Distribution of Saprophytic Fungi Antagonistic toFusarium Culmorumin Two Differently Cultivated Field Soils, with Special Emphasis on the GenusFusarium

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Abstract
The purposes of the present study were to search for antagonistic fungi to control seed-borne diseases of cereals caused by Fusarium culmorum (W.G.Sm) Sacc. and to use these results to compare the distribution of non-pathogenic Fusarium spp. and other fungi antagonistic to Fusarium culmorum in soil and on straw particles in an organically and a conventionally cultivated field. The organic farm had been cultivated according to the principles of Steiner (1963) since 1952. The sites were similar with respect to climatic conditions, soil type and vegetation. There was no difference in the total number of antagonistic fungi isolated from the two differently cultivated fields, but the results for Fusarium spp. showed effects of the actual crop as well as the cropping system. Soil sampling over a three year period at the organically cultivated farm in two crops—winter wheat or a mixture of grass and clover—showed almost twice as many species of Fusarium in the mixed crop compared to monoculture. In mixed crop fields, the percentage of F. culmorum in relation to total isolations of fusaria was 20% in the organically cultivated field compared with 45% in the conventionally cultivated field. These results indicate that pathogenic fusaria may be suppressed by antagonistic fusaria to a larger extent in the organically cultivated field than in the conventionally cultivated field. In accordance with this, a higher number of antagonistic fusaria was found in the organically farmed field (14) compared to three in the conventionally farmed field. This was partly a result of a higher number of isolated fusaria and a higher number of different species of Fusarium in the organically cultivated soil (total number of non-pathogenic fusaria was 10 in the conventionally cultivated field and 56 in the organically cultivated field). However, it also seems to reflect an enrichment of fusaria with antagonistic properties towards F. culmorum. Thus, the occurrence of F. culmorum was 1.7 times higher in the organically cultivated field while the occurrence of its antagonists was 4.6 times higher in the organically compared with the conventionally cultivated field.