Disease resistance (R) protein that induces localized, salicylic acid-dependent defenses (PubMed:11141561). Confers resistance to powdery mildew (e.g. Erysiphe cichoracearum UCSC1) (PubMed:11141561, PubMed:15155802, PubMed:17565954). Expressed in leaves after powdery mildew infection (e.g. Erysiphe cichoracearum UCSC1) (PubMed:15155802). Induced in seedlings by the beneficial symbiotic fungus Trichoderma atroviride (PubMed:22942755). Ecotypes susceptible to Erysiphe cichoracearum, such as cv. Columbia, are lacking RPW8.1 and RPW8.2 but contain in place HR4. Belongs to the plant RPW8 protein family. Not present in cv. Columbia. The sequence shown is from strain cv. Ms-0.