The effects of two purified fractions (formerly D-SXM and ND-SXM) produced in vitro by defoliating (Vd312D) and non-defoliating (Vd315ND) strains of Verticillium dahliae were studied on twigs of Olea europaea cvs Frantoio and Leccino. Symptoms, such as leaf curling, yellowing, vein clearing and defoliation, which are observed on the two cultivars naturally affected by Verticillium wilt, were produced by these fractions. Physiological changes were induced during the first seven days after the absorption of solutions containing ND-SXM or D-SXM. Both fractions increased the transpiration flow from abaxial leaf surfaces. Cell membrane and antioxidant activity were the most important action sites of ND-SXM and D-SXM. ND-SXM influenced malondialdehyde concentration in ‘Leccino’ leaves, while D-SXM increased the percentage of electrolyte leakage in ‘Frantoio’. Both fractions reduced the total non-enzymatic antioxidant activity on the leaves of the treated twigs. The total phenol content increased in both cultivars, without differences to the control. Variations on electrolyte leakage and total antioxidant activity were effective in discriminating the two tested olive cultivars for V. dahliae tolerance or susceptibility. If V. dahliae strains Vd315ND and Vd312D produce ND-SXM and D-SXM in the infected plants, these metabolites may move via the xylem sap, accumulate in the leaves and induce changes that will lead symptoms on the leaf by compromising the cell membranes physiology.
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