The pioneering research of Kuć and colleagues (reviewed in Kuć, 1982; da Rocha & Hammerschmidt, 2005) led to the development of the concept of systemic acquired resistance (SAR), in which prior challenge with a microbe causing a limited necrotic lesion led to the induction of resistance to a subsequent challenge by a range of pathogens. Resistance was induced systemically in leaves adaxial to the site of initial challenge. Salicylic acid (SA) was subsequently identified as a key signal molecule leading to priming of defences (Kumar, 2014).The discovery of the induced SAR pathway immediately encouraged exploration of the use of SA to activate resistance and protect crops from infections in the field (Sticher et al., 1997). Salicylate itself