LAUSR

Although the vascular pathogen Fusarium oxysporum (Fo) is notorious for being the causal agent of Fusarium wilt disease, the vast majority of Fo strains are harmless soil and root colonisers. The latter Fo's are often endophytes colonising roots intracellularly without negatively affecting plant fitness. Actually, most of them, like Fo47, are beneficial providing biocontrol to various root pathogens. Interestingly, also pathogenic Fo inoculated on a resistant host (i.e. avirulent Fol) can reduce susceptibility to virulent Fo strains via a mechanism called "cross protection". It has been hypothesised that cross protection is based on activation of a resistance protein of the host upon recognition of a cognate Avirulence (Avr) protein of the pathogen. Currently, it is unknown whether the biocontrol activity of Fo endophytes utilizes similar mechanisms as cross protection conferred by avirulent pathogens, and whether both provide a quantitative similar level of protection. Here, we show that in tomato biocontrol activity of the Fo47 endophyte to the pathogen Fo f.sp. lycopersici (Fol) is more effective than cross protection induced by avirulent Fol strains activating either I, I-2 or both resistance proteins upon recognition of respectively Avr1 or the Avr2/Six5 pair. These findings imply that cross protection and biocontrol utilize different mechanisms to reduce susceptibility of the host to subsequent infections.