Mycelial development of Fusarium oxysporum in the vicinity of tomato roots

The patterns of mycelial development (length and branching) of five strains of Fusarium oxysporum were measured in the vicinity of tomato and wheat ro ots. Two strains were of f. sp, lycopersici, two of f. sp. radicis-lycopers ici and the fifth was a non-pathogenic strain currently used as a biocontro l agent. Hyphal extension and branching were measured microscopically using a CCD camera and an image analyser. Furthermore, the role of soluble root exudates, insoluble root materials, glucose supply and nitrogen supply (cas amino acids) on mycelial development was investigated. Each strain had its own pattern of development in the absence of a root. Fungal development of all five strains was stimulated in the vicinity of roots irrespective of pl ant species but there was no chemotropic response towards or away from the root. Both pathogenic and non-pathogenic F. oxysporum populations exhibited their own characteristic growth and development features which were not re lated to their pathogenicity. Growth stimulation was mainly related to the presence of organic nitrogen in the soluble exudates. It is proposed that s ignalling and recognition mechanisms between the host plant and the pathoge nic or non-pathogenic strains are likely to occur on or in the root rather than external to the root.