JOURNAL OF AGRICULTURAL SCIENCE IN FINLAND
Maataloustieteellinen A ikakauskirja

Vol. 62: 265—273, 1990

Yield reduction of oat cultivars in relation to disease
development caused by barley yellow dwarf virus

P. PELTONEN-SAINIO 1 and R. KARJALAINEN 2

1 Department of Crop Husbandry, University of Helsinki
00710 Helsinki, Finland

2 Department of Plant Pathology, University of Helsinki
00710 Helsinki, Finland

Abstract. The effects of barley yellow dwarf virus on the development, grain yield and
yield components of oat cultivar Veli and breeding lines Hankkija 78152 and 78033 were studied
in two years. Cultivar differences to BYDV infection were best observed at a low infection
level. Single tilleranalysis indicated close correlation between symptom severity and reduction
in main yield components. Early infection caused greatest yield losses in all cultivars. BYDV
strongly reduced both plant height and harvest index. Mild infection reduced the grain yield
by 2—B %, but severe infection by 36—41 °/o. The number of grains and panicle weight were
strongly reduced, but the 1000-grain weight was only slightly affected after severe BYDV-
infection. Implications of these results for disease control are discussed.

Index words: barley yellow dwarf virus, yield loss, epidemiology

Introduction

Barley yellow dwarf virus (BYDV), the type
member of the plant luteovirus group, is trans-
mitted in a persistent circulative manner by
aphids (Oswald and Houston 1951). Five
distinct isolates of BYDV (MAV, RPV, RMV,
SGV, PAY) have been described in northern
America (Rochow 1977, 1979). BYDV is the
cause of a serious virus disease on main cereal
species all over the world (Plumb 1977), and
crop losses of up to 70 *Vo have been reported
(Gill 1980).

Rational disease control strategies require
information of yield losses caused by the dis-
ease. BYDV occurs in Finnish oat fields nearly
every year, and if the weather favours the ear-
ly spread of aphids into the field, significant
yield losses are likely to occur. Oat fields in
Finland are often small and situated at some
distance from the main farm, and therefore
the monitoring of aphids may be difficult
resulting in great yield losses.

This study was designed to provide infor-

265

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madon of how BYDV affects oat yield charac-
teristics, at what time of plant growth infec-
tion affects yield most seriously, and how cul-
tivars differing in their susceptibility to BYDV
suffer from the disease. The results reported
here are from two years, 1986, when infection
was moderate, and 1988, when infectionpres-
sure was very high.

Materials and methods

The data reported in this study are based
on two years’ field experiments carried out at
Viikki Experimental Farm of the University
of Helsinki. Three spring oat genotypes were
selected for the trials, cultivar Veli, suscepti-
ble to BYDV, and lines Hankkija 78033 and
78152 (from now on referred to as Hja 78033
and 78152), moderately resistant or less sus-
ceptible to BYDV. Randomized block design
was used in both years, and the trials were set
up with six replications, half of which were
inoculated with aphids. Plot size was 10 m 2
and normal herbicide treatments and fertili-
zation levels were used. Inoculated plots were
surrounded by guard plots in order to prevent
virus-transmitting aphids from spreading into
control plots.

In Finland, barley yellow dwarf virus is ef-
fectively transmitted by Rhopalosiphum padi.
Therefore, samples of R. padi were collected
from the fields near the trial field, and they
were put into a breeding cage, where the aphid
population rapidly increased. Inoculation with
aphids was done according to Russell (1978)
and Gill (1980) so that small pieces of oat
leaves containing aphids were distributed in
the central parts of the plots. When the leaf
pieces died, the aphids moved to the neigh-
bouring oat plants. The number of aphids per
tiller was monitored in infected and control
plots, and an exact number of aphids was
added to all infected plots.

Control plots were kept free from aphids
by spraying them regularly with insecticides.
In 1988 (26. 6.), all aphids were controlled by
insecticides in order to avoid damage caused

by insects to the crop. Also, in 1988 the natu-
ral spread of aphids was so effective that ar-
tificial infection was not needed. Virus con-
centration in plants at various stages of de-
velopment was monitored by ELISA (Clark
and Adams 1977) using RPV antiserum.

Several parameters were recorded during
the growing period. Plant height was mea-
sured six times from ten plants per plot. The
development of green-leaf area was monitored
by estimating the non-green leaf area on three
upper leaves once a week from 60 plants per
plot. It appears to be more accurate to esti-
mate the non-green leaf area than the green-
leaf area.

Two kinds of disease measurements were
carried out. The development of BYDV in
whole plots was monitored once a week by es-
timating the number of BYDV-infected plants
per plot using the following scale:

Class Number of BYDV-infected
plants per plot (10 m 2)

o—3
4—6

l
2

7—143
15—254

26—445
45—746
75—1117

112—1868
9 over 186

In addition, single-tiller analyses were car-
ried out according to Richardson et al.
(1975) and King (1976). Five hundred tillers
of the Finnish variety Puhti were labelled and
rated for disease severity according to the fol-
lowing scale:

Flag leaf BYDV
diseased leaf area %

Class

01
I—3o2

31—60
61—90
91—100

3
4
5

In this case infection time was observed and
the tillers labelled. The labelled tillers were col-

266



lected before harvest and subjected to yield
component analysis.

In the single tiller test the mean value of 100
tillers was used in each disease class for com-
paring the relationship between disease severi-
ty and yield components. In a large scale test,
grain yields and thousand grain weights were
determined after harvest. The data were sub-
jected to several statistical analyses. Correla-
tion and regression were computed between
disease severity and yield components. Yield
analysis was done by variance analysis.

Results

Disease development

In all experiments, Veli was most suscepti-
ble to infection by barley yellow dwarf virus,
and Hankkija’s breeding lines were less sus-
ceptible. Cultivar differences were clear in-
dicating that our inoculation technique works
under field conditions. Veli was about twice
as infected as Hja 78152.

In 1986, infection started at a later stage of
oat development, but the number of aphids
in the field increased rapidly, and the virus
was quickly transmitted throughout the field
(Fig. 1). Also, in 1986 the growing season was
warm, and rainfall was below normal most of
the season. High temperature favoured the
rapid spread of the aphids in the latter part
of crop growth.

In 1988, cultivar differences were less clear,
although Veli was still consistently more sus-
ceptible than the other cultivars. In 1988 the
growing season was exceptional in many
aspects. Throughout the season, rainfall was
below normal and the temperature was excep-
tionally high. As the weather was favourable
for aphids, BYDV infection progressed rapid-
ly in early growing season (Fig. 2), and in 1988
the oat plots were already completely infected
by the time infection had only started in 1986.
Aphids spread naturally very early into the
plots in 1988 compared with 1986. Despite
several chemical treatments to control aphids

Fig. I. Disease development of barley yellow dwarf virus
(BYDV) on three oat cultivars in 1986.

Fig. 2. Disease development of BYDV on three oat cul-
tivars in 1988.

Fig. 3. Disease developmentof BYDV on three oat cul-
tivars in control and BYDV-inoculated plots in 1988.

267



268

in control plots, we were unable to totally pre-
vent them, and there was some BYDV in con-
trol plots in both years (Fig. 3). Virus concen-
tration as determined by ELISA was highest
when 50 % of the leaf area was infected.

Reduction in the green-leaf area related to
disease development was estimated by evalu-
ating the non-green leaf area once a week (Fig.
4). The green-leafarea on the two uppermost
leaves was first destroyed in Veli and later in
both lines. This suggests that the length of
green-leaf area duration might be one com-
ponent of resistance in oats to barley yellow
dwarf virus.

Effects of BYDV infection on plant growth
and yield

In order to assess how symptom severity is
correlated with main yield components of
oats, extensive single-tiller analyses were made
from samples collected in a naturally infected
oat field of cultivar Puhti. The results indi-
cate (Table 1) that all yield components were
reduced as virus symptoms increased. The
number of grains was less affected than grain
weight or panicle weight, which might be due
to the compensation effect (Fig. 5).

Table I. Relationship between disease severity of barley
yellow dwarf virus and oat yield components.

Disease severity 1000-grain Number Panicle
on flag leaf weight of grains weight
% g g

0 32.5 44 1.443
15.5 33.1 44 1.459
45.5 27.7 38 1.067
75.5 29.5 40 1.213
100 27.3 40 1.092
Significance *** ** ***

H.S.D. SV( 1.6 5 0.166

Further, samples from the three cultivars
were taken at different stages of infection in
order to clarify how infection time affects
yield components. The results consistently
showed (Table 2) that early infection caused
greatest yield losses in all cultivars.

Grain weight was particularly affected by
early BYDV infection (Fig. 6). This experi-
ment confirms field observations about early
infestation of aphids leading to significant

Fig. 4. Development of non-green leaf area on three cul-
tivars under disease stress caused by BYDV in 1986.

Fig. 5. Relationship between yield components and
BYDV disease severity of oat cultivar Puhti.



Table 2. Effect of infection time by barley yellow dwarf virus on oat yield components. A=Veli, B =Hja 78033,
C =Hja 78152.

Infection
time

1000-grain weight Panicle weight Number of grains
g g

ABC ABC ABC

Early
Late

21.3 21.4 18.7
31.5 32.4 31.5
34.7 34.7 33.5
*** ��� ***

1.7 2.1 1.6

0.817 0.761 0.715
0.908 1.616 1.391
1.438 2.087 1.612

38 35 39
28 50 43
42 60 48

*** *** **

Control
Significance
h.s.d. SV.

*«* *** * * *

0.207 0.259 0.166 6 8 5

crop losses. As expected, BYDV infection
reduced plant height even under moderate dis-
ease pressure (Table 3), and it also appeared
to reduce harvest index by s—lo5 —10 % (data not
shown). Table 4 summarizes yield component
data from the 1988 experiment. It is evident
that panicle weight and grain number are
strongly affected by BYDV infection in all cul-
tivars, but only the grain weight of Hja 78152
was statistically significantly reduced. This re-

Table 3. Effect of BYDV-infection on plant height (cm).

Veil Hja 78033 Hja 78152

Control 68.0 63.2 69.5
BYDV-infected 61.7 57.0 62.5
Difference 6.3 6.2 7.0
Significance *** *** ***

H.S.D.5 * 2.1 2.1 2.0

Table 4. Effects of BYDV-infection on yield components in 1988

Yield component Cultivar

Veli Hja 78033 Hja 78152

Number of grains
Control 34.7 100

27.0 78
33.1 100
23.6 71

39.9 100
27.4 69BYDV-infected

Significance *«* ***

H.5.D.,,,. 3.1 3.0 2.7
Panicle weight (g)
Control 0.86 100

0.68 79
0.98 100
0.68 69

1.06 100
0.69 65BYDV-infected

Significance ��� � **

H.S.D.j % 0.09 0.10 0.09

1000-grain weight (g)
Control 24.2 100

24.7 100
N.S.

28.8 100
27.6 96
N.S.

25.5 100
24.1 95BYDV-infected

Significance *

H.S.D.SV . 0.9 1.2 1.3

N.S. =non-significant

Fig. 6. Effects of BYDVinfection time on the 1000-grain
weights of oat cultivars Veli, Hja 78033, and Hja 78152.

269



Table 5. Effects of BYDV-infection on grain yield of oat
cultivars in 1986 and 1988.

Cultivar

Veli Hja 78033 Hja 78251

Grain yield (g/m 1 )

1986:
Control 374 100 452 100 438 100
BYDV-infected 367 98 418 92 417 95
Significance N.S. N.S. N.S.

6O 111 69
1988:
Control 189 100 222 100 257 100
BYDV-infected 111 59 139 63 164 64
Significance *** ** ***

25 56 35

N.S. =non-significant

suit deviated from our 1986 data, where the
grain weight of all cultivars was affected, and
further data are thus needed to confirm the
role of grain weight in yield losses.

Grain yield measurements from infected
and control plants indicated (Table 5) that no
statistically significant yield losses were no-
ticed in 1986, but in 1988 all cultivars were sig-
nificantly affected, yield reductions being
36—41 %. In general, grain yield measure-
ments are affected by large plot variation, and
yield component analyses are needed to clari-
fy the effects of disease on yield characteris-
tics.

Discussion

The data presented in this study clearly in-
dicate that barley yellow dwarfvirus, when it
occured early in plant development, reduced
all major yield components as well as plant
height thus lowering the total grain yield. A
crop loss study made in Australia (Smith and
Smith 1982) revealed that early inoculation of
wheat with BYDV reduced yield from 9 to
79 %, while late inoculation lowered it only
by 6 to 9 %. Recent data by Gildow and
Frank (1988) also emphasize the importance
of early infection by BYDV in reducing oat
yield thus confirming some previous crop loss
studies (Endo and Brown 1957, Yount et al.

1985). It seems apparent that when BYDV in-
fects oats at an early stage of crop growth, the
virus reduces tillering and increases floral
abortion, which has negative effects on yield
components and the total grain weight. In ad-
dition, infection may reduce root development
(Burnett 1984), which could disturb water
and nutrient uptake from the soil. BYDV in-
fection also accelerates the senescense of
leaves thus reducing overall photosynthesis.
This may explain the reduction in 1000-grain
weight and panicle weight. In most studies
(Boulton and Catherall 1980, Burnett and
Gill 1976, Parry and Habgood 1986) grain
weight and panicle weight were reduced by
BYDV infection.

Here we present results from two years. In
1986 infection occurred late in oat develop-
ment, when most yield components had al-
ready been formed (Teno and Gaunt 1980).
However, most yield components were strong-
ly affected, but the total grain yield was not
significantly reduced. Possibly the virus did
not reach a concentration high enough to in-
duce disease and did not significantly reduce
total yield. Particularly in the first part of
summer 1986, the cool weather probably
slowed down the activity of aphids, which
delayed the onset of BYDV infection. How-
ever, when the weather warmed up later, the
number of aphids rapidly increased and
BYDV was transmitted into oat fields (Fig. 1).

In 1988, it was very warm throughout the
summer, and aphids spread rapidly at an early
stage of oat development (Fig. 2). All yield
components were strongly reduced, and the
total grain yield was also significantly reduced.
Our results confirm some previous data
(Smith and Smith 1982) which suggest a
linear relationship between the percentage of
plants infected with BYDV at an early stage
of crop growth and grain yield.

Development of barley yellow dwarf disease
on three cultivars revealed that Veli was al-
ways the most susceptible and Hja 78152 the
most resistant one. Our dataalso suggest that
cultivar differences are best observed when in-

270



fection is moderate, as in 1986. Further, our
inoculation technique appeared to work well,
and differences in oat cultivar resistance to
BYDV can be screened using such a field
method. Many barley cultivars carry specific
resistance genes to BYDV (Jedlinski 1984),
but in oat cultivars the resistance is mainly
non-specific (Comeau 1984). However, sev-
eral oat cultivars with high level of resistance
have been released (e.g. Brown and Jedlinski
1978).

Resistance in oats to BYDV appears to
correlate with virus concentration (Hammond
et al. 1983, Skaria et al. 1985), and breeders
have used virus concentration as a selection
criterium to improve the resistance of oat lines
to BYDV. In this study, virus concentration
was monitored by ELISA and using antiserum
against an RPV isolate. This antiserum
reacted well with the isolates occurring in the
test fields indicating that BYDV was trans-
mitted mainly by Rhopalosiphum padi and
perhaps by Sitobion avenae. The highest virus
concentration occurred when the visually es-
timated leaf disease severity was around 50 %.

Harvest index has also been correlated with
BYDV resistance in the field (Comeau and
Barnett 1979), and our results showed that
BYDV infection clearly reduced it. In addi-
tion, we found that green-leaf area duration
might also be a valuable trait describing oat
cultivar resistance to BYDV. In all cases the
most resistant cultivars appeared to have the

longest period of green-leaf area duration. As
this character is rapid and easy to measure,
it might be a practical way to improve the re-
sistance to BYDV. However, it is important
first to test whether improved resistance to
BYDV can be screened by this method with-
out increasing late maturing genotypes in oat
populations.

In summary, these experiments have dem-
onstrated that barley yellow dwarf virus, when
it occurs early in the growing season, can
cause significant yield reductions. Average an-
nual crop losses in the USA are 3.8 °/o, about
2 % in Australia, and 7 % in Canada (Gill
1980, Burnett 1984). However, once in every
5—7 years, an epidemic spread of BYDV can
cause 20—30 % yield reductions. Similar type
of crop losses are also likely to occur in Finn-
ish oat fields. For instance, a rather late and
moderate infection in our 1986 experiment
reduced all yield components indicating that
even a late infection has a potential to reduce
yield. However, when infection starts early,
and the weather favours aphid development,
drastic yield losses are evident, as was shown
in the 1988 experiment.

Acknowledgements. Financial support from the Acad-
emy of Sciences and the Ministry of Agriculture and For-
estry is greatfully acknowledged. We are grateful to Mr
Jouko Närhi and Ms Elina Rantala for technical assistance
and to Dr Rose (Scotland, U.K.) for the kind gift of the
RPV antiserum.

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Ms received October 16, 1989

SELOSTUS

Viljan kääpiökasvuviroosin eteneminen
kaurakasvustoissa ja vaikutus kauran
sadonmuodostukseen

Pirjo Peltonen-Sainio
Kasvinviljelytieteen laitos
Helsingin yliopisto, 00710 Helsinki

Reijo Karjalainen
Kasvipatologian laitos
Helsingin yliopisto, 00710 Helsinki

Helsingin yliopiston koetilalla tutkittiin vuosina 1986
ja 1988 ohran kääpiökasvuviruksen (barley yellow dwarf
virus, BYDV) vaikutusta kauran sadonmuodostukseen.
Tutkimuksen tarkoituksena oli selvittää tuomikirvojen
(Rhopalosiphumpadi) levittämän BYDVrn etenemistä eri-
asteisesti alttiissa kauroissa ja infektion vaikutusta jyvä-
satoon ja satokomponentteihin.

Koejäseninä olivat ohran kääpiökasvuvirukselle selvästi
altis lajike Veli sekä jalostuslinjat Hja 78033 ja Hja 78152,
jotka Hankkijan kasvinjalostuslaitoksen aiempien havain-
tojen mukaan ovat Veli-kauraa kestävämpiä BYDV-saas-
tuntaa vastaan.

BYDVrn vaikutusta kauran sadonmuodostukseen tut-
kittiin seuraamalla kasvustojen pituuskasvua ja merkit-

272



seinällä kasvustosta eriasteisesti saastuneita kasveja, jotka
kerättiin pois tuleentumisen jälkeen. Näistä punnittiin röy-
hypaino, 1000 jyvän paino ja laskettiin röyhyn jyvälu-
kumäärä. Koeruutusadot puitiin ja punnittiin. Itse tau-
din etenemistä tutkittiin laskemalla BYDV-saastuneiden
kasvien lukumäärä koeruuduissa kerran viikossa. Lisäk-
si kunkin koejäsenen kuudestakymmenestäkasvista ar-
vioitiin viikoittain kolmen ylimmän lehden vihreän leh-
tialan kesto.

Tulokset osoittavat, että viljan kääpiökasvuviroosi sel-

västi heikensi tutkittuja satokomponentteja, lyhensi kortta
ja aiheutti satotappioita kaikille koejäsenille. Samoin heik-
keni satoindeksi, joka kuvaa jyvien osuutta maanpäälli-
sen kasvimassan painosta. Satotappiot aiheutuivat siitä,
että BYDV-saastunta selvästi lyhensi vihreän lehtialan kes-
toa, joka oli lyhin altteimmalla koejäsenellä Velillä.

Satotappiot olivat sitä suurempia, mitä-aikaisemmin
kirvat siirsivät viruksen kauroihin, kuten vuonna 1988,
jolloin kirvoja oli runsaasti. Toisaalta myöhäinenkin
BYDV-saastunta, kuten vuonna 1986, heikensi satoa.

273