MILDEW LOCUS O Mutation Does Not Affect Resistance to Grain Infections with Fusarium spp. and Ramularia collo-cygni

MILDEW LOCUS O defines a major susceptibility gene for powdery mildew, and recessive mlo resistance alleles are widely used in breeding for powdery mildew resistance in spring barley. Barley powdery mildew resistance, which is conferred by mlo genes, is considered to be costly in terms of spontaneous defense reactions and enhanced susceptibility to cell-death-inducing pathogens. We assessed fungal infestation of barley (Hordeum vulgare) grain by measuring fungal DNA after natural infection with Fusarium spp. and Ramularia collo-cygni or after inoculation with Fusarium spp. in the field. Powdery-mildew-resistant mlo5 genotypes did not show enhanced Fusarium spp. or R. collo-cygni DNA content of grain over four consecutive years. Data add to our understanding of pleiotropic effects of mlo-mediated powdery mildew resistance and contributes to the discussion of whether or not application of barley mlo mutations may support pathogenesis of cell-death-inducing fungal pathogens under field conditions.