The resistance of 33 major olive cultivars to Verticillium dahliae was assessed in four experiments conducted under controlled conditions. Nine-month-old nursery olive plants were inoculated with a defoliating isolate (V117) of V. dahliae . Resistance was evaluated by assessing symptom severity using a 0–4 rating scale and estimating the area under disease progress curves with reference to the maximum value potentially reached over the assessment period (AUDPCP). The percentage of plants killed and that of plants that recovered from the disease were used as additional parameters for classifying the cultivars. Twenty-six of the 33 cultivars were found to be susceptible or extremely susceptible to the defoliating V. dahliae isolate. They exhibited values for AUDPCP higher than 45% with mortality higher than 37.5%. A second group of cultivars, which included `Cipresino', `Koroneiki', `Oblonga', and `Sevillenca', were classified as moderately resistant because they showed an important reduction of the final mean severity values and of values for AUDPCP that ranged from 23% to 42%. `Changlot Real', `Empeltre', and `Frantoio' were resistant to the defoliating isolate of V. dahliae . The resistance of `Empeltre' and `Frantoio', although previously reported, was consistently confirmed, because the two cultivars exhibited no dead plants and had very low values for AUDPCP and final disease. This is the first report of resistance of `Changlot Real' to Verticillium wilt based on ability of the plants to recover from infection and the absence of dead plants. These three cultivars will be useful for inclusion in Verticillium wilt-breeding programs.

The resistance of 26 olive ( Olea europaea L.) cultivars to the defoliating pathotype of Verticillium dahliae Kleb. was evaluated in experiments under controlled conditions by stem puncture inoculation. The area under disease progress curve with reference to the maximum value potentially reached over the assessment period (AUDPCP), calculated from the symptom severity values (0–4 rating scale), was the main parameter for assessing resistance, and the percentage of dead plants (PDP), the final mean symptom severity (FMS), and the disease recovery were used as additional parameters. Five cultivars were catalogued as extremely susceptible showing values of AUDPCP, PDP, and FMS higher than 70%, 50%, and 3.0, respectively. Six other cultivars exhibited AUDPCP values ranging from 50% to 70% and FMS higher than 3.0 and were classified as susceptible. A group of 11 cultivars, including ‘Koroneiki’, was moderately susceptible with AUDPCP ranging from 31% to 50%. Finally, ‘Frantoio’, ‘Grosal de Albocafer’, ‘Kato Drys’, and ‘Manzanilla Picúa’ showed maximum AUDPCP values of 22%, no dead plants, and slight symptom severity, being classified as resistant. Stem puncture inoculation was an effective tool for identifying resistance in olive cultivars, but a reduction or a delay in the disease symptom expression of plants was observed regarding the symptom progress observed in plants root dip-inoculated in previous works of resistance assessment. These differences were more pronounced in susceptible than in resistant cultivars.

Verticillium wilt of olive, caused by Verticillium dahliae Kleb., is one of the most important diseases affecting olive crops in the Mediterranean area. With the aim to evaluate the role of Phloeotribus scarabaeoides (Bernard) (olive bark beetle) as a dispersal vector of V. dahliae, several experiments were conducted in semi-controlled conditions from May 2009 to April 2012. Groups of olive trees (2.5-year-old) certified free from V. dahliae were covered by a mosquito net and exposed to adults of P. scarabaeoides by three different ways: (1) branches or trunks collected in several olive orchards from trees severely affected by Verticillium wilt and showing apparent entry holes (mating galleries) of P. scarabaeoides; (2) adults of olive bark beetle extracted from damaged branches collected in the field; (3) adults from damaged branches that were superficially inoculated with V. dahliae. The fungus V. dahliae was not detected either by microbiological and molecular techniques from shoots of olive trees with galleries of the insect or from any of the tissues of the collected beetle adults from the galleries. Additionally, Verticillium wilt disease symptoms were not observed in olive trees exposed to the olive bark beetles. Moreover, the pathogen was never detected from any beetle adults that were recovered from the mating galleries of branches or trunks collected in several olive orchards from trees severely affected by Verticillium wilt. We conclude that P. scarabaeoides is not a vector of V. dahliae under the investigated experimental conditions.

The use of genetic resistance is likely the most efficient, economically convenient and environmentally friendly control method for plant diseases, as well as a fundamental piece in an integrated management strategy. This is particularly important for woody crops affected by diseases in which mainly horizontal resistance mechanisms are operative, such as Verticillium wilt, caused by Verticillium dahliae. In this study, we analyzed the variability in resistance to Verticillium wilt of olive trees in progenies from five crosses: ‘Picual’ × ‘Frantoio’, ‘Arbosana’ × ‘Koroneiki’, ‘Sikitita’ × ‘Arbosana’, ‘Arbosana’ × ‘Frantoio’ and ‘Arbosana’ × ‘Arbequina’ and their respective reciprocal crosses. Additionally, seedlings of ‘Picual’ and ‘Frantoio’ in open pollination were used as controls. In October 2016 and 2018, the fruits were harvested, and seeds germinated. Six-week-old seedlings were inoculated by dipping their bare roots in a conidial suspension of V. dahliae, and disease progress in terms of symptom severity and mortality was evaluated weekly. Additionally, seedling growth was evaluated every two weeks. At the end of the experiment, no significant differences were found for any of the assessed parameters when reciprocal crosses were compared. These results suggest that there is no maternal or paternal effect in regard to the heritability of resistance. In addition, this study identifies the best crosses for obtaining the highest number of resistant genotypes, highlighting the importance of the selection of specific cultivars to optimize the breeding process.