Nonhost resistance of plants to powdery mildew—New opportunities to unravel the mystery

A better understanding of the genetics and molecular mechanisms underlying plant nonhost resistance, which is strong and durable, bears the potential for targeted employment of this valuable trait to control host pathogens. However, because nonhost resistance operates at the plant-species level, it often has been beyond the reach of breeding programs that are based on allele combination within a given crop species. Recently, the use of mutant and gene-silencing approaches in Arabidopsis thaliana and barley (Hordeum vulgare), together with the development of nonhost-susceptible barley lines, open up new possibilities to discover genes involved in nonhost resistance and to unravel the underlying mechanisms. In many of these studies, host and nonhost interactions with appropriate and inappropriate powdery mildew fungi, respectively, have been used, which therefore fulfil an important role as model systems for the study of nonhost resistance to fungal pathogens.