The 2012 ASHS Annual Conference

Verticillium wilt of olive, caused by the soilborne fungus Verticillium dahliae Kleb., represents currently the main phytosanitary limitation in olive orchards both for its destructive potential and control difficulties. In the framework of an integrated disease management strategy, the use of resistant cultivars represents an useful tool because of its low cost, efficiency and environmental friendliness. Most of the olive cultivars currently in use have been catalogued as susceptible or extremely susceptible to the highly virulent defoliating pathotype of V. dahliae, and only a reduced number of the evaluated cultivars showed a considerable level of resistance to the development of symptoms. The objective of this work was to select new olive genotypes showing higher levels of resistance to Verticillium wilt than current cultivars that could be used as new cultivars, rootstocks or genitors in future breeding cycles. For that, genotypes from open pollination of different cultivars as well as wild olive material from different origins have been evaluated. Plants were no-inoculated (water) or inoculated by dipping their roots in a conidia suspension of a defoliating isolate of V. dahliae and placed in growth chamber under controlled environmental conditions suitable for symptoms development for 16 weeks. ‘Picual’ (susceptible) and ‘Frantoio’ (resistant) were used as controls. Disease reaction was evaluated weekly by using a 0–4 severity scale. Symptoms started 4 weeks after inoculation in ‘Picual’ and 2 weeks in the most susceptible genotypes, whereas absence of symptoms throughout the evaluation period was observed in some genotypes from breeding progenies and wilds. Some of the evaluated genotypes were classified as highly resistant on the basis of external symptoms development and percentage of dead plants. The most resistant genotypes will be propagated for future trials to confirm their disease reaction under controlled and field conditions.