Powdery mildew resistance genes in the Ml‐a and Ml‐k regions on barley chromosome 5

The literature was surveyed for information relating to powdery mildew resistance genes in the Ml‐a and Ml‐k regions on barley chromosome 5. All data available from tests of recombination involving genes in these regions are listed, as well as data on additional genes linked in coupling to a gene in the Ml‐a region. The infection type, degree of dominance and resistance spectra are also recorded for all genes where possible. By combining this information and making the assumption that differences in the expression of disease resistance are an indication of the action of genes in different loci, evidence is found for several loci in the Ml‐a region. Thirteen different genes, the named Ml‐a genes, can with certainty be assigned to this region. However, evidence is given which indicates that a total of around 30 genes probably belong to the Ml‐a region. The Ml‐k region probably has two closely linked loci Ml‐k and JMl‐nz , and is different from the Ml‐a region in that only two genes, Ml‐k and JMl‐nz , have been found. This region thus appears to be less complex than the Ml‐a region.