Comparative Assessment of Verticillium dahliae Tolerance in 77 Olive Cultivars

Verticillium wilt of olive (VWO), caused by the vascular soilborne fungus Verticillium dahliae, is one of the most devastating diseases of olive cultivation in the Mediterranean area. The adoption of tolerant genotypes is considered an efficient strategy to reduce its impact in the absence of effective chemical control. In the present study we assessed the response of seventy-seven olive cultivars (Olea europaea L.) to the defoliating pathotype of V. dahliae under controlled inoculation conditions. Five plants per cultivar were inoculated and compared with non-inoculated controls. Disease progression was monitored weekly for ten weeks and measured through three complementary parameters: Relative Area Under the Disease Progress Curve (RAUDPC), Final Mean Severity (FMS), and Percentage of Dead Plants (PDP). Statistical analyses, including ANOVA followed by Tukey’s HSD, correlation evaluation, and principal component analysis (PCA), were applied to classify cultivars into five susceptibility classes. Notable variability was observed among cultivars, with 7.8% classified as Highly Resistant (HR), 24.7% as Resistant (R), 46.8% as Moderately Susceptible (MS), and 20.8% as Susceptible (S) or Extremely susceptible (E). The cultivar Ghiacciolo showed the highest level of tolerance, displaying only slight symptoms and no statistically significant difference from the non-inoculated control, whereas ‘Carbuncion’, ‘Giogolino’, and ‘Pampagliosa’ exhibited more severe disease than the susceptible reference ‘Picual’. Strong correlations among RAUDPC, FMS, and PDP confirmed the consistency of the disease assessment framework, while PCA revealed distinct clustering patterns according to resistance level. Overall, these findings provide reliable evidence for the selection of olive cultivars suitable for areas vulnerable to V. dahliae.