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Mycological Society of merica
The Influence of Qualitative and Quantitative Radiation on Reproduction and Spore Germinationof Four Phytophthora SpeciesAuthor(s): O. K. Ribeiro, G. A. Zentmyer and D. C. ErwinSource: Mycologia, Vol. 68, No. 6 (Nov. - Dec., 1976), pp. 1162-1173Published by: Mycological Society of America
Stable URL: http://www.jstor.org/stable/3758748Accessed: 12-08-2014 10:40 UTC
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2/13
THE
1NFLUENCE OF
QUALITATIVE
AND
QUANTITATIVE
RADIATION
ON
REPRODUCTION
AND
SPORE
GERMINATION OF
FOUR
PHYTOPHTHORA
SPECIES
O.
K.
RIBEIRO,
G. A.
ZENTMYER,
AND
D.
C.
ERWIN
Department
of
Plant
Pathology,
University of
California,
Riverside, California92502
SUMMARY
The
influence
of
visible and
near-visible
radiation
on
the
reproduction
and
spore
germination
of
Phytophthora
capsici,
P.
cinnamomi,
P.
mega-
sperma
var.
sojae
and
several
isolates
of P.
palmivora,
was
investigated
utilizing
a
synthetic
medium
and
a
12
h
light/12
h
dark
cycle.
In
general,
near-UV
radiation
(8
to
100 uW
cm-2),
significantly
enhanced
asexual
sporulation
n
P.
capsici
and P.
palmivora.
Phytophthora
cinnamomi
and
P.
megasperma
var.
sojae,
when
exposed
to
light,
failed to
produce
sporangia.
Differentiation
of
zoospores
from
sporangia produced
under
specific
regions
of the visible and near-visible
spectrum
differed
among
isolates.
Significantly
fewer
sporangia
produced
under
near-UV radiation
differentiatedand
released
zoospores.
Oospore
production
was
significantly
higher
in
the far-red
wavelengths
at
8
,W
cm-'.
At
100
/,W
cm-2,oospore
production
was
less than
that
obtained
in
darkness.
Germination
of
oospores appeared
o
be
independent
of
the
quality
and
quantity
of
radia-
tion received
during gametogenesis.
The influences f
light
on
fungi
are
many
and
varied
(9,
19,
23).
In
the
genus
Phytophthora,
nvestigations
n the
effect
of visible
and near-
visible radiationon sporulation ave indicated hat the response o light
differswith
the
species
(1,
5,
10, 11, 15,
17,
22, 28,
36).
Sporangium
production
s
abundant
n
some
species
n
response
o
light
(1,
7, 11,
12,
16, 22,
30,
31),
while other
species
are
either
inhibited
(10),
or fail
to
respond
(1,
11,
34).
It
is also
known
that
light
inhibits the
formation
of
oospores
of
Phytophthora
spp.
(11,
13,
14, 15, 17,
22,
24).
More
recent
investigations
with
P.
palmivora
(15,
16),
indicate
that
short
wavelengths
(450
nm)
inhibit
oospore
production
and enhance
forma-
tion
of
sporangia,
while
longer
wavelengths
(700
nm),
enhance
oospore
production. Reports
(2,
5, 8, 15, 28), also indicate that greater num-
bers of mature
oospores germinate
when
exposed
to
blue
(400-450
nm)
and/or
far-red
(700-750
nm)
regions
of
the
spectrum.
The
majority
of
these studies
have
investigated
only
one
phase
of the life
cycle
of
1162
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RIBEIRO
ET AL.:
RADIATION AND
PHYTOPHTHORA
Phytophthora
using
continuous
light
and either natural
agar
media
or
natural substrates. We
have
attempted
to
approximate
field conditions
more closely by employing an alternate 12 h light/12 h dark cycle,
selected
wavelengths
in
the
visible and
near-visible
spectrum,
and radia-
tion
approximating
average
intensities
recorded over a
period
of
one
year
in an
avocado
grove
in
southern
California.
MATERIALS
AND METHODS
The
fluorescent
lamps
and filters used to
generate
radiant
flux
density
within
specific regions
of
the
visible
and
near-visible
spectrum
have
been
described in detail (36). Radiation at 8 ,W cm-2, in the blue, red and
far-red
regions
of
the
spectrum
utilized
a
system
described
by
Ribeiro
et al.
(28).
The
intensities of
all
lamps
were
monitored
frequently
throughout
the
duration
of
experiments
and
adjusted
to
maintain
equal
radiant flux
densities for
each
spectral region
throughout
the
visible
and
near-visible
spectrum.
A
diurnal
light cycle
(12
h
light/12
h
dark),
at
25
-
1
C was
used
in
this
study.
The
culture
medium
used for
growth
and
irradiation
of the
fungus
has
been described
(27). Eight
ml of
the
synthetic agar
medium
was
dispensed
into
each 60-mm
plastic petri
dish.
Each
dish was
inoculated
with
a
cylindrical
5-mm-diam
plug
taken from 5-da-old
cultures
growing
on
the
synthetic
medium
(two plugs
of
opposite compatibility
types
placed
2
cm
apart
for
heterothallic
species,
a
single
plug
in
the
center
of
the dish
for homothallic
species).
Inoculated dishes were
immediately
placed
under the
different
light
sources.
The
petri
dish
lids transmitted
all
wavelengths greater
than
293 nm.
Dark controls were
placed
in a
blackened 1.3 cm
thick
wooden
box,
wrapped
with two
layers
of
heavy
duty aluminum foil.
All
experiments
were
terminated
at
10 da
and observations
made
immediately
thereafter. Numbers of
sporangia
and
oospores
were counted
with the aid
of a
microscope
in 5
random
fields
of
1.5
mm2,
for each
petri
dish.
Oospore germination
tests were
conducted
after 30 da
incubation
by
the method
of
Ribeiro
et
al.
(28).
Indirect
germination
of
sporangia
was observed
by
flooding
cultures with
6
ml
sterile
deionized distilled water and
chilling
at
9
C
for 40
min.
Each
treat-
ment
was
repeated.
The
Phytophthora
spp.
used
in
this
study
were
as follows:
Phytoph-
thora
capsici
Leonian
(P504
Al,
[ATCC
32067],
and P505s
A2
[ATCC
32068],
from
pepper [Capsicum sp.])
;
Phytophthora
cinnamomi Rands
(Pc97
A1,
from
Camellia
sp.,
and Pc
40
A2,
from avocado
[Persea
americana
Mill.])
;
Phytophthora
megasperma
Drechs.
var.
sojae
1163
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MYCOLOGIA,
VOL.
68,
1976
A.
A.
Hildb.
(P174,
from
soybean
[Glycine
max
(L.)
Merr.]);
Phytophthora
palmivora
(Butl.)
Butl.
(P253
A1,
P255
A2,
P376
A2,
P611 A1, P613 A1, P622 A1, P623 A2, P794 A1 and P795 A2, all
from
cacao
(Theobroma
cacao
L.)
and
isolate P377
A1,
from Durio
zibethinus
Murr.
Number
designations
refer
to the
Phytophthora
stock
culture
collection
maintained in
the
Department
of
Plant
Pathology,
University
of
California,
Riverside.
RESULTS
Sporangial
production
of
P.
palmivora,
in
general,
was
significantly
stimulated (P = 0.01) by radiation in the near-UV and blue
regions
of
the
spectrum
(FIGS.
1-4
and
9).
There
was, also,
an
apparent
relationship
between
the
intensity
of
radiation
and
production
of
sporangia;
increasing
intensities
from
8
pjW
cm-2
to
100
,LW
cm-2
generally
resulted
in
greater
sporangia
production
in
3
of
the
4
isolates
tested.
The
P.
palmivora
isolates
from
Nigeria
(FIG.
1),
Cameroon
(FIG.
2),
Malaysia
(FIG.
3),
Brazil
(FIG.
4),
and
Central America
(FIG.
9),
represented
a
wide
ecological
range.
Phytophthora capsici
produced abundant sporangia when exposed to radiation in the near-
UV-blue
region
of
the
spectrum,
and
rarely
in
darkness
(FIG.
10).
Phytophthora
cinnamomi
and
P.
megasperma
var.
sojae
did not
produce
sporangia
directly
in
the
synthetic
medium
under
any
condition
of
light
quality
and
irradiation
used in
this
study.
Indirect
germination
of
sporangia
(i.e.
by
differentiation and
release
of
zoospores),
of P.
pal-
mivora,
varied
with
the
isolate
(FIGS. 5-8).
In
general, significantly
fewer
(P
=
0.01)
sporangia
produced
under near-UV
irradiation
germinated
indirectly,
except
for
the Cameroon
isolates
(FIG. 6).
Phytophthora
cinnamomi
produced
oospores
in
all
regions
of
the
visible
and
near-visible
spectrum
at
8
and 60
uW
cm-2
(FIG.
11).
Oospore production
at
these
intensities were
significantly
higher
(P
=
0.05)
than
that obtained
in
darkness.
At
100
,uW
cm-2,
however,
oospore production
in
all
wavelengths
was
significantly
less
than
in
dark-
ness
(Fig.
11).
At
8
MUW
m-2,
in
the
far-red
region
of the
spectrum,
P.
capsici
and
P.
palmivora
showed
an increase in
oospore production
over
that obtained in
darkness
(FIGS.
12
and
13),
while
P.
megasperma
var. sojae (FIG. 14), produced as many oospores as in darkness. The
near-UV-blue
regions
of
the
spectrum
were
inhibitory
to
oospore
forma-
tion
for P.
capsici
(FIG.
12),
P.
palmivora
(FIG.
13),
and P.
mega-
sperma
var.
sojae
(FIG.
14),
when
compared
to
oospore
production
in
darkness.
Oospore production
of
P.
cinnamomi
was
only
inhibited
at
high
intensity (100
MtW
cm-2).
Percentage germination
of
oospores
1164
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RIBEIRO
ET
AL.:
RADIATION AND
PHYTOPHTHORA
1165
P.
PALMIVORA
8eW
cm-2
ISOLATES
6o
c
I 60oW cm-2
I
IOO0/W
cm-2
200
- -
150
-
b
n
b
o
a
z
100
-
50-
m
d
d
c
0
i
*
*
* * * *
* 0*
3
c
f
c
200-
-
a
a
J
2
_
150
-
00
b
o
2
50-
cd d
d
d
d
O
E
200-
-|
0.?
50
c
FIGS.
1-4.
Effects of
the
quality and
quantity of
radiation
on
sporangia pro-
duction by isolates of P. palmivora. 1. Nigerian isolates (P611 A1, P613 A1).
2.
Cameroon
solates (P794
A; P795
A2). 3. Malaysian isolates
(P377 A
P374
A2). 4. Brazilian
isolates
(P622 A1;
P623
A2).
Bars
having
the
same
letter
are not
significantly
different
from each
other (P
=
0.01).
*
Indicates
that
sporangia produced
were
too
numerous to
count
accurately by
the
method
employed.
Z
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MYCOLOGIA,
OL.
68,
1976
RED RED
SPECTRAL
REGIONS
FIGS.
5-8.
Effects of the
quality
and
quantity
of radiation on
indirect
germina-
tion
of
sporangia by
isolates of P.
palmivora.
5.
Nigerian
isolates. 6.
Came-
roon isolates.
7.
Malaysian
isolates.
8.
Brazilian
isolates. Bars
having
the
same
letter
are
not
significantly
different
from
each other
(P
=
0.01).
1166
I-
(.
z
0
QL
O3
-J
I-
-4
0
LJ
c_
-I
0
z
co
NEAR BLUI
UV
E
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7/13
RIBEIRO ET
AL.: RADIATION
AND PHYTOPHTHORA
P.
PALMIVORA
Jt
T,
55
t 5
5f
rl
:
r:
,:
)
,
Z
r
,55:
''
,1
,
,
,..
f.
r.t
ft
...'
r'.f
r
.Z
,r:r
I
It
,
,
.t.'
,'.'.'
...'
t.
:t.
t.
..'
.'.
.
15S'
t..
r
..5
t..
555
rr
r
r
(
I
...
.:::
:...
||. .
...
:.:.-
ii
::-:-
JC
- ---
.'..
.'..
..5
.t.
(
rf;
"-'
"-'
(
'-"
"-'
.55
5'.
Z
t.
t.
.
Sf
..
..'
55
..5
.5.
.'.'.
.55
...
.'.'.
.'.'.
JC
a
K..
*--
..
i,
I
~'.*.'
1K$
;.,;
.5.
y^:
g3 8
iW
cm-2
LI
60/zW
cm-2
I
I
100,
W
cm-2
*
a
.'.'.
t.
...
55
r.t.
2..
.'
.'.'.
.'.'.
,
r'Z
r'.'.
.'.'.
.'.'.
i.
..'.
..
r
f.
55
,
)
)
(
)
)
L
I
,'.'.'
;'.'.'
C..'
rt
C
b
al
I
I.'
:.:.
:--:
::.::
i
C
d
I
...
I-
:.
: :
.: .
.'
I
.S
e
10
P.
CAPSICI
b
C c
:
...
c
c
r7'
NEAR
UV
c
BLUE
DAY-
LIGHT
RED FAR
INFRA
DARK
RED
RED
SPECTRAL
REGIONS
FIGS.
9
and
10.
Comparative
effects
of
the
quality
and
quantity
of
radiation
on
two
Phytophthora species.
9. P.
palmivora
(Central
American
isolates
P253
A'
and
P255
A2).
10. P.
capsici (P504
A'
and
P505s
A2).
Bars
having
the
same
letter
are
not
significantly
different
from
each other
(P
=
0.01).
*
Indicates that
sporangia
produced
were too
numerous to
count
accurately by
the method
employed.
200 -
9
-J
I
L.
a.
0
0
u
2
150
-
100
-
50-
CM
E
E
1)
200
-
CD
0
Z
150
8/12/2019 Ribeiro et al. (1976) - The Influence of Qualitative and Quantitative Radiation on Reproduction
8/13
MYCOLOGIA,
VOL.
68,
1976
0
-J
w
0
LL
0
E
o
E
10
0
o
a
0
o
2
SPECTRAL REGIONS
FIGS. 11-14.
Effects
of
the
quality
and
quantity
of radiation on
oospore pro-
duction
of
four
Phytophthora
species.
11.
P.
cinnamomi
(Pc97
A1
X
Pc40
A2).
12. P.
palmivora
(P254
A1 X P255
A2).
14. P.
megasperma
var.
sojae
(P174).
Bars
having
the
same
letter
are
not
significantly
different
from
each
other
(P
=
0.05).
*
Indicates that
oospores produced
were
too numerous
to count
accurately
by
the method
employed.
1168
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9/13
RIBEIRO
ET
AL.:
RADIATION AND
PHYTOPHTHORA
1169
0o-
P.
CINNAMOMI
8W
15
90 -
80
-
|i
60,iW
cm-2
70 - 0
IOO
W
cm-2
60 -
50-
40-
a
20-
bc
bc
b
bc
10-
b
Aflbb
bc
1oo-
16
o00-
P.
CAPSICI
16
90 -
80-
70
-
s
60-
50-
z
O
40-
a
-
30
-