Reaction of Some Olive Cultivars to Verticillium dahliae Isolates Agent of Vascular Wilt: A Comparative Study

Verticillium dahliae Kleb. the causal agent of vascular wilt is an important pathogen of olive trees in growing areas of the world. To evaluate the reaction of the susceptibility of different commercial olive cultivars to the pathogen, six months old of eight commercial olive cultivars including Bladi, Kalamon, Koroneiki, Konservalea, Manzanilla, Mission, Rooghany, Sevillana and Zard cultivars and wild olive were root-dip inoculated. Nine-month-old nursery olive plants were inoculated with a non-defoliating (VCG4B, ND) or a defoliating (VCG1, D) isolate of V. dahliae. Resistance was evaluated by assessing symptom severity using a 0-4 rating scale and estimating the area under disease progress curves. Interaction between isolates of V. dahliae with different pathotypes and olive cultivars show that the defoliate pathotype cause higher disease severity index and stem colonization (p< 0.01). The percentage of plants killed and of those which recovered from the disease and stem colonization Index were used as additional parameters for including a particular cultivar into a defined category. One cultivar, ‘Bladi’, were susceptible or extremely susceptible to both pathotypes of V. dahliae. A second group showed differences of resistance depending on the pathotype used. They were susceptible or extremely susceptible to the D pathotype but resistant or moderately susceptible to the ND one. Finally, ‘Kalamon’ and ‘Koroneiki’ were resistant to both pathotypes of the pathogen. The resistance of these cultivars was evident by the plant ability to recover from infection with either isolates.