View of Yield reduction of spring wheat in relation to disease development caused by Septoria nodorum

Maataloustieteellinen Aikakauskirja Vol. ^62; 255—263. 1990

Yield

reduction of spring wheat in relation to disease

caused

Septoria nodorum

REIJO KARJALAINEN and SINIKKA KARJALAINEN Department

of

of

SF-00710Helsinki, Finland

Abstract. Effects of Septoria nodorum onthe grain yields and yieldcomponentsof three spring wheat cultivarswerestudied inFinland using artificial field inoculationoverthree^years.

At low infectionlevel, in 1986,grain yieldwasreduced inall cultivars by2—loVo, but statistically insignificantly.In 1984severeinfection reduced the grain yields of cultivars Kadett and Tähti by27 Vo and 32 Vo, respectively,whilein 1985the yield of Tähtiwasreduced by

16Vo and that of Kadett by 18Vo.

Grain weightswerereduced under low disease stress by3 —5 ^%,while underseveredis- easestressthe reductions were 7—20Vo.

Disease strongly reduced ^thegreen-leafareaduration compared with fungicide-treated plots.

Examination of single tillers showed that all yieldcomponents weresignificantlyreduced. The disease amountonsecond leaves correlated best with grain weight loss.

Implicationsof these results for controlling the damage caused by S. nodorum inspring wheatarediscussed.

Index ^words; Septorianodorum, yieldloss, springwheat

Introduction

Septoria nodorum Berk., the cause of glume blotch disease of wheat, ^has become oneof themost important cereal diseases in northern Europe and many otherpartsof the world inrecent decades (Eyal 1981,^Kinget al. 1983a).Increasing Septoria severity is like- lytobe relatedtochanges in cultivars and hus- bandry practices, which have provided new opportunities for disease outbreaks inmany areas.Crop losses causedby S. nodorum vary

from 5 ^% to 70 ^% (reviewed by ^King _etal.

1983a, Karjalainen 1985), and in Finland previous studies (Karjalainen et ai. 1983,

Karjalainen 1985) have shown yield losses of 10—35^% dependingonthe year and the cul- tivar. Yield reduction might be relatedto the reduction in photosyntheticrate aswell asto the reduction in overall photosynthesis, which is ^mainlydue to disease-induced speeding up of_senescence(Scharen and^Krupinsky 1969, JOURNAL OF AGRICULTURAL SCIENCEIN FINLAND

Spierz 1973, Karjalainen and Salovaara 1988).^•

Septoria has been_amajor wheat pathogen in Finland for _a long time (Mäkelä 1973), and our climate together with field charac- teristics favour its epidemic development. In

mostyearssummers arecool and there_arefre- quentrains. Inaddition, wheat fieldsare of- tensmall and surrounded by lakesor forests which provide the humidity in wheat canopy necessary for diseasedevelopment. In recent years farmers in southern Finland, in par- ticular,have increasingly startedtousegrowth regulators and extra nitrogen as well as in some cases zerotillage, which all may havea disease speedingeffect. However, these farm- ers have found it necessary toregularly use fungicides to control leaf diseases. Septoria epidemicscanbe sporadic, and careful disease monitoring may allow to forecast the risk of Septoriaoccurrenceandatthesametime help to avoid unnecessary ^treatments while pro- viding information _on the _accurate spray timing for fungicide application (Royle etal.

1986).

The purpose of this studywas toprovide more information on how Septoria affects someyieldcharacteristics ^{of spring}wheat cul- tivars under severeand mild epidemic condi- tions.

Materials and methods

Yield reduction in spring wheat caused by Septoria nodorum was studied in the years 1984—1986. Threecultivars, susceptible Tähti and Hankkija’s Tapio, and moderately resis- tantKadett, wereused in fieldtestscarried out atthe University Farm of Viikki of the Univer- sity of Helsinki. Experimentswerecarried out inarandomized block design with 6—B repli- cations, ^{half of} which ^were inoculated with S. nodorum. All inoculated plots were sur- rounded by guard plots toprevent inoculum spread into control plots. Standard fertiliza- tion and herbicidetreatments were used. In

1986,0.5 1/ha of Tilt was applied on some plots of Tähti and Tapio just before flag leaf

emergencein order to evaluate the effect of a fungicide to control Septoria.

Inoculationwas done by spraying S. nodo- rum spore suspensiononto testplots. Mixtures of three fungal isolates collected fromsouth- ern Finland were used. The fungus was cul- tured on oatmeal agar in petri dishes under

NUV light for 7—lo days. The dishes were then flooded with sterile water and spores werereleased by gently rubbing the agarsur- face with a spatula. Spore suspensions of about 10⁶ spores/ml with ^some ’Tween 20’

were used for inoculation.

In 1984 and 1985test plotswereinoculated twice,^atthe third leafstageandoneweek af- ter that. In 1986, three inoculations ^were done, ^{starting at} the third leafstage. Inocu- lations ^were done late ⁱⁿ the evening, using 50 ml of spore suspension per plot.

Disease development was monitored by counting and labelling 60 plants per plot and estimating the_percentage of diseased leafarea on three upper leaves. Green-leafareadura- tion _was monitored by visually estimating non-green leafarea, ^whichwas moreaccurate to estimate than green-leafarea.

Before harvest, the 60 labelled tillers per plotwerecollected andtheir^yieldcomponents were analyzed. Grain yields and thousand grain weights_wereanalyzedfrom larger data.

Single-tilleranalysis_wasalso carriedout by labelling 60 tillers ina large commercial field of cultivarTapio. Before harvest the labelled tillersweretaken for yield^component analy- sis.

Correlation, regression, and variance ana- lyses were computed from yield data.

Results

Disease development

Patterns of disease development of Septoria nodorumonthree spring wheatcultivars ^are presented from two years, 1984 and 1986, when conditions for infection varied greatly.

In 1984 the weatherwasvery suitable forrapid disease development because of frequent

rains, ^and even the first ^leaveswere rapidly covered^by diseased lesions. ^Inthisyear (Fig.

1) the late but susceptible cultivar Tähti was slowlyinfected^atthe beginning of the grow- ing period, but afterear emergenceinfection advanced quickly. Asimilarpattern of disease development was noticed ^{for all} three culti- vars so thatKadett wasconsistently themost resistant and Tähti themost susceptible one, while Tapio was intermediate.

In 1986 the weather was unsuitable for rapid disease development because therewas a long rainless period in the growing season.

Disease developmentontwoupper leaveswas monitored onTähti and Kadett. In general, infection started slowly despite several inocu- lationstoinducedisease build-up sothat only about 30^% of the first leaves of susceptible Tähtiwas destroyed_atthe end of July, while the first leaveswere totally destroyedatthat time in 1984. In 1986, the first leaves of Kadett wereonly slightly infected (Fig. 2), and Kadett was again clearly more resistant than ^Tähti throughout the growing period.

Aseparateexperiment_was also carriedout in 1986to test the effectiveness of fungicide treatments (Tilt) to reduce disease develop- ment. Treatments before flag leaf emergence efficiently prevented disease build-up onboth Tähti and Tapio (Fig. 3).

Developmentof leaf^{area(cm2 )on} cultivars Kadett and Tähtiwasmonitoredover athree-

weak period under severe disease stress in 1984. At the beginning, leafarea waslarger onsusceptible and larger-leafedTähti^thanon Kadett, but the leaf area of Tähti rapidly reduced toward the ^endof the period com- pared with that of resistant Kadett (Fig. 4).

In 1986,the effect of disease onreducing green-leaf_{area was}monitored by visuallyes- timating the non-green leaf area on flag leaves. Reduction in green-leafarea appeared tofollowasimilarpattern onboth Kadett and Tähti (Fig. 5), and moreresistant Kadett ap- peared toprolong upper leaf green area du- ration slightly longer than susceptible Tähti.

However, at the end of the period therewas

Fig.I. Diseaseprogressof Septorianodorumonthe flag leaves of spring wheat cultivarsTähti,Tapio,and Kadett in ^1984.

Fig. 2. Diseaseprogressof S. nodorumonthe flag and second leaves of spring wheat cultivars Tähti and Kadett in 1985.

Fig. 3. Effects of Tilt-treatment ^ondisease progress^of S. nodorumonthe second leaves of spring wheat culti- vars Tapioand Tähti.

hardly any difference between thesetwo cul- tivars. Fungicide treatments(Tilt) effectively prolonged green-leaf area duration of both Tähti and Tapio (Fig. 6), suggesting that a fungicide treatmentmayhelp preserve more green-leaf _area for photosynthesis, which in turnproduces _anincreased ^supplyof assimi- lates to be translocated into the graincom- pared to untreated control.

Effects of

In 1984 and 1985 the weatherwas suitable for disease development, and the yield data

Table 1. Effect of Septoria infection ongrain yieldand grain weightof spring wheat cultivar Tähti in 1984—1985.

Grain Ratio 1000- ^Ratio yield graingrain

kg/ha weight,

g 1984

Control 4617 100 39.3 100

Septona-inoculated 3156 68 31.6 80

Significance ^{****** *�}

L.S.D._5% 623 1.6

1985

Control 2540 100 33.3 100

Se/WoWa-inoculated ^{2140 84 28.8 86}

Significance ^{** «*}

L.S.D.j% 290 3.1

Table2, Effect of Septoria infection ongrain yieldand grain weightof spring wheat cultivar Kadett in 1984^—

1985.

Grain Ratio 1000- Ratio yield graingrain

kg/ha weight.

g 1984

Control 6287 100 41.5 100

Septo/w-inoculated 4603 73 33.1 80

Significance ^{***� �*}

L.S.D._s% 850 1.2

1985

Control 3305 100 38.0 100

.S'ep/ona-inoculated 2723 82 35.5 93

Significance ^* N.S.^N.S.

L.S.D., 450 2.9

N.S.⁼non-significant Fig.4. Development of flag leafareaunder disease stress

conditions in 1984onthe cultivars Tähti and Kadett.

Fig. 5. Reduction in green-leafarea of the flag leaves of cultivars Tähti and Kadett under disease stressin 1986.

Fig. 6. Effects of Tilt-treatment onthe green-leafarea development of theflagleaves of cultivars Tähti and Ta- pio in 1986.

show (Tables 1 ^&2) that S. nodorum is capa- ble of causing significant yield reductionsto wheat crops. In 1984, the disease reduced the grain yields of susceptible Tähti and ^more resistant Kadett by 32 ^% and 27 ^%, respec-

tively (Table 1). The grain weights of both cul- tivars weresignificantlyreduced,by 20 ^%.In

1985 the yields of alltestcultivarsweregener- ally very low, and the yield of Tähti was reduced by 16^%and that of Kadett by 18 °/o.

The grain weight of Tähti was again signifi- cantly reduced (Table 2).

In 1986 therewas along dry period during the experiment, and S. nodorumwasunable to grow rapidly into the upper parts of the wheat canopy. Thus grain yields were only slightly reduced. Disease-induced yield reduc- tions for^{all three}cultivars, Tähti, Kadett, ^and Tapio, were statistically insignificant (Table 3), although the yield of^{Tähtiwas reduced} by over400 kg/ha. The yields of Kadett and Tapio wereless affected by the disease. Ta- ble 4 summarizes the yield data from Tähti and Kadett overthree years showing that only the yield ofmore susceptible Tähti _was sig- nificantly affected by thedisease, whilea more stabletrait,grain weight, indicates significant reductions for both cultivars.

Yieldcomponent datawere also obtained from a single-tiller assessment experiment from cultivar Tähti. Results indicated (Table 5) that all yieldcomponents were significant- ly reduced by the infection. As results from previous studies (e.g. Karjalainen 1985) had suggested that grain weight is a stablecom- ponent of grain yield, which characterizes yield reduction in areliable way, single-tiller assessments werecarried^{outon acommercial} plot of Tapio in order to assess the amount of diseaseontwoupperleaves^andtofindout whichleaf, leaf lor leaf2,^correlatesbest^with grain weight reduction. Fig. 7 indicates that in general theamount of diseaseoneither leaf correlates wellwith grain weight reduction, but the second leaf appears to be an even better indicator of grain weight loss than the

first one.

Table 3. Effect of Septoria infectionongrain yieldsand grain weightsof spring wheat cultivarsTähti, Kadett,and Tapioin 1986.

Grain Ratio 1000- Ratio Cultivars

yield grain

kg/ha weight.

g Tähti

Control 4280 100 40.9 100

Septoria-inoculated 3847 90 39.3 96 Significance N.S.N.S. N.S.N.S.

L.5.D.,,, 637 4.4

Kadett

5127 100 44.9 100

Control

Septor/a-inoculated 5019 98 42.6 95 Significance N.S.N.S. N.S.N.S.

L.S.D._s 1385 5.6

Tapio

Control 4986 100 43.7 100

Septonu-inoculated 4710 94 42.3 97

Significance N.S.N.S. N.S.N.S.

L.S.D.,* 491 9.3

N.S.⁼non-significant

Table4. Combineddata ^overthree^yearsof the effects of Septoria^ongrain yields and 1000-grain weights of cul- tivars Tähti and Kadett in 1984—1986.

Grain Ratio 1000- Ratio

yield grain

Cultivars

grain

kg/ha weight.

g Tähti

Control 3999 100 38.7 100

Sepfon'a-inoculated 3277 82 33.8 87

Significance ^{** ***� ��}

L.5.D.,,,. 545 2.5

Kadett

4775 100 41.4 100

Control

Septor/o-inoculated 4117 86 37.7 91

Significance N.S.N.S. ^**

L.S.D., ^{1091 3.6}

N.S.⁼non-significant

Table 5. Effect of S. nodorumonyieldcomponentsof springwheat cultivar Tähtiin 1986.

Number Ear 1000-grain of grains weight weight,

per ear g g

Control 22.4 ^0.84 37.4

Septoria-inoculated 18.7 0.62 32.6 Significance ^{� ��*** ***���}

l.s.d._5% 1.7 0.08 1.3

Discussion

Our resultssuggest that under humid_con- ditions favourable for disease development, S. nodorumcan causeyield losses as highas 20—32 ^%. In thepast ten years there have been several rainy summers (e.g. 1981, 1984, 1985, 1987) and severe occurrences of S. no- dorum.

There _are two types of epidemic develop- ment of S. nodorum, sudden outbreaks and gradual epidemics (Royle et al. 1986). In a sudden outbreak disease lesions appear simul- taneouslyon all^upperleaves, usually early in cropgrowth. These outbreaksarerelatedwith a single heavy rain that moves the basal in- oculum50—60cm upwards within the crop.

Inoculumtransport also depends on the size of the raindrops because large drops produce large splash droplets (Brennan et al. 1985).

In gradual epidemics the disease arises on successive leaf layersasthey appear during the sustained weather period suitable for inocu-

lum travel andinfection. InFinland, ^gradual epidemics _are probably more common than sudden outbreaks, and infection in the field often appears to follow this_pattern.

A severe Septoria infection ^{seems to} have complex reasons. A previous rainy _season probably affects nextyear’s epidemic condi- tions by providing abundant infected plant de- bris on the soil because in Finland the fall is often wet, which makes ploughing difficult.

Ifthe firstpart of the growingseason is cool and wet, inoculumcanbe transportedtonew wheat crops early, and if there are several rainy days between mid-June and late July, the disease^cangradually progress from lower to upper canopy.

Our results in 1986 showed that _{even un-} der unsuitable dry conditions S. nodorumcan reduce wheat yield by s—lo5—10 ^%. Even in a rainless period, Septoria may survive and de- velop in the canopy because in lateseason dew provides humidity for several hours. ^How- ever, practical experiencesuggeststhat hot and

Fig. 7. Correlationbetween S. nodorum severity and grain weightonthe first and second leaves of cultivar Tapio

dry weather for several weeks (e.g. in 1983 and 1986) effectively retards Septoria develop- ment.

In this paperwehave shown that Septoria- infection speeds up senescense and shortens green-leafareaduration. This inturnreduces overall photosynthesis and decreases the sup- ply ofassimilates ^{thatcan be} translocated^to the grain. It was thus logical that the grain weight was strongly affected in this experi- ment.Our results also showed that fungicide treatment effectively reduced disease develop-

mentand particularly prolonged flag leaf pe- riod thus also lengthening grain-filling time.

This is in accordance with earlier data (Spierz 1973) indicating thata fungicide treatment given_at the right timecan effectively reduce disease and increase grain yield. Inourexperi- mentsfungicide treatmentsincreasedthe grain yields of spring wheat by 5—30 ^%compared with untreated controls. Although infection seems to reduce green-leaf area and overall photosynthesissodrastically, it may have only asmall effect onthe patternof assimilate dis- tribution (Wafford and Whitbread 1976).

In our experiments all yield components werestrongly affected by infectionasrevealed by the single-tiller experiment, which is in line with earlier data (Jones and ^Rowling 1976, Wafford and Whitbread 1978,Karjalainen etai. 1983). In general, early infection appears toreduce yield less than_alate _one (Jones and

Rowling 1976, Verreet et al. 1987), and single-ear yields in particular arestrongly af- fected by late infection. Field data (Brön-

nimann 1968, ^Spierz 1973, ^{Nelson et al.}

1976, Scott and ^Benedikz 1977, ^Wafford and Whitbread 1978, Karjalainen et al.

1983,^Verreetetal. 1987) show quite consis- tently that wheat is sensitive toS. nodorum atalaterstageof development, and greatest losses occur after late infection. Sometimes losses caused by early infectionare compen- sated by other^{yield components}if the infec- tion is weak _ormoderate (Jones and^Rowling

1976, Wafford and Whitbread 1978), but compensation is probably not effective

enoughtoprevent yield losses afterseverein- fection. In Finland, wheat ismost often ^in- fected in late season, ^and as theamount ^of rain increases towards the end of the growing season, Septoria infection frequently speeds up atthe same time. Yield losses ^{in Finnish} wheat^cropsthus^seemtobe^mainly duetolate Septoria attacks.

These data indicate yield losses of 20—

30^% under_severe and s—lo5—10 ^% under mild disease conditions. Previouslywereported a 10^%reduction in one cultivar ^and oneyear (Karjalainen etal. 1983). In the rainy years of 1981, ^1984, 1985,^and 1987,^therewas of- tenas much Septoria in manyfarmers’ ^fields as inour experimental fields. However, ^dis- ease distributioneveninasingle field varies.

Estimates of national losses caused ^{by S.}

nodorum in Finland arenot available,^butan- nual yield losses of up to 8 °7o have been recorded ^{in Great}Britain.^Kingetal. (1983 b) have providedalinear regression equation be- tween disease severity and yield loss. It indi- cated a yield loss of 1.011 °7o for each 1 ^% increment in severityonthe flag leaf andaloss of0.551 ^%for each 1^% incrementonthesec- ond leaf. Our single-tiller analysis donein a commercial field of cultivar Tapio suggested that theamount of diseaseon the second leaf correlates best with grain yield loss. Under northern growingconditions ^thesecond leaf may beabetter crop lossestimatethan the flag leaf because in^thefield it is ^oftenmorereli- ableto estimate theamountof disease (with- outinoculation)onthe second thanonthe flag leaf.

Theuseof fungicidestocontrol wheat dis- eases hasincreased ^{in the}past few years. In some areasin southern Finland winter wheat is sprayed first at the stemextension phase mainly to control mildew and again laterto control Septoria. In Finland Septoria seems to cause greatest crop losses rather late ⁱⁿ crop growth, and one spraying with optimal timing would^probably be sufficient. In this experiment, one application immediately af-

ter flag leaf emergence drastically reduced

Septoriadevelopment and lengthened green- leafarea duration. Similarresults ^{have been} reported by ^Spierz (1973) and Obst (1985).

The use of simple forecasting rules (Tyl-

desley and ^Thompson 1980,Obst 1985) and information of the previous year’s weather

and ploughing conditions will be^animportant step towards the rational planning ofchemi- cal control ofthe Septoria diseasein Finland.

Acknowledgements.Financial supportfrom the Aca- demyof Finland and the Ministry of Agriculture and For- estryis greatfully acknowledged.

References

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Ms received October 6, 1989

SELOSTUS

Septoria-i2i\iA\n vaikutus kevätvehnän satoon Reijo Karjalainen

Sinikka Karjalainen

Helsingin yliopiston kasvipatologian laitos 00710Helsinki

Tutkimuksessa selvitettiin Septoria-laudin vaikutusta kolmen kevätvehnälajikkeen,Tähden,Hankkijan Tapion jaKadettin, satoon jaeräisiin satokomponentteihinvuo- sina 1984—1986. Kokeet tehtiin Helsingin yliopistonVii- kinkoetilalla saastuttamalla koeruudut laboratoriossa kas- vatetusta Seploria nodorum -sienestä tehdyllä itiöseok- sella. Osa Tähti- ja Tapio-ruuduistakäsiteltiin Tillillä juuri ennen lippulehden puhkeamista.

Taudin kehitystä kasvustossa seurattiin arvioimalla tie- tyinvälein tautilaikkujenmääräkahdella ylimmällä leh- dellä. Samanaikaisesti määritettiin ylälehtien kuihturais- aste. Sadonkorjuun jälkeenlaskettiin jyväsato ja 1000-jy- vänpaino jamääritettiin satokomponentit yksilöpuiduista Tapion jaTähden tähkistä.

Säävaikuttaa ratkaisevasti Septoha-taudin leviämiseen.

Vuodet 1984ja1985olivat sateisiaja viileitä,jollointauti levisi nopeasti kasvuston alaosistaylälehtiin^jatähkiin asti.

Vuosi 1986oli kuuma jakuiva,taudille epäsuotuisa.Kai- kissa kokeissa Septoriaa vastaan kestävin oli Kadett ja altteinTähti, Tapio sijoittui näiden väliin.

Vuonna 1984Kadettin jyväsato oli27 ^%jaTähden 32^%pienempikuin saastuttamattomanverranteen. Kum- mankin 1000-jyvän paino aleni20^%. Vuonna 1985sa- dot olivat yleensäalhaisia, jaTähden sadonalennus oli

16^%jaKadettin 18^%. 1000-jyvänpainotalenivatvas- taavasti 14^%ja7^%.Vuonna 1986Septoriaaoliniin vä- hän,ettäsadonalennukset olivat tilastollisesti merkityk- settömiä.

Tauti alensi huomattavasti kaikkia Tähden satokom- ponentteja. Tapio-viljelykseltäotettu näyteosoitti,että taudin määrä sekä lippulehdelläettä erityisestitoiseksi ylimmällälehdellä korreloi selvästi 1000-jyvän painon ale- nemiseen, mikä satokomponentti yleensä kuvaa luotet- tavasti Seploria-taudin vaikutusta.

Vihreän lehtialan seurantaosoitti,että.Sep/ono-infektio nopeuttaakasvin kuihtumista,jolloin yhteyttävälehtiala pienenee jayhteyttämisaika lyhenee,minkä seurauksena jyväkoko pienenee.Tillinvaikutus lieneekinperustunut osinsiihen, että^{se paitsi}vähensi taudin kehitystä myös vaikutti lehtialan säilymiseen vihreänä pidempään. Tu- lokset viittaavat siihen,että Suomessa torjuntakäsittely onpaikallaansateisina kesinä. Torjunnanparasajoitus näyttää olevan lippulehden puhkeamisen ja tähkälletulon välillä,jolloin käsittelyestäätehokkaasti patogeenipopu- laation etenemisen kasvustossa ja lehtien ennenaikaisen kuihtumisen. Viileänä kasvukautena torjunta pidentää myöhäisten lajikkeidenkasvuaikaa entisestään.