Effects of nutritional sources on growth of one non-pathogenic strain and four strains of Fusarium oxysporum pathogenic on tomato

As part of an investigation into the factors influencing the colonization o f the rhizosphere and the root tissues of host plant, by pathogenic and non -pathogenic strains of Fusarium oxysporum, the effect of a range of carbon (C) sources on the growth habits of five strains of F. oxysporum were compa red. The strains used were two F. oxysporum f, sp. lycopersici (Fol strains ), two F. oxysporum. f sp. radicis-lycopersici (Forl strains) pathogenic on tomato and strain Fo47, a non-pathogenic strain of F. oxysporum, currently used as a biocontrol agent to reduce severity of fusarium diseases on seve ral crops. Radial extension rates on solid media were measured using solubl e saccharides (glucose, xylose and D galacturonic acid), polysaccharides (c arboxymethyl cellulose, xylan and pectin) and soluble and insoluble extract s of tomato roots as C sources. Growth parameters were estimated by fitting a logistic equation to biomass data recorded from liquid culture using the same C sources. The strains were characterized by means of the pattern of radial extension rates an the various C sources, and the two Forl strains were discriminated further from the other strains. The growth parameters were unique features of each F. oxysporum strains, whatever the C source. The pathogenic strain s did not exhibit particular abilities in degrading the cell wall component s. II was concluded that growth habits related to carbohydrate utilization are unique to each strain of F. oxysporum and that these traits are not rel ated to pathogenicity.