Variations of Phenoloxidase Activities as a Consequence of Stresses that Induce Resistance to Fusarium Wilt of Tomato

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Abstract
The variations over 7–8 day of peroxidase (PO) and polyphenoloxidase (PPO) activity have been investigated in tomato plants the roots of which had been subjected to stresses (heat, chloroform and a non‐pathogenic form of Fusarium oxysporum) that induce resistance to Fusarium oxysporum f. sp. lycopersici.All treatments induced increase of PO and PPO activity that reached a maximum 3 days after the treatments in leaves, 4 days in stem and roots and were higher in leaves than in other parts. Activity decreased to levels for the control plants after 8 days.Inoculation with Fusarium oxysporum f. sp. lycopersici further stimulated PO and PPO activity in all treated plants over that caused by the treatments alone. Again, activity of treated plants was lower than in controls 7 days after inoculation.It is concluded that 1. increased PO and PPO activity in tomato is a systemic response to cellular injury caused in the root by heat, chloroform and non‐pathogenic Fusarium oxysporum, 2. these treatments do no prevent the pathogen from interacting with the plants and inducing further enzyme increase, 3. treated plants react more strongly to the challenge inoculation than untreated plants.