Major Genes for Powdery Mildew Resistance in Research and Breeding of Barley: A Few Brief Narratives and Recommendations

Genetic resistance is a sustainable way to protect crops against diseases and breeding resistant varieties is a significant aim. However, diseases are caused by pathogens which have different life cycles and the importance of individual evolutionary forces plays a key role in the adaptation of their populations. Therefore, strategies in the use of genetic resistance resources in different plant pathosystems can differ. There are numerous ma-jor genes of hypersensitive resistance against powdery mildew, one of the commonest diseases of barley, but these genes conform to the gene-for-gene system of the extremely diverse and adaptable pathogen. When such resistances are transferred into commercial varieties, their efficiency in the field is soon overcome and their replacement with new-ly-developed resistant varieties is slow. Hence, major genes of specific resistance should not be used in barley breeding programs. Only one monogenic, non-hypersensitive, non-specific and durable major resistance Mlo is known. This predominates in central and western European spring varieties and should also be widely adopted by barley breeders elsewhere and in other crops where this type of resistance is found. In this pa-per, relevant aspects of breeding barley against powdery mildew are discussed with conclusions supported by practical examples and future directions of barley improve-ment are proposed.