Involvement of resistance induction by Penicillum oxalicum in the biocontrol of tomato wilt

Penicillium oxalicum, a biocontrol agent for Fusarium oxysporum f.sp. lycopersici, was tested for its ability to induce resistance against tomato wilt. P. oxalicum and F. oxysporum f.sp. lycopersici were placed at separate sites on tomato plants or in soil, avoiding a direct interaction between the fungi. P. oxalicum induced resistance as expressed by a reduction in disease severity, area under disease progress curve and stunting induced by the pathogen. P. oxalicum colonized the tomato rhizosphere during the experiments but it was not detected inside stems, demonstrating that P. oxalicum and Fusarium oxysporum f.sp. lycopersici remained spatially separated. Biological control was observed both in sensitive and 'resistant' cultivars, indicating the role of a general resistance mechanism. In both cultivars P. oxalicum treatment alone did not produce disease symptoms. Therefore P. oxalicum could be a suitable biocontrol agent in cases of cultivar resistance failure. These results suggest that P. oxalicum can trigger defence mechanisms in the plant.