CORRELATION BETWEEN ECOLOGICAL APTITUDES OF DIFFERENT STRAINS OF FUSARIUM AND THEIR EFFICIENCY IN THE PROTECTION OF FLAX AGAINST VASCULAR FUSARIOSIS

Thirteen strains of Fusarium solani and F. oxysporum were isolated from an initial lot of 96 and submitted to 11 different tests to determine their ecological aptitudes. Results showed a great diversity with respect to performance. Significant total correlations with the strain aptitudes to protect flax against vascular fusariosis in one soil (efficacy) were obtained for three characters: quantity of microconidia produced (negative correlation), respiratory activity, and antagonistic effect in soil in the presence of a pathogenic fungus (positive correlations). Other properties were studied, such as mycelial growth, production of macroconidia, production of chlamydospores, spore germination aptitude, inhibiting effect of secretions against F. oxysporum f.sp. lini, saprophytic development in disinfected soil, and aptitude to maintain their development and activity in soil; all these properties showed generally high partial correlations with respect to efficacy. The multiple correlations obtained for different aptitude associations tested were clearly more significant than simple correlations. The results suggest that competition among Fusarium spp., here illustrated by efficacy, can be interpreted as a complex power corresponding to the sum of different particular aptitudes, notably: global activity, mycelial growth, sporulation, spore germination capacity, and secretion of compounds inhibiting competing germs. If selection of antagonistic Fusarium strains for biological control were based upon a single criterion, this would be arbitrary in part; a multiple-step selection would be recommended. The present work was performed on a single soil and with a limited number of strains; consequently, further experiments are required.