Fusarium circinatum, the causal agent of pine pitch canker (PPC) disease, has been present in Europe since its detection in Spain in 2004. It causes substantial damage and losses in forest nurseries and pine plantations. Symptoms found in the nurseries include reduced germination of seeds, the wilting of seedlings, shoot and tip dieback, and, finally, the death of seedlings. In adult pines the main symptom is a bleeding canker on the main stem or thick branches. Dieback symptoms in the crown are also common. Economic loss caused by this disease is significant, and there is no known control or way to at least reduce the symptoms caused by this pathogen. Thus, the objective of the work reported in this thesis was to find an environmentally friendly way to minimize the losses caused by the PPC pathogen. The selection of tolerant or resistant hosts is one way to reduce the impact of the disease. Our results confirmed that F. circinatum is basically a pine pathogen; the rest of the conifers tested showed resistance to the disease. Among Pinus spp., P. radiata proved to be the most susceptible host, while P. pinea did not develop any symptoms of the disease after being inoculated with the pathogen. Biological control methods have been shown to be a real alternative to the use of fungicides in many plant diseases. More specifically, the antagonism of some fungal endophytes against other fungi can be used to control phytopathogens. In this study, a total of 139 fungal endophytes exhibited antagonism against F. circinatum in vitro. Some of these fungi belonged to species that have the potential to be biological control agents (BCAs). A representative subset of these endophytes was tested on pine seedlings in the field to confirm the antagonism previously shown in vitro. Two isolates of the species
Chaetomium aureum and Alternaria sp. reduced the symptoms caused by F. circinatum in the P. radiata seedlings, but no effect was recorded in the other four pine species tested. The hypovirulence caused by mycoviruses is another successful biological control method used for some plant diseases. In this study three novel viral strains were found in a single isolate of F. circinatum. These strains were sequenced and described as members of two new species of the Mitovirus genus. Finally, another study demonstrated that the Spanish population of F. circinatum commonly hosts these strains. In general, this work represents a substantial advance in the
study of environmentally friendly alternatives in the management of PPC disease.