Secondary metabolites released into the rhizosphere by Fusarium oxysporum and Fusarium spp. as underestimated component of nonspecific replant disease

Background and aims A study was performed to investigate the role of fungal metabolites released into the rhizosphere of replanted orchards as a potential biotic component of tree growth decline. Methods The phytotoxicity of the gamma ray-sterilized crude culture filtrates of sixteen fungal species originating from replanted apple orchards was tested in a bioassay. Low molecular weight compounds released by Fusarium spp. were analyzed. Results The fungal culture filtrates affected seedling growth and health with an activity that varied from growth inhibition to promotion. Three out of the six species of Fusarium tested produced species-specific mycotoxins such as equisetin and enniatin B and D (