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Ce volume regroupe les textes issus du programme Casdar « Semence et Sélection Variétale » finalisés en 2015, 2017 et 2019. Le numéro a été coordonné par le Comité Scientifique du Comité Technique Permanent de la Sélection des plantes cultivées (CTPS).Nouvelles méthodes d'évaluation des résistances variétales aux bioagresseurs; The barley national collection, made of 570 French accessions, was evaluated during three years for tenagro-morphological traits in a multisite network (heading, plant height, loading, spike compactness, spikerow number, disease susceptibilities). Furthermore, the whole collection was genotyped for a set of 1056SNPs. Field evaluation results show a wide diversity for all observed traits. The use of empiric selectionindex on disease traits (barley leaf rust, powdery mildew, leaf blotch, net blotch, Ramularia leaf spot)makes it possible to define two different panels of 43 accessions (winter and spring types) showing highlevel of resistance for each studied pathogen. From SNPs genotyping data, clustering analysis of thewhole collection exhibits the importance of winter vs spring type and spike row number as factors toexplain genetic structure. A first approach of GWAS between markers and traits indicates a total of 1666significant associations (p

National audience; Genetic resistance is the only way to control mosaic damage in winter barley. At least 18 resistance genes are known, but until recently, rym4 was the most used by breeders to control Barley yellow mosaic virus-1 (BaYMV-1), predominant in France and Barley mild mosaic virus (BaMMV). However, since 2009, new significant damage has been observed in malting barley in a widening production area, indicating possible overcoming of resistance, with the development of BaYMV-2. The objectives of the Mosa-hordeum project were to: identify new viruses or pathotypes; develop new detection tools; confirm cultivar resistance observed in field using MB tools; confirm efficiency of resistance genes cited in literary reviews; quantify impact on yield and malting quality. A complete viral inventory was carried out 2013- 2016 on affected barley crops in 108 sites using: real-time PCR; Sanger sequencing; Next-Generation Sequencing; and serological tests. A new tool, based on derived Cleaved Amplified Polymorphic Sequences (dCAPS), developed to investigate BaYMV-1 and 2 distributions, demonstrated that BaYMV-2 is predominant (> 95%) in diseased samples. BaYMV-1 and BaMMV were also identified in co-infection with BaYMV-2 on susceptible cultivars. Comparison of yield components, malting and beer quality obtained on healthy/contaminated plots with couples of cultivars revealed variation in yield losses, up to 3t/ha, reduction in number of spikes and kernels/m², smaller kernels, slight increase in protein content and decrease of malt extract. Phylogenetic analyses indicated that the rym4 resistance-breaking ability of BaYMV-2 independently evolved on multiple occasions. In limited number of trials, rym5 resistance was overcome by a variant of BaMMV. The implantation of differentials in 21 contaminated trials confirmed the efficiency of 11 resistance genes against the BaYMV-2/BaMMV complex. To monitor BaYMV and BaMMV resistance for registration in the National List real-time PCR appears more efficient than dCAPS. These findings will help breeders achieve sustainable resistance.