Verticillium wilt of olive tree (Olea europaea L.) (VWO), caused by the soil-borne fungus Verticillium dahliae Kleb., is considered one of the most devastating diseases affecting this crop in many are as, particularly in the Mediterranean Basin. It can only be effectively confronted by implementing an integrated disease management strategy. Preventive measures such as the treatment of the root systems of pathogen-free certified propagationjplanting material at the nursery stage with microbial antagonists emerges as a promising alternative. Species of the soil-borne fungus Trichoderma have been widely described as biocontrol agents (BCAs) of severa! phytopathogenic fungi by means of different mechanisms, including the ability to colonize root tissues endophytically and to elicit systemic resistance in plants. In this studywe aimed to evaluate the potential ofT. harzianum CECT 2413 as effective BCA ofVWO. Strain CECT 2413 has shown to be able to in vitro overgrow different representatives of V. dahliae pathotypes infecting olive: i.e., highly-virulent, defoliating (D) and midly-virulent non-defoliating (ND) isolates. Inhibition of Verticillium growth in media where strain CECT 2413 had previously grown showed that this ability might be dueto the excretion of secondary metabolites or cell wall degrading enzymes. Furthermore, monitoring of in vitro direct confrontaban assays between an eyfp-labelled derivative of V. dahliae and a gfp-labelled transformant of CECT 2413 by confocal laser scanning microscopy (CLSM) revealed that mycoparasitism is one ofthe mechanisms involved in this antagonism. Indeed, typical coiling structures of T. harzianum around V. dahliae hyphae were clearly observe d. When a suspension of conidia of T. harzianum CECT 2413 were applied by irrigation to roots ofnursery-propagated, three-month-old olives (cv. Picual) prior to the treatmentwith a D isolate ofthe pathogen, disease symptoms were significantly reduced compared to that observed in control plants. Moreover, increase in the number and size ofleaves in plants treated with Trichoderma was also reported. Finally, colonization of olive roots surface by T. harzianum CECT 2413 during a prolonged period oftime was demonstrated by CLSM. In summary, T. harzianum CECT 2413 is an efficient colonizer of olive roots andan effective BCA against the D pathotype of V. dahliae

Supported by ERDF-­cofinanced grants (AGR-­‐6038, AGR-­‐5948, Consejería de Economía, Innovación y Ciencia, Junta de Andalucía, Spain, and NUTESCA S.L. (Jaén, Spain).

Trabajo presentado en la 12th European Conference on Fungal Genetics (ECFG12), celebrada en Sevilla del 23 al 27 de marzo de 2014.

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