CHEMICAL AND BIOLOGICAL INDUCERS OF SYSTEMIC RESISTANCE TO PATHOGENS PROTECT CUCUMBER AND TOBACCO PLANTS FROM DAMAGE CAUSED BY PARAQUAT AND CUPRIC CHLORIDE

Oxidative damage has been implicated in the necrotization of plant tissues by incompatible pathogens, including those that induce systemic acquired resistance (SAR). In this study, prooxidant chemicals were employed to evaluate the hypotheses that i) localized oxidative damage that culminates in necrosis can induce SAR and ii) SAR can protect tissues from oxidative damage. Paraquat (PQ), acifluorfen (AF), and sodium chlorate (SC) induced SAR to Colletotrichum lagenarium in cucumber. PQ and SC, but not AF, also induced SAR to tobacco mosaic virus (local lesions) and Peronospora tabacina in tobacco. Pathogens and chemicals that triggered SAR to pathogens also systemically enhanced resistance to damage by PQ and CuCl2. Local protection from PQ was afforded by salicylate and a synthetic cytokinin known to induce local resistance to pathogens.