The Fusarium Circinatum Gene Fcrho1, Encoding a Putative Rho1 GTPase, Is Involved in Vegetative Growth but Dispensable for Pathogenic Development

Fusarium circinatum is the causal agent of pine pitch canker (PPC), one of the most devastating forest diseases worldwide. This fungus causes severe damping-off in pine seedlings and growth reduction, wilting and the development of cankers in pine forests and plantations. A draft of the complete genome sequence of this phytopathogen was recently made available. This information was used to annotate in silico the gene Fcrho1 as a putative homolog of Rho1 GTPase genes. In this study, we generated Fcrho1 deletion mutants in two F. circinatum wildtype strains isolated from damaged trees in northern Spain. For that, we used a modified version of the OSCAR methodology, an approach not previously used in F. circinatum that allows the generation of deletion constructs in a single cloning step. The conidiation and spore germination of the resulting deletion mutants were not affected, neither the hyphal morphology. However, the mutant strains showed significantly reduced growth in vitro and more foamy macroscopic hyphal morphology than their corresponding ectopic and wildtype strains. Finally, an in vivo virulence assay showed that the reduced in vitro growth rate characteristic to the deletion mutants does not impact their pathogenicity.This study was supported by two research projects: AGL2015-69370-R “Next Generation Sequencing (NGS) technologies for the study of Fusarium circinatum mycoviruses” (MINECO/FEDER, UE) and AGL2012-39912 “Biological control of Pine Pitch Canker disease by the use of Fusarium circinatum mycoviruses” (Ministerio de Economía y Competitividad). This article is based upon work from COST Action FP1406 PINESTRENGTH (Pine pitch canker–strategies for management of Gibberella circinata in greenhouses and forests), supported by COST (European Cooperation in Science and Technology). E. Jordán Muñoz-Adalia is a receipt of grants from the European Social Fund and from the Consejería de Educación de Castilla y León (JCyL) (ORDEN EDU/1083/2013). A scholarship granted by the University of Valladolid (Ayudas para estancias breves en el desarrollo de tesis doctorales convocatoria 2017; EB17) supported the mobility of E. Jordán Muñoz-Adalia. The work performed at the IHSM “La Mayora” was supported by research grant AGL2016-80048-R “The micovirus as tools for the biological control of Verticillium and Fusarium Wilts. Elucidating the mechanisms that regulate the virus-fungus-plant interaction” (Ministerio de Economía y Competitividad).Peer reviewe