Local and systemic resistance against fungal pathogens of tomato plants elicited by a compost derived from agricultural residues

A transgenic GUS-expressing strain of the root-infecting fungal pathogen Fusarium oxysporum f.sp. radicis-lycopersici was used to inoculate the roots of tomato plants (Lycopersicon esculentum Mill.) grown on a compost mix made from grape marc wastes and extracted olive press cake (GM-EPC). Plants exhibited an enhanced defensive capacity against the pathogen as compared with control plants grown on peat. Pathogen viability and growth in the potting mixes, as determined by GUS activity measurements and by colony forming unit enumeration, was not affected. Interestingly, the pathogen was not able to penetrate and colonize the root tissue. Moreover, the sterilized compost extract was also able to protect the plants. Induction of systemic resistance by the compost was assessed using the foliar pathogen Septoria lycopersici and by PR gene expression analysis carried out in leaves of tomato plants grown on the GM-EPC compost. Our data strongly indicate that induction of plant defence response is the main mechanism of biological control mediated by the GM-EPC compost.