Development and validation of an inoculation method to assess the efficacy of biological treatments against Verticillium wilt in olive trees

Verticillium wilt in olive trees, caused by the soil-borne fungus Verticillium dahliae, is one of the most serious diseases of this crop due to high tree mortality and the difficulty of control. One of the major constraints to developing control measures against this disease is the lack of inoculation methods to evaluate the effectiveness of treatments. Here, we compared five inoculation methods for screening biological control agents (BCAs). The soil infested with cornmeal sand medium at 20 % w/w performed the best, and its effectiveness was further tested in olive plants treated with six BCAs, four strains of the fungal species Fusarium moniliforme, F. oxysporum, Gliocladium roseum and Phoma sp., and two fermented mixtures of several yeasts and bacteria. Strains of F. oxysporum, Phoma sp. and two mixtures of microorganisms significantly decreased the severity of the disease in potted plants of the susceptible olive cv. Picual.