The powdery mildew disease resistance gene Ml(La) was found to belong to a locus on barely chromosome 2. We suggest that this locus be designated MlLa. Linkage analysis was carried out on 72 chromosome-doubled, spring-type progeny lines from a cross between the winter var 'Vogelsanger Gold' and the spring var 'Alf'. A map of chromosome 2 spanning 119cM and flanked by two peroxidase gene loci was constructed. In addition to the Laevigatum resistance locus the map includes nine RFLP markers, the two peroxidase gene loci and the six-row locus in barley.

The RAPD technique was found to provide reliable genetic markers in barley. A linkage study of 23 RAPDs, 28 RFLPs, and 29 gene loci was conducted on 72 chromosome-doubled haploid progeny lines from a barley cross. The resulting linkage map covered 680 cM, about half of the barley genome. RAPD markers were distributed throughout the map, but a higher than expected frequency of tightly linked RAPDs was observed. Several cases of skewed segregation ratios were observed, but the RAPD markers segregated in ratios similar to their linked loci, confirming that they were reliably scored. In separate crosses, two amplified RAPD products, generated by different primers, were shown to reside in corresponding chromosomal positions. The RAPD markers seem a realistic alternative to RFLP markers in linkage analysis of barley.