studied for their
ability to improve plant growth. However, the propagation
and maintenance of AMF culture is critical due to their
obligate biotrophic nature. Trap culture method of AMF
spore development is widely used to obtain a mixed inoculum.
Although the trap culture method is comparable to other
method, the culture from this method is not pure. Freshly
collected soil samples can be maintained in this method to
minimize the loss or viability of the AMF spores (Brundrett et
al., 1999). Depending on the dominant AMF species and host
plant involved, the propagation of AMF varies in trap culture.
Arbuscular mycorrhizal fungal inoculation has been shown
to increase the growth of most crop plant species. In addition
to plant growth, AMF also help plants to withstand various
environmental stress including salinity (Abdel Latef and
Chaoxing 2011; Navarro et al., 2012), drought (Asrar and
Elhindi 2011) and protects plant from pathogen attack (Nair
et al., 2014). Hajiboland et al. (2010) reported that the
mycorrhizal inoculation increased tomato plant growth at 5
-1
dS m salinity. Wu et al. (2010) reported that orange plants
had low accumulation of reactive oxygen species content than
non-mycorrhizal plants under salinity. Mycorrhizal inoculation
reduced salinity effect and increased the plant growth of
pepper (Kaya et al., 2009) and citrus (Wu and Zou 2009).
However, propagation and storage of this obligate biotroph is
still unachievable by all farmers.
Effect of mycorrhizal inoculation on the growth
parameters
The mycorrhizal inoculation collected from
Saemangeum reclaimed land had more than one AMF species
Gopal Selvakumar, Kiyoon Kim, Denver Walitang, Mak Chanratana, Yeongyeong Kang, Bongnam Chung, and Tongmin Sa
as inoculum. Depending upon the plant rhizosphere, the
amount of individual species varied. The trap culture
mycorrhizal inoculum had an overall positive effect on plant
growth in both maize and sudangrass. The percentage
increment in height was higher in maize plants with an
average of 23% (Fig. 1A and D) than in sorghum sudangrass
with 4% height increment. Mycorrhizal maize plants had
longer roots by an average of 22%, whereas, mycorrhizal
sudangrass root length increment was by an average of 26%
for all inoculants (Fig. 1B and E). This result is similar with
the previous report by Lee et al. (2015) that mycorrhizal
inoculation increased maize shoot and root length compared
to non-mycorrhizal plants.
Mycorrhizal inoculum increased the shoot dry weight of
maize and sudangrass. The average increase in dry weight for
maize plants was 36%, whereas in sudangrass was 40% (Fig.
1C and F). The highest dry weight of maize plants was
observed for the plants inoculated with SS3 inoculum,
whereas sudangrass inoculated with SS4 had the highest dry
weight. The increase in dry weight with mycorrhizal inoculation
also reported by Wu and Zou (2009). Abdel-Fattah and Asrar
(2012) reported that the mycorrhizal inoculation increased
dry weight of wheat under salinity.
611
Mycorrhizal colonization and spore production in
different hosts Mass production of mycorrhizal inoculum
is vital for the application on a large scale. Several different
methods were employed to propagate AMF such as single or
monosporic (Fracchia et al., 2001; Selvakumar et al., 2016),
hairy root (de Souza and Declerck 2003), solid substrate
(Millner and Kitt 1992; Douds et al., 2010), aeroponic
(Mohammad et al., 2000), and hydroponic (Tajini et al.,
2009). However, storing the propagated AMF spore requires
technical skills and preliminary knowledge, thus making it
difficult for farmers. One of the common practices to
maintain the propagated spores is trap culture method. The
use of single host for several plant cycles reduce the diversity
of AMF spores (Trejo-Aguilar et al., 2013), however, plant
rotation from C3 to C4 or vice versa may promote diverse
AMF species (INVAM – International Culture Collection of
(Vesicular) Arbuscular Mycorrhizal fungi). In the present
study, we used two different host plants which were commonly
used for AMF propagation.
Mycorrhizal inoculation increased colonization in maize
and sudangrass plants. Spore production increased after the
nd
2 cycle of plants in maize and sudangrass (Fig. 2A and D).
After the first plant cycle, none of the trap culture showed
higher spore count than reference spores. After the second
Fig. 1. AMF inoculation effect on maize and sorghum-sudangrass plant growth. (A) maize plant height; (B) maize root length; (C)
maize shoot dry weight; (D) sorghum-sudangrass plant height; (E) sorghum-sudangrass root length; (f) sorghum-sudangrass shoot
dry weight.
612
Trap Culture Technique for Propagation of Arbuscular Mycorrhizal Fungi using Different Host Plants
Fig. 2. Mycorrhizal response to different host plants after two plant cycles. (A) and (D) AMF spore count; (B) and (E) mycorrhizal
colonization; (C) and (F) arbuscules abundance after first and second plant cycle, respectively.
plant cycle, only trap culture SS3 had higher spore count then
reference spores. Initial spore counts were same for all
st
treatments, however, the 1 cycle of propagation had lower
count than reference AMF, which resulted in the lower spore
nd
inoculation of the 2 plant cycle. However, higher propagated
spores were observed in maize hosts than those in sudangrass
nd
after the 2 plant cycle. In our previous study (Lee et al.,
2015), we found that maize plant favored spore propagation
when used with the same reference spores. After the first and
second plant cycles, maize plants showed higher colonization
than sudangrass (Fig. 2B and E). The same trend was observed
st
for arbuscules abundance. After 120 days or the 1 plant cycle,
only two trap cultures had higher arbuscules abundance than
nd
that of reference spores, however, after the 2 plant cycle,
five of the trap cultures had higher arbuscules abundance than
reference spores (Fig. 2C and F).
Conclusions
In summary, mycorrhizal trap cultures had more positive
effect on maize plants than sudangrass. Maize plants showed
higher percentage of growth parameters than sudangrass in
response to mycorrhizal inoculation. After multiple plant
cycles, AMF propagation became active in trap culture method
in terms of colonization. The efficiency of mycorrhizal
propagation and mycorrhizal interaction with host should be
checked after several plant cycles to understand the biology
of AMF and to store for a long time. Further molecular
identification of propagated AMF spores may help to
understand compatibility of spores for trap culture technique.
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