Resistance to powdery mildew in populations of barley landraces from Morocco

Forty one populations of barley landraces collected from Morocco were screened for resistance to powdery mildew and a number of different resistance genes were detected. Test populations were sourced from the collection of the International Centre for Agricultural Research in the Dry Areas (ICARDA), Aleppo, Syria. Eighteen populations of landraces (about 44%) showed resistant reactions and 38 resistant single plants were selected, increased and screened as seedlings. Fourteen of these lines were tested with 17 differential isolates of powdery mildew and 24 lines were tested with 23 isolates. The isolates were chosen according to their virulence spectra observed on the Pallas isolines differential set. Eight lines (566-2-2, 569-3-3, 570-2-2, 576-1-1, 576-1-4, 592-1-5, 592-3-1 and 594-1-2) selected from six populations of landraces showed resistance to all powdery mildew virulence genes prevalent in Europe. About 84% of all reaction types were classified as resistant (scores 0, 1 and 2). The most frequent score was 2 (64%). Thirty-one lines (82%) showed reaction type 2 against more than 50% of isolates used. It was impossible to postulate which specific allele or alleles for resistance are present in 24 of the tested lines. However, presence of reaction types 0, 1 and 2 indicate that these lines may have many alleles fur resistance. Among specific resistance alleles the most common was allele Mlat (Atlas resistance). This allele was postulated to be present in thirteen (34%) of the tested lines. The use of newly identified sources of resistance to powdery mildew in barley breeding is discussed.