TEMPERATURE ALTERATION OF PHENOTYPIC EXPRESSION
OF SPRING WHEAT RESISTANCETO STAGONOSPORA NODORUM SPOT 1
WILMAR C. DA LUZ2 and GAR? C. BERGSTROM3
- ABSTRAC'r - The spring wlieat Triticum aestivum L. eultivars Fortuna, Newana, and Manitou, previ-ously known as susceptible, moderately resistant, and resistant, respectively, to Stagonospora nodorum
spot, caused bj Phaeosphaeria nodorum, were maintained at postinoculation temperatures of 12, 18, 20, 24 or 28 C. At 20 °C, reactions weresimilai to those previouslyreported for ali tultivars with Forttna being thà most severely attacked by the fungus. liowever, resistance to Stagonospora nodo-rum spot was markedly influenced by temperatures of 24 °C; the Manitou reaction changed from • resistant to susceptible. The moderately resistant reaction of Newana was unchanged with temperatures
of 18 to 280C, Minirnal djsease severity occurred at 120C in ali gezmplasms evaluated. There were no significant differences in percentage of leaf arca showingsymptoms among cpltivars at 28 °C. Maximum disease development and the higbest number aí lesions per cm2 were observed in plants of Fortuna • and Newana lcept at 18-24 °C and in plants of Manitou kept at 24 °C. Incubation period was reduced as the temperature increased from 12 to 24 °Cin ali germplasms tested. These data suest thattem-perature migM be one factor responsible for contrasting resulta in resistance tests and for the absence of durable resistance to Stagonospora nodoním spot in Brazil, -
Index terms: Triticum aestivum, F/zaeosphaeria nodonjm, leaf spot disease.
ALTERAÇÃO PELA TEMPERATURÁDA EXPRESSÃO FENOTEPICA DA RESISTÊNCIA DO TRIGO A STAGONQSPORA N000RUM
RESUMO -. As cultivares de trigo, Triticum aestivum L., Fortuna, Newara e Manitou, antesconhecidas. respectivamente como cultivares suscetíveis, moderadamente resistente e resistente á manctia-foliar induzida por Sta9onospora nodorum, foram submetidas a regimes de temperatura p6s-inocul5o de 12, 18, 20,24 e 28 °C. Em temperaturas de 20 °C, a resistência das cultivares foi similar à anteriormen-te estabelecida. Entretanto, a resistência à Stagonospora noo'o,um foi marcadamente influenciada pela temperatura de 24 C, e a reaçfo da cultivar Manitou mudou de resistente para suscetível. A resistência moderada de Newana n5o foi modificada com temperatura de 18 a 28 ° C. O mínimo de severidade da doença ocorreu a .12 °C, em todos os germoplasmas avaliados. NSo houve diferença na percentagem de sintoma foliar, entre a cultivares mantidas a 28 °C. O máximo de desenvolvimento da doença e o
má--ximo número de lesaes por cni2 foram observados em plantas das cultivares Fortuna e Newana manti-das de 18 até 24 °C, e em plantas da cultivar Manitou mantimanti-das á 24 ° C. O período de incubaçfo foi reduzido de acordocom o aumento de temperatura de 12 a 24 °C, em todos os germoplasmas avaliados. Estes dados sugerem que a temperatura pode ser um fator responsável por resultados conflitantes em testes para resistência e pela ausência do resistência durável a Stagonospo,'a nodorum no Brasil.
Ternos para indexaçffo: Triticum aestivum. Phaeasphaeria nddorum, mancha.foliar.
INTRODUCTION
.Stagoriorpora nodorum . sjot, induced. by
Phaeosphaeria nodorum (Mulier) Hedja. (anam.
Stagonospora nodorum (Berk.) Cast & Gerin.), is vi important component of the wheat (Triticum
Accepted for publication on December 12,1985. 2
Eng. - Agr.; EMBRAPA/Centro Nacional de Pesquisa de Trigo (CNPT), Caixa Postal 569, CEP 99100 Passo Fundo, ES, Brasil.
Dàpartment aí Plant Pathology, Cornelltiniveisity, Ithaca.NY 14853. •. .
acstivuin L.) leaf spot syndrome in Brazil (Luz 1981). In Brazil, Stagonospora nodorum spot and scab combined reduced yields by an estimàted 8% to 10% ia Rio Grande do Sul, Brazil, in 1981--1982 (Luz 1984). In Brazil, wheat cultivars regarded as resistant to Stagonospora nodorum
spot in some years developed severe symptorns under fleld éonditions. Furtherniore, glasshouse tests for resistancè to Stagonospora nodorum spot ia Brazil have usuaily been done at ambient posti-noculation teMperatures and pr'olonged wetness with a mixture of severa! isolates (Fernandes et ah 1980, Picininiet ai. 1980) or in controiledenvi- Pesq. agropec. bras., Brasília, 21(6):625-629,jun. 1986.,
626 W.C. DA LUZ and G.C. BERGSTROM
ronanene for 72 hours after inoculation foilowed by transfer to ambient glasshouse environments (Prestes et ai. 1982). These testa have produced inconsistent resulta (Fernandes et ai. 1980) and, iii some experimenta, no resistant cultivara were identified (Picinini et ai. 1980). Although wheat cultivar resistance to P. nodorum has been reported for many years, the absence of a durable resistance to this microorganisrn is not well understood. In addiüon, cultivara reported as resistant to
Stago-nospora nodorum spot in one part of the world may appear susceptible in another (King et ai. 1983). It was suggested that variable reaction of a cultivar to Stagonospora nodorum spot was due to variabiity in pathogen isolates, dlffering envi-ronmental conditions during experimenta, or different inethodologies (Rufty et ai. 1981).
A range ofvariation for virulence in P. nodorum
lias been reporte d previously (Allingham & Jackson 1981, Thornas 1962). The severity of
Stagonos-pora nodoruni spot lias been sliown to be increased by prolonged periods of leal wetness (Eyal et ai. 1977, 1-lolmes & Colhoun 1974, Thomas 1962). The effects of temperature ou the causal fungus have been documented. Pycnidiospore germination occurs from 5 to 37 °C witli VI optimum range of 20 to 25 0C (Rapilly & Skaienikoff 1974). Fungus growth is optirnal at temperatures of 20-24 0C witli limits near 4 and 320C (Wiese 1977). Efftcts of temperature ou the compatible liost/fungus interaction have also been documented. Disease development was greatest between 20 and 27 0C (Wiese 1977). Increases in ternperature caused a decrease in latent period (Sliearer & Zadoks 1974). High preinaculatian temperatures predisposed wheat planta to susceptibility (Rosielle 1968, Thomas 1962).
This paper presents resulta of a study to evaluate the effect of postinoculation temperature on expression of differential cultivar resistance to
Stagonospora nodorum spot. Components of disease development assessed were total foliar necrosis, lesian number, and incubation period.
MATERIALS AND METHODS
Seeda of three spring wheat cultivars, Fortuna, Newana and Manitou, previausly designated susceptible, moder- Pesq. agrapec. bras., Brasília, 21(6):625-629,jun. 1986.
ately zeslstant, and resistant, respecüvely. ta Stagonos-poro nodorum spat, were obtained from Dr. A.L. Scharen (USDA, Bozeman, MT, USA).
Oaltures of a P. nodorum isc,late, also received from Dr. A.L. Scharen, were maintained at 4 0C and the moeu-lum was increased for ten days on V-8 juice api at
21 ± 1 °C under near UV light with a photoperiod aí 12 hr.
Plants (flve per pot) aí each cultivar were grown in autoclaved soil in 11 cm diameter clay pata in a controlled climate chamber. Plants at growth stage 23 (five leaves unfolded, main shoot and three fiilers) (Zadoks et ai. 1974) were sprayed with suspensions of 106 pycni&os-pores/mi using a pressurized sprayer (Model SMC, Sanborn Manufacturing Company). Immediately alter inoculation, planta were transferred to a mist chamber for 48 hrof leal wetness at temperatures aí 12, 18, 20, 24 or 28 C. Failowing this period, planta were transferred
tu
a growth chaxnber maintained at 80% relative humidity at the respective teznperature. The experimental desivi used was a spht piot with temperature treatments as main plats and cultivar treatnents as subplots. A single mist chaniber and a single postinoculation incubaflon chamber, each' with adjustable temperatura, were used for the entire study. Temperature treatments were ordered randonily and were replicated (ocr times temporally. Subplots consisted aí singie pots aí live inoculated planta aí each cultivar and were arranged randomly within each main piot. Nanmnoculated planta were maintained as controla.Incubtion pexiod (time fiam inoculation to flrst visible symptoms) was observed on each of the first four leaves for each wheat cultivar at each temperatura.
The number of lesions per cm 2 was recorded seven days alter inoculation by superimposing a piece aí plastie, on which twenty 1 cru2 areas had been scribed, on the upper surface aí eacli aí the four frrst leaves.
Disease develapment was estimated ten days after inoculatian as percentage aí leal area showing symptoms based on a scale slightly modified from one used iii spot blotch evaluation (Luz 1982) as follows: slight, symp-tomless tu 15%; moderate, 16% to 45%; severe, greater than 45% aí leaf axea showing symptoms.
The data were stibjected to analyses aí variance and the statistically significant differences among treatments were determined by Fisher's "protected" least significant difíerence test. Regression analysis was done additianally to determine the relatianship between the disease parasita-tesa (percentages af leal area shawing symptoms, number aí lesions per em2 and incubatian period) and temperature,
RESULTS AND DISCUSSION
The resulta of tlie experimenta are sliown isa Figs. 1,2, and 3. The regression analysesofvarious
TEMPERATURE ALTERATION OF PHENOTYPIC.EXPRESSION 627
discase parameters vs. temperature are show ia Table 1. Coefflcients for terms ia equations were significant at P- 0.05 Quadratic models represented most of the relationships between temperature and the parameters measured, indicating curvilinear relationships. 80 70 a a
n
-b i:fiE:
o
dd 12 1820 24 28 Temperature (0)FIO. 1. Effect of temperature ort Stagon osp ora nodorum
spot development In wheat cultivara differing in resistance. Disease development was estimated as percentage of leaf arca showing symptoms ten days after inocutation. Categorias ofStagonospora nodorum spot severity are separated by dotted
tines as follows: stight, symptntess to 15%; moderate, 16 to 45%; severa, greater than 45% of leaf arca showing symptoms. Means for an individual cultivar at various temperatures labelled with a common letter are not significantly different by the "protected" LSD test at Pe 0.05. CV % 13.0 and "protected" LSD7.8 for main plots, CV %- 13.2 and "protected' LSD- 7.6 for subpl ots.
An increase ia susceptibility ofwheat cultivars following expoure to higli temperature up to 240C was observed (Fig. 1). The wheat cultivar Fortuna, designated as susceptible, developed severe symptoms at 20 to 240C. Manitou, usually reported as resistant to P. nodorum, showed slight disease development from 12 to 20 °C btit was as severely diseased as Fortuna at 240C. Newana, designated as moderately resistant, developed only moderate symptoms at 24 °C, favorable for severe disease development ira both Fortuna and Manitou.
There were no significant differences ia percentage of leaf arca showing symptoms among cultivars at 280C. The number of lesions per cia increased progressively with increasing temperature from 12-240C (Fig. 2) Incubadora period.was reduced as temperature increased from 12 to 240C (Fig. 3). Minimai disease severity ocurred at 12 °C ira ali cultivars evaluated. The optirnum temperature range for disease development was 18 to 240 for cultivar Fortuna and Newana and 240C for Manitou.
R Fortuna 12 DNewana a a • Mandou b a 8 b a
f;
Temperature (C)FIO. 2. Effect of temperatura on number of lesions par cm2 lnduced by Phaeosphaerie nodorwn seven
days after inocutation ora leaves of ttiree wheat cultivara. Means for each cultivar at various temperatures labelled wilh a common letter are not significantly different by die "protected" LSD test at a 0.05 CV%- 13.7 and "protected" LSD - 4.5 for main plots, CV % = 11.9 and "protected" LSD- 1.9 for subplots.
The results showing 18-240C as optimum temperatures for disease development support the concept that Stagonospora nodorum spot is a disease associated with warm weather, and agrees with the observation that the disease is more severe both ia late-sowa wheat and late ia the wheat growing season (Luz 1986).
These results support ia part the reported optimum temperature range for disease develop-ment of 20-270C (Wiese 1977). Our results are alio consistent with reports of optimal pycnidios-pore germinatioa at 20 to 250C (Rapilly & Skaje-nilcoff 1974). Alteration c,f expression ofresistance in the cultivar Manitou ocurred at 240C whea this cultivar showed severe disease development.
628 W.C. DA LUZ and G.C. BERGSTROM Thomas (1962) found thatP. nodorum infection,
was not affected by temperatures of 18, 24 or 300C during the mist period. However, higli preinoculation temperatures predisposed wheat
plants to severe Stagonospora nodorum spot development (Rosielie 1968, Thonias 1962). Results presented here definidvely indicate that postinoculation temperature is also important for expression of disease symptoms. -
Temperature alteration of phenotypic expression of resistance creates probiems in testing wheat germplasms for P. nodorum resistance. Resistance tests for Stagonospora nodotum spot produce variable results (Fernandes et ai. 1980, Picinini et ai. 1980, Rufty etal. 1981) that may be explained by differences in virulence (Ailingham & Jackson 1981, Thomas 1962), long durations ofhumidity (Eyal et ai. 1977, Holmes & Colhoun 1974), preinoculation temper8tures (Rosielie 1968, Thomas 1962), or different methodologies (Picinini et ai. 1980, Rufty et ai. 1981). li s also possibie that postinoculation temperature had an effect on those resuits. Therefore, relative resistance of cultivars to Stagonospora nodorum spot may be recorded with less variabiity if experiznents are carried out at standardized temperatura regimes. Similarly, postinoculation temperature has alio been observed to alter the phenotypic expression of resistance to other wheat leaf spotting fsngi (Luz 1986).
Whether wheat plants should be maintained at the optimum temperature for disease deveiopment during gerinplasm screening should be a function ofwhether or not such environment is commonly found in the target wheat growing area. If it is, characterization of wheat germplasrns displaying temperatura-sensitiva reactions to Stagonospora nodorum spot and other leaf spot diseases is strongly recornmended. 140 120 100 80 c .2 60 CO n 40 c 12 18 20 24 28 Temperature (0)
F I G. 3.. Effect of temperatura on incubation period of
Phaeosphaeria nodorum on leaves of three
wheat eultivars. Means for each cultivar at variou! temperaturas Iabelled with a cnmon Ietter are not signifiçantiy different by the "protected"
LSD test atP- 0.05, CV %- 14.2 and "protected"
LSD - 3.9 for main plots, CV % 13.5 and
"protected" L.SD - 3.5 for subplots.
TABLE 1. Regression analysis of percentage of leaf area showing Stagonospora nodo,vm spot syrnptoms, number of
lesions par cm2 and incubaüon period, vs. temperatura in three spring wheat cuitivars. Regression equat i onsa Factors
Ma nitou Newana Fortuna
Leafarea(%). y=.44+S.34x Showingsymptoms vs. temperatura Number of lesions! y- .7.45+ 0.58x cm2vs.temperatUre Incubation period vs. temperatura y. 368.29 - 26.43x + O.51x 2 y- .111.63+ 12.32x y--180.1+21.x -0.26x 2 -046x 2 y •18.60+2.02x y.'-26.20+3.34x .0031( 2 + 0 . 071(2 y - 396.51 - 30.03x y-418.06 + 0 . 611(2 •33.17x + 0.691(2
a Ali regressions are represented by quadratic modeis with the exception of % leaf area showirig symptoms vs. tempera-tura and number of Iesions/cm2 vs. temperatura for cultivar Malitou. y • disease parameter, x - temperature. Pesq. agropec. bras., Brasilia, 21(6):625-629,jun. 1986.
TEMPERATURE ALTERATION OF PHENOTYPIC EXPRESSION 629
ACKNOWLEDGEMENTS
This research was conducted at Corneil
Univer-sity. The authors gratefully acknowledge the financial support provided by Cornell Agricultura! Experiment Station J-latch Project 153-412 and by EMERAPA (Brazilian Enterprise of Agricultura! Research). Appreciation is also extended to Dr. A.L. Scharen tor providing the P. nodorum
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