Linkage of the hordein loci Hor1 and Hor2 with the powdery mildew resistance loci Ml-k and Ml-a on Barley chromosome 5.

The linkage relationship among the loci Hor1, Hor2, Ml-k and Ml-a on the short arm of chromosome 5 was studied by progeny testing the F2 generation of two crosses. The loci Hor1 and Hor2 code for polypeptides of the storage protein hordein (prolamin) and the loci Ml-k and Ml-a determine the resistance reaction with some powdery mildew fungi cultures. The order of the loci is Ml-k, Hor1, Ml-a, and Hor2, the first named being nearest the centromere. The recombination percentage between Hor1 and Hor2 was determined in the F1 and F2 generations in both crosses, the combined estimate being 7.4±0.9 per cent. The recombination percentage estimated between Ml-k and Hor1 was 4.0±1.3, between Hor1 and Ml-a, 5.3±1.1, and between Ml-a and Hor2, 6.1±1.2. The estimates involving the Ml- loci were all probably a little too high.