Endopeptidase polymorphism and linkage of the Ep‐D1c null allele with the Lrl9 leaf‐rust‐resistance gene in hexaploid wheat

The aim of this study was to test whether the null allele Ep‐D1c of the endopeptidase Ep‐D1 can be used as a marker for the Lrl9 leaf rust resistance gene. The frequency of Ep‐D1c was determined in 1134 winter wheat, spring wheat and spelt breeding lines and varieties. Only eight lines were found to carry Ep‐D1c. Six of these lines originated from crosses with RL6040, the gene donor for Lrl9. The other two lines were leaf‐rust susceptible in the seedling stage and therefore did not carry Lr19. The genetic distance between Ep‐D1c and Lr19 was determined in a reciprocal cross between the lines FAP75184 (Ep‐D1c, Lr19) and FAP75106 (Ep‐D1a, leaf‐rust susceptible in the seedling stage). Out of 840 F2 seedlings screened, 162 were homozygous for Ep‐D1c. From 150 of these F2 plants, F3 seedlings were screened for segregation for leaf‐rust resistance with isolates avirulent on Lr19. Only one F2 plant produced susceptible F3 progeny indicating a recombination event between Ep‐D1c and Lr19. From these data, a genetic distance of 0.33 ± 0.33cM between Ep‐D1c and Lr19 was calculated. The results show that Ep‐D1c is a useful marker for a practical breeding programme allowing the rapid identification of plants homozygous for Lrl9.