Suppression of Corky Root of Tomatoes in Soils from Organic Farms Associated with Soil Microbial Activity and Nitrogen Status of Soil and Tomato Tissue

In greenhouse experiments, corky root of tomatoes (Lycopersicon esculentum L.) was less severe in soil from organic farms than in soil from conventional farms when soil collected in the fall was infested with various concentrations of microsclerotia of Pyrenochaeta lycopersici. Maximum disease severity was obtained at inoculum levels of 104 and 10 5 microsclerotia per milliliter of soil. When soil samples were sterilized by gamma radiation, the increase in disease severity was greater for soils from organic farms than for soils from conventional farms, indicating that biological disease suppression might have been higher in organically managed than in conventionally managed soils ...