Euphytica (2008) 162:449–456

DOI 10.1007/s10681-007-9611-3

Combining ability analysis of Fusarium head blight resistance in western European wheat lines

Rebecca S. Zwart · Hilde Muylle · Johan Van Huylenbroeck · Erik Van Bockstaele · Isabel Roldán-Ruiz

Received: 27 April 2007 / Accepted: 22 October 2007 / Published online: 3 November 2007© Springer Science+Business Media B.V. 2007

Abstract The inheritance of Fusarium head blight(FHB) resistance was investigated in eight westernEuropean wheat lines using a half-diallel of F1

crosses. The parents and F1 crosses were point-inocu-lated, with a highly aggressive isolate of Fusariumgraminearum, in replicated Weld and glasshouse trials.Type II resistance was assessed by measuring the %FHB spread and % wilted tips. There was a good cor-relation between the two disease parameters, % FHBspread area under the disease progress curve(AUDPC) and % wilted tips AUDPC (r = 0.86,P < 0.01). Correlation coeYcients between the Weldand glasshouse environments were r = 0.46 (P < 0.01)for % FHB spread AUDPC and r = 0.40 (P < 0.05) for% wilted tips AUDPC. Both general combining ability(GCA) and speciWc combining ability (SCA) eVectsinXuenced the inheritance of FHB resistance, suggest-ing that in this set of parents both additive andnon-additive (dominance or epistatic) eVects inXuence

the inheritance of type II FHB resistance. HighlysigniWcant GCA-by-environment (P < 0.0001) andSCA-by-environment (P < 0.005) interactions werealso observed. SpeciWc combinations of western Euro-pean wheat varieties were identiWed with type II FHBresistance at a level equal to or more resistant than thewinter wheat variety ‘Arina’.

Keywords Fusarium graminearum · Fusarium head blight · Half-diallel · Triticum aestivum · Type II resistance · Wheat

AbbreviationsAUDPC Area under the disease progress curveFHB Fusarium head blightGCA General combining abilityQTL Quantitative trait lociSCA SpeciWc combining ability

Introduction

Fusarium head blight (FHB) is a destructive diseasethat is widespread throughout the temperate cereal-growing regions of the world (Parry et al. 1995). FHBcauses signiWcant quality and yield losses, as well asthe accumulation of hazardous mycotoxins in thegrain. Numerous Fusarium spp. have been associatedwith FHB in wheat (Triticum aestivum L.), withF. graminearum Schwabe (teleomorph = Gibberellazeae (Schwein) Pech) and F. culmorum (W. G. Smith)

R. S. Zwart (&) · H. Muylle · J. Van Huylenbroeck · I. Roldán-RuizApplied Genetics and Breeding, Institute for Agricultural and Fisheries Research (ILVO) – Plant, Caritasstraat 21, Melle 9090, Belgiume-mail: rebecca.zwart@ilvo.vlaanderen.be

E. Van Bockstaele Faculty of Bioscience Engineering, Department of Plant Production, Ghent University, Coupure Links 653, Ghent 9090, Belgium

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the predominate species present in western Europe(Parry et al. 1995; Snijders 1990b).

Considerable genetic variation in resistance toFHB has been reported throughout the world andgenetic resistance is considered to provide the mosteconomical and eVective control of FHB (Bai andShaner 1994). The quantitative nature of inheritanceof FHB resistance (Bai et al. 1999; Buerstmayr et al.1999, 2002; Gervais et al. 2003; Liu et al. 2005; Pail-lard et al. 2004, Schmolke et al. 2005; Semagn et al.2007) and the considerable inXuence of environmen-tal conditions, such as temperature, humidity, plantdevelopment stage and abundance of inoculum, onthe expression of FHB resistance (Parry et al. 1995;Bai and Shaner 1996; Klahr et al. 2007; Meidaneret al. 2001) add to the challenges of breeding FHB-resistant wheat varieties. The complex nature of FHBresistance has been described as consisting of severalcomponents: type I resistance prevents initial infec-tion; type II resistance prevents spread of the patho-gen within the plant head; type III resistance preventskernel infection; type IV resistance provides toleranceto yield losses; type V resistance prevents the accu-mulation of mycotoxins in the grain (Schroeder andChristensen 1963; Mesterházy 1995).

To date, the most resistant and most widely utilisedsource of FHB resistance throughout the world isSumai 3, a spring wheat originating from China thatprimarily provides type II FHB resistance. Althoughresistance to FHB is non-species and non-race spe-ciWc (van Eeuwijk et al. 1995; Mesterházy et al.2005), the identiWcation and genetic analysis of diVer-ent sources of resistance in adapted varieties, in addi-tion to exotic wheat lines, is critical to the continuedimprovement of FHB resistance in wheat (Liu et al.2005). IdentiWcation of western European winterwheat varieties and breeding lines with moderateFHB resistance is advantageous as these lines wouldprovide a useful level of resistance in an agronomicbackground adapted to grain production areas inwestern Europe. The genetic basis of FHB resistancein the European winter wheat gene pool has beenstudied in only a few sources: For example, Renan(Gervais et al. 2003), Arina (Paillard et al. 2004;Semagn et al. 2007), Dream (Schmolke et al. 2005),Cansas (Klahr et al. 2007).

In addition to the identiWcation of new sources ofFHB resistance, the value of moderately resistantwheat lines as potential parents in breeding programs

needs to be assessed. Understanding the inheritanceof FHB resistance in a given genetic background iscritical for the eYcient and eVective exploitation ofthe resistance in breeding and selection strategies.The diallel cross is a commonly used experimentaldesign to estimate combining abilities in a set ofparental lines. Diallel crosses have been used to studythe inheritance of FHB resistance in cereals such aswinter wheat (Hall and Van Sanford 2003; Buerstm-ayr et al. 1999; Snijders 1990a), spring wheat (Mardiet al. 2004), barley (Takeda and Wu 1996), wintertriticale (Oettler et al. 2004), and winter rye (Mieda-ner et al. 1993). These studies concluded, in general,that the variation in FHB resistance is primarilyattributed to additive eVects. However highly signiW-cant genotype-by-environment eVects must also betaken into consideration (Hall and Van Sanford 2003;Mardi et al. 2004).

The objectives of this study were to estimate thegeneral combining ability (GCA) and speciWc com-bining ability (SCA) eVects controlling type II FHBresistance across environments in a set of westernEuropean winter wheat lines and to identify potentialcombinations of parents with suitable levels of FHBresistance for future selection.

Materials and methods

Parents and crosses

Eight winter wheat varieties and advanced breedinglines were crossed in all possible pair-wise combina-tions, without reciprocals to produce 28 F1 lines. Theparental genotypes were chosen on the basis of theiroverall resistance to FHB resistance as assessed in apreliminary Weld spray-inoculation trial conducted in2004 at Clovis Matton N.V., Avelgem-Kerkhove,Belgium (Table 1). The parental winter wheat varie-ties ‘Centenaire’, ‘Tulsa’, ‘Tuareg’, ‘Elegant’,‘Astuce’, ‘Attlass’ are currently listed on the EUCommon Catalogue of Varieties of Agricultural PlantSpecies 2007. ‘Arina’ was also included as parent inthe diallel as it is a well characterised source of FHBresistance in western European winter wheat (Paillardet al. 2004; Semagn et al. 2007). ‘BZ113698’ is ahigh yielding advanced breeding line that was one ofthe most susceptible lines to FHB in the preliminaryspray-inoculation trial.

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FHB resistance evaluation trials

The resistance levels of the parents and F1 crosseswere evaluated in point-inoculation trials conductedat the facilities of ILVO-Plant (Melle, Belgium) intwo environments: the Weld and the glasshouse. TheWeld trial was sown on 28 October 2005 and the glass-house trial was sown on 13 December 2005. Plotswere sown by hand and consisted of single rows con-taining eight seeds (with 10 cm spacing). The experi-mental layouts were randomised complete blockdesigns with two replicates in each environment. Tocontrol seed-borne diseases the seed was treated with‘Celest’ (Syngenta), at a seed dressing rate of 6 �l/gseed.

Inoculum was prepared from a highly aggressivesingle-spore isolate of F. graminearum isolate ‘IFA65’ in liquid mungbean medium as described byBuerstmayr et al. (2002). The concentration of macro-conidia was determined using a Bürker countingchamber and adjusted to 100,000 conidia/ml. Ali-quots of the inoculum were stored frozen at ¡20°Cuntil required. To ensure that the F. graminearum iso-late was highly aggressive, the aggressiveness of theisolate was tested prior to the inoculation period usinga Petri dish infection test as described by Lemmenset al. (1993).

Ten spikes per line were inoculated by injecting10 �l of conidial suspension into a single spikelet,

located one-quarter of the length down the spike fromthe distal tip. Inoculated spikes were identiWed withself-adhesive labels and the initial inoculated spikeletwas identiWed by cutting oV a small portion of the topof the spikelet with scissors. FHB disease symptomswere evaluated on days 10, 14, 18, 22, and 26 afterinoculation by recording (i) the number of bleachedspikelets downwards from the initial inoculatedspikelet (% FHB spread, assuming 20 spikelets perinoculated spike), and (ii) the number of inoculatedspikes showing premature death of the portion of thespike distal to the initial inoculated spikelet (% wiltedtips). An area under the disease progress curve(AUDPC) was calculated for both disease traitsaccording to Buerstmayr et al. (1999).

Statistical analysis

Statistical analyses were performed using the softwarepackage SPSS v11.5 for Windows (SPSS Inc.,Chicago, IL, USA). Analysis of variance (ANOVA)for individual environments (Weld and glasshouse) andacross environments were performed to determine thesources of variation for % FHB spread and % wiltedtips observed at each of the Wve evaluation dates andfor the AUDPC data. Least-square means, based on ageneral linear model were used to estimate GCA andSCA eVects of the F1 crosses across environmentsaccording to GriVing’s (1956) experimental model 1

Table 1 Line name, breeding company, countries in which the variety is currently listed in the national variety catalogue, pedigreeand Fusarium head blight (FHB) disease score of the eight western European winter wheat lines used as parents in the half-diallel

a FHB score on a scale of 1 (resistant)–9 (susceptible) in a preliminary Weld spray-inoculation trial conducted in 2004 at Clovis MattonN.V. (Avelgem-Kerkhove, Belgium)b BEL—Belgium; DEU—Germany; NLD—Netherlands; AT—Austria; CHE—Switzerland; FRA—France

Name Breeding company National variety listb Pedigree FHB scorea

Centenaire Jorion V & Fils SA, Belgium BEL Estica/Vivant 2

Tulsa Landbouwbureau Wiesum BV, Netherlands

BEL, DEU, NLD, AT

ZE89-1366/Toronto 2

Tuareg Nordsaat Saatzucht GmbH, Germany DEU Kris/Dekan 2

Elegant Deutsche Saatveredelung GmbH, Germany

DEU Line/Acona//Beaufort 2

Arina Delley Semences et Plantes AG, Switzerland

CHE Moisson/Zenith 2

Astuce R2n, France FRA Audace/Rialto//Rialto 3

Attlass Svalöv Weibull AB, Sweden FRA WH6469-69/WH30890 5

BZ 113698 W. von Borries-Eckendorf GmbH & Co, Germany

– ZE89-2836/ZE89-1366 7

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(Wxed eVects), and method 4 (no parents or recipro-cals) using the software DIALLEL-SAS05 (Zhanget al. 2005). Genotype-by-environment interactionvariance was partitioned into variance attributed toGCA-by-environment eVects and SCA-by-environ-ment eVects.

Results

There were signiWcant diVerences in % FHB spreadand % wilted tips among the parents and F1 crosses.In the Weld, FHB spread at day 26 ranged from 1.0spikelet/spike (Elegant) to 8.0 spikelets/spike(Tuareg), and the % wilted tips at day 26 ranged from20% (BZ113698) to 95% (‘Attlass’ and ‘Tuareg’). Inthe glasshouse, FHB spread at day 26 ranged from 1.4spikelets/spike (BZ113698) to 10.9 spikelets/spike(‘Tuareg/Attlass’ F1), and the % wilted tips at day 26ranged from 10% (‘Astuce/BZ113698’ F1) to 85%(‘Tuareg/Attlass’ F1). The overall mean (parents andF1 crosses) for % FHB spread AUDPC was slightlyhigher in the Weld than in the glasshouse (121.2 § 8.4and 97.9 § 10.4, respectively). The overall mean for% wilted tips AUDPC was also higher in the Weldthan in the glasshouse (681 § 33.3 and 440.3 § 28.1,respectively).

In both environments, the means for % FHBspread AUDPC and % wilted tips AUDPC were sig-niWcantly (P < 0.01) correlated with % FHB spreadand % wilted tips, respectively, observed at each ofthe Wve evaluation dates (Table 2). There was a goodcorrelation between the two disease parameters %FHB spread AUDPC and % wilted tips AUDPC inboth environments (Table 3). Thus, the combiningability analysis was conducted using only % FHB

spread AUDPC data. In the glasshouse, ‘Tuareg’,‘Astuce’ and ‘Attlass’ were signiWcantly (P < 0.05)more susceptible to % FHB spread AUDPC than thecontrol winter wheat variety ‘Arina’, while in theWeld, only ‘Tuareg’ was signiWcantly less resistantthan ‘Arina’.

ANOVA revealed highly signiWcant diVerencesbetween environments and among genotypes (Table 4).There was highly signiWcant variation for type II FHBresistance for both GCA and SCA eVects, as well as forGCA-by-environment and SCA-by-environment inter-actions. Estimates of GCA and SCA eVects, means ofthe two environments and overall mean for % FHBspread AUDPC for the eight parental wheat lines areshown in Table 5. A negative combining ability valueindicates a contribution from the parent towards greaterresistance, while a positive value indicates a contribu-tion towards greater susceptibility.

When analysed across environments, the wheatlines ‘BZ113698’, ‘Centenaire’, ‘Arina’, ‘Tulsa’

Table 2 Correlations between AUDPC calculations and the evaluations at each of the Wve dates (day 10, 14, 18, 22 and 26) for % FHBspread and % wilted tips in the two environments (Weld and glasshouse)

**SigniWcant at 0.01 probability level

% FHB spread at

% FHB spread AUDPC % Wilted tips at

% Wilted tips AUDPC

Field Glasshouse Field Glasshouse

Day 10 0.46** 0.31** Day 10 0.40** 0.30**

Day 14 0.89** 0.85** Day 14 0.86** 0.84**

Day 18 0.94** 0.96** Day 18 0.96** 0.93**

Day 22 0.97** 0.98** Day 22 0.94** 0.97**

Day 26 0.94** 0.97** Day 26 0.87** 0.92**

Table 3 Correlations between the two FHB disease parameters(% FHB spread AUDPC and % wilted tips AUDPC) and the twoenvironments (Weld and glasshouse)

*, **SigniWcant at the 0.05 and 0.01 probability level, respec-tively

% FHB spread AUDPC glasshouse

% wilted tips AUDPC Weld

% wilted tips AUDPC glasshouse

% FHB spread AUDPC Weld

0.46** 0.86** 0.35*

% FHB spread AUDPC glasshouse

0.46** 0.78**

% wilted tips AUDPC Weld

0.40*

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and ‘Astuce’ all had negative GCA eVects, howevereVects were not signiWcant. The genotypes ‘Tuareg’and ‘Attlass’ exhibited signiWcant positive GCAeVects, indicating that in general these lines con-tribute towards susceptibility for type II FHB resis-tance in F1 crosses. These lines were in fact the twomost susceptible lines in the set of parents(Table 5). SigniWcant SCA eVects for resistancewere found in the F1 crosses ‘Centenaire/Elegant’,

‘Tulsa/Elegant’ and ‘Tuareg/Elegant’. The resis-tance levels of these F1 crosses were higher thanexpected based on the average type II FHB resis-tance level of the respective parents of the crosses.SigniWcant SCA eVects for susceptibility werefound in the crosses ‘Centenaire/Tuareg’, ‘Tulsa/Tuareg’ and ‘Elegant/BZ113698’. These F1 crosseswere more susceptible than predicted from the aver-age parental performance.

Table 4 Mean squares and their signiWcance level for type II FHB resistance (% FHB spread area under the disease progress curve)in the eight parent half-diallel in the two environments (Weld and glasshouse) and combined analysis

a GCA = General combining abilityb SCA = SpeciWc combining ability

Source Field Glasshouse Combined

df MS MS df MS

Environment (ENV) 1 25986**

Replications within ENV 1 23 19463** 2 9743

Genotype 27 9213** 11937** 27 323042**

GCAa 7 4244 31135** 7 17587**

SCAb 20 10951** 5217* 20 9997**

Genotype*ENV 27 9185**

GCA*ENV 7 17793**

SCA*ENV 20 6173**

Error 27 2484 2398 54 2441

CoeYcient of variation (%) 40 52 45

R2 (%) 79 84 82

Table 5 Estimates of speciWc combining ability (SCA) eVects,general combining ability (GCA) eVects, means of the two envi-ronments (Weld and glasshouse) and overall mean for % FHB

spread area under the disease progress curve for the eight west-ern European winter wheat parents of the half-diallel.

*, **SigniWcant at the 0.05 and 0.01 probability level, respectivelya LSD (0.05) for testing signiWcance of GCA eVects = 60.3; LSD (0.05) for testing diVerences between GCA eVects = 91.1

LSD (0.05) for testing signiWcance of SCA eVects = 69.3; LSD (0.05) for testing diVerences between SCA eVects with a commonparent = 105.8; LSD (0.05) for testing diVerences between SCA eVects with no common parent = 94.6

Parent SCA eVecta GCA eVecta Parental means

Tulsa Tuareg Elegant Arina Astuce Attlass BZ113698 Field Glasshouse Overall

Centenaire ¡26.6 83.3** ¡68.5* 7.5 ¡3.0 21.0 ¡13.8 ¡22.9 86.0 72.4 79.2

Tulsa 74.3* ¡63.5* ¡4.3 ¡6.3 ¡1.5 28.1 ¡13.9 32.5 105.1 68.8

Tuareg ¡87.4** ¡18.7 ¡30.9 17.6 ¡38.3 46.0** 222.6 193.6 208.1

Elegant 39.0 55.3 52.8 72.2* 11.5 0.0 34.6 17.3

Arina 17.5 ¡35.7 ¡5.3 ¡19.9 94.9 39.5 67.2

Astuce ¡22.0 ¡10.6 ¡8.7 127.9 202.3 165.1

Attlass ¡32.3 32.8* 148.1 196.6 172.3

BZ113698 ¡24.9 53.5 16.0 34.8

Mean 95.7 107.5 101.6

LSD (0.05) 98.3 150.4 79.3

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Figure 1 shows the observed % FHB spreadAUDPC of the F1 crosses in comparison with theexpected value of the F1 crosses as predicted on thebasis of the parents contributing solely additive geneaction. Deviations from the regression line are due toSCA eVects plus error in estimating the % FHBspread AUDPC (Falconer and Mackay 1996). F1

crosses below the regression line performed betterthan expected based on the performance of the par-ents, while F1 crosses above the regression line per-formed worse than expected based on theperformance of the parents. Clearly, non-additive(dominance or epistatic eVects) inXuence the inheri-tance of type II FHB resistance in this set of wheatgenotypes.

Discussion

Genotype-by-environment interactions for FHB resis-tance have been reported in several cereal crops(Mesterházy 1995; Miedaner et al. 2001; Mardi et al.2004; Oettler and Wahle 2001; Oettler et al. 2004;Hall and Van Sanford 2003). Thus, in an attempt tominimise environmental inXuences and to observe thetrue resistance level of the wheat genotypes in this

study, point-inoculation trials were conducted in twoenvironments, in the Weld and in the glasshouse.Many studies into the complex inheritance of FHBresistance have applied single spikelet inoculationmethods to reduce the diVerences in disease inci-dence, type I resistance, among test lines and deter-mine speciWcally the spread of the disease within aspike, type II resistance (Bai et al. 1999). OverallFHB resistance was initially used to select the paren-tal wheat lines of the diallel, however, in the combin-ing ability analysis the parents and F1 crosses wereevaluated speciWcally for type II FHB resistance. Theadvanced breeding line ‘BZ113698’ was included inthe diallel as one of the most susceptible wheat lineswith low overall FHB resistance evaluated in a pre-liminary trial, however, this line proved to have a typeII FHB resistance level not signiWcantly diVerent (atthe 5% conWdence interval) from that of ‘Arina’.Thus, while ‘BZ113698’ may have good type II FHBresistance (resistance to fungal spread), the poor over-all FHB resistance rating in the spray-inoculation tri-als indicates that it possess low type I FHB resistance(resistance to initial infection).

‘Arina’ is a well-documented source of FHB resis-tance in the European winter wheat gene pool (Ruck-enbauer et al. 2001) and was also included in a diallelstudy of overall FHB resistance by Buerstmayr et al.(1999). QTL for FHB resistance have been identiWedin ‘Arina’ on chromosomes 1BL and 6BS (Semagnet al. 2007) and 6DL and 4AL (Paillard et al. 2004).None of the wheat lines in the diallel were signiW-cantly more resistant for % FHB spread AUDPC than‘Arina’ and three of the eight parents (‘Tuareg’,‘Astuce’ and ‘Attlass’) were signiWcantly more sus-ceptible than ‘Arina’ for type II FHB resistance.

One highly aggressive isolate of F. graminearumwas used in this study since FHB resistance in wheatis considered non-speciWc (van Eeuwijk et al. 1995)and non-signiWcant genotype-by-isolate interactionshave been reported in several studies (Buerstmayret al. 2002; Mesterházy et al. 2005). Maternal eVectsinXuencing the inheritance of FHB resistance inwheat have been reported as small or non signiWcant(Buerstmayr et al. 1999; Van Ginkel et al. 1996; Halland Van Sanford 2003; Liu et al. 2005), thus recipro-cal F1 crosses were not included in the diallel crossingscheme. The high correlation (r = 0.86) observedbetween the % FHB spread and the % wilted tips con-Wrms the strong correlation between these two traits

Fig. 1 Observed and expected values for % FHB spread areaunder the disease progress curve (AUDPC) in F1 crosses be-tween eight western European winter wheat genotypes. The ex-pected % FHB spread AUDPC of each F1 cross is the sum of thegeneral combining ability of the two parental lines. The dottedlines show the positions of deviations from the regression of §2 standard errors of the F1 cross means. F1 crosses with signiW-cant speciWc combining ability eVects for type II FHB resistanceare labelled

0

50

100

150

200

250

0 50 100 150 200 250

Expected % FHB spread AUDPC

Ob

evresF

% d

ps B

Hdaer

AC

PD

U

Centenaire/Elegant F1

Tulsa/Elegant F1

Tuareg/Elegant F1

Centenaire/Tuareg F1 Tuareg/Tulsa F1

Elegant/BZ113698 F1

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(r = 0.96) reported by Buerstmayr et al. (2002).Repeated evaluations of disease progress from day 10to day 26 after inoculation were recorded for bothFHB disease traits (% FHB spread and % wilted tips)to measure the AUDPC. In this way, not only the Wnalpercentage of infected spikelets and wilted tips, butalso the progression rate in early stages of diseasedevelopment was evaluated (Bai et al. 1999). How-ever, a single observation taken 22 days after inocula-tion would have been as eVective as the AUDPC inassessing resistance. Several other studies conWrmthat maximum genetic diVerences for type II FHBresistance have been obtained at day 22 (Bai et al.1999; Snijders 1990a; Buerstmayr et al. 2002).

Identical evaluation methods for type II FHB resis-tance conducted in the Weld and glasshouse identiWedhighly signiWcant genotype-by-environment interac-tions, indicating the importance of evaluating wheatgenotypes in more than one environment in order toget a true representation of the level of FHB resis-tance. The correlation coeYcient (r = 0.46) betweenthe Weld and glasshouse trials was higher than thosereported by Hall and Van Sanford (2003), who alsoused identical evaluation methods on a set of wheatgenotypes both in the Weld and greenhouse (r = 0.36and r = 0.14). These authors raised concern for resultsbased solely on greenhouse evaluations. Environmen-tal conditions play a crucial role in the developmentof FHB in wheat and variation in FHB symptomexpression due to environmental interactions remainsa major challenge for accurate assessment of FHBresistance.

Highly signiWcant (P < 0.0001) genetic variationfor type II FHB resistance was identiWed for bothGCA and SCA eVects, indicating that in this set of par-ents, type II FHB resistance is conditioned by bothadditive and non-additive gene action. The signiWcantSCA eVects for ‘Elegant’ suggest the presence ofdominance or epistatic gene action in speciWc crosscombinations. All crosses with signiWcant SCA eVectstowards increased resistance, including the two mostresistant crosses in the diallel, involved the parent‘Elegant’. This parent was also involved in a cross(‘Elegant/BZ113698’) with signiWcant SCA eVectstoward susceptibility, revealing the negative interac-tion of genes from the two most resistant parentalgenotypes in the diallel. Importantly, lines with signiW-cant GCA (‘Tuareg’ and ‘Attlass’) and SCA (‘Cente-naire/Tulsa’, ‘Tulsa/Tuareg’ and ‘Elegant/BZ113698’)

eVects towards susceptibility were identiWed, signify-ing that avoidance of these crosses will facilitate thereduction of FHB susceptibility in breeding material.SigniWcant GCA-by-environment and SCA-by-envi-ronment interactions indicate that symptoms for typeII FHB are not stable across environments and trials inadditional environments, as well as repeating the trialsin the same environment, would increase the accuracyof the estimates of GCA and SCA eVects and conWrmthe results of this study.

Statistically signiWcant eVects for both GCA andSCA in diallels of winter wheat have been previouslyreported in point inoculation trials withF. graminearum (Hall and Van Sanford 2003) andspray inoculation trials with F. culmorum (Buerstm-ayr et al. 1999). SigniWcant SCA eVects for FHBresistance have also been identiWed in diallel studiesinvolving winter rye (Miedaner et al. 1993) and win-ter triticale (Oettler et al. 2004). Although SCAeVects were signiWcant in these studies, suggestingdominance or epistatic gene action inXuenced inheri-tance of FHB resistance in speciWc crosses, additiveeVects for FHB resistance were predominant. In con-trast, non-additive genetic components were reportedto have no inXuence over the control of overall FHBresistance in a F. graminearum spray-inoculation trialconducted using spring wheat lines (Mardi et al.2004) and in a diallel of European winter wheat linesspray inoculated with F. culmorum (Snijders 1990a).

IdentiWcation of moderate FHB resistance innumerous winter wheat sources is essential in order tocombine genetic backgrounds with acceptable agro-nomic traits and suitable end-use quality with ade-quate levels of FHB resistance. In addition,partitioning the genetic variance attributed to FHBresistance into GCA and SCA eVects will aid plantbreeders devise the most eYcient and eVective breed-ing and selection strategies for these moderately resis-tant wheat lines. In this study we have combinedalternative sources of western European winter wheatlines with moderate type II FHB resistance than pre-viously described. Genetic variation for type II FHBresistance in this set of wheat lines was attributed toboth additive and non-additive eVects and highly sig-niWcant environmental interactions. While the mostresistant F1 crosses were not produced strictly bycrossing the two parents with the lowest negativeGCA eVects (the best general combiners for FHBresistance), promising combinations of the parents for

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the improvement of FHB resistance in western-Euro-pean winter wheat backgrounds were identiWed.

Acknowledgements We wish to thank J. Dermaut andL. Vandenabeele (Clovis Matton N. V., Belgium) for conduct-ing preliminary spray-inoculation trials and for supplying seed,M. Lemmens (IFA-Tulln, Austria) for supplying the Fusariumisolate, M. Kang (LSU AgCenter, USA) for access to DIAL-LEL-SAS05 program code and K. Succaet (ILVO-Plant,Belgium) for technical assistance. This study was funded byIWT-Flanders.

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