VOL. 53, NO. 4, CAN. PLANT DIS. SURV. DEC. 7973
191
RHIZOPHYDIUM GRAMINIS (CHYTRIDIALES): MORPHOLOGY, HOST
RANGE ,AND TEMPERATURE EFFECT
D.J.S. Bar;
Abstract
Rhizo h dium q r a m i n i s , an o b l i g a t e p a r a s i t e of r o o t c e l l s was found i n
soil-winter
wheat growing a r e a s of O n t a r i o . I n l a b o r a t o r y t e s t s
an i s o l a t e from wheat grew a b u n d a n t l y on b a r l e y (Hordeum v u l q a r e ) ,
Aqropyron r e p e n s , Bromus
iaponicus,
Ciqitaria
sanquinalis,
Elvmus
c a n a d e n s i s , Lolium perenne, and Zea m a s but p o o r l y or n o t a t a l l on o a t s
(Avena s a t i v a ) , 13 o t h e r s p e c i e s of Gramineae and 9 commercial p l a n t s i n
other
families.
R.
raminis
was a l s o found i n O n t a r i o on s i x
nonqraminaceous hosts,
Tw: i s o l a t e s from P l a n t a q o major f a i l e d t o i n f e c t
The morphology of 2. g r a m i n i s i s d i s c u s s e d and a non- sexual o r i g i n
wheat.
of t h e r e s t i n g s p o r e s i s suggested. The fungus grew between 5 and 21 C
with optimum about 15-19 C.
Introduction
I
The c h y t r i d i a c e o u s fungus Rhizophvdium
q r a m i n i s was f i r s t r e p o r t e d by Ledingham ( 3 )
on roots o f wheat and Panicum from O n t a r i o
and Massachusetts.
More r e c e n t l y , MacFarlane
(4) found t h i s fungus on c e r e a l s , g r a s s e s ,
Chenopodium,
Stellaria,
and
tobacco
in
Zngland.
I n O n t a r i o , g. q r a m i n i s was one o f
fungi
commonly
found
four
zoosporic
a s s o c i a t e d w i t h wheat s p i n d l e s t r e a k mosaic
The p o s s i b i l i t y of it b e i n g a
v i r u s (1).
vector
of
WSSM
v i r u s prompted f u r t h e r
i n v e s t i g a t i o n on morphology, d i s t r i b u t i o n i n
Ontario,
h o s t range, and t e m p e r a t u r e e f f e c t .
Methods
I
Rhizophvdium s r a m i n i s Ledingham was found
on t h e roots of w i n t e r wheat s e e d l i n g s grown
i n s o i l from v a r i o u s f i e l d s a t 15-18 C f o r 3
t o 4 weeks.
To i n c r e a s e t h e number of
f r u i t i n g b o d i e s and t o make roots e a s i e r t o
examine
microscopically,
the
roots
of
s e e d l i n g s removed from t h e s o i l were r i n s e d
i n t a p water, t h e young p l a n t s p o t t e d i n sand
and watered w i t h h a l f - s t r e n g t h Hoagland's
s o l u t i o n . The f r u i t i n g bodies were u s u a l l y
abundant a f t e r a f u r t h e r 2 t o 3 weeks a t 1518 C.
P r e v i o u s f a i l u r e t o f i n d t h e fungus o n
roots of p l a n t s grown i n sand (1) c a n be
a t t r i b u t e d t o t e m p e r a t u r e which o c c a s i o n a l l y
exceeded 29. c.
The
fungus was t r a n s m i t t e d t o o t h e r
s e e d l i n g s by growing s e e d l i n g s around an
i n f e c t e d wheat p l a n t i n sand i n a 4- inch p o t
f o r 2-3 weeks.
The t e s t s e e d l i n g s were t h e n
repottea
i n sand.
The fungus h a s been
maintained on wheat i n t h i s manner f o r o v e r 4
years.
Host
range
and
temperature
Biosystematics
Research
Institute,
A g r i c u l t u r e Canada, O t t a w a , O n t a r i o , K1A OC6
e x p e r i m e n t s were done w i t h a n i s o l a t e from a
m i x t u r e of s o i l s c o l l e c t e d from wheat f i e l d s
near Brantford, Ontario.
Observations and results
Morpholoqy
Rhizophydium
q r a m i n i s o c c u r s on root
h a i r s and e p i d e r m a l c e l l s of wheat,
barley,
and
certain
g r a s s e s and weeds.
It i s
recognized by s p h e r i c a l s p o r a n g i a on t h e
s u r f a c e of root c e l l s (Fig. I), or by t h e
cup-shaped w a l l s of empty s p o r a n g i a f o l l o w i n g
zoospore r e l e a s e (Fig. 2 ) . The h o s t c e l l i s
p e n e t r a t e d by a f i n e germ t u b e which grows
i n t o a s p a r i n g l y branched r h i z o i d (Fig. 2)
w h i l e t h e e x t e r n a l zoospore c y s t e n l a r g e s and
becomes a sporangium.
The empty s p o r a n g i a
and r h i z o i d s c l e a r l y d i s t i n g u i s h t h e fungus
from t h e protozoa or from PVthium s p o r a n g i a
which a r e a t t i m e s s u p e r f i c i a l l y s i m i l a r t o
the
globular,
e x t e r n a l s p o r a n g i a o f 3.
graminis.
Sporangia of a l l i s o l a t e s t h a t I have
examined
from
Ontario
were
typically
6-36 um diam and o c c a s i o n a l l y
spherical,
ovate.
Larger s p o r a n g i a , r e p o r t e d up t o 100
um diam (3), were n o t s e e n on e i t h e r f r e s h l y
c o l l e c t e d p l a n t s or on p l a n t s grown i n sand.
A t m a t u r i t y s p o r a n g i a r e l e a s e zoospores by a
sudden b u r s t i n g of a t h i n a p i c a l p o r t i o n of
t h e sporangium w a l l .
The zoospores, which
s w i m away immediately, v a r y from s p h e r i c a l ,
2-2.5 pm diam t o e l l i p t i c a l , 2x3-1.5X4 pm and
have one l i p i d body, 0.5-1.5 p m diam, and one
posterior flagellum.
The f l a g e l l u m l e n g t h s
of f i v e i s o l a t e s d i f f e r e d a s f o l l o w s :
10-12,
12.5-14,
13-15, 14-15.5, and 15-16 p m .
The
measurements i n c l u d e t h e v e r y
fine
and
whiplash end 1.5 p m i n
difficult- to- see
length.
R e s t i n g spores a r e 10-18 p m diam and have
a h y a l i n e or v e r y p a l e brown o u t e r w a l l 0.5-
192
VOL. 53, NO. 4, CAV. PLANT DIS. S U R V . DEC. 7973
F i g u r e s 1-3. Rhizophydium graminis on root hairs of wheat. 1) Mature sporangium; 2 ) Empty sporangium following discharge of zoospores, note the
rhizoids inside the root hair; 3) T w o thick- walled resting spores. A l l figures at the magnification shown in F i g . 3.
1 .O p m t h i c k and a h y a l i n e i n n e r w a l l 0 . 5 p m .
The o u t e r w a l l i s a t f i r s t smooth b u t becomes
roughened when mature ( F i g . 3 ) . I have n o t
been a b l e t o c o n f i r m e a r l i e r o b s e r v a t i o n s (3)
t h a t r e s t i r g s p o r e s r e s u l t a f t e r f u s i o n of
rhizoids.
Although root h a i r s u s u a l l y a r e
i n f e c t e d by many l a r g e and s m a l l t h a l l i w i t h
I
believe
resting
interlacing rhizoids,
spores a r e a s e x u a l because o f t e n a s o l i t a r y
r e s t i n g s p o r e was s e e n w i t h o u t any s i g n of
f u s i o n t o an a d j a c e n t c y s t o r r h i z o i d .
Temperature e f f e c t on qrowth
The
maximum t e m p e r a t u r e measured among
t h e roots i n sand c u l t u r e was 20-21 C;the
estimated
optimum
growth, based on t h e
abundance of s p o r a n g i a , was between 15 and 1 9
C.
The fungus a l s o grew a t 5 C which was t h e
lowest temperature t e s t e d .
Resting spores
o c c u r r e d a t 5 t o 2 1 C and were e x c e e d i n g l y
abundant a t 20- 21 C.
Survival
The fungus h a s s u r v i v e d 9 y e a r s , t h e
longest period tested,
i n air- dried soil
stored
in
a
greenhouse
i n which t h e
t e m p e r a t u r e v a r i e d from a b o u t 15 t o 30 C.
Distribution
I n 1 9 7 1 B. g r a m i n i s was r e c o v e r e d from 15
o u t of 19 s o i l samples c o l l e c t e d i n wheat
f i e l d s i n southern Ontario, including t h e
f o l l o w i n g c o u n t i e s : E l g i n , Haldimand, Huron,
Kent,
and Lincoln.
I t h a s been recovered
from s o i l a t t h e C e n t r a l Experimental Farm,
Ottawa,
and
a t Amherst I s l a n d i n Lake
Ontario.
It i s t h e r e f o r e p r o b a b l y p r e s e n t i n
a l l wheat growing a r e a s of O n t a r i o .
In
a d d i t i o n , it was found i n muck s o i l i n which
v e g e t a b l e c r o p s had been grown f o r many y e a r s
from t h e Bradford Marsh, Simcoe County.
Host r a n q e
Plants
were
recorded
as
susceptible,
l i g h t l y infected o r r e s i s t a n t t o
of E . q r a m i n i s from wheat.
an
isolate
-
Susceptible
S u s c e p t i b l e s p e c i e s were
i n f e c t e d a t l e a s t a s s e v e r e l y a s cv. Kent
w i n t e r wheat: mature s p o r a n g i a were abundant
on epidermal c e l l s and r o o t h a i r s and t h e
fungus was a b l e t o s u b s i s t on t h e t e s t p l a n t
a f t e r removal of t h e i n f e c t e d wheat p l a n t
from t h e p o t .
Susceptible p l a n t s includsd
w i n t e r wheat (Triticum a e s t i v u m L. cv. Kent) ,
durum wheat (2. durum Desf.
cv. Ramsey) ,
b a r l e y (Hordeum v u l q a r e L.
cv. Vantage) ,
f i e l d corn
may^ L. cv. Dekalb) , sweet
corn (Zea maw v a r . ruqosa Bonsf .) , p e r e n n i a l
r y e g r a s s (Lolium perenne L.!,
Aqropyron
r e p e n s (L.) Beauv. , Bromus j a p o n i c u s Thumb. ,
D i s i t a r i a s a n q u i n a l i s (L.) Scop. , and Elvmus
canadwnsis L.
(a
-
Light infection
Lightly infected plants
had a few mature s p o r a n g i a on r o o t s and
possibly
only
succumbed t o E . q r a m i n i s
because of t h e f a v o r a b l e t e s t c o n d i t i o n s .
The fungus e i t h e r d i d n o t s u r v i v e o r was
b a r e l y d e t e c t a b l e on t h e t e s t p l a n t s when t h e
i n f e c t e d wheat p l a n t was removed from t h e
pot. S p e c i e s i n c l u d e d i n t h i s c a t e g o r y were
cabbage ( B r a s s i c a o l e r a c e a v a r . c a p i t a t a L.
cv. Golden Acre), cress (Lepidium s a t i v u m
L.) , r i c e (Orvza s a t i v a L. cv. Blue Bonnet) ,
l e t t u c e (Lactuca s a t i v a L. cv. Grand Rapids) ,
Aqropyron trachycaulum (Link) Malte. , Avena
byzantina K. Koch, &.
s t e r i l i s L.,
Bromus
i n e r m i s Leyss.,
Festucn r u b r a L . ,
Holcus
l a n a t u s L., and Hordeum bulhosum.
-
Plants
were c o n s i d e r e d
Resistant
r e s i s t a n t i f e n c y s t e d zoospores f a i l e d t o
develop
into
mature
sporangia.
It is
i n t e r e s t i n g t o n o t e t h a t w i t h i n t h e genus
Avena, w i l d o a t s (5. f a t u a and 5. b a r b a t a )
and t h e c u l t i v a t e d v a r i e t i e s S t o r m n t and
Garry were completely r e s i s t a n t , whereas on
cv. C l i n t l a n d 6 0 a few a b o r t e d s p o r a n g i a
were s e e n w i t h t h e i r germ t u b e s walled- off by
host plug material.
I n c o n t r a s t , t h e wild
ll
I 1
---
VOL. 53, NO. 4, CAN. P L A N T DIS. SURV. DEC. 1973
g r a s s e s A.
b z a n t i n a and A. s t e r i l i s were
l i g h t l y infect:d.
R e s i s t a n t p l a n t s included
o a t s (Avena s a t i v a L. cv. Stormont, Garry, and
C l i n t l a n d 60), m e t (Beta v u l q a r i s L . ) , g r e e n
bean
(Phaseolus v u l q a r i s L. cv. H a r v e s t e r ) ,
Mansf.
p a r s l e y ( P e t r o s e l i n u g crispum ( M i l l . )
cv. Moss C u r l ) , Avena b a r b a t a B r o t . , Avena
f a t u a L.,
Dactvlis glomerata L.,
and=
p r a t e n s i s L.
-
193
A s e a r c h of
t h e l i t e r a t u r e shows t h a t
a p a r t from t h e r a t h e r s c a r c e r e p o r t i n g s of E.
g r a m i n i s (1, 3, 4), a s p e c i e s of Rhizophvdium
h a s been found p a r a s i t i c on E r i c a g r a c i l i s i n
(S),
and
in
Germany
E.
Switzerland
patellariurn
was
reported
parasitic
on
c o r t i c a l c e l l s of cabbage ( 2 ) .
However, most
s p e c i e s of Rhizophvdium o c c u r on a l g a e i n
a q u a t i c h a b i t a t s or have been i s o l a t e d on
from
soil.
p i n e p o l l e n or o t h e r b a i t s
S e v e r a l have been grown i n p u r e c u l t u r e on
c h e m i c a l l y d e f i n e d media but a l l a t t e m p t s by
t h e a u t h o r t o grow g. q r a m i n i s on a l g a e , p i n e
p o l l e n , or i n p u r e c u l t u r e have, so f a r ,
failed.
I n a d d i t i o n t o t h e h o s t range t e s t s
r e c o r d e d above, E . g r a m i n i s h a s been found on
a number of o c c a s i o n s on p l a n t s o t h e r t h a n
wheat.
I n a sample of muck ( o r g a n i c ) s o i l
from t h e Bradford Marsh, R. q r a m i n i s grew
a b u n d a n t l y on barnyard g r a s s (Echinochloa
c r u s - q a l l i (L.) , Beauv.) , p u r s l a n e ( P o r t u l a c a
o l e r a c e a L.) , and common g r o u n d s e l ( S e n e c i o
Ac k now ledg men ts
vulqaris
L.),
which
grew
frominadvertently c o l l e c t e d with t h e soil.
The
The a u t h o r t h a n k s n r . J. T. S l y k h u i s and
f u n g u s grew on wheat grown i n t h i s s o i l b u t
Miss M. E. E l l i o t t f o r t h e i r comments a f t e r
n o t on cabbage, c a r r o t (Daucus c a r o t a L:),
r e a d i n g t h i s manuscript.
c e l e r y ( A p i u m q r a v e o l e n s L.) , l e t t u c e , onion
(Allium
L.) ,
parsley,
tomato
(-rsicum
esculentum M i l l . ) , o r Oenothera
b i e n n i s L.
Literature cited
On two o c c a s i o n s i n 1973 R. q r a m i n i s was
found on p l a n t a i n ( P l a n t a q o major L.) from
Vineland and P o r t Colborne. On each o c c a s i o n
a t t e m p t s t o t r a n s m i t t h e fungus t o wheat were
unsuccessful.
1.
Barr,
J. S., and J . T. S l y k h u i s .
Zoosporic f u n g i a s s o c i a t e d with
wheat s p i n d l e s t r e a k mosaic i n O n t a r i o .
Can. P l a n t D i s . Surv. 49:112-113.
D.
1970.
R.
a m i n i s was found on f i v e o t h e r
o c c a s i o n r i n 1 9 7 3 on t h e f o l l o w i n g g r a s s e s
and weeds c o l l e c t e d i n O n t a r i o : Aqropvron
revens,
redroot
pigweed
(Amaranthu s
retroflexus L.) , s h e p h e r d ' s p u r s e ( C a p s e l l a
b u r s a - D a s t o r i s (L.) Medic .) , w i l d s t r a w b e r r y
( F r a q a r i a v i r q i n i a n a Duchesne) and Polvsonum
a v i c u l a r e L.
2.
3.
Ledingharn, G. A.
1936.
Rhizophvdium
q r a m i n i s n. s p . , a p a r a s i t e of wheat
roots. Can. J. Res., C . , 14:117-121.
These f i n d i n g s s u g g e s t t h e r e a r e h o s t
s p e c i f i c s t r a i n s of E . q r a m i n i s because t h e
i s o l a t e from wheat s e v e r e l y i n f e c t e d o n l y
graminaceous p l a n t s
whereas
the
fungus
o c c u r r e d n a t u r a l l y on non-graminaceous weeds
from s e v e r a l
locations.
Moreover,
two
i s o l a t e s from P l a n t a a o major f a i l e d t o i n f e c t
wheat under f a v o r a b l e t e s t c o n d i t i o n s i n t h e
1a b o r a t o r y
4.
MacFarlane, I . 1970. Laqena r a d i c i c o l a
and Rhizophvdium q r a m i n i s , two common
and
neglected fungi.
Trans. B r i t .
MyCole SOC. 55: 113-116.
5.
Stalder,
L.,
and F. Schutz.
1957.
Untersuchungen
uber
die
kausalen
Zusammenhange d e s E r i k a w u r z e l s t e r b e n s .
Phytopathol. Z. 30: 117- 148.
.
Gaertner,
A.
1960.
Einiqes
zur
E r n a h r u n g s p h y s i o l o g i e von Rhiiophvdiurn
p a t e l l a r i m Scholz.
Arch. Mikrobiol.
36 :06-50.