Interactions virus-fungus- insect in pine pitch canker disease

Abstract

The ascomycetous fungus Fusarium circinatum Nirenberg & O'Donell is the causal agent of pine pitch canker disease (PPC), one of the most devastating forest diseases worldwide. PPC has been reported in fourteen countries throughout America, Africa, Asia and Europe. So that, it is though that more than ten million hectares of pine forests and plantations are threatened by this disease in Europe. F. circinatum is mainly considered a necrotroph when it infects conifers via stem,however its ecological role as an endophyte in several herbaceous plants as well as a possible saprophyte in litter have been recently reported. The overall aim of this Thesis was to analyze the interactions that take place among members of the PPC pathosystem . For this purpose, we carried out six scientific works focused on the study of relationships between three main elements of the PPC: viruses, fungi and insects. Firstly, a review about the use of fungal viruses (mycoviruses) in biocontrol of forest diseases was elaborated. Secondly, the complete genome of F. circinatum was used as query for in silico annotating five candidate genes putatively related with fungal virulence. The proposed annotation was based in the comparison with previously characterized genes in other Fusarium species and gene ontology. Fungus-virus interaction was addressed in a third study by high throughput sequencing of RNA. In this work, we studied the anti-viral response performed by the fungus against three previously described Mitovirus spp. (FcMVl, FcMV2-1 and FcMV2-2). As a result, new data about FcMV2-2's genome were provided in addition to new insights about the RNA silencing process in the fungus. In a fourth study, deletion mutants of F. circinatum lacking the earlier annotated gene Fcrhol were generated. Our results revealed not lethal effects of gene deletion even though Fcrhol was an effective regulator of vegetative growth in vitro. Otherwise, we evaluated the effect of single and co-infection by FcMVl and FcMV2-2 in lacease enzyme production, mycelial growth and fungal pathogenicity in Pinus radiata D. Don seedlings.