The effectiveness of rhizosphere microorganisms to control Verticillium wilt disease caused by Verticillium dahliae Kleb. in olives

Soil is an important natural resource for the existence of plants, animals, and microorganisms. In this study, the effectiveness of some biological preparations from soil-derived microorganisms against Verticillium wilt caused by Verticillium dahliae, which is a very important disease in olive, was investigated. Harpin protein (Messenger Gold), Mycorrhiza (ERS)-Trichoderma harzianum strain (T22 Planter Box), and different combinations of these treatments were used as biological preparations against V. dahliae. Additionally, the effectiveness of Bordeaux mixture, which is an important component in sustainable agriculture and is widely used by the farmers, was added to this study in order to compare soil microorganisms. Plants have been observed every month for a year, and after 12 months, the plants were evaluated according to the scale of 0–4. As a result, high efficacy results have been obtained in Messenger Gold, Messenger Gold + ERS-T22 Planter Box + Bordeaux mixture, and Messenger Gold + Bordeaux mixture applications (P ≤ 0.05). Application of Messenger Gold and in combination with Messenger Gold suppressed the Verticillium wilt disease in the parts of the trees where the symptoms occurred, and these trees showed regeneration by new shoot development. The application of ERS-T22 Planter Box and Bordeaux mixture suppressed the Verticillium wilt, and the disease symptoms have not spread to the other parts of plants. However, no shoot formation occurred in these diseased parts. According to our results, it is considered that Harpin protein may have a positive effect on the activation of xylem in olive and induces the pathogen host defenses. In addition, the presence of some beneficial microorganisms can restrict the fungal sporulation and growth of V. dahliae. Therefore the Harpin protein can be used as a biological control agent in combination with other antagonism microorganisms.