ribeiro et al. (1976) - the influence of qualitative and quantitative radiation on reproduction

8/12/2019 Ribeiro et al. (1976) - The Influence of Qualitative and Quantitative Radiation on Reproduction

1/13

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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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3/13

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



4/13

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



5/13

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



6/13

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



7/13

RIBEIRO ET

AL.: RADIATION

AND PHYTOPHTHORA

P.

PALMIVORA

Jt

T,

55

t 5

5f

rl

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r:

,:

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r

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r.t

ft

...'

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r

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...'

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15S'

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5'.

Z

t.

t.

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Sf

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55

..5

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JC

a

K..

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i,

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~'.*.'

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..

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.'.'.

,

r'Z

r'.'.

.'.'.

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i.

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r

f.

55

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)

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(

)

)

L

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,'.'.'

;'.'.'

C..'

rt

C

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i

C

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I

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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


8/13

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



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

-

ribeiro et al. (1976) - the influence of qualitative and quantitative radiation on reproduction

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