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International audience; Barley yellow dwarf (BYD) is one of the main viral diseases of small-grain cereals. This disease, reported on numerous plant species of the Poaceae family, is caused by a complex of eight viral species including the species Barley Yellow Dwarf Virus-PAV (BYDV-PAV), frequently found in western Europe. Resistance sources against BYDV-PAV are scarce and only identified in perennial Triticineae. Some BYDV-resistant wheat lines have been obtained by introgressing these resistances into bread wheat germplasms. Genetic and biological characterization of the resulting lines has been undertaken. However, little information on the resistant behaviour of these lines during the early stages of the infection process is available. To evaluate the resistance of two genetically distinct resistant lines (Zhong ZH and TC14), 1740 young plantlets, belonging to susceptible reference hosts (barley cv. Express and wheat cv. Sunstar), Zhong ZH or TC14 wheat lines, were inoculated in controlled conditions with French BYDV-PAV isolates. The infection process was monitored during the first 21 days after inoculation (DAI) using a semi-quantitative ELISA. A standardized protocol including five successive samplings of leaves from all inoculated plants and the collection of plant roots at the end of the monitored period was carried out. This protocol enabled an assessment of the infection percentage and the evolution of the viral load in plants from the 7th DAI to the 21st DAI. Statistical analyses of the BYDV infection kinetics using raw ELISA data, a model of the time-dependent variation of the percentage of infected plants and the area under concentration progress curves (AUCPC) demonstrated that Zhong ZH and TC14 lines (1) reduce the development rate of the BYD disease during the first days of infection, (2) decrease the infection efficiency of BYDV-PAV isolates, in the leaves, from 98.7% for susceptible plant genotypes to 81.9% and 71.7% for Zhong ZH and TC14, respectively, (3) reduce the virus load in the leaves of infected plants and (4) are not spared from BYDV infection, as 95.1% of Zhong ZH and 90.2% of TC14 inoculated plants accumulated viral particles in roots and/or in leaves at 21 DAI. These results confirm the BYDV-partial resistant behaviour of both Zhong ZH and TC14 lines. The development rate of the disease was the single parameter that allowed the distinction between the two resistant sources present in the tested lines

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.

The evolution of adult plant resistance towards powdery mildew (caused by Blumeria graminis f. sp. tritici) was investigated in 11 wheat populations cultivated for 10 years in a French network for dynamic management (DM) of wheat genetic resources. The aims of the study were to compare the evolution of resistance in sites submitted to different powdery mildew pressure and to investigate the implication of specific resistance gene action in adult plant resistance. For this, 7 of the 11 populations were characterized for their composition of specific resistance genes (results presented in a former paper). Even though no population differed significantly from the initial PA0 pool for mean adult plant resistance, divergence appeared among the final populations. The populations with the highest adult plant resistance level originated from sites where powdery mildew pressure is known to be high (Vervins, Le Rheu), whereas populations with the lowest adult plant resistance corresponded to areas with no, or very low, powdery mildew pressure (Toulouse, Montreuil-Bellay). A residual effect of defeated specific resistance genes was hypothesized, as lines accumulating at least two specific resistance genes appeared more resistant. Additional quantitative resistance seemed to be involved in adult plant resistance. DM lines appeared then as an interesting source of variability for resistance towards powdery mildew. Moreover, as these lines had been grown in mixed populations they may be appropriate as components of a composite cultivar.

A collection of 87 ancient wheat genotypes, 67 Triticum monococcum, 13 Triticum boeoticum, seven Triticum urartu and one cultivar of the modern wheat Triticum aestivum (variety 'Arminda') were evaluated for resistance to the cereal aphid Sitobion avenae, the main damaging aphid pest on winter wheat in Europe. The intrinsic rate of natural increase (r m ), which is regarded as a good estimate of the fitness of an aphid population, was used as an indicator for the level of plant resistance. Differentiation of the 88 plant genotypes into four distinct groups was achieved with a cluster analysis of the r m values. The modern wheat 'Arminda' was more susceptible than any of the ancient wheat genotypes tested (r m = 0.24, i.e. the aphid population doubled every 2.6 days). A second group of 19 plants ranged from relatively susceptible to moderately resistant (0.17 < r m < 0.21). Fifty-one plants were allocated to a third group and classified as resistant (0.09 < r m < 0.16). The last group contained 17 genotypes with a high level of resistance where aphid fitness was greatly reduced (0.02 < r m < 0.09, i.e. the aphid population doubled every 11.4 days or 7.7 days, respectively). Clustering of the accessions into the different phenetic groups did not follow the geographical origin of the wheat genotypes or the species to which they belong. These results show that ancient diploid wheats, all characterized by the genome A, present considerable interest for plant breeding for resistance to S. avenae in modern wheat. The potential use of these strong and partial sources of resistance for introduction of a stable and durable form of resistance to S. avenae in wheat 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.

International audience; During 2 years and at five locations in Europe, 56 winter wheat genotypes were evaluated for resistance to Fusarium head blight (FHB). The genotypes were both parents and selected recombinants taken from the following populations previously tested for FHB resistance: 'Arina'/'Forno', 'Arina'/'Riband', 'Dream'/'Lynx', G16-92/'Hussar', 'Renan'/'Récital', SVP-72017 × 'Capo' and 'Capo'/'Sumai-3'. In addition, a few control lines were included. FHB resistance was evaluated in replicated experiments under artificial inoculation, disease severity was assessed by repeated visual scorings. The highest level of FHB resistance was found in lines selected from crosses of FHB-resistant winter wheat × 'Sumai-3'. The best lines selected from crosses of moderately resistant winter wheat with susceptible winter wheat were similar in their resistance response to the resistant parent. The level of FHB resistance was correlated with stability of resistance. Susceptible wheat lines tended to exhibit severe symptoms under high disease pressure. The symptoms on resistant lines remained comparatively low even under high disease pressure.

International audience; Serial passage experiments (SPE) of a Barley yellow dwarf virus-PAV (BYDV-PAV) isolate were performed on Zhong ZH and TC14 wheat lines to evaluate the durability of their resistance to BYDV. At different passage numbers (from the 2nd to the 114th), biological properties of the produced isolates were recorded either by monitoring infection percentages and virus titers of the first 3 weeks of viral infection or by measuring their impact on yield components. Statistical analyses using the area under pathogen progress curves and the area under concentration progress curves demonstrated that these two resistant lines induce, after only a few passages, a selection of variant(s) with significantly modified infection abilities. Isolates resulting from SPE performed on these lines induced important decreases of yield components. These results indicate that the use of Zhong ZH and TC14 lines in BYDV-resistant breeding programmes should be approached with caution

International audience; Barley yellow dwarf disease (BYDD) is one of the main viral diseases of small grain cereals. This disease, reported on numerous plant species of the Poaceae family, is caused by a complex of viral species including the species Barley yellow dwarf virus-PAV (BYDV-PAV, family Luteoviridae, genus Luteovirus), frequently found in western Europe. Resistance sources towards BYDD are scarce. Indeed, breeding-resistant genotypes is a long and expensive process. Thus, estimating the durability of the resistance genes before the achievement of selection would be an asset for breeders. One isolate of BYDV-PAV has been serially passaged on two hosts, 'Zhong ZH' and 'TC14', carrying a gene for partial resistance. The resulting viral population showed an increase of the speed of development of the infection in controlled conditions. In this study, these viral populations were evaluated in a 3-year field trial, including a susceptible host, 'Rendezvous', and a host carrying the resistance gene of 'TC14' in a 'Rendezvous' background, to assess the effect of serial passages in field conditions. Results indicate that isolates issued from serial passages on hosts carrying a gene for partial resistance induced increased damage in field conditions when compared with the initial isolate. Yield losses are mainly due to a decrease of the number of kernels per square metre. The interest on using partial resistance gene to control BYDD is discusse

International audience; Vector efficiency of 44 clonal lines (clones) of Sitobion avenae belonging to 31 different genotypes (distinct patterns for five microsatellite loci) originating from Western France was evaluated by transmitting the isolate PAV4 of BYDV-PAV to barley seedlings. Variation in transmission rates from 3.7% to 92.5% was observed, with significant effects of the aphid clone, of the plant species on which clones were collected, and of the reproductive mode of the clones. When genotypes are considered instead of clones, a continuum in transmission rates was observed. A subset of S. avenae clones was tested for transmission of one (10 clones) and 13 (4 clones) other BYDV-PAV isolates, and a clear clone effect modulated by an isolate effect was observed. Crosses were made between clones with different vectoring phenotypes and their F1 progeny were tested for PAV4 transmission. The narrow sense heritability of the PAV transmission character was rather high in the F1 families (h(2)=0.5)! and the segregation analyses suggested an oligo/polygenic determinism of this character. The possibility of generating new transmission variants by sexual reproduction and its consequences on transmission mechanism studies and on BYD epidemics are discussed

Soilborne wheat mosaic virus (SBWMV)is a Furovirus transmitted by the plasmodiophoraceous fungus, Polymyxa graminis. Resistant cultivars of wheat (Triticum aestirum) to SBWMV have already been described. The resistance encountered mostly includes root infection without viral migration to foliage. In this study, the reaction ofaddition lines (L1, L1S, L2, L3, L4, L7,) and the partial amphiploid derived from wheat (Vilmorin 27) and Thinopyrum intermedium has been evaluated. Lines L1, L3, L7, L1S and cultivar Vilmorin 27 are susceptible to SBWMV. Lines L4 and TAF 46 are root infected only. Chromosome 4Ag 1 in L4 is thought to have an equivalent reaction to that one found in the mostly encountered resistance. Another type of resistance in a wheat line (L2) with the added chromosome 3Agi of Th. intermedium has been characterized. In this line, L2. no SBWMV particles were detected on their roots by enzyme-linked immunosorbent assays. Contrary to observations made on lines L1, L1S, L3, L4, L7, amphiploid TAF 46, and the wheat cultivars (Festival, Fandango. Vilmorin 27). no resting spores of P. graminis were found on roots of L2 2 months post inoculation. It is suggested that the disomic addition line L2 is immune to SBWMV.

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.

A collection of 433 Aegilops tauschii was screened for response to infection with Stagonospora nodorum. Resistance similar or marginally superior to the range observed in spring wheat genotypes was readily identified. Three lines, RL5271, Aus18911, and Aus21712, were resistant to a range of pathogen isolates and were similar in resistance to a highly resistant French line, No.33. Accessions of Ae. tauschii assessed as resistant or susceptible as seedlings had corresponding reactions when tested as adult plants, with resistance being commonly expressed as restricted lesion development. Infection frequency differed between some Ae. tauschii lines. Seedling resistance in synthetic bread wheats was expressed partially or not at all depending on both the tetraploid and the tetraploid/Ae. tauschii combination. Assessment of adult responses among a range of synthetics showed occasional expression of moderate resistance around the level observed among reference bread wheat cultivars of similar maturity. Disease escape associated with late maturity was common. One synthetic wheat, #231, derived from a resistant Ae. tauschii, exhibited low adult disease expression associated with late maturity. This line was resistant in seedling tests and seedling resistance was dominant in F1 hybrids to bread wheat.