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Leaf stripe, caused by the fungus Pyrenophora graminea Ito et Kuribayashi [anamorph Drechslera graminea (Rabenh. ex. Schlech.) Shoemaker], is an important seed-borne disease of barley (Hordeum vulgare L.). The objective of this study was to verify the reliability of a PCR-based marker (MWG2018) associated with the resistance gene Rdg2a and to assess the leaf stripe resistant phenotype in barley breeding programs. A large number of barley cultivars and accessions were thus evaluated for their reaction to a highly virulent monoconidial isolate (Dg2) of the pathogen and genotyped for the allele of the molecular marker. Several resistant genotypes were identified and four were shown to possess the same allele as the cultivar Thibaut (the resistant parent of the original mapping population in which Rdg2a was identified) at the marker locus. One of them, cv. Rebelle, is being used as a source of leaf stripe resistance in winter barley breeding programs. The allelic composition at the MWG2018 locus was verified in several resistant lines bred from five crosses, in which Rebelle acted directly or indirectly as donor of the resistance. The results showed that the resistant phenotype of the lines was always associated with the resistance allele of the molecular marker, thereby demonstrating its reliability for selecting leaf stripe resistance. The MWG2018 PCR-based marker can therefore be proposed as a tool to assess the resistant phenotype. [ABSTRACT FROM AUTHOR]