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 Mla13 resistance alleles, in order t o identify the inheritance of the resistance and to test for linkage w ith the MIa locus on chromosome 1H(5). A total of 27 genes were identi fied. 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 m onofactorial dominant inheritance was identified in the majority of th e lines. Three of the tested lines possessed recessively inherited gen es 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 resist ance 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 fu rther lines a possible allelism to this locus was indicated by the abs ence of recombinant progeny plants. By using more than two isolates fo r linkage analysis, it was possible to identify additional genes for m ildew resistance, reaching a maximum number of four genes in the same line. In some cases, a different inheritance was observed for the resi stance of the same line against different isolates. It was assumed tha t different genes exist, each being effective against a different isol ate.