Genetic studies on the powdery mildew resistance of winter barley lines derived from Hordeum spontaneum accessions collected in Israel

The genetics of the powdery mildew resistance of 15 Hordeum spontaneum-derived winter barley lines were studied in testcrosses with selected cultivars carrying the MIa12 and MIa13 resistance alleles, in order to identify the inheritance of the resistance and to test for linkage with the MIa locus on chromosome 1H (5). A total of 27 genes were identified. Only one of these genes (in line ‘1–12 x Dura’) could eventually be allelic to a gene previously identified in H. spontaneum Koch. A monofactorial dominant inheritance was identified in the majority of the lines. Three of the tested lines possessed recessively inherited genes and in one line a dominant and a recessive gene were identified. In respect to the reaction of the lines against European mildew cultures, lines with a bifactorially inherited resistance had a broader resistance spectrum than those with a monofactorial inheritance, while lines carrying recessive factors showed a moderately expressed resistance. In three cases a linkage with the MIa locus was found, while in two further lines a possible allelism to this locus was indicated by the absence of recombinant progeny plants. By using more than two isolates for linkage analysis, it was possible to identify additional genes for mildew resistance, reaching a maximum number of four genes in the same line. In some cases, a different inheritance was observed for the resistance of the same line against different isolates. It was assumed that different genes exist, each being effective against a different isolate.