Non‐host resistance of barley is associated with a hydrogen peroxide burst at sites of attempted penetration by wheat powdery mildew fungus

Summary In barley, non-host resistance against the wheat powdery mildew fungus (Blumeria graminis f.sp. tritici, Bgt) is associated with the formation of cell wall appositions and a hypersensitive reaction in which epidermal cells die rapidly in response to fungal attack. In the interaction of barley with the pathogenic barley powdery mildew fungus (Blumeria graminis f.sp. hordei, Bgh), these defence reactions are also associated with accumulation of H(2)O(2). To elucidate the mechanism of non-host resistance, the accumulation of H(2)O(2) in response to Bgt was studied in situ by histochemical staining with diaminobenzidine. H(2)O(2) accumulation was found in cell wall appositions under appressoria from Bgt and in cells undergoing a hypersensitive reaction. A mutation (mlo5) at the barley Mlo locus, that confers broad spectrum resistance to Bgh, did not influence the barley defence phenotype to Bgt. Significantly, Bgt triggered cell death on mlo5-barley while Bgh did not.