Résumé
Preharvest hormetic doses of UV‐C radiation can decrease the susceptibility of tomato leaves to Botrytis cinerea L. infection. UV‐C light treatments have been shown to be very effective for reducing disease development in several species, including tomato ( Solanum lycopersicum L.). Treating cultivated tomato plants with UV‐C light is of interest not only because of the disinfecting effects of UV‐C light but also because of its ability to stimulate plant defences (SDP) against diseases, provided that the applied doses are high enough to be effective while low enough to prevent deleterious effects. In the present study, the effects of UV‐C light on plants were evaluated by biochemical analyses, including analyses of the activities of antioxidant enzymes and phenylalanine lyase (PAL); the concentration of malondialdehyde (MDA), an indicator of membrane integrity; and chlorophyll fluorescence parameters, such as the maximum quantum efficiency of photosystem II ( F V / F M ) and the Strasser performance index (PI). In this work, treatments with single doses of 0.85 kJ/m 2 of UV‐C light were found to significantly increase plant defences against B. cinerea , reducing the affected leaf area by 51% compared to the affected area of control plants. This decrease in susceptibility was associated with increased PAL activity and the amount of bound phenolics compared to levels in control plants (not treated with UV‐C).