Complex populations of minor pathogens associated with roots from barley plants infected by barley yellow mosaic virus.

NOTE

Complex populations

of

minor

pathogens

associated

with

roots

from

barley

plants

infected by

barley

yellow

mosaic

virusr

IJDENBERG,

P.,

KUMMERT,

J.

and LEPOIVRE,P. 2

Laboratoire de Pathologie végétale

Abstract

The purpose of the present contribution is to describe the main fungi associated with roots

of BaYMV infecred barley.

Polymyxa graminis

Led.

is a

vector

of

several soil-borne viruses

of

cereals

and

weeds,

including barley yellow

mosaic

virus

(BaYMV) (INoUYE ans SAITo, 1975). P. graminis was shown to be closely associated

with other fungi found in young rootlets, root hairs and superficial cortical

cells

of

wheat

(Nor-r

et

al., l98l)

or

grasses, _{including Lolium} perenne

(LaanuvEne,1979). These fungi cause little visual damage and have been

called <minor pathogens>. Although minor root pathogens may interact

rvith the infection process

of

other pathogenic agents

(Selr,

1979), and

despite

their

possible role

in

BaYMV transmission, they attracted little

attention so far.

The inoculation of the zoosporic fungus was done by planting 3-day-old

seedlings of winter barley (cv. Gerbel) in a mixture (2:

l)

of sand and

natu-rally infected soil (loam collected from a field where barley expressed

cha-racteristic BaYMV symptoms

in

the spring).

Received November 9, 1986. Accepted February l, 1988.

Faculté des Sciences Agronomiques de Gembloux, avenue Maréchal Juin, 13, B-5800 Gembloux

-

138

-Four seedlings disinlected by treatment

lor

2 min

in

HgClz (0.1go) and

lv{anoxol OT (BDH; 2 ppm), rvere planted in each pot, soil moisture being

kept saturated with water. Plants were maintained beni'een 17"C and 22'C

under natural light

in

a greenhouse.

Roots from the greenhouse inoculated plants and from BaYi\'IV-infected

plants lrom the lield, rvere collected, rvashed in running tap water, and

stain-ed by boiling for 2 min in 0.033 q0 cotton blue in lactophenol ; they rvere then

dipped

for

one day in lactophenol belore microscopic observations.

Zoospores contained in a droplet

ol

water

in *hich

inlected roots had

been soaked, \\'ere lixed by exposure

to

a

solution

ol

osmic acid (190

rv./v.), dried, and then stained bi'adding an equal volume

ola

cristal violet

solution (0,005 %).

Three species

ol

zoosporic lungi were most lrequently'observed in the

roots of barlel'seedlings placed in naturalll' BaYiVIV-contaminated soil, or

in the roots

ol

BaYMV-inlected plants collected from the field : Polymyxa

graminis, Otpidium brassicae (Wor.) Gang and Lagena radicicola

Vander-pool and Led.

Zoosporangia and yegetatiye plasmodia

ol

P.

graminis ç'ere observed

after staining rvith cotton blue, in roots ol seedlings gro\\ n in contaminated

soil, but not in steriiized soil (Fig. 1). Clusters ol resting spores of P.

grami-rzls rvere observed in unstained root cells

ol

the plants about 20 days alter

potting in contaminated soil (Fig. 2), as in those of the plants directly col-lected from the field. When rootlets ol plants u'ith zoosporangia or mature

resting spores of P. grantinrs rvere kept in water, they released bifiagellate

zoospores (Fig. 3) rvhich could be conlused u'ith the zoollagellate Cerco-bodo

(HoIANDE,

1952).

With O.

brassicqe, inlection

of

roots

ol

either seedlings,

or

BaYMV-infected plants lrom the lield, resulted in the formation

ol

stellate resting

spores

(Fig.4),

about 25 pm in diameler, often closell'packed in the host

cells.

The zoosporic fungi Rhizophidium graminis Led. and Ligniera pilorum

Fron. and Gaillat, rvere occasionally observed. L. pilortrm induced a

slvel-ling

ol

infected root hairs in a number

ol

seedlings (Fig. 5).

R.

graminis

rvas observed as zoosporangia outside host cells, as well aS resting Spores

attached to srvollen empty cells, as described by Ledingham (1936).

The Oomycete

L.

radicicola shorved thalli which'nvere attached

to

the

point

ol

penetration by a collar (Fig. 6) _; such inlection resulted in the lor-mation

ol

a zoospore.

Finally, dark

sclerotia

ol

a

Deuteromycete identilied as Phialophora radicicola Cain (Fig. 7) rvere olten present _{in (or} near) vascular tissues

ol

the barley roots,

in

close association rvith lignitubers (Fig. 8).

Our

observations shorv the complexity

ol

the populations

of

minor

pathogens associated w'ith roots

ol

field

BaYlvlV-infected barley plants,

and

ol

barley seedlings grown

in

a contaminated soil.

Although barley yelloiv nosaic is recognized as

a

fungus transmitted

soil-borne viral disease , there is no experimental prool concerning the

iden-tity ol

its vector(s). Indeed, the obligate parasite nature ol P. graminishas

hampered undubious demonstration

of

its involvment as BaYIvlV vector.

Because

ol

the lack

of

pure or axenic culture

ol

the fungus , evidence for

its role as vector had been deduced from correlations betlveen fungal and

virus inlection

(lNouvr

and

SAtto,

1975). The high rvater soil content

required

lor

optimal BaYMV transmission erplains rvhy zoosporic fungal

parasites u'ere considered as possible vector, since these fungi are

com-monll'lound in

cool moist condition,

in

association rvith barley roots

of

inlected plants.

A

complex population ol minor pathogens is also present in the roots of

wheat plants infected by the wheat spindle streak mosaic virus (SllrxHuts

and B,A.nn, 1978). In this case, rvhen isolates of each species of the

zoospo-ric lungi rvere placed in soil surrounding the roots ol sap-inoculated rvheat

plants, the virus rvas transmitted only b1'sand mixed rvith roots from plants

inlected rvith

P.

grarninis

(Slr:rHuts

and B,rRn, 1978). Such single

spo-rangial or unifungal isolates have not been reported so

lar

for P. graminis

on barley.

Recently, using immuno-microscopy, Le,NceNne Bc and VeN DEn

Wal

(1986) _{did not} find any virus particles in close relation with either P.

grami-rirs, or Lagena sp. . The results do not so far exclude the latter lungus as

a possible vector

ol

BaYMV.

Remerciements

Ce travail a été réalisé dans le cadre d'une recherche subventionnée par l'Institut pour

-140-References

HorraNoe, A. 1952. La classe des Chrysomonadines. In.' Traité de Zoologie (Ed. Grassé

P.P.) lvlasson and Cie, Paris, I : 519-692.

lNouyE, T. and S,rrro, Y. 1975. Barley yellow mosaic virus. CMI/AAB Descriptions of plant

i,irases 143,3pp.

Lrsnlivene, R.E. 1979. Resorving ploblems of old pastures.ln: <<Soil-borne plant patho-gens>. (Ed. Shippers,8., and Crams, W.) Academic Press, London:3ll-326. L.rrcexsrnc, W.C. and V,rr Drn \\',rr., D. 1986. Identilication ol barley I'ellorv mosaic

virus by'immunoelectron microscopl in barley but not in Polymyxa graminis or Logena

radicicola. Netherlands Journal of PIant Pathology 92: 133-136.

Leorrcu..rrt, G.A. 1936. Rhizophidium graminis n. sp., a parasite ol rvheat rooLs. Canadian

Journal of Reseorch Cl.1: I I7-121.

NoLr, 8.L., Ror.r.rrxe, C.P., S\llrH, S.H., and Cor-e, H. Jr. l98l Further evidence lor the

association ol Polymy.ra graminis nith the transmission ol rvheat spindle streak mosaic

v irus. P hy topa t hology 1 | : 1269 -l 21 2.

S,rL.r, G.A. 1979. The increasing inreresr in ,, minor-pathogens>. 11.' <Soil-borne plant

palhogens >. (Ed. Schippers, 8., and Crams, W.) Academic Press, London: 289-312.

Srt"lrnurs, J.T., and B.rsn, D.J.S. 1978, Confirmation ol Polymyxa graninis as a \,ecror of

w

"s

ë

zQU

i S i\N,:..::i\

N

Fig. l. _- \'egetatir e plasmodia ol Pof my.ra grarrinis

]R.,.

&

1..,,,','# t:rll i r:f:s.1, . _:.Nrr:i\\

\&

;r ' ;1\11:;r ::

tr'\

i.,\

\

Fig. 3. _- Billagellate zoo5porei relcaserl lrom rocrs inl:;ted rrith zoosporangia or nalure resting 5pores

ol P. graminis ..ii.ii::il.iii:ès, I :i .:... \\::l::: -. iS'S:, ::: : :::1\i: iisf'\.r:\.r:\r:4, . ..r:..1 ii.:... _{i \\::l::: -. iS'S:,} : : :::1\i: iisf'\.r:\.r:\r:4, . ..r:. : : \\it ;tl ] : I\a i:i .:t.t .$\\: ,.i \r'-:r:i:t:..i-ri\S:\i i:::1.':r:: \i,.( i Fig. 1.

-- -

144-Fig. ?. .._ Derk sclerotia of Phiolophoro radicico[a

,,iS\iN\..

.i.s

'S . l.t r _"{

i*'

'

*N

I)ivers

-

Varia

NEDERLANDSE TERIVIINOLOGIE OP HET GEBIED VA T' CEWASBESCHERNîINC

ln het recente verleden zijn Nvee terminologielijsten versihenen op het terrein yan de

gen,as-bescherming.

I ' < Lijst van gervasbeschermingskundige termen D uitgeeeven door de < Commissie \ oor

ter-minologie van de Nederlandse Plantenziektekundige Ver;niging, i61 pagina's).

2 " < Terminologie op het gebied van de onk ruidkunde voor her Nederlandse taalgebied r

(CO-TONT)(22 pagina's). _{De beide brochures zijn r.erkrijbaa: resp. bij}

:

1' de Nederlandse Plantenziektekundige Vereniging, posrbus _11_6700 A.{ \\-aeenrnqen

(Nederland)

2' COTONT per adres CABO, postbus 16, \!'ageningen (,:.-ederland).

Naast deze lijsten over terminologie zijn er ook lijsien rerschenen over.r*ederlandse namen

van plantenziekten:

bij landbourvgervassen (r'erschenen in no l0,zl ran Gervasbes;herming januari 1979)

bij bloembolgervassen (r'erschenen _{als supplement n. I ran cerrasbescherming lE juli}

I 987)

bij gekrveekte houtge*assen (r'erschenen als onderdeel no I van Ceriasbeschermins 1972)

bij lruitgervassen (verschenen als onderdeel n' I _'ar Gervasbescherming I973)

Deze laatste vier lijsten zijn eveneens nog verkrijbaai bij ie Nederlandse

plantenziekrekundi-ge Vereniging.

De v.o.Fy.To.z./A.E.R.z.A.P. rvensr de bekendheid ran deze lijsten zo'eel mogerijk te stimuleren. Hierdoor willen we het gebruik van de juiste terminoloeie in ons vakeebied

bevor-deren en onge\\,enste terminologie vermijden.

De termen in de lijsten zijn gerangschikt in allaberische yolgord: en na elke term bevindt zich de nodige uitleg. ook onge$enste termen zijn in de li;sten opgenomen. De namenlijsten

zijn hoofdzakelijk _{per rvaardprant gerangschikr mer bijklmden regisrers achreraan.}

In beide commissies kwam de terminologielijsr tot stand door een srmenqsrljng van Neder_

landers en Vlamingen.

De Voor:irter r'.d. \'.O.Fy.To.Z.

lll*::'l$

_

146

_

INITORMATIONS

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