Mechanisms involved in biocontrol by microbial inoculants

— Biological control offers alternative environmentally friendly strategies for the control of phytopathogens in agriculture and horticulture. Biocontrol metabolites are designed so that they do not have any adverse effects on host plants or on indigenous microflora and, in addition, resistance to these metabolites does not appear to develop. As promising alternatives to chemical pesticides, some biocontrol agents have been found to produce a variety of antifun- gal secondary metabolites and lytic enzymes. The 2,4-diacetylphloroglucinol is a secondary metabolite produced by Pseudomonas fluorescens F113, a strain capable of protecting sugar beet against the causal agent of 'damping off', Pythium ultimum; environmental and genetic factors involved in 2,4-diacetylphloroglucinol production are discussed. Stenotrophomonas maltophilia strain W81 (P) produces chitinase and protease enzymes and is capable of conferring plant protection against the disease-causing activity of Pythium ultimum in vitro; transposon mutagenesis and subse- quent in vivo assays have demonstrated that the biocontrol ability of W81 (P) is mediated by lytic enzyme production.