Powdery Mildew Resistance Genes in 127 Northwest European Spring Barley Varieties

One hundred and twenty-seven spring barley varieties grown in Denmark since 1979 were characterized for resistance genes using 30 powdery mildew isolates. The resistance genes are traced in the pedigrees to verify the results. Eleven named genes, 12 tentatively named genes/resistances and six unknown resistances were found. Resistance in many varieties was based on combinations of either known genes or of known and new factors. The following five new or relatively new resistance genes more or less effective against the present powdery mildew populations were detected: the ‘Mlo’ resistance conferred by the recessive mlo gene with the characteristic infection type 0/(4), ‘Ricardo’ and ‘Turkish’ sources having gene Mla3 in common and ‘Turkish’ with Ml(Tu2) in addition. In three varieties the new resistance Ml(IM9) was found in combination with different Mia alleles. Variety ‘Jarek’ has two new unidentified resistances.