Resistance to powdery mildew in selections from barley landraces collected in Greece

Twenty barley (Hordeum vulgare L.) landraces from Greece were tested for resistance to powdery mildew (Erysiphe graminis f. sp. hordei). Landraces originated from a collection of Polish Gene Bank, IHAR Radzikow, Poland. Thirteen landraces (65%) expressed resistance reactions and from those 37 single-plant lines were selected. These lines were tested at the seedling stage with 23 differential isolates of powdery mildew. The isolates were chosen according to their virulence spectra as observed on the 'Pallas' isoline differential set and on 8 additional differential cultivars. Fiveteen lines originating from five landraces (4917, 4919, 4926, 4928 and 4935) expressed resistance to all isolates used. In 31 tested lines it was impossible to determine which specific allele or alleles for resistance are present. However, expression of infection types 0, 1 and 2 for the isolates tested indicated that 26 from these lines may have several alleles for resistance. Three different resistance alleles (Mlat and Mla6+ Mla14) were postulated to be present in the lines either alone or in combination with other unidentified genes. Allele Mlat was postulated to be present in 4 and alleles Mla6 + Mla14 were postulated to be present in 2 of the tested lines. The value of landraces for diversification of powdery mildew resistance genes available to barley breeders was discussed.