Decline in Numbers and Inoculum Potential of Sclerotium oryzae in Field Soil

Full text

Ecology
and
Epidemiology
Decline
in
Numbers
and
Inoculum
Potential
of
Sclerotium
oryzae
in
Field
Soil
W.
W.
Bockus
and
R.
K.
Webster
Assistant
professor,
Department
of
Plant
Pathology,
Kansas
State
University,
Manhattan,
KS
66506;
and
professor,
Department
of
Plant
Pathology,
University
of
California,
Davis,
CA
95616.
Research
supported
by
the
California State
Rice
Research
Board,
the
California
Solid
Waste
Board,
and the
California
Air
Resources
Board.
Accepted
for
publication
20
October
1978.
ABSTRACT
BOCKUS,
W.
W.,
and
R.
K.
WEBSTER.
1979.
Decline
in
numbers
and
inoculum
potential
of
Sclerotium
oryzae
in field
soil.
Phytopathology
69:
389-392.
A
calculated
half-life
of
1.9
yr
was
obtained
for
sclerotia
of
Sclerotium
sulfate
and
penicillin
G
was
a
good
measure
of
the inoculum
potential
of
S.
oryzae
rototilled
into
field
soil
to an
18-cm
depth
with
or
without
an
oryzae.
Initially
the
inoculum
potential
of freshly-produced
sclerotia
amendment
of
dried,
noninfested
rice
residue.
During
the first
4
wk,
living
incorporated
in
field
soil
declined
rapidly
due
to
the
rapid
loss
in
the
ability
sclerotia
incorporated
in
soil
germinated
80%
when
recovered
from
soil
and
of
sclerotia
to
germinate,
but
the
total
numbers
of
sclerotia
decreased
only
placed
on
water
agar.
Germination
of
sclerotia
on
water
agar
declined
to
slightly.
After
the
rapid
decline,
inoculum
potential
stabilized
and
20%
after
6
mo
and thereafter
stabilized
between
20
and
30%.
Treatment
thereafter
is
expected
to
be
influenced
largely by
a
decline
in
actual
numbers
with
0.5%
NaOCl
indicated
that
loss
of
germinability
was
due to
dormancy
of sclerotia.
Because
the
decline
in
numbers
of sclerotia
of
S.
oryzae
was
but not
to
complete
death
of
sclerotia.
Number
of
sclerotia
per gram
of
soil
relatively
slow (half-life
=
1.9
yr),
alternate
year
cropping
of
rice
would
not
that
germinated
when
placed on
water
agar amended
with
streptomycin
be
expected
to
control
stem
rot.
Additional
key
words:
Magnaporthe
salvinii.
Magnaporthe
salvinii
Krause
and
Webster
(Sclerotium
oryzae
areas
in
a
field.
Each
area
(basin)
was
surrounded
by
a
dirt
levee
30
Catt.)
causes
stem
rot
of
rice
(Oryza
sativa
L.).
Soilborne
sclerotia
cm
high
X 1
m
wide.
The
experimental
field
had
never
been
cropped
serve as
the
overwintering
propagules
for
survival
of the fungus.
to
rice
and
no
sclerotia
of
S.
oryzae
were
detected
in
the
soil.
The
After
fields
are
flooded,
sclerotia
float
to the
surface
of
paddy
sclerotia
were
sprinkled
on
the
soil
surface
and
thoroughly
mixed
water.
Floating
sclerotia
contact
emerging
rice
plants
and
into
the
soil
(Yolo
sandy
loam)
to an
18-cm
depth
using
a
hand-
germinate,
and the
mycelium
infects
tillers
at
the
water
line
(10).
operated
rototiller.
Propagules
were
introduced
at
a
rate
of
3-5
Sclerotia
are
produced
on
or
in
infested
tissues
as
the
rice
plants
sclerotia
per
gram
of
soil, which
corresponds
to
a
moderate
mature and
either remain
in
crop
debris
or
are
dislodged
and
infestation
level
(14,16).
There
were
three
treatments
of sclerotia
scattered
on
the
soil
surface
during
harvest.
Subsequent
tillage
and
four
replicate
basins
for
each
treatment.
Treatments
included:
incorporates
the
sclerotia
into
the
soil.
Efforts
to
control
stem
rot
(i)
sclerotia
incorporated
in
the
soil
along
with
4.5
kg
of chopped,
have
been
directed
toward
minimizing
inoculum
by
cultural
dried,
noninfected
rice
residue;
(ii)
sclerotia
rototilled
into
the
soil
practices
(14-16).
without
residue;
and
(iii)
sclerotia
killed
with
propylene
oxide
in
a
Park
and
Bertus
(11)
recovered
viable
sclerotia
after
190
days
sealed
(24
hr)
quart
mason
jar
before
incorporation.
Four
from
air-dry
soil
and
after
133
days
from
moist
rice-field
soil.
noninfested
basins
served
as
controls.
The
16
basins in
the
field
Nisikado
and
Hirata
(9)
reported
viability
of air-dry
sclerotia
after
were
in
a
randomized
complete
block design.
The
field was
3
yr
in
a
20
C
incubator.
Tullis and
Cralley
(12)
buried
infested
rice
occasionally
sprinkler-irrigated
to
supplement
the
rainfall
and
straw
and
sclerotia
10-15
cm
deep
in field soil
and reported
that
provide
a
total
average
annual
precipitation
of
45-50
cm.
3.7%
of
the sclerotia
were
viable
after
6
yr.
These
studies
did
not,
During
1.5
yr
the
basins
were
sampled
periodically
and
the
however,
distinguish
between
decline
in
numbers
of
sclerotia
and
number
of
sclerotia
per
gram
of
soil
determined.
At
each
sample
decline
in
percentage
germination
(germinability)
after
various
date
30
soil
cores
(1.8
cm
in
diameter
and
15
cm
deep)
were
periods
of
time.
Such
information
is
essential
because
there
are
collected
at
random
from
each
basin with
a
standard
soil-core
correlations
(8,13,16)
between
viable
sclerotia
per
gram
soil,
sampler.
The
30
cores
were
bulked
in
a
paper
bag,
air-dried,
and
disease
severity,
and
yield
loss
due
to stem
rot.
Although
Webster
et
mixed,
and
then
four
50-g
subsamples
were
taken
from
each
bag
al
(14)
reported
the
effect
of
various
residue
management
practices
and
the
number
of
sclerotia
determined.
Krause
and
Webster's
on
vertical
distribution
and
survival
of
sclerotia
of
S.
oryzae
under
extraction
method
(7)
enables
the
recovery
of
90-95%
of
the
continuous
rice
culture,
decline
in
sclerotial
numbers
and
changes
sclerotia
in
a
soil
sample.
in
inoculum
potential
of
S.
oryzae
in
field
soil
in
the absence
of
the
Determination
of
percent
germination
of
sclerotia.
Viability
of
living
host
have
not
been
reported.
sclerotia
has
been
determined
by
placing
them
on
water
agar
(7,14),
where
germinated
sclerotia
produced
the conidial
state
of
M.
MATERIALS
AND
METHODS
salvinii
(Nakatea
sigmoidea
(Cav.)
Ham).
For
this
study
percent
germination
on water
agar
(1.5%
Difco
Agar
Flake) amended
with
Measurement
of
inoculum
decline
in
the
field.
Sclerotia
of
six
streptomycin
sulfate
and
penicillin
G
each
at
100
ppm
(WA+)
was
isolates
of
M.
salvinii
produced
on
a
sterile
rice-rice
hull
mixture
used.
Sclerotia
were
placed
on
WA+
in
petri
dishes
and
incubated
according
to Krause
and
Webster's
method
(7)
were
used
to
infest
30
cm
below
continuous
fluorescent
lights
(about
690
lx)
for
14
field
soil
artificially.
The
six
isolates
(B-6,
D-6,
D-15,
D-19,
D-43,
days
at
24
±
2
C.
Sclerotia
tested
for
germination
were
extracted
and
D-55)
represented
both
mating
types
and
varied
in
sclerotia
from
soil
from
basins
with
sclerotia
alone
(treatment
ii).
On
each
production,
growth
rate, and
virulence
(3).
Equal quantities
of
sample
date
200
sclerotia
from
each
replicate
basin
were
placed
on
sclerotia
of
each
isolate
were
mixed
and
incorporated
in
3
X
3
m
WA+.
To
study
the
effect
of
surface
sterilization
on
percent
germination,
some
sclerotia
were
shaken
for
30
min
in
a
0.5%
00031-949X/79/000073$03.00/0
aqueous
NaOCI
solution,
rinsed
in
sterile
distilled
water,
and
01979
The
American
Phytopathological
Society
placed
on
WA+.
Vol.
69,
No.
4,1979
389

In
another
study
sclerotia
were
extracted
from
soil
from
a
of sclerotia
decreased
approximately
35%
during
the
1.5-yr
grower's
rice
seedbed
in 1977
before the
field was
flooded.
The
experiment.
sclerotia
were
plated directly
onto
WA+
or
were
exposed
to
the
Percent
germination
of
sclerotia.
Sclerotia
introduced
without
NaOCI
treatment
before
being placed
on
WA+.
residue
into
the
soil
in
the
fall
of
1976
initially
germinated
about
Tests
for
infectivity
of
sclerotia.
To determine
the
correlation
of
80%
on
WA+
(Fig.
2).
During
the
overwintering
period (November
declines
in
percent
germination
of
sclerotia
on
WA+
and
in
1976-May
1977)
percent
germination
was
progressively
less
with
infectivity,
samples
of
sclerotia
with
different percentages
of
each
sampling.
Thereafter
percent
germination
stabilized
between
germination
on
WA+
were
used
to
inoculate
rice
plants
grown
in
20
and
30%
(May
1977-January
1978).
Although
the
data
are
not
the
greenhouse.
Soil
from
basins
with
sclerotia
alone
(treatment
ii)
presented,
sclerotia
introduced
in
the
soil
together
with
noninfested
was
sampled
I
wk,
1.5
mo,
4.5
mo,
and
7
mo
after
incorporation
of
rice
residue
followed
an
essentially
identical
pattern
of
sclerotia
in
the
soil.
progressively
less
and
then
stabilization
of
percent
germination.
Rice
plants
of
the
M-5
cultivar
(California
Cooperative
Rice
This decline
in
germination
on
WA+
was
not
due
to complete
death
Research
Station,
Biggs,
CA
95917)
were
grown
in
the
greenhouse
of
sclerotia
because
a
30-min
exposure
to
0.5%
aqueous
NaOCl
in
20-L
plastic
buckets
and
thinned
to
five
plants
per
bucket
14
days
before
plating
on
WA+
resulted
in
75%
or
more
germination
of
the
after
seeding
(8).
A
glass needle
was
used
to
place
a
sclerotium
on
sclerotia
regardless
of
the
sampling
date
(Fig.
2).
In
another
test
400
each
tiller
at
the
water
line
65
days
after
planting.
The
sclerotia
were
sclerotia
extracted
from
soil
from
a
grower's
field
germinated
held
against
the
tillers
by
the
water
meniscus.
A
drip-irrigation
25.5%
on
WA+,
but
400
sclerotia
extracted
from
the
same
soil
and
system
was
used
to
maintain
a
constant
water
level
in
each
pot
so
exposed
to
NaOCI
before
being
plated
on WA+
germinated
72.5%.
that
the
sclerotia remained
at
the
tiller-water
interface
during
the
Percent
infectivity
vs.
inoculum
potential
Two
hundred
sclerotia
3-wk
experiment.
For
each
sample
date,
200
tillers
were
inoculated
from
each
of the
four
germination
classes
produced
17.0, 16.0,
10.0,
and
50
noninoculated
tillers
served
as
controls.
For
each
sampling
and
4.5%
infection,
respectively,
when
inoculated
individually
onto
200
sclerotia
also
were
placed
on
WA+.
The
percentage
of
rice
tillers
(Fig.
3A).
All
noninoculated
tillers
remained
healthy.
infected
tillers
was
determined
after
3
wk,
Infections
appeared
The
correlation
coefficient
for percent
germination
on
WA+
vs.
as
small,
black,
elongated
lesions
at
the
water
line
(8).
percent
infection
was
0.96.
In
another
experiment,
sclerotia
were
placed
on
top
of
7-cm,
At
each
of
the
four
sample
dates
100
sclerotia
produced
34,
19,
freshly
cut,
65
day
old
tillers
in
petri
dishes.
Five
sclerotia
were
18,
and
7
infections,
respectively,
when placed
on
pieces
of
green
placed
on
top
of
each
of
five
green
rice
pieces
in a
petri
dish
lined
rice
tillers
in
petri
dishes
and
incubated for
12
days
(Fig.
3B).
with
moist
filter
paper.
Sclerotia
were
placed
far
enough
apart
on
Correlation
coefficient
for
percent
germination
on
WA+
vs.
the
tiller
pieces
so
that
stem
rot
lesions
from
adjacent
sclerotia
did
percent
infection
was
0.94.
Both
tests
were
repeated
and
again
not
coalesce.
produced
a
high
coefficient
of
correlation.
For
each
of
the
four
sample
dates
(I
wk,
1.5
mo,
4.5
mo,
7
mo),
100
sclerotia
were
obtained
from
treatment
(ii)
and
placed
on
the
DISCUSSION
tiller
pieces.
For
each
sample
date
200
sclerotia
also
were
placed
on
WA+.
All
petri dishes
were
incubated
at
24
±
2
C
under
continuous
For
the
conditions
of
this
study
the calculated
apparent
half-life
fluorescent
lights
for
12
days,
at
which
time
the
number of
stem
rot
(17)
for
decomposition
of
S.
oryzae
sclerotia
in
soil
is
1.9
yr.
lesions
initiated
by
single
sclerotia
were
counted.
Numbers
of
sclerotia
decrease
presumably
because
of
degradation
by
soil
organisms.
Sclerotia
killed
before
incorporation
in
soil
RESULTS
decreased
at
the
same
rate
as
living
sclerotia
indicating
that
persistence
of
sclerotia
is
passive
and
probably
due to
the resistance
Inoculum
decline
in
the
field.
Numbers
of
sclerotia
declined
in
all
of
the
sclerotial
rind
to
microbial
degradation.
However,
Ferguson
three
treatments.
The
rate
of
decrease
was
similar
whether
sclerotia
(2)
reported
that
killed
sclerotia
of
Sclerotinia
sclerotiorum
and
were
living
or
dead
when
incorporated
in
soil
(Fig.
1).
The
numbers
Sclerotium
delphinii
were
colonized
by
various
soil
organisms
but
90
I
o
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4
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6
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1
2
t II
II I
MONTH
AND
YEAR
1976
1977
1978
Fig.
1.
Decline
in
numbers
of
sclerotia
of
Sclerotium
orvzae
after initial
MONTH
AND
YEAR
infestation
of
field
soil.
Initially
sclerotia either
were
incorporated
in
the
soil
with
healthy
rice
residue
(open
circles),
alone (triangles),
or
dead,
ie,
Fig.
2.
Decline
in
percent
germination
of
sclerotia
of
Sclerotium
oryizae
exposed
to
propylene
oxide
and
then
incorporated
(closed
circles). Each
after various
times
in
field
soil.
Sclerotia
were
incorporated
in
field
soil,
point
represents
the mean
number
of sclerotia
extracted
from
16
50-g
soil
periodically
extracted,
and
either
washed
in
a
NaOCI
solution
before
being
samples
from
four
replicate
areas.
LSD
(P
=
0.05)
=
46.6
for
sclerotia
placed on
water
agar
(open
circles)
or
plated
directly
onto
water agar
incorporated
with
rice
residue,
17.3
for sclerotia
incorporated
alone,
and
(closed
circles).
Each
point
represents
the
percent
germination
of
800
27.8
for
dead
sclerotia.
sclerotia
extracted from
four
replicate
areas. LSD
(P
=
0.05)
=
7.5.
390 PHYTOPATHOLOGY

that
living
sclerotia
were
rarely
colonized.
It
is
not
known
if
killed
dishes.
Results
from
this
study
also
showed
that
a
high
percentage
and
living
sclerotia
of
S.
orvzae
are
differentially
colonized
by
soil
of
sclerotia
incorporated
in
an
experimental
field
soil
for
several
organisms,
what
effect
colonization
has
on
the
recoverability
of
months
did
not
germinate
on
WA+.
This
decrease
in
percent
sclerotia
from
soil,
or
which
organisms
are
involved
in
sclerotial
germination
was
due
to
dormancy
of
a
high
percentage
of
the
degradation.
sclerotia
because
treatment
with
NaOCI
increased
germination
Bockus
et
al.(
I)
reported
that
the
competitive
saprophytic
ability
from
about
20%c
to
at
least
75%.
It
is
not
known
if
sclerotia
in
the
of
S.
orvzae
derived
from
sclerotia
was
restricted
in
field
soil.
In
field
are
later
released
from
this
dormancy.
those
tests
S.
orvzae
did
not
colonize
rice
residue
or
organic
matter
Percent
germination
of
sclerotia
placed
directly
on
WA+
was
in
soil
and
produce
additional
sclerotia.
Our
results
confirm
this
highly
correlated
with
percentage
of
sclerotia
that
initiated
stem
rot
earlier
finding,
living
sclerotia
incorporated
in
soil
along
with
disease.
However,
only
one-fifth
as
many
sclerotia
initiated
disease,
chopped,
noninfested
rice
residue
decreased
in
numbers
at
the
same
compared
with
percent
germination
on
WA+.
Environmental
rate
as
living
or
dead
sclerotia
incorporated
alone,
conditions
as
well
as
ability
to
germinate
apparently
influence
Webster
et
al
(14)
reported
that
sclerotia
recovered
from
infection.
However,
percent
germination
of
sclerotia
placed
standing
rice
stubble
and
straw
in
the
fall
immediately
after
harvest
directly
on
WA+
can
be
used
to
indicate
the
"relative
infectivity"
of
germinated
76-92%
on
water
agar.
Others
reported
that
sclerotia
different
samples
of
sclerotia.
recovered
from
soil
from
a
rice
field
in
the
spring,
after
they
had
The
term
"inoculum
potential"
has
been
defined
by
Garrett
(4)
as
overwintered,
germinated
only
25%
on
water
agar
(5,7).
Keim
and
"energy
of
growth
of
a
pathogen
available
for
infection
of
a
host
at
Webster
(6)
reported
a
significant
reduction
in
percent
germination
the
surface
of
the
host
organ
to
be
infected."
He
further
stated
that
of
sclerotia
of S.
orvzae
after
29-day
incubation
in
moist
soil
in
petri
the
nutritional
status
of
potentially
infective
units
and
their
numbers
influence
the
inoculum
potential
(4).
When
comparing
soil
samples,
therefore,
germinated
sclerotia
per
gram
of
soil
is
a
useful
estimate
of
the
inoculum
potential
of
S.
or'zae
because
it
7.5
-
I
I u
I
I
I •takes
into
account
the
number
of
sclerotia
in
the
soil
and
the
17
I
relative
ability
of
S.
orvzae
to
initiate
disease
from
those
sclerotia.
5
-
The
number
of
germinated
sclerotia
per
gram
of
soil
in
the
seedbed
15.0
has
been
correlated
with
disease
severity
and
yield
loss
(8,13).
S12.ABased
on
percent
germination,
there
was
an
initial
rapid
decline
//
in
the
inoculum
potential
of
freshly-produced
sclerotia
incorpor-
o
12.5
ated
in
field
soil
(Fig.
2).
This
rapid
decline
occurred
even
though
w
actual
numbers
of
propagules
in
the
soil
were
virtually
unchanged.
-
10.0
0
After
the
initial
rapid
decline,
inoculum
potential
stabilized
at
a
r
=.96
level
where
a
relatively
low
percentage
of
sclerotia
were
functional
Z
7.5
/m=.20
at
any
time.
During
this
period
the
change
in
inoculum
potential
was
slow
and,
assuming
no
subsequent
large
change
in
percent
i
.o
b
=
1.93
germination
of
sclerotia
occurs,
further
decreases
in
inoculum
5.0
-
potential
should
be
due
to
a
decrease
in
actual
numbers
of
sclerotia
per
gram
of
soil.
2.5
-
The
initial
rapid
decline
in
inoculum
potential
that
occurred
during
the
overwintering
between
rice
crops
would
influence
the
0
amount
of
disease
in
continuous
rice
culture.
The
slower
subsequent
decrease
in
actual
numbers
of sclerotia
should,
0
I0
20
30
40
50
60
70
80
90
however,
be
more
important
to
the
effectiveness
of
crop
rotation
PERCENT
GERMINATION
ON
WATER
AGAR
for
controlling
stem
rot
of
rice.
Reports
that
alternate
year
rice
cropping
is
not
an
effective
control
measure
for
stem
rot
(
12,14)
are
supported
by
our
results
showing
that
sclerotia
of S.
oryzae
persist
(half-life
=
1.9
yr)
in
field
soil.
Thus
short-term
rotations
of
rice
with
35
1
I
I
I
1
I
1
nonhost
crops
would
not
be
expected
to
lower
the
inoculum
potential
of
S.
oryzae
below
the
economic
threshold
(13).
30-
B
LITERATURE
CITED.
25
1.
BOCKUS,
W.
W.,
R.
K.
WEBSTER,
and
T.
KOSUGE.
1978.
The
competitive
saprophytic
ability
of
Sclerotium
oryzae
derived
from
mm
20
sclerotia.
Phytopathology
68:417-421.
z
2.
FERGUSON,
J.
1953.
Factors
in
colonization
of
sclerotia
by
soil
organisms.
(Abstr.)
Phytopathology
43:471.
Z
15
3.
FERREIRA,
S.
A.,
and
R. K.
WEBSTER.
1975.
The
relationship
of
W
r=.94
sporulation,
sclerotia
production,
and
growth
rate
to
virulence
and
fitness
of
Sclerotium
oryzae.
Phytopathology
65:972-976.
1U
10
-
4.
GARRETT,
S.
D.
1960.
Inoculum
potential.
Pages
23-56
in
Plant
0
b=.86
Pathology.
J.
G.
Horsfall
and
A.
E.
Dimond,
eds.
Vol.
III
Academic
Press,
New
York.
675
pp.
5.
KEIM,
R.
1974.
Effects
of
biotic
and
abiotic
factors
on
viability
of
Sclerotium
oryzae.
Ph.D.
thesis.
University
of
California,
Davis.
63
pp.
0
16.
KEIM,
R.,
and
R.
K.
WEBSTER.
1974.
Effect
of
soil
moisture
and
0
10
20
30
40
50
60
70
80
90
temperature
on
viability
of
sclerotia
of
Sclerotium
oryzae.
Phyto-
pathology
64:1499-1502.
PERCENT
GERMINATION
ON
WATER
AGAR
7.
KRAUSE,
R.
A.,
and
R.
K.
WEBSTER.
1972.
Sclerotial
production,
viability
determination
and
quantitative
recovery
of
Sclerotium
oryzae
Fig.
3.
Correlation
of
percent
sclerotia
of
Sclerotium
oryzae
initiating
stem
from
soil.
Mycologia
64:1333-1337.
rot
infections
with
percent
germination
of
sclerotia
on
water
agar.
Samples
8.
KRAUSE,
R.
A.,
and
R.
K.
WEBSTER.
1973.
Stem
rot
of
rice
in
of
sclerotia
that
germinated
different
percentages
on
water
agar
were
either
California.
Phytopathology
63:518-523.
individually
inoculated
onto
rice
tillers
in
the
greenhouse
(A)
or
placed
on
9.
NISIKADO,
Y.,
and
K.
HIRATA.
1937.
Studies
on
the
longevity
of
cut green
rice
tillers
in
petri
dishes
in
the
laboratory
(B).
sclerotia
of
certain
fungi
under
controlled
environmental
factors.
Ber.
Vol.
69,
No.
4,1979
391

Ohara
Inst.
7:535-547.
various
tillage
methods.
Phytopathology
66:97-101.
10.
OU,
S.
H.
1972.
Rice
diseases.
Commonw.
Mycol. Inst.,
Kew,
Surrey,
15.
WEBSTER,
R.
K.,
C.
M.
WICK,
J.
BOLSTAD,
and
R.
KEIM.
1974.
England.
369
pp.
Manipulating
culture
practices
to
minimize
stem rot
disease
of
rice.
II.
PARK,
M.,
and L.
S.
BERTUS.
1932.
Sclerotial
diseases
of
rice
in
Pages
71-73
in
Proc.
15th
Rice
Technical
Working
Group,
Fayetteville,
Ceylon.
2.
Sclerotium
oryzae
Catt.
Ceylon
J.
Sci.,
Sect.
A,
11:343-359.
AR,
March
11-14.
91
pp.
12.
TULLIS,
E.C.,andE.
M.
CRALLEY.
1941.
Longevityofsclerotiaof
16.
WEBSTER,
R.
K.,
C.
M.
WICK,
D.
H.
HALL.,
D.
LINDBERG,
the
stem
rot
fungus,
Leptosphaeria
salvinii.
Phytopathology
and
A.
LINDBERG,
SR.
1972.
Effects
of
various
methods
of
31:279-281.
rice
residue
management
on
Sclerotium
oryzae
inoculum
level,
13.
WEBSTER,
R.
K.
1974.
Relationships
between
inoculum
level,disease
stem
rot
disease
severity
and
yield,
a
progress
report.
Pages
59-60
severity
and
yield
reduction
in
stem
rot
of
rice.
Proc.
Am.
Phytopathol.
in
Proc.
14th
Rice
Technical
Working
Group,
Univ.
of
Calif.,
Soc.
1:106-107.
Davis,
June.
101
pp.
14.
WEBSTER,
R.
K.,
J.
BOLSTAD,
C.
M.
WICK,
and
D.
H.
HALL.
17.
YARWOOD,
C.
E.,
and
E.
S.
SYLVESTER.
1959.
The
half-life
1976.
Verticle
distribution
and survival
of
Sclerotium
oryzae
under
concept
of
longevity
of
plant
pathogens.
Plant
Dis.
Rep.
43:125-128.
392
PHYTOPATHOLOGY