Defence responses triggered by Blumeria graminis f.sp. hordei in non‐host wheat genotypes results in a decrease in Puccinia triticina infection

Non‐host resistance is the resistance of plants against all so‐called non‐adapted pathogens, and is considered the most durable and efficient immune system of plants. We investigated barley powdery mildew ( Blumeria graminis f.sp. hordei , Bgh )‐triggered defence responses in seven wheat genotypes, and the induction of resistance by this non‐host pathogen to challenge infection with leaf rust, Puccinia triticina Eriks (formerly known as Puccinia recondita f.sp. tritici ). Bright‐field and ultraviolet microscopy revealed that although the germination of conidia on non‐host wheat leaves was generally lower than on host barley leaves, the 100% germination on Mv Mambó and only 50% germination on Mv 1 wheat genotypes are the two extremes. If we consider only the germinated conidia, papilla formation was the most frequently observed interaction on Mv 2 (90%) and Mv 4 (88%) genotypes. Epidermal cell death was pronounced on Mv Mambó (31%), but rare on Mv 2 (10%) and Mv 4 (11%), and a mesophyll hypersensitive response could even be detected. At sites of penetration attempts accumulation of H 2 O 2 was shown by 3,3′‐diaminobenzidine staining. Ascorbate peroxidase, glutathione S‐transferase and catalase enzyme activities were augmented by 24.5%, 40.4%, and 21.5%, respectively, in wheat leaves 2 days after Bgh infection. Primary inoculation with Bgh , although with high variability, reduced the number of pustules in all wheat genotypes at first and third leaf stages upon inoculation with leaf rust races 12 and 61 by 10%–70% depending on the genotype, leaf stage and rust race.