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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.

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).

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; 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.