COLONIZATION OF STERILIZED SOIL AND FLAX ROOTS BY STRAINS OF FUSARIUM-OXYSPORUM AND FUSARIUM-SOLANI

Several studies showed that nonpathogenic strains of Fusarium competing either saprophytically or parasitically with the pathogen could be used to control Fusarium-wilts of plants. Nine strains of F. oxysporum and F. solani were compared for their specific ability to colonize a sterilized soil and the cortex of flax roots growing in the soil precolonized by these strains. Introduced at the initial concentration of 1.0 x 10(3) CFU/g into the steamed soil, the nine strains of Fusarium grew and reached a plateau after 2 weeks. The inoculum densities at the plateau were statistically different showing that these strains did not have the same ability to colonize a sterilized soil. There were clear differences in the ability of these strains to colonize the roots of flax growing through the soil. The percentage of root fragments colonized by Fusarium was not correlated with the population density in soil, showing that the ability to colonize soil and the ability to colonize the root are different properties of the same strains. The two nonpathogenic strains that are the best in reducing the percentages of plants infected by the pathogen also were the best root colonizers. But these results did not allow us to draw any conclusions about the existence of a relationship between the ability of the strains to colonize the root and their ability to induce biological control of wilts.