JOURNAL OF THE SCIENTIFIC AGRICULTURAL SOCIETY OF FINLAND
Maataloustieteellinen Aikakauskirja

333

Voi. SS: 333-344, 1983

Effects of Septoria nodorum Berk, on yield and yield com-
ponents of spring wheat

*REIJO KARJALAINEN, **AINO LAITINEN and TAPIO JUUTI
Departments ofPlant Pathology and Plant Breeding, University ofHelsinki,

SF-00710 Helsinki 71, Finland

'Hankkija Plant Breeding Institute, SF-04300 Hyrylä, Finland

Abstract. Data from two experiments was analysed in order to determine the effects of Septoria
nodorum Berk, on the yield of spring wheat. In the first experiment the cultivar Hankkija’s Taava was
artificially inoculated with low spore concentration suspensions of S. nodorum. The resulting disease
reduced grain yield by 10 %, 1000-grain weight by 14 %, and hectolitre weight by 5.7 %. An examination
of the ears from the main stems revealed that the pathogen induced a reduction in all yield components but
especially in grain number/ear and grain weight.

In the second experiment a total of 28 cultivars or lines were studied and the correlation between grain
yield/ear and disease severity was found to be negative but low. No consistent trend among the
correlations was seen and some susceptible cultivars suffered only slightly from the disease while other
fairly resistant cultivars showed great losses.

The results are discussed in relation to compensatory mechanisms and potential disease tolerance in
wheat.

Introduction

Septoria nodorum Berk., the cause of glume blotch disease of wheat, is
a major wheat pathogen in many parts of the world (SHIPTON et al. 1971).
Numerous reports have shown that the glume blotch disease has rapidly
increased in importance in recent years causing severe reductions in wheat
yields (EYAL 1981). The reason for this trend seems to be partly explained by
the fact that local wheat cultivars have been replaced with short, high-
yielding susceptible varieties over large areas and these varieties facilitate
outbreaks of the disease (SAARI and WILCOXSON 1974, RAJ ARAM and DUBIN
1977). Simultaneously there have been changes in cultivation practices such

as the use of minimum tillage which promotes the epidemiological build-up
of inoculum; wheat stubble being an important source of primary inoculum
for disease development (HARROWER 1974, JENKYN and KING 1977).
Moreover, the reduced use of crop rotation and the increased use of

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334

fertilizers may have also contributed to the occurrence of Septoria epidemics
in many intensive wheat growing areas (EYAL 1981).

S. nodorum attacks wheat at all growth stages, and can infect all aerial
parts of the plant (BAKER 1978). The relationship between symptom expres-
sion and yield reductions is not consistent since the pathogen is capable of
causing considerable yield reduction even at a moderate level of infection
(BRÖNNIMANN 1968, SHIPTON 1968, OBST 1977). The effect of early
infection by this pathogen on final yield reduction may be more important
than has previously been expected. Early infection may disturb tillering and
influence the primary development of the ear thus reducing the potential
number of sites for assimilate deposition and consequently reducing yield
(SCHAREN and TAYLOR 1968).

Considerable empirical evidence indicates that major yield losses occur
when infection takes place at later development stages (BRÖNNIMANN 1968,
SPIERZ 1973, WAFFORD and WHITBREAD 1978). This has been explained by
the observed fact that the greatest increase in dry weight of wheat grain
occurs when photosynthetic assimilates are translocated to the ear after its
emergence (WOOLHOUSE 1981, LUPTON 1982). Numerous experiments
show that S. nodorum not only causes a heavy reduction in the rate of
photosynthesis but also reduces the duration of the green-leaf-area period
(SCHAREN and KRUPINSKY 1969, SPIERZ 1973, WAFFORD and WHITBREAD
1976). Hence the infection causes a decreased supply in the amount of
assimilates that can be translocated to the grain, and may thus reduce 1000-
grain weight (SPIERZ 1973).

Precise estimates of national crop losses due to glume blotch disease are
poorly known, but in England and Wales national surveys have revealed
yield losses of up to 8 % in years when infection was severe (KING 1977), and
the economic significance of the disease has been shown to be important
(DOODSON 1981). In Finland no estimates of the economic importance of 5.
nodorum are available, but there is every reason to assume that during the last
few rainy years it has caused significant yield and quality reductions (KAR-
JALAINEN and LAITINEN 1982).

The present paper reports on the effect of infection by 5. nodorum on the
yield and yield components of spring wheat.

Materials and Methods

The data reported in this study were based on two trials carried out at the
experimental farm of the Hankkija Plant Breeding Institute. The objective of
the first trial was to study the effects of S. nodorum on yield and yield
components using Hankkija’s spring wheat cultivar Taava.

Normal plant breeding plots (8 m 2) with four replications arranged in a
randomized block design were used. Standard fertilization and herbicide
treatments were applied.

The first experiment consisted of the following treatments: uninoculated
control, plots inoculated with S. nodorum, and plots sprayed with three



kinds of fungicides. The following fungicide treatments were performed:
spraying before anthesis with 2 kg/ha Benlate, with 2 kg/ha Maneb, and with
a mixture of Benlate 0.25 kg/ha + Maneb 2.4 kg/ha respectively, and
spraying at the postfloral stage with Benlate 1 kg/ha.

Three inoculations with S. nodorum were carried out starting before flag
leaf emergence. The final treatment was made after anthesis. The inoculum
consisted of about 104 spores/ml. The preparation of inoculum and the
culturing techniques of the fungus have been previously described in detail
(KARJALAINEN et ai. 1983). After inoculation all plots were irrigated to keep
them wet, thus encouraging a successful disease build-up. The assessment of
the disease on the different plots was made on the flag leaf and ear of 40
randomly labelled stems by estimating the percentage area covered by S.
nodorum lesions. The assessment was made two weeks after the last inocula-
tion.

The second experiment consisted of a variety test carried out with small
plots to screen spring wheat cultivars for S. nodorum resistance. The details
of the experiments have been previously described (KARJALAINEN et ai.
1983). The purpose of this study was to examine the relationship between
disease severity and yield loss (g/ear yield). Before harvesting the labelled
tillers were cut and the yield components were counted. Alter harvesting the
1000-grain weight was determined. The percentages of diseased area (leaf area
values of the wheat leaves) were transformed using the arc-sin transforma-
tion. Variance analysis for comparing the yield between different treatments
was calculated. Regression analysis, correlation analysis, and Path-coefficient
analysis were also calculated according to LI (1975) in order to define the
main effects caused by 5. nodorum on yield and yield components.

Results

Efects of inoculation on yield and yield components

Artificial inoculation with low concentration of Septoria nodorum
reduced grain yield by 10 % and 1000-grain weight by 14 % (Table 1).
Inoculation also induced reduction in hectolitre weight (5.7 %). All fungicide
treatments caused statistically significant yield increases: 21—30 % relative to
the untreated control (Table 1). The fungicide treatments increased 1000-
grain weight and hectolitre weight.

The results of the data recorded of the single tillers are presented in Table
2. Inoculation reduced all yield components; the loss in ear yield was 38.5 %,

in grain number/ear 17.8 %, in 1000-grain weight 28.4 %, and in spikelet
number/ear 4.4 %. The fungicide treatment increased all the yield compo-
nents recorded (Table 2).

3 335



336

Table 1. Effects of artificial inoculation with low spore concentration on the yield, maturation time,
1000-grain weight and hectolitre weight of the spring wheat cultivar Hankkija’s Taava in
comparison to wheat grown in untreated control and fungicide treated plots.

Hectolitre
Yield Growth time 1000- GW weight

Treatment kg/ha ratio days g kg

Untreated 2610 100 109 37.5 68.9
Septoria-inocul. 2350 90 107 32.3 65.0
Benlate 2 kg/ha and

1 ” 3370 129»»* 109 40.4 70.0
Maneb 2 kg/ha and
Ben. 1 kg/ha 3380 130»»» 110 40.4 70.3
Ben. 0.25 kg/ha +

Man. 2.4 ” 3150 121»»» 109 41.0 70.5
F 20.96»»»

Table 2. Effects of artificial inoculation with low spore concentration on the yield components of the
spring wheat cultivar Hankkija’s Taava in comparison to wheat grown in untreated control and
fungicide treated plots.

Treatment Yield/ear 1000- Grain number/ear Spikelet
GW number/ear

Untreated 1.09 36.43 30.16 14.90
Septoria-inoculation 0.67 26.10 24.79 14.24
Maneb 2 kg/ha + Benlate 1 kg/ha 1.26 40.04 31.51 15.03
LSD 0,05 0.30 9.43 4.17 5.02

Relationship between disease severity and yield loss

In order to test which yield components were most affected by disease
stress a correlation analysis was computed. The results of the data based on
single tillers obtained from the yield loss trial are presented in Table 3. The
relationship between yield (g/ear) and ear severity is negatively significant
(r=0.36, p<0.05), and the correlation between yield and flag leaf severity is
negative but weak. The ear yield seems to be most strongly correlated with
grain number/ear (r=0.71, p<0.001), and 1000-grain weight (r=0.57,
p<0.01). The yield component and disease severity data was subject to path-
analysis in order to partition the correlation coefficients into direct and
indirect effect. The path-analysis clearly reveals that grain number/ear and
1000 grain weight had major direct effects on the yield/ear on a single tiller
basis (Fig. 1). The path-diagram not only indicates that disease directly
reduces grain yield but also indirectly reduces grain number and grain
weight. It also shows that grain number and grain weight had the largest
direct contribution to grain yield.



337

Table 3. Correlation coefficients between disease severity and yield components. The data is based on
single tillers taken from the yield loss trial.

Yield/ear Ear Septoria Leaf Septoria 1000-GW Spikelet
number/ear

Ear Septoria -0.36»
Leaf Septoria -0.26 0.48»
1000- GW 0.57»» -0.21 -0.26
Spikelet number/ear 0.34» -0.31» -0.11 -0.26
Grain number/ear 0.71»»» -0.37» -0.26 0.00 0.58»»

», »», »»», indicates the following levels of significance; p<0,05, p<o,ol, p<o,ool, respectively.

Table 4. Correlation coefficients between disease severity and yield components. The data is based on
single tillers taken from small plot trials of 28 different cultivars and lines of spring wheat.

Yicld/ear 1000-GW Grain Spikelet Leaf Septoria
number/ear number/ear

1000-GW 0.46»»
Grain number/ear 0.59»» -0.38»
Spikelet number/ear 0.39» -0.09 0.56»»
Leaf Septoria -0.34» -0.24 -0.09 -0.32»
Ear Septoria -0.22 -0.43» 0.14 -0.07 0.55»»

The results of the data recorded from 29 cultivars are presented in Table
4. The correlation between ear yield and disease severity is negative, but the
coefficients are low. A detailed demonstration of the relationship between
disease severity and ear yield on different cultivars is shown in Figures 2,3 &

Fig. 1. Path-coefficient analysis of disease severity and yield components. The data is based on single tillers
taken from the yield loss trial.



338

4. Figure 4 demonstrates the combined disease rating (flag leaf value + ear
value) in relation to yield loss calculated from the difference between non-
inoculated and inoculated plots. The greatest losses were detected in Ulla,
Ruso, Tapio, Tähti, Kadett, Drabant, Allen, Maris Butler and CI 13406. The

Fig. 2. Relationship between leaf disease severity and yield/ear for 28 cultivars and lines of spring wheat.

Fig. 3. Relationship between ear disease severity and yield/ear for 28 cultivars and lines of spring wheat.



339

smallest reductions in yield were found in Norröna, 80149, Cl 12463, T8347,
Hja 22159, Hja 21600 and Hja 21182.

A path-diagram was also constructed from the data on cultivar trials (Fig.
5). The results confirm the previous findings (Fig. 1) since again grain
number and grain weight had major direct effects on the total yield/ear and
the effects on total yield/ear due to disease were of the same magnitude.
However, only half of the total variation is accounted for by these variables.

Fig. 4. Combined disease rating (flag leaf value + ear value) in relation to yield loss calculated as the
difference between non-inoculated and inoculated plots. The data is based of 28 cultivars and lines of
spring wheat.

Fig. 5. Path-coefficient analysis of disease severity and yield components. The data is based on single tillers
taken from small plots of 28 different cultivars and lines of spring wheat.



340

Discussion

The present experiments support the prevailing idea that Septoria
nodorum can cause significant yield reduction even with a moderate level of
infection (OBST 1977). Theresults reported here show a yield reduction of 10
% in relation to untreated control plots using a moderately susceptible
cultivar, Hja Taava (see KARJALAINEN et al. 1983). The yield component
which was most affected was 1000-grain weight, thus confirming the results
of several experiments (BRÖNNIMANN 1968, SPIERZ 1973, NELSON et al.
1976). The hypotheses that S. nodorum causes a reduction in photosynthesis
and shortens the green-leaf-area period are in accord with the results of this
experiment. We found that in inoculated plots the maturation time was
shorter than in the untreated control plots and further evidence can be seen
from the fact that in the plots that received fungicide treatments the matura-
tion time was 2—3 days longer than it was in the inoculated plots. This latter
observation confirms the results of SPIERZ (1973) who demonstrated that
Maneb and Benomyl, or their mixtures, can delay the spread of S. nodorum
in the wheat crop with the result that the flag leaf remains green longer and
the grain-filling period is lengthened.

Physiological studies have indicated that Septoria infection may enhance
translocation because it is known to accelerate the grain maturation rate and
the onset of foliar senescence (SCHAREN et al. 1975). WAFFORD and WHITE-
BREAD (1976) have found that despite large lesions on the leaves and a
reduction in total plant growth, S. nodorum infection appears to alter the
export of assimilates from a leaf to only a limited extent, and it also seems to
have only a small effect on the pattern of assimilate distribution. The results
of SCHAREN et al. (1975) support this assumption since they found that the
export of metabolites from Septoria-miected flag leaves did not vary greatly
between control plants and inoculated plants.

The fungicide treatments caused significant yield increases in relation to
untreated and inoculated plots. However, conclusions from this can only be
applied to the field situation with great caution since a number of factors can
affect the results of this kind of experiment. First of all, the fungicides used in
this experiment only partially prevented S. nodorum infection since disease
was observed on treated plots, too. The fungicides may also control other
foliar diseases and this may lead to an erroneous interpretation of the yield
reduction by S. nodorum (JAMES 1974, JAMES and GAUNT 1979). Further-
more fungicides may cause harmful side-effects on the plant and thus lower
the yield or fungicides may have some curative properties and this may cause
yield increases without preventing the occurrence of disease (FEHRMANN et
al. 1978, JAMES and TENG 1979, COOKE et al. 1981). Recent findings of
SMEDEGAARD-PETERSEN (1982) have also revealed that inhibition of the
saprophytic fungal flora on cereal leaves with fungicides increases yield since
saprophytic fungi deprive the host of energy.

The conclusion that can be drawn from the above arguments is that a
comparison between inoculated and untreated control plots may be a rather
reliable way to evaluate the effects of Septoria on wheat yield and this type of



341

comparison may have applications to the field situation. The present results,
where a yield loss of 10 % was seen in the inoculated plots compared to the
control plots, seem to be fairly realistic, but we emphasize that this experi-
ment resulted in fairly low yield levels even in the control, plots because of
unsuitable weather conditions.

The yield component analysis showed that both 1000-grain weight and
grain number/ear were heavily affected by the infection. These results agree
with several experiments which have indicated that inoculation at a late
developmental stage causes the greatest reduction in grain weight (JONES and
ODEBUNMI 1971, WILLIAMS and JONES 1972, JONES and ROWLING 1976).
These results may be explained by the observed fact that late infection mainly
affects grain weight since this yield component develops later compared to
other yield components which develop during early stages (TENG and
GAUNT 1980).

Heavy infection seems to alter all yield components and hence reductions
in the total yield of single tillers are evident. However, this experiment
detected that in some tillers reduction in 1000-grain weight was compensated
by more grains being filled per ear. This observation agrees with those of
WAFFORD and WHITBREAD (1978) and JONES and ROWLING (1976) and
their conclusion that compensatory mechanisms might be too weak after
heavy infection to prevent large yield losses is also confirmed by our results
(Table 2).

The present results suggest that path-analysis can be a powerful tool for
analyzing the relationship between disease severity ratings and yield compo-
nent factors. Constructing a path-diagram can be a clear and simple way to
visualize disease effects as it partitions direct factors from indirect factors as
they affect yield. For example, the present data reveals some interesting
points regarding the different yield components. We found that grain
number was the most important factor in determining the final yield/ear
although several studies done on healthy wheat (WOOLFIOUSE 1981) show
that kernel weight is the biggest contributor to the final yield/ear. Our
experiments seem to confirm the idea that when wheat is attacked by S.
nodorum it compensates for lower kernel weight by the development of more
kernels.

The hypothesis that S. nodorum causes a reduction in yield which is not
correlated with symptom expression (OBST 1977) was evaluated in this study.
The results support this idea since we found that the correlation between
disease severity and yield loss were low and our comparison between
different cultivars with regard to yield loss in relation to disease severity
shows many inconsistencies (Fig. 3). Some cultivars such as Pilot, Kadett,
Drabant and Maris Butler, which have been found to be rather resistant to S.
nodorum (KARJALAINEN et ai. 1983), were seen in this study to suffer great
yield losses. On the other hand some cultivars such as Hja 21600 and Hja
22159, which had been found to be fairly susceptible to S. nodorum (KAR-
JALAINEN et ai. 1983), were seen in this experiment to suffer only a small
yield reduction.

These inconsistencies may possibly be explained by the phenomena of



342

tolerance (BRÖNNIMANN 1968, 1982) however they may also be explained
by experimental error since reliable yield comparisons require a large number
of replications and careful disease assessment (SCOTT and BENEDIKZ 1977,
GAUNT 1981). More experiments are needed to test the above assumption
that some susceptible cultivars have tolerance to S. nodorum.

Acknowledgements
We are grateful to Professors Eeva Tapio and Peter Tigerstedt for critical reading of the manuscript.

We thank Ms. Eila Lonka and Ms. Sinikka Karjalainen for technical assistance, and Mr. Lassi Kontula for
his computer support. The English text was kindly revised by Ms. Heather MacKenzie and Ms. Sinikka
Karjalainen. This work was supported by grants from the August Johannes and Aino Tiuran maatalouden
tutkimussäätiö and this support is gratefully acknowledged.

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344

SELOSTUS

Septoria nodorum Berk, -sienen vaikutus vehnän satoon ja sato-
komponentteihin.

Reijo Karjalainen

Kasvipatologian ja Kasvinjalostustieteen laitos, Helsingin yliopisto, 00710 Helsinki 71

Aino Laitinen ja Tapio Juuti
Hankkijan kasvinjalostuslaitos , 04300 Hyrylä.

Vehnän lehti- ja tähkävioituksen aiheuttajaa Septoria nodorumia Berk, tutkittiin kahdessa
kokeessa Hankkijan kasvin jalostuslaitoksen Anttilan koetilalla. Ensimmäisessä kokeessa
Hankkijan Taava-lajiketta saastutettiin keinotekoisesti alhaisella itiömäärällä. Tulokset osoitti-
vat taudin alentavan jyväsatoa 10 %, 1000-siemen painoa 14 % ja hehtolitran painoa 5,7 %.

Torjunta-ainekäsittelyt lisäsivät jyväsatoa ja satokomponentteja.
Toisessa kokeessa selvitettiin 28 kevätvehnälajikkeen tai -linjan taudinankaruuden ja

satotappion välistä korrelaatiota. Alustavat tulokset osoittivat, että taudinankaruus ei aina
ollut suorassa yhteydessä sadonalennukseen, vaan eräät alttiit lajikkeet, kuten Luja ja Hankki-
jan Ulla, kestivät tautia hyvin, kun taas kohtalaisen kestävillä lajikkeilla, kuten Kadett ja
Drabant, tauti alensi satoa huomattavasti. Tutkimuksesta ilmenee, että Septoria nodorum
-sieni aiheuttaa kohtalaisen runsaana esiintyessään merkittäviä sato- ja laatutappioita.