Azoxystrobin Activity on Rhizoctonia solani and its Efficacy ... - Iresa

Short Communication
<strong>Azoxystrobin</strong> <strong>Activity</strong> on Rhizoctonia solani and its Efficacy
Against Rice Sheath Blight
Subramanian Sundravadana and Devadason Alice, Department of Plant Pathology,
Sasthan Kuttalam, Department of Agricultural Entomology, and Ramasami
Samiyappan, Center for Plant Protection Studies; Tamil Nadu Agriculture University,
Coimbatore - 641 003, India
_____________________________________________________________________________
ABSTRACT
Sundravadana, S., Alice, D., Kuttalam, S., and Samiyappan, R. 2007. <strong>Azoxystrobin</strong> activity on
Rhizoctonia solani and its efficacy against rice sheath blight. Tunisian Journal of Plant Protection
2: 79-84.
Sheath blight, caused by Rhizoctonia solani is one of the major diseases affecting rice crop. We
investigated the effect of azoxystrobin on R. solani growth (in vitro) and its efficacy against rice sheath
blight, under field conditions. The results revealed that azoxystrobin at 1, 2, and 4 ppm, completely
inhibited mycelial growth of R. solani. Field study showed that foliar spray of azoxystrobin at 125, 250,
and 500 g/ha significantly suppressed (> 64%) the development of sheath blight and enhanced yield level
(> 60%). For controlling sheath blight disease, the optimum rate of azoxystrobin was 125 g/ha. Our
results showed also that there was no residue in rice matrices at harvest time and no phytotoxicity at the
highest concentration of azoxystrobin (500 g/ha).
Key words: <strong>Azoxystrobin</strong>, chemical control, mycelial growth, residue, Rhizoctonia solani, rice, sheath
blight
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Sheath blight is the most damaging
disease of rice. It has the potential to
cause severe economic loss. Heavily
infected plants produced poorly filled
grains (9). The disease is caused by
Rhizoctonia solani. Under favorable
conditions, infected plants build up a huge
population of fungal sclerotia in the soil
and rice cropping becomes uneconomic.
Fungicides are commonly used in fields
where sheath blight is a limiting
Corresponding author: S. sundravadana
sundravadana@rediffmail.com
Accepted for publication 29 November 2007
production factor. The strobilurin
fungicides were introduced recently
against a broad range of pathogens
(Phytophthora capsici, Alternaria
alternata, Ascochyta rabiei, Puccinia
hemerocallidis and Phomopsis sp.) (11, 1, 3,
6, 4). These fungicides reduced disease
development and subsequent inoculum
production and increased yield. The
objectives of this study were to evaluate in
vitro activity of azoxystrobin against
mycelial growth of R. solani, its efficacy
on sheath blight incidence under field
conditions, and its harvest time residues.
R. solani was isolated from infected
rice sheath. Then, the isolate was incubated
on potato dextrose agar (PDA) medium at 28
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Vol. 2, No. 2, 2007

± 2°C. The fungicide used in the
experiments is a concentrate suspension of
<strong>Azoxystrobin</strong> (Amistar).
A 6 mm diameter agar disk from the
margin of an actively growing culture of R.
solani was incubated in Petri dishes
containing PDA amended with
azoxystrobin at concentrations of 0, 0.25,
0.5, 1, 2, and 4 ppm at 28 ± 2°C, 70% RH
for 3 days. Inhibition of the radial growth
was expressed in percentage, as indicated
in the following fomula: M i = (M c -M t ) / M c
X 100, with M i = Percent of mycelial
growth inhibition, M c = Control colony
diameter, and M t = Colony diameter in
medium amended with azoxystrobin.
Sclerotia of 7 day-culture of R. solani were
dipped in 100 ml beaker, containing
different concentrations (0, 0.25, 0.5, 1, 2,
and 4 ppm) of azoxystrobin in an aqueous
solution, then seeded separately at the
center of each Petri plate containing 2%
agar and incubated at 28 ± 2°C, 70% RH.
Radial growth of mycelia was measured 5
days later.
Field experiment was laid out with
rice (ADT43) under randomized block
design, with three replications in 5m x 4m
plots. The efficacy of azoxystrobin at six
concentrations (0, 31.25, 62.50, 125, 250
and 500 g/ha) was evaluated and compared
to carbendazim (500 g/ha). Three sprays
were applied, since the initial appearance
of sheath blight and following a 15 day
interval. Sheath blight incidence was
evaluated with the Relative Lesion Height
(RLH) (8). Therefore, Percent Disease
Index (PDI) was calculated as indicated
below (12). The phytotoxic effect of
azoxystrobin was recorded on plants after
each spray in the field trials. The grain yield
was recorded from individual treatment
and expressed in per hectare, as indicated
below:
RLH (%) =
Lesion height (cm)
Plant height (cm)
x 100
PDI =
Sum of numerical rating
Total number of plants observed
x
Maximum disease grade
100
At harvest time, azoxystrobin residues
in rice matrices (grain, straw, husk and
bran) were determined using high
performance liquid chromatography
(HPLC). The rice matrices were extracted
with acetonitrile: water (90:10 v/v) and
partitioned with an equivalent volume (100
ml) of dichloromethane plus ½ equivalent
volume of 5% NaCl solution in a
separating funnel for about 1 min. The
sample extract was cleaned up with a
cartridge (Florisil column clean up), the
cartridge was conditioned with 5 ml of
hexane: dichloromethane (50:50 v/v)
before sample loading (250 ml) and
washing with 5 ml of dichloromethane and
ethyl acetate (90:10 v/v). <strong>Azoxystrobin</strong>
was eluted from the cartridge using 5 ml of
dichloromethane and ethyl acetate (70:30
v/v). The elute was evaporated (on a rotary
evaporator at 40°C) to near dryness and
redissolved the residue in a 10 ml of
acetonitrile and an aliquot (20 µl) was
injected into the HPLC. <strong>Azoxystrobin</strong> was
separated on a Lichro sphere ® 60-RP
column using a mobile phase of
acetonitrile: water (80:20 v/v) at a flow
rate of 1 ml/min and at a wavelength of
255 ηm. A recovery assay was carried out
using rice matrices plus 0.05, 0.1 or 0.2
ppm of azoxystrobin.
<strong>Azoxystrobin</strong> at three concentrations
(1, 2 and 4 ppm) effectively inhibited in
vitro mycelial growth of R. solani.
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Vol. 2, No. 2, 2007

Whereas, at 0.25 and 0.5 ppm mycelial
growth inhibition over control ranges from
33 to 39% from mycelia and 66 to 81%
from sclerotia (Table 1). Similarly,
azoxystrobin inhibited the spore
germination and mycelial growth of
Alternaria alternata and Cladosporium
macrocarpum on wheat and Ascochyta
rabiei on chickpea (1, 3). Strobilurins have
been shown to inhibit the germination and
pre-penetration growth of several plant
pathogenic fungi (10).
Table 1. Effect of azoxystrobin on the in vitro mycelial growth of R. solani
<strong>Azoxystrobin</strong>
concentration (ppm)
From mycelia
(mm)
Mycelial growth
Inhibition
over control (%)
From
sclerotia
(mm)
Inhibition
over control
(%)
0.25 60.23c 33.08 25.21c 66.00
0.5 54.67b 39.26 13.90b 81.26
1.0 0.00a 100.00 0.00a 100.00
2.0 0.00a 100.00 0.00a 100.00
4.0 0.00a 100.00 0.00a 100.00
Control 90.00d - 84.20d -
* In a column, means followed by a common letter are not significantly different at the 5% level by DMRT
Table 2. Efficacy of azoxystrobin on sheath blight incidence and grain yield of rice
Fungicide dose (g/ha)
<strong>Azoxystrobin</strong> 31.25
<strong>Azoxystrobin</strong> 62.5
<strong>Azoxystrobin</strong> 125
<strong>Azoxystrobin</strong> 250
<strong>Azoxystrobin</strong> 500
Carbendazim 500
2.22a
(8.55)
Percent Diseases Index (%)
Time after transplanting (days)
30 45 60 75
2.20a 14.23d 32.81d 42.21d
(7.95) (22.06) (34.85) (40.44)
2.20a 12.36c 29.40c 38.45c
(7.95) (20.46) (32.71) (38.19)
2.20a 7.82a 15.63a 23.53a
(7.95) (15.98) (22.88) (28.51)
2.20a 7.35a 15.36a 23.12a
(7.95) (15.44) (22.66) (28.21)
2.21a 7.35a 15.00a 23.10a
(7.75) (15.44) (22.35) (28.19)
9.23b
(17.48)
25.35b
(30.36)
33.25b
(34.98)
Disease
reduction over
control (%)
Yield
(q/ha)
8.84 40.42
19.30 45.92
64.98 62.49
69.23 62.52
69.23 62.58
36.20 55.32
2.20a 21.44e 47.71e 67.40e
Control
- 33.21
(8.37) (27.53) (43.68) (55.54)
∗ In a column, means followed by a common letter are not significantly different at the 5% level by
DMRT
* Values in parentheses are arcsine–transformed values
In control plots, sheath blight
incidence increased progressively from
PDI 2.20 (30 days) to PDI 67.40 (75 days).
<strong>Azoxystrobin</strong> at 31.25 and 62.5 g/ha
slightly suppressed the sheath blight
development, whereas at 125, 250 and 500
g/ha, it reduced more than 64% disease
incidence and increased more than 60%
rice yield (Table 2). Since there were no
significant differences among 125, 250 and
500 g/ha rates in term of decline sheath
blight incidence and yield response, we
consider 125 g /ha as the optimum rate for
sheath blight control. Besides, all
azoxystrobin concentrations did not
produce any phytotoxic effect. Therefore,
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Vol. 2, No. 2, 2007

foliar application of azoxystrobin
effectively control the diseases incidence
like the agents of southern stem rot
(Sclerotium rolfsii), head blight (Fusarium
graminearum), and leather rot
(Phytophthora cactorum) (14, 5, 13).
<strong>Azoxystrobin</strong> means recovery from
three fortified (0.05, 0.1 and 0.2 ppm) rice
matrices (grain, straw, husk and bran) were
86.96%, 84.71% and 82.36%, respectively
(Table 3). Therefore, under the specified
conditions no interfering peaks were
observed on the chromatogram of the
samples. The instrument did not detect
residues of azoxystrobin even at the
highest applied concentration. Then, we
can suppose that the residues of
azoxystrobin in rice matrices were below
the limit of detection of the instrument
(0.004 µg/g of sample). Considering the
U.S. Environmental Protection Agency
(EPA), the maximum residue limits
(MRLs) for azoxystrobin in rice grain,
straw and hulls are, respectively 5, 12 and
20 ppm (7). Therefore, it seems that
azoxystrobin in our trials was rapidly
metabolized in rice plants. Chen et al. (2)
obtained a similar result in Chinese
cabbage. Hence, foliar application of
azoxystrobin to control sheath blight is
very unlikely to cause acute and chronic
health risk.
Table 3. Recovery percentage of azoxystrobin in fortified rice samples
Rice matrice
<strong>Azoxystrobin</strong> recovery (%)
0.05 ppm 0.1 ppm 0.2 ppm
Mean
recovery
(%)
Recovery
factor
(RF)
Grains 80.12 82.86 97.91 86.96 1.15
Straw 85.12 81.32 87.69 84.71 1.18
Bran & Husk 80.00 84.90 82.18 82.36 1.21
* Determinability of the instrument = 0.004 µg/g of sample.
____________________________________________________________________________
RESUME
Sundravadana S., Alice D., Kuttalam S., et Samiyappan R. 2007. Activité de l’azoxystrobine sur
Rhizoctonia solani et son efficacité contre la brûlure de la gaine foliaire du riz. Tunisian Journal of
Plant Protection 2: 79-84.
La brûlure de la gaine foliaire, causée par Rhizoctonia solani, est l’une des principales maladies du riz.
Nous avons étudié l’effet de l’azoxystrobine sur la croissance in vitro de R. solani et son efficacité contre
cette maladie en plein champ. Les résultats ont révélé que l’azoxystrobine à 1, 2 et 4 ppm, inhibe
complètement la croissance mycélienne de R. solani. L’étude au champ a montré que la pulvérisation
foliaire de l’azoxystrobine à 125, 250 et 500 g/ha supprime significativement (> 64%) le développement
de la brûlure de la gaine foliaire et augmente le rendement (> 60%). Pour contrôler cette maladie, la dose
optimale d’azoxystrobine était de 125 g/ha. Nos résultats ont indiqué aussi qu’il n’y avait pas de résidus
dans les plantes du riz au moment de la récolte et pas de phytotoxicité avec la plus haute concentration
d’azoxystrobine (500 g/ha).
Mots clés : <strong>Azoxystrobin</strong>e, brûlure de la gaine foliaire, croissance mycélienne, lutte chimique, résidus,
Rhizoctonia solani, riz
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Vol. 2, No. 2, 2007

____________________________________________________________________________
.2007
ملخص
صندرافادانا،‏ سوبرامانيان ودافاداصون أليس وساسثان كوتالام وراماسامي سامييابان.‏
على الفطر Rhizoctonia solani ونجاعته ضد لفحة الغمد الورقي للأرز.‏
تأثير الأزوكسيستروبين
Tunisian Journal of Plant Protection
2: 79-84.
تع د لفحة الغمد الورقي التي يحدثها الفطر Rhizoctonia solani من أهم الأمراض التي تصيب الأرز.‏ تمت دراسة تأثير
R. solani
الأزوكسيستروبين
في
الأزوكسيستروبين بتراكيز
نمو الفطر
في البلور
ونجاعته ضد هذا المرض في الحقل.‏
أظهرت النتائج أن
جزء بالمليون يثبط كليا النمو الغزلي للفطر.‏ وبينت الدراسة في الحقل أن الرش
125 و 250 و
1 و 2 و 4
الورقي بالأزوكسيستروبين بالجرعات
الإنتاجية وتزيد
500 غ/هك تحد معنويا
كانت الجرعة المثلى لمكافحة هذا المرض
(>64%) من تطور لفحة الغمد الورقي
أظهرت نتائجنا كذلك
عدم وجود
125 غ/هك.‏
.(60%

13. Rebollar-Alviter, A., Madden, L. V., Ellis, M.A.,
2005. Efficacy of azoxystrobin, pyraclostrobin,
potassium phosphite and mefenoxam for control
of strawberry leather rot caused by Phytophthora
cactorum. Online. Plant Health Progress
[doi:10.1094/PHP-2005-0107-01-RS]
14. Rideout, S. L., Brenneman, T. B., and Culbreath,
A. K. 2002. Peanut disease management utilizing
an in-furrow treatment of azoxystrobin. Plant
Health Progress [DOI: 10.1094/PHP-2002-0916-
01-RS].
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