Brothers in arms: Fusarium oxysporum vs. Fusarium oxysporum

Fusarium oxysporum (Fo) is a root-colonizing fungus that can be detrimental or beneficial to the plant. Pathogenic Fo isolates colonize the vasculature causing wilt disease. Most Fo strains, however, are harmless endophytes conferring biocontrol to various root pathogens. How endophyte-mediate resistance (EMR) is conferred is unknown. We report Fo-induced EMR in tomato to be correlated with induction of localized cell death and the specific accumulation of two plant proteins, NP24 (a PR-5) and a β-glucanase, in the xylem sap. Pattern-triggered immunity (PTI) appears not to be required for EMR, as the latter response was still mounted in PTI-compromised tomato, despite their hyper-colonization by endophytic Fo isolates. Notably, co-inoculation of a virulent and an avirulent Fo strain on a resistant plant can also reduce susceptibility of a host to a virulent strain. We found this type of cross protection induced by avirulent pathogens in tomato to be less potent than EMR induced by endophytic Fo, implying distinct mechanisms to be involved in inducing resistance to pathogenic Fo. Application of Fo endophytes could provide a sustainable alternative to the employment of fungicides. Therefore, a methodology to mass-produce Fo spores and to monitor their effects in crops was developed. A pilot study in a potato field showed that Fo endophytes do not negatively affect yield. This protocol can now be used as a stepping stone to assess biocontrol potential of Fo under field conditions for various crops. The thesis elaborates on molecular mechanisms involved in EMR and provides directions for further research