Salicylic acid is associated with improved growth and resistance of olives (Olea europaea L.) to Verticillium wilt

To improve the growth of olive and find a suitable approach for controlling Verticillium dahlia in this plant, treatment of different cultivars by salicylic acid (SA) was evaluated. Nine-month-old seedlings of Koroneiki, Marry, Rowghani, and Zard cultivars were pre-treated with 0, 5, and 10 mM SA at 15-days intervals, and then roots were inoculated by dipping into a defoliating isolate of V. dahliae. The dry weight of different tissues was measured separately at the end of the trial (14 weeks after inoculation). The response was assessed by grading the severity of symptoms on the 0-4 scale and calculating the area under the disease progress curve. Also, the concentration of phenolic compounds in the root tissues, the activity of the superoxide dismutase enzyme, the final intensity of symptoms, and the percentage of dead plants were measured. Foliar spray of 10 mM SA increased the vegetative growth of the olive cultivars. The results showed that treatment with SA decreases the severity of Verticillium wilt. The root phenol level and the activity of superoxide dismutase were significantly higher in the plants treated with 10 mM SA as compared to the control plants. Disease progression had a negative relationship with the superoxide dismutase activity and total phenols of the roots in olive cultivars.