Exserohilum monoceras 1125 host range

Abstract

A total of 54 plant species, including varieties and breeding lines from 14 families and 33 genera were screened against Exserohilum monoceras, a fungal pathogen with potential as biocontrol agent for barnyard grass, Echinochloa crus-galli. The selected plant species were treated with spore suspensions at about 2.5 x 107 spores/ml concentration in glasshouse conditions supplemented with 24 h dew. The ability of the fungus to infect the plants was evaluated by disease incidence and disease severity which translated into disease index (DI). The disease index of Echinochloa crus-galli var. crus-galli,E. crus-gallivar. formosensis and E. stagnina were 4 (dead) while those for E. colona and E. oryzicola were 3 (severely damage). Among the economic plants tested, only Zea mays was infected with a disease index of 2 (tolerant). Young Imperata cylindrica was dead (DI = 4), however the older plant showed hypersensitive reaction (DI = 2). Other plants that were infected were Cymbopogon sp. (DI = 1), Paspalum sp. (DI = 3) and Rhynchelytrum repen (DI = 3). Exserohilum monoceras did not infect selected varieties of rice in Malaysia, such as MRQ 50, MRQ 74, MR 219, MR 220 and MR 84. Vegetables and medicinal plants used in the test were also not infected.

Full text

267
S. Tosiah, J. Kadir, M. Sariah, A.S. Juraimi, N.P. Lo and S. Soetikno
J. Trop. Agric. and Fd. Sc. 38(2)(2010): 267– 274
Host range of Exserohilum monoceras 1125, a potential biological
control agent for Echinochloa spp.
(Pelbagai perumah untuk Exserohilum monoceras 1125, agen kawalan biologi yang
berpotensi untuk kawalan Echinochloa spp.)
S. Tosiah*, J. Kadir**, M. Sariah**, A.S. Juraimi**, N.P. Lo* and S. Soetikno***
Keywords: Exserohilum monoceras, host range, Echinochloa spp., bioherbicide
Abstract
A total of 54 plant species, including varieties and breeding lines from 14
families and 33 genera were screened against Exserohilum monoceras, a fungal
pathogen with potential as biocontrol agent for barnyard grass, Echinochloa
crus-galli. The selected plant species were treated with spore suspensions at
about 2.5 x 107 spores/ml concentration in glasshouse conditions supplemented
with 24 h dew. The ability of the fungus to infect the plants was evaluated
by disease incidence and disease severity which translated into disease index
(DI). The disease index of Echinochloa crus-galli var. crus-galli, E. crus-galli
var. formosensis and E. stagnina were 4 (dead) while those for E. colona and
E. oryzicola were 3 (severely damage). Among the economic plants tested, only
Zea mays was infected with a disease index of 2 (tolerant). Young Imperata
cylindrica was dead (DI = 4), however the older plant showed hypersensitive
reaction (DI = 2). Other plants that were infected were Cymbopogon sp.
(DI = 1), Paspalum sp. (DI = 3) and Rhynchelytrum repen (DI = 3). Exserohilum
monoceras did not infect selected varieties of rice in Malaysia, such as MRQ 50,
MRQ 74, MR 219, MR 220 and MR 84. Vegetables and medicinal plants used in
the test were also not infected.
*Strategic Resources Research Centre, MARDI Headquarters, Serdang, P.O. Box 12301, 50774 Kuala Lumpur,
Malaysia
**Plant Protection Department, Faculty of Agriculture, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor,
Malaysia
***CAB International, MARDI Headquarters, Serdang, P.O. Box 12301, 50774 Kuala Lumpur, Malaysia
Authors’ full names: Tosiah Sadi, Jugah Kadir, Sariah Meon, Abdul Shukor Juraimi, Lo Nyok Piang and
Soetikno Sastroutomo
E-mail: tosiah@mardi.gov.my
©Malaysian Agricultural Research and Development Institute 2010
Introduction
The genus Echinochloa composed of about
53 species (Micheal 1973). The most
cosmopolitan and economically important
member of the genus is the taxon of E. crus-
galli complex commonly known as barnyard
grass. Azmi (1998) reported that there are
ve important species of Echinochloa in
rice granary areas in Peninsular Malaysia
namely E. crus-galli (E. crus-galli var. crus-
galli and E. crus-galli var. formosensis),
E. oryzicola, E. colona, E. stagnina and
E. picta. Echinochloa colona and E. stagnina
are perennials while others are annual
species. Echinochloa crus-galli complex,
locally known as rumput sambau, consist of
E. crus-galli var. crus-galli and E. crus-galli
var. formosensis. Echinochloa crus-galli var.
crus-galli, E. crus-galli var. formosensis and
E. oryzicola closely resemble each other,

268
Host range of Echinochloa
thus they were grouped under the E. crus-
galli complex. The signicant characteristic
differentiating the varieties are short awn
or awnless with open spikelets (E. crus-
galli var. formosensis) and long awn with
closed or compact panicles (E. crus-galli
var. crus-galli) (Azmi 1998). Echinochloa
oryzicola closely resemble E. crus-galli var
formosensis but it has bigger seeds. Tasrif et
al. (2004) reported that there are 10 ecotypes
of E. crus-galli complex in Malaysia and
they vary genetically.
In Peninsular Malaysia, E. crus-galli
complex is found in all rice granaries,
namely Muda (Kedah), Kemubu (Kelantan),
Kerian (Perak), Projek Barat Laut
(Selangor), Seberang Perak and Sungai
Manik (Perak), Besut (Terengganu),
Seberang Perai (Pulau Pinang) and Kemasin
Semarak (Kelantan). Azmi (1992) reported
that only 10 plants of E. crus-galli per m²
can cause yield reduction of approximately
18.7% of rice (representing 1 t/ha).
Research on biological control agents
against E. crus-galli have been intensied in
Asia since early 1990s. Among the fungal
pathogens that have been suggested as
biocontrol agents were Cochliobolus lunatus
(Tsukamoto et al. 1997) and Exserohilum
monoceras (Septosphaeria monoceras)
(Zhang et al.1996). Tsukamoto et al. (1997)
reported an approximate 80% reduction in
dry matter was achieved when different
botanical varieties (subspecies) of E. crus-
galli was treated with virulent isolates of
E. monoceras and C. lunatus.
Besides E. monoceras, Bipolaris
sacchari, Curvularia geniculata, C. lunata
var. aeria, Dactylaria dimorhospora and
Exserohilum oryzae were also isolated from
E. crus-galli in the Philippines (Zhang
et al. 1996). In Korea, Colletotrichum
graminocola showed strong pathogenicity in
a wide range of growth stages of E. crus-
galli var. praticola and E. crus-galli var.
caudata (Yang et al. 2000). Exserohilum
monoceras was also reported as potential
bioherbicide and not pathogenic on
planted rice varieties in China (Huang et
al. 2001) and in Vietnam (Khanh 2002).
In Malaysia, E. longirostarum has good
control on Rottboellia cochichinensis (itch
grass) (Kadir et al. 2003) and E. crus-galli
(Ng 2007).
Host range evaluation is an important
step in the determination of the safety of
fungal pathogens considered for use as
bioherbicides. The pathogens selected for
biocontrol use should not infect crop species
and other non-target plants grown in the area
where the pathogens intended to be used to
control target weeds.
Surveys carried out in 2004–2005 in
Malaysian granaries (Tosiah et al. 2009)
found that E. monoceras was a promising
fungal biocontrol agent isolated from
barnyard grass. However, reports on
host range of E. monoceras are limited.
In Malaysia particularly, no report of
E. monoceras associated with plant disease
has been published. Thus, the objective of
this study was to determine the host range of
E. monoceras isolate 1125, the indigenous
fungus isolated from E. crus-galli as part of
its development as bioherbicide.
Materials and methods
Inoculum production
Small pieces of E. monoceras mycelium
from working culture kept in MARDI were
aseptically transferred to petri dishes (9 cm
diameter) containing fresh Potato Dextrose
Agar (PDA). The plates were sealed with
paralm and kept in dark incubator at
28 ± 2 °C for 7 days. Agar plugs (5 mm
diameter) from the margin of the colonies
were used as seed inoculum. V8 juice
agar (200 ml V8 juice Campbell’s ®,
18 g of granulated agar and add up to 1
litre using distilled water) was used as a
medium for conidia production. The fungus
was incubated at 28 ± 2 °C light/dark
photoperiod. Conidia were harvested 14 days
after the incubation by ooding the plates
with 10 ml distilled water and scraping
the surface with plastic spatula. Resulting
suspension was adjusted to the preferred
concentration using a hemacytometer.

269
S. Tosiah, J. Kadir, M. Sariah, A.S. Juraimi, N.P. Lo and S. Soetikno
chosen for the host range test included
several grasses that are closely related to
Echinochloa (Family Poaceae), various
modern rice varieties developed by MARDI,
other problematic weeds, crop plant of
economic importance in Malaysia and crops
reported as host to Bipolaris, Curvularia,
Dreschlera and Exserohilum (Table 1).
A total of 54 plant species, including
varieties and breeding lines from 14 families
and 33 genera were evaluated. The number
of plants and development stage tested
varied depending on the growth habit of the
species. Each pot or polybag was planted
with one to ve plants, depending on the
plant type. Basically, the plant species were
evaluated based on their physiological age at
4 to 6-leaf stage. Echinochloa crus-galli was
included as a control in each batch of plants
tested. All plant species were sprayed with
20 ml spore suspensions at 107 spores/ml
concentration and covered with plastic bags
to maintain humidity and left for 24 h.
Target host inoculation
In this experiment, different species of
Echinochloa at 4-leaf stage were inoculated
with spore suspension at about 2.5 x
107 spores/ml concentrations. The spore
suspensions were prepared as simple
emulsion by adding 1% corn oil (Lam Soon
Edible Oil Sdn. Bhd.) and 0.2% of maxi
green (Saleswide Sdn. Bhd.), a commercial
non-ionic surfactant and sticker. The 20 ml
of spore suspensions was sprayed onto the
plant using hand sprayer. The sprayer nozzle
was held at about 30 cm away from the
target plant to form an even spreading and
sprayed until run off. Treatments were done
in three replications. The plants were placed
in the glasshouse at a temperature range of
28–38 ± 2 °C and covered with plastic bags
over night to maintain humidity.
Host range determination
Host range evaluation was done based on
Wapshere (1974). The species that were
Table 1. Reaction of Exserohilum monoceras 1125 to the plant tested
Family/order Species Variety Disease Disease
incidence index
A). Plants taxonomically related to Echinochloa species
Poaceae
Panicoideae Echinochloa crus-galli var formosensis 100 4
Echinochloa crus-gall var crus-galli 100 4
Echinochloa orizycola 100 3
Echinochloa colona 100 3
Echinochloa stagnina 100 4
Zea mays Suwan 1, 100 2
Mas madu 100 2
Digitaria sp. 100 0
Paspalum sp. 100 3
Imperata cylindrica 100 4
Other poaceae Cynodon sp. 0 0
(Turf grasses) Azonopus sp. 0 0
Zoysia zenith sp. 0 0
Axonopus afnis 0 0
Axonopus compressus 0 0
Other poaceae Brachiaria sp. 100 2
Rhynchelytrum repen 100 3
Cyperaceae Cyperus sp. 0 0
(cont.)

270
Host range of Echinochloa
Table 1. (cont.)
Family/order Species Variety Disease Disease
incidence index
Oryzoideae Oryza sativa L. (modern rice MR 185 0 0
varieties of Malaysia) MR 84 0 0
MRQ 50 0 0
MRQ 74 0 0
MR 220 0 0
MR 219 0 0
MR 159 0 0
MR 167 0 0
MR 81 0 0
B). Plants reportedly infected by Bipolaris, Curvularia, Dreshslera, Exserohilum and
Helminthosporium and their teleomorphs in Malaysia
Poaceae Cymbopogon sp. 100 1
Zingiberaceae Kaemperia galanga 0 0
C). Vegetable
Brassicaceae Brassica oleracea Cabbage 0 0
(KK-Cross)
Cauliower 0 0
Broccolli 0 0
Brassica juncea Unknown 0 0
Brassica chinensis Unknown 0 0
Lactuca sativa Unknown 0 0
Cucurbitacae Cucurmis sativa Unknown 0 0
Luffa acutangular Unknown 0 0
Benincasa hispida Unknown 0 0
Fabaceae Vigna sp. MKP 5 0 0
Malvaceace Abelmoschus esculantus Unknown 0 0
(L.) Moench
Solanaceae Capsicum annum Long chilli 0 0
(MC 12)
Bell pepper 0 0
(Bluestar)
Solanum melongena MT11 0 0
Lycopersicum esculentum Unknown 0 0
Amaranthaceae Amaranthus viridis Unknown 0 0
Convolvulaceae Ipomea aquatica Unknown 0 0
D). Potentially economic medicinal plants
Acanthaceae Andrographis sp. 0 0
Acanthaceae Asystasia intrusa 0 0
Lamiaceae Pogostemon sp. 0 0
Lamiaceae Orthosiphon sp. 0 0
Mackinlayaceae Centella asiatica 0 0
Phyllanthaceae Phyllanthus naruri 0 0

271
S. Tosiah, J. Kadir, M. Sariah, A.S. Juraimi, N.P. Lo and S. Soetikno
Experimental design
All experiments were done in complete
randomized design with three replications
and repeated twice. Each replication consist
of different plant that being tested with
E. crus-galli as control. All experiments
were done in a glasshouse structure in
MARDI Serdang with temperature range
from 26 °C (night) to 38 °C (noon).
Disease assessment
Disease incidence was recorded as the
percentage of plants showing visible leaf
symptoms. Disease index (DI) was used to
evaluate the host range of the fungi. It was
calculated using the equation below and the
value of disease index was rounded to the
whole number, which consist of 5 classes;
0 = immune, 1 = resistant, 2 = tolerant, 3 =
severely damaged and 4 = dead.
DI (disease index)
= ∑ (severity rating x number of
plants in that rating)
Total number of plants
Results and discussion
Effect on target host
All the Echinochloa spp. were infected
by E. monoceras isolate 1125 but
with different disease index (DI) value.
Echinochloa crus-galli var crus-galli and
E. crus-galli var formosensis had DI = 4,
while E. orizycola and E. colona had DI = 3
(Table 1A).
Host range determination
All vegetable species and modern rice
varieties tested were immune to the fungus
E. monoceras 1125 (Table 1A and 1C). No
symptom of the disease developed when
the fungus was inoculated to these plants.
However, the fungus caused disease on Zea
mays, Imperata cylindrica, Rhynchelytrum
repens, Brachiaria sp. and Paspalum
sp.. The disease index of Zea mays and
Brachiaria was 2 and considered as tolerant
to the fungus infection. The disease on Zea
mays was observed mostly on the lower
leaves and the plant recovered after the
development of new shoots (Table 1A).
Disease index of Paspalum sp. and
Rhynchelytrum repens was 3 and the plants
were severely damage. Disease index of 4
was shown by Imperata cylindrica and died
after 10 days of inoculation. However, when
the fungus was inoculated on older plant
of I. cylindrica, although all plants were
infected, the disease index was only 2 and
therefore considered to be tolerant to the
disease. All the medicinal plants tested were
immune (Table 1D) to the fungus except
for Cymbopogon (Table 1B) which showed
tolerant (DI = 2) to the fungus. Cymbopogon
also has been reported as the host of
Curvularia sp. (Sivanesan 1987; Tosiah et
al. 2004).
Zhang et al. (1996) found that
E. monoceras caused large necrotic
lesions on E. crus-galli, E. colona and
E. glabrescens but was not pathogenic to
rice. They described the disease symptoms
as necrotic eck within 24 h and chlorosis
and a diffuse, general, water-soaking
reaction followed by rapid collapse and
necrosis of the infected tissues 2 days
after treatment (DAT). The latter symptom
described was similar to our observations
on E. crus-galli var. crus-galli and E. crus-
galli var. formosensis, although in this case
the total collapse of the plants was only
observed 6 to 8 DAT which might be due to
the difference of the physiological age of the
plant used in the study, that is 4-leaf stage
compared to 2-leaf stage used by Zhang et
al. (1996). In addition, the plants used in
this study were exposed to the dew for only
16 h.
Although the fungus was isolated
from E. crus-galli var. crus-galli, it can
also infect other Echinochloa spp. such as
E. colona, E. crus-galli var. formosensis,
and E. orizycola. Results showed that both
E. crus-galli var. crus-galli and E. crus-
galli var. formosensis were susceptible to
E. monoceras compared to E. colona and
E. orizycola. Zhang and Watson (1997) also
found that E. crus-galli and E. glabrescens

272
Host range of Echinochloa
were more susceptible compared to
E. colona. According to Azmi (1998),
E. glabrescens is synonym to E. crus-galli
var. formosensis.
The host range studies indicated that
E. monoceras isolate 1125 was safe to all
the rice varieties tested, suggesting that the
rice plant is not a host of E. monoceras.
This study is consistent with ndings by
Gohbara and Yamaguchi (1994), Zhang and
Watson (1997), Huang et al. (2001) and
Khanh (2002). The fungus was also safe to
vegetable crops and medicinal plant tested in
the studies.
Among the grasses tested, effect of
E. monoceras was conned to Imperata
cylindrica and Rhynchelytrum repens.
This is the rst report of I. cylindica
and R. repens as hosts to E. monoceras.
However, studies are needed to determine
the efcacy of the fungus in controlling
I. cylindica and R. repens. Both Zea mays
cultivars tested in the studies, developed
minor symptoms upon inoculation with the
pathogen. However, these were restricted to
the lower leaves and the new shoots were
healthy and grew normally after the lower
leaves senesced. This nding conformed to
Hailmi (2006), who also found that maize
is resistant to E. monoceras. Zhang and
Watson (1997) demonstrated that although
maize was infected by E. monoceras in
the glasshouse, it did not infect the plant
when applied in the eld. The infection
on maize might be due to simulated
condition in the glasshouse which facilitated
optimum condition for infection and disease
development may articially increase the
perceived host range of the organism being
tested.
Conclusion
Exserohilum monoceras isolate 1125 has the
potential to be developed into bioherbicide.
However, in our rice granaries there are
other weeds that also play important roles
in reducing rice yield, such as weedy rice,
Leptochloa chinensis and Monocchoria
vaginalis. Attempts to introduce host specic
biocontrol agents may result in shifting these
weeds to become more dominant. Although
host specicity was an important character
used in selecting a biological control
agent, it is an advantage if the fungus also
attacked L. chinensis sp. and M. vaginalis,
or as an alternative the bioherbicide that
will be developed contains other fungi
with potential to control L. chinensis
sp. and M. vaginalis. However, it must
be remembered that biological control
was introduced to full the sustainable
agriculture concept which is not to totally
eradicate the weeds but to control it below
the threshold level because these weeds can
act as refuge for natural predators.
Acknowledgement
This research was conducted in partial
fullment of the rst author’s doctoral
dissertation. The authors thank Mr S.
Mahendra and Ms Zanariah Zainal Abidin
for their technical assistance. The project
was sponsored by IRPA – 01-03-03-0119
EA001.
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Host range of Echinochloa
Abstrak
Sebanyak 54 spesies tumbuhan, termasuk varieti dan titisan pembaikbakaan
daripada 14 famili dan 33 genera telah disaring terhadap kulat Exserohilum
monoceras yang merupakan kulat patogen yang berpotensi sebagai agen kawalan
biologi rumput sambau (Echinochloa crus-galli). Kajian di dalam rumah
kaca dijalankan dengan semburan kulat pada kepekatan 2.5 x 107 spora/ml
dengan tempoh lembap selama 24 jam. Kebolehan kulat ini untuk menjangkiti
tumbuhan-tumbuhan tersebut dinilai melalui indeks penyakit (IP) yang dicerap
daripada bacaan kejadian penyakit (disease incidence) dan keterukan penyakit
(disease severity). Didapati indeks penyakit (IP) bagi Echinochloa crus-galli var.
crus-galli, E. crus-galli var. formosensis dan E. stagnina ialah 4 (mati), manakala
E. colona dan E. oryzicola ialah 3 (rosak teruk). Bagi tanaman ekonomi
hanya Zea mays yang dijangkiti dengan indeks penyakit 2 (toleran). Imperata
cylindrica yang muda mati (IP = 4), tetapi yang lebih tua menunjukkan reaksi
hipersensitif (IP = 2). Tumbuhan lain yang dijangkiti ialah Cymbopogon sp.
(IP = 1), Paspalum sp. (IP = 3), dan Rhynchelytrum repen (IP = 3). Exserohilum
monoceras tidak menjangkiti varieti terpilih padi Malaysia seperti MRQ 50,
MRQ 74, MR 219, MR 220 dan MR 84. Ia juga tidak menjangkiti sayuran-
sayuran dan tanaman ubatan yang digunakan dalam kajian ini.
Accepted for publication on 23 August 2010