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International audience; Identifying genotypes carrying the dwarfing genes Rht-B1 and Rht-D1 would be of great interest for wheat (Triticum aestivum L. em Thell) breeding. Two RFLP loci were found to be linked to those two genes, Xpsr 144-4B with Rhr-B1 on chromosome 4BS and Xglk578-4D with Rht-D1 on chromosome 4DS, by genotyping two F-2 populations, Renan (Rht-B1b) x Camp-Remy and Rendez-Vous (Rht-D1b) x Roazon. Utilisation of these markers in breeding schemes is discussed.

International audience; Stripe rust, caused by Puccinia striiformis f. tritici, is one of the most widespread and destructive wheat diseases in areas where cool temperatures prevail. The wheat cv. Renan, carrying the specific gene Yr17, has shown effective resistance for a long time, even though some pathotypes overcame the Yr17 gene. The objectives of this study were to locate and map genetic loci associated with adult-plant resistance (APR) to stripe rust in a recombinant inbred line population derived from a cross between Renan (resistant) and Recital (susceptible). Field assays were performed for 4 years (1995, 1996, 2005, and 2006) to score disease-progress data and identify APR quantitative trait loci (QTLs). Three QTLs, QYr.inra-2BS, QYr.inra-3BS, and QYr.inra-6B, with resistance alleles derived from Renan were detected in 1995 to 1996 with the 237E141 pathotype, which is avirulent against genotypes carrying Yr17. These QTLs were stable and explained a major part of the phenotypic variation seen in 2005 to 2006, when the 237E141 V17 pathotype was used. Each of these QTLs contributed approximate to 4 to 15% of the phenotypic variance and was effective at different adult plant stages. Interactions were observed between some markers of the Yr17 gene and three Renan QTLs: QYr.inra-2BS, QYr.inra-3BS, and QYr.inra-6B. Resistance based on the combination of different APR types should provide durable resistance to P. striiformis.

In this study two Sources of resistance to Barley yellow dwarf virus (BYDV), both originating from Thinopyrum intermedium, were combined in a single genotype, line ZT, using GISH (genomic in situ hybridization) and a new molecular marker of the partial resistance gene Bdv2. Susceptible wheat cv. Sunstar, the translocation line TC14 carrying Bdv2, the addition line ZH with the group-2 chromosome arm carrying resistance, and line ZT with both resistances were inoculated with five strains of Barley yellow dwarf virus-PAV. The tests confirmed the resistance of TC14 and ZH and revealed an additive effect of the two sources of resistance in ZT. The resistance of line ZT was characterized by 1 proportion of infected plants significantly lower than the parental lines TC14 and ZH (42% vs. a mean of 76% for the parents) and a very low virus titre (area under the virus concentration progress curve of 1.2 vs. a mean on 6.3 for the parents).

gime was performed with phenotypic indices which combine the main characters introduced in general wheat breeding. The analysis of the 2 first cycles was based on the comparison of the final population (PAwith the initial population (PA or with the 16-parent group introduced in PA It shows the efficiency of such a scheme with an increase in mean level for most characters studied. Moreover, the intrapopulation variability estimated by phenotypic variances (and genetic variances for PAremained at the same level except for the characters that were intensively selected. These evaluations provide a basis for discussion on a better way to insert and apply recurrent selection in a wheat breeding strategy.

Cinquante-six familles S 1 et leurs descendances S 2 issues d'une population de ble tendre en selection recurrente utilisant un gene de sterilite mâle dominant ont ete evaluees pour leur resistance a la fusariose de l'epi. Les tests de resistance ont ete realises au champ avec contamination artificielle et ont ete repetes sur 2 campagnes culturales pour les S 1 . Les symptomes sur epi et sur grain ont ete notes, ainsi que l'effet de la maladie sur le rendement et le poids de 1000 grains par comparaison avec un temoin non inocule (...)

L’utilisation de la sélection récurrente, généralisée pour les espèces allogames, est peu fréquente chez les espèces autogames du fait des difficultés d’obtention de populations de départ et d’hybridation pour les inter-croisements. Pour une étude méthodologique incluant sélection récurrente et création variétale (lignées) chez le blé tendre, une population PA a été réalisée. Elle a pour origine 16 parents lignées pures choisis pour leurs performances propres et leur complémentarité dans une optique d’amélioration large. Sa création résulte d’inter-croisements selon un schéma pyramidal équilibré à partir de croisements manuels. Les caractéristiques de cette population, base de départ d’une étude méthodologique présentée ultérieurement, sont analysées et discutées pour de nombreux caractères utiles à l’amélioration du blé. Sur la base des valeurs moyennes et de la variabilité intra-population, cette analyse révèle l’intérêt de la combinaison multiple des lignées parentales et l’efficacité de la série de recombinaisons appliquée dans le schéma pyramidal., Recurrent selection, though largely used in outbreeding species, is rarely introduced in self breeding species selection schemes because of initial population production difficulties and of difficult hybridization for intercrossing. For a methodological study including recurrent both selection and pure-line breeding in wheat, an artificial population named PA has been introduced. It comes from 16 parents chosen for their own value and their complementarity for large breeding purposes. It has been produced by manual intercrossing on a pyramidal balanced pattern. The population features are presented and discussed for many characters useful in wheat breeding improvement. This study shows the positive effects of the multiple combination of parents and the efficiency of four recombination cycles introduced in this pyramidal crossing scheme for mean values and intrapopulation variability.

Cinq cultivars de blé d’hiver représentant un gradient de tolérance à la septoriose sont contaminés à 2 stades de leur développement. La concentration en acide abscissique (ABA) est déterminée dans les épis aux stades laiteux et pâteux du grain. Les symptômes sur feuilles et épis sont notés en cours de végétation. Le poids de 1 000 grains est mesuré à la récolte. L’ABA s’accumule dans les épis septoriés proportionnellement aux symptômes observés. Le niveau de la relation entre les pertes de rendement et l’accumulation d’ABA dépend du stade de développement de la plante au moment de l’infection. L’utilisation de l’accumulation d’ABA en tant que marqueur de la tolérance est discutée., Five winter wheat varieties showing differences in tolerance to Septoria nodorum were inoculated at the stages of stem extension and early heading. Abscissic acid (ABA) content was determined in the ears at milky and mealy stages. Disease ratings were made on symptoms developing on ears and flag leaves and on the yield expressed in 1 000-grain weight (table I). The infected ears accumulated ABA and this accumulation was highly correlated with ear symptoms (table II and fig 1). The level of the relationship between yield losses and ABA accumulation depends on the growth stage of the plant at the time of infection. When the infection took place at the stage of stem extension, there was a high correlation between yield losses and ABA accumulation in the ears of the latest maturing cultivars (fig 2). The earliest maturing cultivar (Talent) showed a significant accumulation of ABA from the milky stage but without correlation with yield losses. These observations suggest that there is a critical period during grain development and maturation. The use of ABA accumulation as marker of tolerance is examined.