Sources of resistance to powdery mildew (Blumeria graminis f. sp hordei) in Moroccan barley land races

Fifty-eight barley (Hordeum vulgare) land races from Morocco were tested for resistance to powdery mildew (Blumeria graminis f. sp. hordei], and a number of resistant land races were detected. Seventeen land races (29%), from which 26 single-plant tines were selected, expressed resistant reactions. These lines were tested at the seedling stage against 23 differential isolates of powdery mildew. The isolates were chosen according to their virulence spectra as observed on the differential set of cv. Pallas near-isogenic tines. Seven lines originating from six land races were resistant to all powdery mildew virulence genes prevalent in Europe. Twenty lines (77%) were moderately resistant (infection type 2) and six lines (23%) expressed resistance (infection type 0) to more than 50% of the isolates tested. In 22 lines (85%), the presence of unknown genes either alone or in combination with known genes were detected. Three different resistance alleles (Mlat, Mlal, and Mla3) were postulated to be present in the tested lines either alone or in combination with other genes. Among specific resistance alleles, the most common was the allele Mlat (resistance of cv. Atlas). This allele was postulated to be present in nine (35%) of the tested lines. Among seven provinces of northern Morocco from which the tested land races originated, the highest percentage of resistant land races was from provinces Oujda and Tetouan. The use of new sources of resistance to powdery mildew in barley breeding is discussed.