What’s Old and What’s New in Concepts of Induced Systemic Resistance in Plants, and its Application

Disease and induced resistance to disease in plants and animals has been with us as long as plants, animals, and their pathogens have coevolved. Observations of induced resistance in plants were reported as early as the late 1800s and early 1900s (Beauverie, 1901; Ray, 1901; Chester, 1933). Muller and Borger (1940) described carefully conducted experiments which established the phenomenon of induced local resistance (ILR) in potatoes to late blight (Phytophthora infestans). Inoculation of potato tubers with cultivar-nonpathogenic races of the fungus induced local resistance to cultivar-pathogenic races. This work, and subsequent studies by Muller and coworkers also established the concept of active defense for resistance, a response after infection, and this proved to be the foundation for work with phytoalexins. Induced systemic resistance (ISR) was analytically established by Kuć et al. (1959) and Ross (1966). Kuć et al. (1959) and Maclennan et al. (1963) demonstrated that apple plants were made systemically resistant to apple scab (Venturia inaequalis) by infiltrating lower leaves with D-phenylalanine, D-alanine and aminoisobutyric acid (AIB). The amino acids did not inhibit the growth of V. inaequalis in vitro at concentrations used for infusion. Ross (1966) and coworkers demonstrated that inoculation of lower leaves of tobacco with a local lesion strain of tobacco mosaic virus (TMV) systemically enhanced resistance to the same strain of the virus. They also established the time required between induction and inoculation for ISR and its persistence. The continued research by Kuć and coworkers verified the reports by Ross and expanded and defined our understanding of ISR and its application for disease control in the greenhouse and field. They demonstrated that ISR was not specific with respect to the nature of the inducer or the biological spectrum of the diseases it protects against. Thus, unrelated fungi, bacteria, viruses, or chemicals induced resistance systemically