12. A REVIEW OF PLANT VIRUS DISEASE IN

PENINSULAR MALAYSIA

Ching Ang ONG* & Wen Poh TING**

Introduction

155

The importance of virus diseases was recognized of late. Hitherto no detailed studes of viruses have been carried out. Of the virus diseases reported in J\'Ialaysia, penyakit merah virus disease of rice is by far the most important, and has been studied by numerous workers (Ou et al., 1965; Ting and Paramsothy, 1970; Ting, 1971; Lim, 1972; Ting and Ong, 1974).

Most of the insect-borne viruses reported in Malaysia are transmitted aphids. This is followed by leafhoppers which is responsible for the transmission of 3 diseases of rice. The only white-fly transmitted virus disease is yellow vein-banding on Agerntum conyzoides. So far no vrus diseases have been reported to be transmitted thrips, mealybugs, mites, nematodes or fungi.

The characteristics of the virus diseases studied in Malaysia are discussed in this paper, including a disease reported to be caused by myeoplasma (Singh et al., 1970) viz .. paji jantan.

Cereals Rice Penyakit merah virus (PMV) disease of rice has been observed in Peninsular Malaysia for a long time (Coleman-Dascas. 1935). However, it ,vas not until 30 years later that the nature of the disease was established ( Ou et 19G5). Earlier workers attributed the disease to nutrient toxicity, nutrient deficiency ( Lockard, 1959 l, nematode and soil acidity. The symptom and host range of the vims are given in Table 1.

Penyakit merah vims is similar to tungro virus in the Philippines. Both viruses are transmitted by N ephotettix virescens and N. apicalis in a non-persistent manner (Ting and Paramsothy, 1970). However, the host range of Pl\'IV and that of tungro virus appear to differ. Echinochloa crusgalli, a symptomless carrier of tungro virus, was not infected by Pl\1V; the symptoms of Eleusine indica infected with penyakit merah and with tungro were found to be different ( Ting, 1971 L In addition, Oryza ridleyi. a susceptible host of tungro virus was shown to be not susceptible to PMV (Ting and Ong, 1974).

The incidence of PMV varies from locality to locality and appears to be cyclic. Yield losses of 69 to 92% have been recorded (Lim and Goh, 1969). The severity is dependent on the variety and time of infection.

The second virus disease reported on paddy is orange leaf. The disease is of limited economic importance, and is transmitted by the leafhopper, Recilia dorsalis (Singh, 1971). The only known host of the virus is 0. sati,:a. Symptoms of affected plants are described in Table 1.

Padi jantan has also been observed by farmers for a long time. The disease is of

* Plant Pathologist and ** Assistant Director, Malaysian Agricultural Research and Develop­ment Institute, Malaysia

Tab

le 1

. C

hara

cter

isti

cs o

f vi

rus

dise

ases

in

Mal

aysi

a

,-=

,==

==

-,=

~--,I

--'-

,~--=

--

-"--

--~

--,-

--_

--~

-'-

--,,

, -

,, ,,

-=

-'v·

,,=

;-~,~

":"l

\for

ph'o

logy

==

=-

Nat

ura

l ,V

irus

:S

ympt

oms

Ho

st r

ang

e ]T

rans

mis

sion

I

1 r~

~-v

ei .0

1

'an

d p

hy

sica

l h

ost

__

__

_ ,

l ·

I _

__

_

re a

w

ns 11

ps

, pro

per

ties

P~

di

IPen

yak

it M

erah

]Y

ello

w t

o o

ran

ge

Ory

za s

ati

va,

!Gra

ft :

-M

in.A

cq.:

lO

n;-_

---

---

-

Pad

i

(Tu

ng

ro)

!dis

colo

rati

on o

f le

af;

0.

fatu

a,

!Sap

: -

Inb

.:

3h

rs.

,mo

ttli

ng

of

yo

un

g

Ech

inoc

hloa

col

onum

, IN

epho

tett

ix

Ret

.:

5d.

!leav

es,

stu

nti

ng

; E

leu

sin

e in

dica

:

vfre

scen

s M

in.I

noc.

: 30

m.

_! _

__

__

__

__

,red

ucti

on

in

till

erin

g.

IN. ni

gro

pic

tus

Ty

pe:

N

P

I '

I P

adi Ja

n ta

n

I Gen

eral

yel

low

ing,

,O

ryza

sa

tiva

!G

raft

; -

(Yel

low

dw

arf)

!s

ever

e st

un

tin

g;

\ S

ap :

-(M

yco

pla

sma)

!e

xces

sive

til

leri

ng

. N

. vi

rcsc

ens

I

Min

.Acq

.:

10m

. In

b.:

20

-,10

d.

Ret

.:

27d.

,M

in.I

noc.

: 10

m.

Pad

i lo

;~;g

e l

eaf

I

!Typ

e:

P _

_ _

Cit

rus

sp.

ITri

stez

a

Pas

sio

n f

ruit

!P

assi

on f

ruit

m

osa

ic

]Lea

ves

ora

ng

e !c

olou

red;

ro

lled

;

!slig

ht

stu

nti

ng

; d

eath

of

pla

nt.

i I Gen

eral

dec

line

; !d

ie-b

ack

of

twig

s 'a

nd

bra

nch

es·

'vei

n cl

eari

ng

; lr

orky

vei

ns;

ls

tem

pit

tin

g;

/yel

low

ing

of

foli

age.

I jC

hlor

otic

sp

ots

; :m

ott

lin

g;

curl

ing

; [p

ucke

ring

; d

isto

rtio

n;

!stu

nti

ng

;

!!so

rter

in

tern

od

es;

rin

g-s

po

ttin

g.

I

10

. I

ryza

sat

1va

i

Gra

ft:

-­S

ap

: -

Rec

ilia

(I

na

zum

a)

I do

na,l

fa

: C

itru

s re

ticu

lata

(M

and

arin

G

raft

: +

o

ran

ge,

Lim

au C

hem

bol,

S

ap :

-L

imau

Ku

pas

, L

irn

au

To

xop

tera

K

op

ek),

C.

sine

nsis

(L

irn

au

citr

icid

ns

Po

ton

g),

C.

aura

nt,i

foli

a (L

irn

au N

ipis

), C

. g

ran

dis

( L

imau

Basa

r),

C.

mic

ro-

carp

a (L

imau

K

atsu

ri),

C

. h

istr

ix

(Lir

nau

Pu

rut,

L

irna

u K

edan

gsa

), C

. li

mon

(L

imau

S

usu

, L

irna

u K

apas

), C

. si

ving

lei

(Ku

mq

uat

), C

. au

ra,n

tiw

m

Min

.Acq

.:

3hrs

. In

b.:

l-

14

d.

Ret

.:

-M

in.I

noc.

: 3

hrs

. T

yp

e:

P

i ( S

tan

dar

d s

ou

r)

I ----•--~

--

/Pas

sijl

ora

edul

is,

P.

foet

icla

, i 1G

raft

: +

P

. la

urif

olia

, P

. li

gula

ris,

,S

ap :

+

IP. qu

aclr

angu

lari

s,

P.

pla

ty-1

Myz

us

pers

icae

, lo

ba,

P.

ma

lifo

nn

is,

Ap

his

gos

sypi

i,

P.

mac

roca

rpa,

P

. vi

tifo

lia

, A

. ca

cc'iv

ora

P.

mol

lisi

ma,

Cas

sia

occi

den-

tali

s, G

om

ph

ren

a g

lobo

sa,

,Che

nopo

diw

m a

ma

ran

tico

lor

!Typ

e:

NP

S

hap

e:

sph

ere

TIP

: 69

-70°

C

DE

P:

10-2

--10

-"

LIV

: 5-

6d.

e--

' en

C

h

Natu

ral

ho

st

Ch

illi

Cu

cum

ber

, P

eriw

ink

le,

Ban

ana

Let

tuce

!Vir

us

:Chi

lli

ven

ial

· m

ott

le

(Cu

cum

ber

mos

aic-

I • Let

tuce

mos

aic

i $y

mp

tom

s

:l\f

ottl

ing,

'v

ein

clea

rin

g,

vei

n b

and

ing

, :,

tunt

ing,

Ji

sto

rtio

n.

IN e

cro

tic

stre

ak

lbu

nch

y t

op

, '

,stu

nti

ng

Sev

ere

mo

ttli

ng

; d

ark

-gre

en b

list

er;

dis

tort

ion

; st

un

tin

g.

Vei

ncl

eari

ng

, ve

illb

andi

ng,

mo

ttli

ng

.

Tab

le 1

. (C

onti

nued

)

ran

ge

! .

. ::

Vir

u -v

ect r·

-·

iMor

phol

~gy

;T

rans

rmss

10n

i!re

latf

on

sht

s an

d p

h:.:s

1cal

___

--~

-,,

···-

----

·· --

~-~

pr

OJJ

!!rt

ies

avs

1<

no

n a

nn

uw

n,

C.

chin

en-

iGra

ft :

+

1Min

.Acq

.:

5s.

! Sh

ape:

fr

ute

scen

s, H

yosy

arn

us

,Sap

: +

:I

nb.:

-·

i

flex

uous

ro

d

Nic

an

dra

phy

salo

ides

, /A

ph

is g

ossy

pii,

IR

et.:

3

hrs

. fT

IP:

55--

G0°

C

ta.b

acum

'Du

tch

A'

;A.

era

cdo

ora

, t:

Win

.Ino

c.:

5s.

DE

P:

10

·'-1

0 '1

'Wh

ite

Bu

rley

', P

hys

ali

s !M

yz1r

n pe

rsic

ae,

iTyp

e:

NP

iL

IV:

7-S

d.

ffor

idan

a,

P.

min

ima

![

t. n

wid

is,

· ;I.

cit

rici

dus,

,A

. sp

ira,

ecol

a,,

'H.

seta

,ria

e

!v11

cope

rsic

wn

esci

lla

entu

m

IGra

ft :

+

' '

:sap

:+

[Cuc

nmis

sat

iovu

s { C

ucu

m­

;ber

), C

ncur

bita

, pe

po

, (P

um

pk

in),

C

. 1na

;;:im

a / (

Squ

ash)

_, M

omor

dica

cha

r­,'

1n

tm

(Bit

ter

cucu

mb

er),

/T

rich

osan

thes

an

qu.i

na

/ ( S

nak

e g

ou

rd),

Ben

inca

sa

ceri

fera

(T

on

g Q

ua,

!M

au

Qu

a),

Cro

tala

ria

1u

sara

moe

nsis

, Ca,

lopo

goni

urn

,nni

cuno

,ides

, C

hen

op

od

ium

,a

mar

anti

colo

r,

Go

mp

hre

na

'q

lobo

sa,

Vin

ca s

inen

sis

(Per

iwin

kle

), A

ma

ryll

is s

p.,

Mus

a, s

a,JY

ient

um

(Ban

an

a),

P

assi

/for

a ed

ulis

, A

.mar

a,n­

)thu

s vi

ricl

is,

Cit

rnll

us

1vul,1

~ct'l

'is,

Co

mm

elin

a

inud

iflo

ra

amor

anti

colo

r,

gfob

osa,

l,a

atnc

a L

ath

yru

s o

do

ratn

s

I [Gra

ft:+

fS

ap: +

,M

yzus

per

sica

e,

1-ip

his

go

ssyp

ii,

A

crac

civo

ra

Riw

palo

siph

1Zm

m

aid·

is

--~

--~

-~

----~

----~

--~

--~

-----------

----

----

----

--~

i

M~

n.A

cq.:

30

s.

:Ino

.:

-]R

et.:

40

m.

iMin

.Ino

c.:

Ty

pe:

N

P

'TIP

: 6

0-G

2''C

!D

EP

: 10

-•-1

0 L

IV:

4-5d

.

i-'

tn

_..,

Natu

ral

ho

st

Brr

rnw

ica

rap

a,

Rad

ish

Gro

un

dn

ut

Lo

ng

bea

n

Orc

hid

s

Tab

le 1

. (C

onti

nued

)

! .

. 'V

iru

s-v

ecto

r S

ym

pto

ms

1Tra

nsm

1ss1

0n

.. la

t·

h"ps

,

__

__

__

__

__

__

_ I_

____

le

!O

DS

l.

-ls

ap: +

T

yp

e:

NP

-···-~

--

·--

Mot

tlin

g,

dis

tort

ion

, st

un

tin

g.

eno

po

aiu

m n

mn

ra,n

tico

lor,

ql

lino

n, B

rass

ica

shi

nens

iH,

B.

rap

a,

B.

ule

race

a

per

­ui

rid-

is,

B.

alb

o-g

lab

rn,

B.

na

pu

s,

B.

oler

a<ie

a,

Go

m.p

hre

na

glo

bo1,

a ------· ---

--~

--·-

---

··---

---·

----

----

---·

·-·-

--

Gro

un

dn

ut

mo

saic

!

1Mot

tlin

g w

ith

pat

ches

lo

f d

ark

-gre

en;

chlo

roti

c sp

ots

an

d

rin

g s

po

ttin

g;

stu

nti

ng

.

Mot

tlin

g,

dis

tort

ion

, st

un

tin

g.

i '

iCym

bidi

um m

osa

ic [

Sun

ken

bla

ck n

ecro

sic

'[ (s

pots

on

un

der

!s

urf

ace

of

leav

es o

n

I !V

an

da

& D

end

rob

inm

'

ispp

. D

iam

on

d

I !s

po

ttin

g a

nd

ch

loro

tic

i

iAra

chis

h

ypo

ga

ea,

Cas

sia,

lo

ccfr

lent

alis

, G

lyci

ne

ma:

,;,

!Cll

lopo

gon1

um 1

mw

n11o

ides

'C

rota

lari

a

an

ag

yro

ides

, lS

tylo

san

thes

gm

cili

s,

'Pha

s!'{

ou.s

vu

lga

ris,

1c

heno

podi

u1n

wm

ara

nti

colo

r

:Vig

na

ses

quip

ed<

.dis

, i V

. si

nen

sis,

C

heno

podi

'ton

'.

amar

anti

colo

r,

C.

qu

ino

a,

C. ·

muc

unoi

des,

Gly

cin

e so

,ia,

I'·i

snm

sai

foum

., P

lwse

oln

8

,vu

lga

ris

;Sp

ato

glo

ttis

i'p

., V

on

da

sp.

, jD

endr

obhc

m s

p.,

Phl

aenu

p11i

8 is

p.,

Co

ttle

ya e

nids

o11,

fC

att

leya

sp

. (T

rue

Dep

th),

;C

assi

a o

ccid

enta

lis,

'C

hen

op

od

imn

am

ara

nii

colo

r,

:c. q

uin

oa

, Da

tu.r

a s

tro

mo

ni-

IA p

his

,go

ssyp

ii,

!Myz

us

per

sica

e,

IL. e

rysi

mi

' !Gra

ft:

'Sap

: "'1

jAp

his

go_

ssyJ

!ii,

1A.

crac

c1vo

7:a,

·M

yzu

s pe

rs1.

cac,

!R

hopa

losi

ph 1

1m

, m

a-id

is

iTos

opf.

era

· ci

tric

idu

s

Gra

ft:+

S

ap

:+

Seed

:+

Ap

his

go

ssyp

ii,

!A.

cra

ccfo

ora

, M

yzu

s p

ersi

cae,

iL.

erys

imi

Min

.Acq

.:

5s.

lnb

.:

-R

et.:

40

--,1

5m.

Min

.Ino

c.:

: N

P

,Ty

pe:

N

P

~~

--1

-

!spo

ts o

n S

pa

thu

glo

ttiB

\s

p.

clo

urb

reak

s.

nm

, G

om

ph

ren

a g

lolr

nsa

!Ch

eno

po

diu

m a

ma

ran

tico

lor,

!S

ap :

+

---·

Hyd

ran

gea

sp

p.

Mo

ttli

ng

, d

isto

rtio

n

,Cas

sfo,

u

ccid

enta

lis,

G

om

-lp

hre

na

glo

bosa

, N

icot

ia11

a lu

luti

no

sa,

,V.

tab

cwn

m,

l,V. ,

ran

thi

fi2

-fi5

°C

! IJ

J•;J

":

10 "

-10

' L

TV

: 40

-Ll8

hrs.

TIP

: D

EP

LIV

:

>--

' ()l

00

Tab

le 1

. (C

onti

nued

)

----

---.

. --

-==

==

==

=~

==

==

=-~

==

==

==

==

==

==

~=

==

==

==

==

==

==

N

t

I I

i !

ho

~tr

a

IVir

us

Sy

mp

tom

s IH

ost

ran

ge

!Tra

nsm

issi

on

Am

ary

llis

Tob

acco

, T

om

ato

, C

hill

i

Su

gar

can

e

Ag

era

tum

co

nyzo

ides

Juss

inea

li

nifo

lia,

Key

es:

I Dar

k

gre

en m

ott

les

I !T

obac

co m

osai

c I 1 S

ever

e m

ott

lin

g

lwit

h d

ark

-gre

en

1 isla

nd

s;

dis

tort

ion

an

d s

tun

tin

g

I i

:Su

gar

can

e m

osai

c S

catt

ered

elo

ng

ated

I

wh

itis

h s

trip

s.

I i I -

IYel

low

ve

in b

and

ing

--~

----

Min

.Acq

. In

b.

---

ivei

ns

app

eare

d a

s !y

ello

w b

and

s w

ith

n

orm

al g

reen

in

terv

ein

al a

reas

; th

ick

erin

g o

f v

ein

s an

d c

url

ing

\Sys

tem

ic y

ello

win

g I I I

iche

nopo

dium

an,

iara

ntic

olor

, /S

ap :

+

1 C,q

wi:

gl

obor

, N

. gl

u 'W

hit

,

Nic

oti

an

a

taba

curn

, G

raft

:+

N.

xan

thi,

N.

glut

inos

a,

Sap

:+

N.

rust

ica

, C

ap

sicu

m

Vec

tor:

-a

nn

uu

m,

Lyc

oper

sico

n es

cule

ntm

n,

Che

nopo

diur

n am

aran

tico

lor,

C

. qu

inoa

, G

om

ph

ren

a g

lobo

sa,

Pha

seoh

ls v

ulg

ari

s, V

ing

a

sine

nsis

, C

ucu,

mis

sa

tivu

s,

Da

tura

str

am

on

ium

, P

hys

ali

s fi

orid

ana,

P

. ·m

inim

a

Sa

cch

aru

m o

ffic

inar

wm

, I !G

raft

: -

Zea

-m

ays

'Gol

den

Ham

mer

' S

ap

:+

'Cin

ta',

So

rgh

um

bic

olor

I

'Rio

' 'A

tas'

I I

Ag

era

tum

con

yzoi

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minor importance. The disease was found to be transmitted by N. vfrescens (Lim and Goh, 1968; Lim, Hi70). Recently mycoplasma like structure was observed in the phloem cells of padi jantan-infected plants (Singh et al., 1970). Similar structures have also been shown to be associated with yellow dwarf disease of rice in Japan and the Philippines.

Fruits Citrus Tristeza is widespread in all the citrus growing districts and all citrus varie­ties, with the possible exception of kumquat ( Citrits swing lei), are affected by the virus (Ting and Arasu, 1970). The disease is one of the main limiting factors in the pro­duction of citrus. The widespread distribution of the virus has been mainly attributed to the vegetative propagation of virus-infected planting materials. The aphid vector, Toxoptera citriciclus is commonly found on citrus. Several major citrus growing areas in Peninsular Malaysia have been abandoned as a result of the disease. Passion fruit Indigenous species of Passifiora e.g. P. f oetida have been frequently observed to be affected by mosaic. Similar symptoms have also been found on passion­fruit vines (P. eclulis, f. fiavicarpa, introduced from Hawaii). Comparative studies of two isolates of the mosaic disease showed that while sharing many common characteristics and properties (Table 1), they can be readily differentiated using indicator plants and aphid vectors. Cassia occiclentalis is highly susceptible to the isolate ,vhich cannot be transmitted by Aphis craccivora and A. gossypii ( Ong and Ting, 1973 l. Results of studies indicated that it is likely that the two viruses are related. Field spread of the viruses is mainly affected through prunning operation as well as by aphids which trans­mit them in the non-persistent manner.

Vegetables lVIost of the vegetables commonly grown in the country belong to the family Cruci­

ferae, Solanaceae, Cucurbitaceae, ancl. Legt,minosae. Vegetables grown have been fre-• quently observed to be affected by viruses. Chilli Field grown chilli plants have been found to be infected by a number of viruses. The most prevalent one is chilli veinal mottle virus, a member of the potyvirns or potato virus Y group. The host range, symptomatology and physical properties of the virus are presented in Table 1. AU the chilli varieties tested so far have been found to be highly susceptible. The virus is transmitted in the non-persistent manner alI the aphid species tested. Chilli plants infected a month after sowing can result in reduction as high as Polyethylene sheet coated with aluminum paint has been found to be effective in reducing disease incidence by repelling the aphid vectors 1975).

Tobacco mosaic virus (TMV) has also been found to infect chilli. The same virus ,vas also found on tomato and brinjal. Comparative studies on some of the TMV iso­lates have shown the possible presence of strains or variants in Peninsular Tomato In addition to TMV, tomato plants have recently been reported to be infected

a virus which causes m .. ,~~-·,,. necrotic streak on the leaves and stems of infected plants (Ong, unpublished). The virus has been found to be readily graft and sap trans­missible from diseased to healthy tomato plants. The following plant species have been found not to be susceptible to the virus:-Chenopoclium amaranticolor; C. guinoa, Capsicum a.nnuurn; Datura stramonium; Gom.­phrena globosa; Hibiscus esculentus; Nfrotictna rustica; N. tabacwn; N. a:anthi; PhaBcolus ·vulgaris; Physalis floriclana; Solanuni melonyena; Vigna sinensis; and V. sesquipedaliB.

Detailed characterization of the virus is currently being carried out. Another virus reported on tomato, cucumber mosaic virus (ClVIV) ,vill be discussed in the following section.

161

Cucumber A number of the vegetables cultivated in the country belong to the family Cucurbitaceae. The major virus disease of cucurbits is ClVIV. The virus has also been found to infect banana (Musa spientum) and periwinkle (Ong, 1971). The properties of the virus are listed in Table 1. Lettuce The occurrence of lettuce mosaic vims on lettuce was first reported in 1973 (Ong). The virus is of minor importance and was probably introduced into the country through infected seeds. Turnip and Radish Brassica rapa and Raphanus sativw;; have been found to be naturally infected by a virus disease which causes mosaic symptoms on both hosts. The virus is readily transmitted by sap inoculation and aphids to other Brassicas, including Chinese cabbage and kai-lan (B. albo-glabra). The host range, symptomatology, physical properties and virus-vector relationship of the virus appear to he similar to those turnip mosaic virus ( Ong, unpublished).

Legumes Groundnut One of the most important leguminous crops grown in Peninsular Malaysia is groundnuts. Field gro,vn groundnuts are commonly observed to exhibit sys­temic mottling. Ting and co-workers (1972) sho,ved that the disease is caused by a virus, groundnut mosaic virus (GMV). The virus is considered to be one of the most wide­spread diseases of groundnut. The characteristics of the virus are listed in Table 1. It is evident that except for C. amaranticolor, the host range of GMV is mainly confined to the family Leguminosae. It is transmitted in a non-persistent manner by all ihe aphid species tested so far. The main vector being Aphis cracC'ivora. Longhean (Vigna sesguipedalis) Surveys carried out in some of the long bean farms have shown that most of the plants are infected with a mosaic disease caused by a virus (Ong, unpublished). The virus is readily graft and sap transmissible and has been found to be transmitted by all aphid species tested. Recently, the virus was found to be seed­

studies have shown that the percentage of seed transmission can vary from 2-50% on time of infection.

Ornamentals Orchid Orchids are one of the most important group of ornamentals grown in the country. The various genera of orchids like 8pathoglottis sp., Vanda sp., Denclrobiurn sp., Phalaenopsis sp., and Cattleya sp. are often found to he infected with cymhidium mosaic virus (Ting and Ho, 1971). In a recent survey of vin,s diseases of orchids it was shown that _4rnchnis Oei cv. Red Ribbon; Aranthera James Storei; Aranda Wendy Scott cv. Greenfield, and Oncidiion Golden Shower cv. Caldwell are frequently infected with cymbidium mosaic virus and/or tobacco mosaic virus-orchid strain. Presently, much effort has been made to produce virus-free planting materials using tissue culture techniques. Hydrangea sp. Virus infected plants showed mottling and distortion of the leaf ( Ting, unpublished). The virus is sap transmissible and the host range of the virus is listed in Table 1. The virus is of limited importance. Others Amaryllis and perhvinkle have been found to be infected with virus diseases. The vin1s on Amaryllis may have been introduced into the country through infected bulbs. Periwinkle are often infected with CMV, and may play an important role in the epidemiology of ClVIV.

Miscellaneous Tobacco Tobacco mosaic virus which has been discussed in the previous section, is the most prevalent virus disease of tobacco. This disease is very widespread throughout

162

the country. The main properties of the virus are presented in Table 1. Sugarcane Planting materials from overseas were found to be infected with a virus. Leaves of infected cane show elongated systemic mottling. The virus is sap transmissible to monocotyledons like maize and sorghum. Attempts to transmit the virus using Rhopalosiphurn maidis and Hysterone1lra setariae, known aphid vectors of sugarcane mosaic virus, have so far been unsuccessful. Ageratum conyzoides Ageratum conyzoides is a common weed found throughout the lowlands in the country. The infected plants normally show yellow veinbanding symp­tom. Studies have shown that the virus Ageratum yellow veinbanding virus, can readily be transmitted through grafting but it is not sap transmissible. It is the first whitefly -transmitted plant virus recorded in the country. The host range of the virus is limited to A. conyzoides. Brinjal, chilli, cucumber, okra, tobacco and tomato are not susceptible to the virus. ( Ong, et al., 1976). Jussiaea linifolia Jussiaea l'inif olia is a common weed generally found in paddy areas. Symptoms somewhat resembling that of Ageratum yellow veinbanding virus have been observed on J. linifolia. The virus has been found to be transmissible through grafting. Attempts to transmit the virus by sap inoculation and insects have been unsuccessful.

Conclusion Studies on plant viruses carried out so far have shoivn that aphids are the most

important arthropod vectors and are usually associated with mosaic type diseases. All the aphid-borne viruses reported are of the non-persistent type. Most of the important virus diseases of rice on the other hand are transmitted by leafhoppers.

In spite of the relatively high temperature and humidity there is no evidence of masking of symptoms caused by viruses. Observations have indicated that virus diseases are equally important in the tropics as compared to temperate areas. The high tempera­tures also does not appear to affect the physical properties of the virus e.g. thermal inactivation point, dilution end point, etc.

Further studies need to be carried out in order to establish the true identity of some of the viruses. Frequently minor differences have been encountered while comparing virus diseases present in Malaysia with those reported in other countries. As a result this has caused some problems in establishing the relatedness of viruses occurring in Malaysia and those elsewhere. The problem is accentuated for viruses where antisera are not available. Comparative studies of viruses which appear to be closely related using standard techniques would be extremely useful.

References 1. COLEMAN-DASCAS, A. E. (1935). Rice experiments in Malaya, 1933-34. Malayan

Agricultural Journal 23, 10-40. 2. LIM, G. S. (1970). Transmission studies of yellow dwarf diseases in West Malaysia.

Malaysian Agricitltural Journal 47, 519-523. 3. --- (1972). Studies of penyakit merah disease of rice III. Factors contribtuing to

an epidemic in North Krian, Malaysia. Malaysian Agricultural Journal 48, 278-294. 4. LIM, G. S. & GOH, K. G. (1968). Leafhopper transmission of a virus disease of rice,

locally known as 'padi jantan' in Krian, Malaysia. Malaysian Agricultural Journal 46, 435-450.

5. ---, --- (1969). Screening of insecticides against Nephotettix spp. Malaysian Agricultural Journal 47, 77-100.

6. LOCKARD, R. G. (1959). Mineral nutrition of the rice plant in Malaya, with special reference to penyakit merah. Department of Agriculture Bulletin 108, Federation of Malaya.

7. ONG, C. A. (1971). Studies of cucumber mosaic virus in West Malaysia. B. Agric. Sc.

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thesis, Fae. of Agric. University of Malaya. 76 pp. 8. (1973). Occurrence of lettuce mosaic virus in Malaysia. MA.RDI Research Bul-

letin 1, 10-14. !t --- (1975). Studies of a mosaic disease of chilli (Capsicicm annuinn L.) in Peninsular

Malaysia. M. Agric. Sc. thesis. Fae. of Agric. University of Malaya, 100 pp. 10. ONG, C. A. & TING, W. P. (1973). Two virus diseases of passion fruit (Passi/fora

edulis f. flavicarpa). MARDI Research Bulletin 1, 33-50. ll. ONG, C. A., TING, W. P. & LIM, Y. C. (1976). A whitefly-borne disease of A,geratum

conyzoides. (In press) 12. OU, S. H., RIVERA, C. T., NAVARATNAM, S. J. & GOH, K. G. (1965) Virus nature

of "penyakit merah" disease of rice in Malaysia. Plant Disease Reporter 49, 778-782. 13. SINGH, K. G. (1971). Transmission studies on orange leaf virus disease of rice in

Malaysia. Malaysian A.gricultural Journal 48, 122-132. 14. SINGH, K. G., SAITO, Y. & NASU, S. (1970). Mycoplasma-like structures in rice plant

infected with "padi jantan". Malaysian A.gricultural Journal 47, 333-337. 15. TING, W. P. (1971). Studies of penyakit merah disease of rice II. Host range of the

virus. Malaysian Agricultural Journal 48, 10-12. 16. TING, W. P. & ARASU, N. T. (1970). A survey of Tristeza virus on citrus in West

Malaysia. Malaysian A.gricultural Journal 47, 299-304. 17. TING, W. P., GEH, S. L. & LIM, Y. C. (1972). Studies on groundnut mosaic virus of

Arachis hypogaea L. in West Malaysia. Experimental Agriculture 8, 355-368. 18. TING, W. P. & HO, T. H. (1971). Disease and pests of orchids. Ministry of Agriculture

and Co-operatives, West Malaysia. 19 pp. 19. TING, W. P. & ONG, C. A. (1974). Studies of penyakit merah disease of rice IV. Addi­

tional hosts of the virus and its vector. Malysian Agricultural Journal 49, 269-274. 20. TING, W. P. & PARAMSOTHY, S. (1970). Studies of penyakit rnerah disease of rice L

Virus-vector interaction. Malaysian Agricultural Journal 48, 10-12.

Discussion T. Soelaeman, Indonesia: (1) Yellow vein banding of Ageratum is found every­

where Indonesia, but studies on this disease is just in the initial stage at Bandung or Bogor. Do you know other hosts than Agera.tu.m?

(2) How about Stachytarpheta yellows in Malaysia? Is this disease also present in Malaysia ?

Answer: (1) So far as our tests were concerned, the virus appears to infect Ageratum conyzoides only, however in our further studies, it is possible that other host may be found.

(2) We are not familiar with this virus in Malaysia. E. W. Kitajima, Brazil: Do you plant corn in Malaysia? If so, are there any

virus diseases on this crop? Answer: Corn is planted in Malaysia mainly for human consumption. Attempts

to grow corn have not developed to the scale where virus diseases are observed. I would not be surprised if viruses occur on maize should large areas be planted to the crop.

M. D. Mishra, India: (1) It seems that you do not have tobacco leaf curl virus in your country. How about any other hosts which may be harbouring tobacco leafcurl virus as in the case of my country?

( 2 J You have mentioned about the use of tissue culture technique in orchid culti­vation, especially for freeing your orchid cultivars from virus infestation. How far it is being used and what is the progress in its use?

Answer: (1) Tobacco leafcurl has been observed on tobacco in Malaysia. We do not have any information on the host range or other host plants which may harbour the virus.

(2) We have only recently started work on the use of tissue culture in combina-

164

tion with heat therapy to produce virus free planting material. Bioassay will be carried out with the material propagated by means of tissue culture technique.

D. A. Benigno, Philippines: (1) Do you have any studies on the strain of sugar­cane mosaic virus'?

(2) Your slide of groundnut mosaic virus seems to be similar to the peanut mottle virus reported in other countries. Why don't you call it peanut mottle Yirns other than groundnut mosaic virus?

Answer: (1) No strain study is carried out at the moment on sugarcane mosaic virus.

(2) Groundnut mosaic virus in Malaysia is very similar to peanut mottle reported by Kuhn, except for minor differences in reaction on indicator plants. Since there is no complete agreement with viruses reported on peanut so far, we have decided to name it as groundnut mosaic virus.