The barley mutant emr2 shows enhanced resistance against several fungal leaf pathogens

Homozygous mlo‐barley plants are resistant to barley powdery mildew but hypersusceptible to the rice blast fungus Magnaporthe oryzae. A mutational analysis was performed in the barley back‐cross line BCIngrid mlo5 which led to the identification of two mutants with enhanced capacity to resist infections by M. oryzae, referred to as enhanced M. oryzae resistance mutants emr1 and emr2. Here, we report on the characterization of emr2 mutant plants which not only show an almost complete reduction in disease severity after inoculation with M. oryzae but are also resistant to the necrotrophic fungi Drechslera teres and Rhynchosporium secalis. Histological analysis revealed that resistance to M. oryzae was based mainly on the formation of papillae at sites of attempted penetration into epidermal cells. There was no progression of fungal growth into the mesophyll. Additionally, because of the presence of the mlo‐allele, emr2‐plants retained resistance to powdery mildew. The emr2‐conditioned broad spectrum resistance was inherited as in a recessive manner. Monitoring of PR‐gene expression and enzymatic activity of peroxidases revealed a constitutively activated defence in emr2.