The aim objective of this study is develops and implements the hypovirulence as a biological control against Chestnut Blight in Portugal. With this work will be studied the biological and molecular markers of the resident population of C. parasitica and in the infected-C. parasitica hypovirus strains to support field application and all variables includes in a biological control method. After biological treatment with hypovirus-infeted C. parasitica strains, persistence and dissemination of the hypovirus will be assessed for predicting durability and maintenance of hypovirulence to control Chestnut Blight. Further, important scientific issues can be studied related with the resilience of the chestnut ecosystem promoted by the C. parasitica hypovirulent strains in spite of the likely climatic changes.basin countries including Portugal. The major olive diseases include the anthracnose (OA) and verticillium wilt (VW), due to their high incidence and related losses. The use of fungicides has been the main control strategy adopted against both diseases. Besides not being completely effective on preventing these diseases, there are numerous environmental risks and toxicity problems associated with it. In the last decades, the implementation of sustainable production methods has been encouraged in Europe. In this context, the International Organization for Biological Control and the EU (Directive 2009/128/EC) have implemented regulations for the promotion of sustainable production methods, with emphasis on the use of biological control as an alternative to chemical control. However, the lack of studies on biological control agents (BCA) against OA and VW of the olive tree could jeopardize that strategy. The endophytic fungi (EF) are a group of microorganisms with great potential to be explored as BCA. Their potential in the biological control against pests and diseases has been recently recognized. Some successful cases of EF application in the biological control against fungal diseases that affect major crops have been reported. As far as we known, no studies regarding exploitation of EF potentialities in the biological control of olive tree diseases have been performed. This project intends to fill this gap, through the identification and selection of olive tree EF, to be used as BCA against two of the major diseases that affect this crop worldwide, the OA and VW.