Fusarium head blight (FHB) caused by Fusarium culmorum is an economically important disease of wheat that may cause serious yield and quality losses under favorable climate conditions. The development of disease-resistant cultivars is the most effective control strategy. Worldwide, there is heavy reliance on the resistance pool originating from Asian wheats, but excellent field resistance has also been observed among European winter wheats. The objective of this study was to map and characterize quantitative traits loci (QTL) of resistance to FHB among European winter wheats. A population of 194 recombinant inbred lines (RILs) was genotyped from a cross between two winter wheats Renan (resistant)/Récital (susceptible) with microsatellites, AFLP and RFLP markers. RILs were assessed under field conditions For 3 years in one location. Nine QTLs were detected, and together they explained 30-45% of the variance, depending on the year. Three of the QTLs were stable over the 3 years. One stable QTL, QFhs.inra.2b, was mapped to chromosome 2B and two QTLs QFhs.inra.5a2 and QFhs.inra5a3, to chromosome 5A; each of these QTLs explained 6.9-18.6% of the variance. Other QTLs were identified on chromosome 2A, 3A, 3B, 5D, and 6D, but these had a smaller effect on FHB resistance. One of the two QTLs on chromosome 5A was linked to gene B1 controlling the presence of awns. Overlapping QTLs for FHB resistance were those for plant height or/and flowering time. Our results confirm that wheat chromosomes 2A, 3A, 3B, and 5A carry FHB resistance genes, and new resistance factors were identified on chromosome arms 2BS and 5AL. Markers flanking these QTLs should be useful tools for combining the resistance to FHB of Asian and European wheats to increase the resistance level of cultivars.

Amélioration des plantes Recherche de géniteurs de résistance à la fusariose de l'épi causée par Fusarium culmorum chez le blé et les espèces voisines L Saur JY Morlais INRA, station d'amélioration des plantes, domaine de la Motte-au-Vicomte, BP 29, 35650 Le Rheu, France (Reçu le 21 décembre 1990; accepté le 29 avril 1991) Résumé — Sur une période de 10 ans, 230 variétés de blé tendre et 334 lignées appartenant à 15 espèces de triticinées ont été évaluées pendant une ou plusieurs années pour leur résistance à la fusariose de l'épi causée par Fusarium culmorum. La contamination a été réalisée par pulvérisation d'une suspension de spores à l'anthèse pour chaque génotype. Aucun niveau de résistance très élevé n'a été trouvé chez les espèces voisines de Triticum aestivum. Les lignées de blé de printemps des zones subtropicales signalées pour leur résistance à Fusarium graminearum se sont montrées assez résistantes à F culmorum dans nos conditions. Les blés tendres d'hiver étudiés présentent une variabilité importante pour la résistance avec de très grandes différences entre les variétés peu sensibles et les variétés très sensibles. Le niveau de résistance à rechercher pour des variétés de blés d'hiver en zone tempérée est discuté à partir de mesures de l'effet du parasite sur le rendement. Fusarium culmorum / résistance / blé / Triticeae Summary — Sources of resistance to head blight caused by Fusarium culmorum in bread wheat and related species. Over a 10-yr period, a total of 230 wheat genotypes and 334 lines from 15 Triticineae species were evaluated for their resistance to head blight caused by Fusarium culmorum. Plants were inoculated in the field by spraying a spore suspension at the anthesis of each genotype. The percentage of infected spikelets was evaluated visually 20 d after contamination and the effect of the disease on thousand grain weight was measured by comparing inoculated and uninoculated plots. The same 4 varieties were used as control every year. The good difference between the susceptible and the resistant controls (fig 1), provided a scale to compare genotypes even if they were not tested during the same years. A wide genetic variation was found in winter wheat, from very susceptible to partially resistant genotypes (table I). The resistance level needed for winter wheat cultivation in the temperate climate of northern France is discussed according to the evaluation of the loss of grain yield due to the disease (table II). Exotic spring wheat varieties reported for their tolerance to Fusarium graminearum were also tolerant to F culmorum under our environmental conditions (table III). Related species did not display a very high level of resistance (table IV). Only the frequency of resistant genotypes is higher in the species Triticum monococcum and Aegilops speltoides.

résistance / Fusarium culmoruml blé / sélection récurrente / sélection précoce / héritabilité Summary — Heritability and recurrent selection for resistance to Fusarium head blight in winter wheat. Fifty-six S 1 families and their S 2 progeny from a winter wheat population with genic male sterility were evaluated for reaction to Fusarium head blight. Families were tested in the field using artificial inoculation. Tests were repeated over 2 years for S 1 families. Disease severity was scored on spikes and seeds. The effect of the disease on yield and thousand grain weight was measured using uninoculated control plots. A significant correlation was found between disease severity and thousand grain weight decrease (table I). Despite significant year x genotype interaction (table II), correlation coefficients between the 2 years for disease evaluation on S 1 families were high (r=0.79 for severity in seeds). Broad sense heritabilities were from 0.8 to 0.9 (table III) and justify early selection for Fusarium resistance in the population. Because of low S 1 -S 2 heritability (table V), using sibs of tested plants instead of offspring is suggested for the recurrent selection scheme.

Fusarium roseum var culmorum / blé / rendement / cultivar Summary — Relationship between head blight symptoms of Fusarium roseum var culmorum and yield losses in wheat. Four winter wheat cultivars were inoculated in field tests by Fusarium roseum var culmorum over a 4-yr period. Several spore concentrations of the inoculum were used each year. The severity of the disease was evaluated using the number of damaged spikelets at the early dough growth stage and the percentage of visually infected seeds at harvest. Yield and 1 000 grain weight losses were measured with reference to an uninoculated control. A significant correlation was found between the number of damaged spikelets and the number of visually infected seeds together with an effect of the variety and the year. On a linear basis, because of a weak year effect, the decrease in 1 000 grain weight is better predicted using the number of visually infected seeds than the number of damaged spikelets. There is a trend for non-linear response curves for 2 varieties. The use of field evaluation of severity of the disease and tolerance of varieties are discussed.Fusarium roseum var culmorum / wheat / yield / cultivar