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Dual role of H<inf>2</inf>O<inf>2</inf> in late stages of root colonization of resistant and susceptible bean plants by Fusarium oxysporum f. sp. phaseoli

Abstract:

This study investigated biochemical and morphological changes associated to oxidative metabolism during late stages, i.e. 25 days after inoculation of Fusarium oxysporum. f. sp. phaseoli (Fop) in susceptible and resistant roots as well as Fop sensitivity to H2O2. Severe cell destruction only occurred in infected susceptible roots, while xylem vessels occlusion was stronger in the resistant genotype. H2O2 accumulation occurred in both infected genotypes being associated with cell destruction in susceptible roots and with apparent maintenance of xylem integrity in the resistant one. The activity of peroxidase, NADPH-oxidase, lipoxygenase, superoxide dismutase, ascorbate peroxidase and catalase increased in inoculated resistant roots, while in susceptible ones only lipoxygenase and ascorbate-peroxidase activities increased. Conidium germination and mycelial growth of Fop were reduced in concentrations above 4 and 8 μM of H2O2, respectively, where 32 μM completely inhibited mycelial growth. H2O2 accumulation seemed to be associated to tissue damage caused by Fop colonization in susceptible roots and to defense responses in some xylem cells in resistant genotype during late stages.