A non-pathogenic strain of Fusarium oxysporum as a potential biocontrol agent against Verticillium wilt of olive

•FO12 culture broth effectively reduced the inoculum density of V. dahliae in soil.•FO12 was able to prevent V. dahliae infections of olive under controlled conditions.•Chlamydospores of FO12 could be used for a commercial formulation to control VWO. The non-pathogenic Fusarium oxysporum FO12 strain isolated from cork (Quercus suber) was one of the most effective treatments against Verticillium dahliae from among more than 200 natural compounds evaluated in previous studies. Based on the results of previous work, the present study aims to determine the potential of FO12 as a biological control agent against Verticillium wilt of olive (VWO). To this end, several in vitro and in vivo experiments were carried out to evaluate the effectiveness of FO12 against V. dahliae. Dual cultures were conducted, showing a significant reduction in the mycelial growth of V. dahliae. However, inhibition zones were not observed in vitro. Four different culture fractions of FO12 were prepared to evaluate their effect on the reduction of viable propagules of V. dahliae in soil and on the disease progression in inoculated plants. Treatments with crude culture broth of FO12 resulted in a total reduction of the inoculum density of V. dahliae in naturally infested soils as well as in the progression of VWO under controlled conditions. Treatments with conidial suspension or chlamydospores were also effective in reducing the inoculum density in the soil and the disease severity in olive plants. This work provides useful information about the efficacy of several FO12-based culture fractions against VWO under controlled conditions, which could be the basis for the development of effective commercial formulations in the coming future.