Resistance and vegetative growth analysis of some olive cultivars in response to a defoliating pathotype of Verticillium dahliae Kleb

Verticillium dahliae Kleb. the causal agent of vascular wilt is an important pathogen of olive trees in growing areas of the world. Nine-month-old nursery olives including ‘Bladi’, ‘Conservalia’, ‘Kalamon’, ‘Koroneiki’, ‘Manzanilla’, ‘Mission’, ‘Marry’, ‘Picual’, ‘Rowghani’, ‘Sevillana’ and ‘Zard’ cultivars were root-dip inoculated with a defoliating (VCG1) isolate of V. dahliae obtained from diseased olives. Resistance was evaluated by assessing symptom severity using 0-4 rating scale and estimating the area under disease progress curves. The percentage of plants killed and final mean severity of symptoms were used as additional parameters for classifying the cultivars. Most of the tested cultivars were susceptible or highly susceptible to Verticillium wilt. However, two genotypes ‘Kalamon’ and ‘Koroneiki’ exhibited high resistance or resistance to this disease. Vegetative growth was reduced in inoculated plants due to infections caused by V. dahliae, although the reduction was remarkably higher in susceptible than in resistantcultivars. Correlation coefficient analyses revealed a negative relation between disease severity and vegetative growth. Dendrogram of olive cultivars based on all parameters represented two main clusters, major and minor. Minor cluster comprised only ‘Kalamon’ and ‘Koroneiki’ cultivars as resistant to V. dahliae. The major cluster could be divided into two groups, exhibiting extremely susceptible or susceptible reaction to V. dahliae.