RFLP MAPPING OF 3 NEW LOCI FOR RESISTANCE GENES TO POWDERY MILDEW (ERYSIPHE-GRAMINIS F SP HORDEI) IN BARLEY

Three new major, race-specific, resistance genes to powdery mildew (Er ysiphe graminis f. sp. hordei) were identified in three barley lines, 'RS42-6O', 'RS137-28*E', and 'HSY-78*A', derived from crosses with wi ld barley (Hordeum vulgare sap. spontaneum). The resistance gene origi ning from wild barley in line 'RS42-6O', showed a recessive mode of i nheritance, whereas the other wild barley genes were (semi)-dominant. RFLP mapping of these three genes was performed in segregating F-2 pop ulations. The recessive gene in line 'RS42-6O', was localized on barl ey chromosome 1S (7HS), while the (semi)-dominant genes in lines 'RS13 7-28E', and 'HSY-78*A'. were localized on chromosomes 1L (7HL) and 7L (5HL), respectively. Closely linked RFLP clones mapped at distances b etween 2.6 cM and 5.3 cM. Hitherto, specific loci for powdery mildew r esistance in barley had not been located on these chromosomes. Further more, tests for linkage to the unlocalized resistance gene Mlp reveale d free segregation. Therefore, these genes represent new loci and new designations are suggested: mlt ('RS42-6O'), Mlf ('RS137-28*E'), and Mlf ('HSY-78A'). Comparisons with mapped QTLs for mildew resistance w ere made and are discussed in the context of homoeology among the geno mes of barley (H-vulgare), wheat (Triticum aestivum), and rye (Secale cereale). Duplications of RFLP bands detected in the neighbourhood of Mlf and mlt might indicate an evolutionary interrelationship to the Ml a locus for mildew resistance.