The concepts of plant pathogenicity, virulence/avirulence and effector proteins by a teacher of plant pathology

During the genomic and proteomic era of plant pathology in the last decade, extensive progress has been made in the understanding of the mechanisms of the interactions between plants and microbial pathogens. New models of pathogenesis have been designed, new biological phenomena have been discovered, a plethora of new molecules and functions have been determined, and new terms and senses have been added to phytopathological language. In this context, however, defects often emerge in many of the papers published on these subjects: the meanings attributed to some new terms are not always unique and do not always adhere to the basic concepts of plant pathology, including those relating to disease, disease cycles, pathogenicity, virulence, and avirulence. This paper discusses this problem, emphasizes established defintitions and proposes new ones, to assist the phytopathology community in unifying terminology for the benefit of our research discipline.