Recombination at the Ml-a Locus in Barley Conditioning Resistance to Erysiphe Graminis F.Sp. Hordei

Attempts were made to recombine the dominant or semidominant resistance genes Ml-a, Ml-a3, Ml-a8 and Ml-a9 from the barley varieties Algerian Ricardo, Heil's Hanna and Monte Cristo, respectively. No recombinants with two resistance genes in the coupling phase were found in a total of 3117 test-cross seedlings from four crosses studied. The true recombination percentages between the genes Ml-a/Ml-a3, Ml-a/Ml-a8, Ml-a/Ml-a9 and Ml-a8/Ml-a9 are between zero and 0.5. One possible recombinant susceptible to Erysiphe graminis f. sp. hordei suggests that the recombination percentage between the recessive genes ml-a/ml-a8 is 0.083.