Microbial enrichment of compost with biological control agents to enhance suppressiveness to four soil-borne diseases in greenhouse.

The aim of the present work was to study if the level and reproducibility of suppressive properties of compost can be increased upon enrichment with biological control agents. A compost made from green waste, organic urban waste and urban sludge was inoculated with commercial formulations of Trichoderma and non-pathogenic Fusarium. The compost showed to be suppressive against some soil-borne pathogens, except R. solani, while such activity was lost after sterilisation. The suppressive effect of enriched compost was assessed in greenhouse trials on cucumber, tomato, bean and basil. The addition of T. harzianum T-22 at 4 g l–1 dosage was able to increase suppressiveness against R. solani of a 40% compost and 60% peat mix and to increase biomass of bean compared to a peat inoculated control. The same enrichment did not reduce suppressiveness of compost against P. ultimum and P. nicotianae, so its addition might be considered a good strategy to increase compost suppressiveness. Disease suppressiveness of sterilised compost was restored by the addition of T. viride TV1 (> 4 g l–1) in P.ultimum/cucumber and in P. nicotianae/ tomato. This study represents a further step toward the development of a substrate able to control a wide range of soil-borne pathogens and in the use of fortified composts for controlling plant diseases.