FLOOD-FALLOWING FOR ERADICATION OF FUSARIUM OXYSPORUM f. CUBENSE

Abstract

The length of F. oxysporum f. cubense in soils submerged under 1 1/2-3 ft. of water in flood-fallowed lakes varied from 25 to 80 days. In soil submerged under 1 inch of water in glasses in the laboratory, survival time varied from 45 to more than 165 days. Survival in submerged sterile soil may be slightly longer than in nonsterile soil, but the differences were small and variable. There was no consistent difference in length of Fusarium survival in sand, clay loam and organic soils when submerged in the laboratory under 1 inch of water. Of various N compounds tested, only cyanamid at a rate of 2000 or more To. per acre reduced the length of Fusarium survival in soils submerged in the laboratory. Temp, profoundly affected Fusarium survival in submerged soils. At 13[degree]C, numbers surviving were 10-20 times greater than in soils submerged at 24-34[degree]C, and survival was at least 90 days longer. As temps, were increased, these differences were reduced. Larger Fusarium populations survived at least 90 days longer when submerged in water or mineral oil in the laboratory as contrasted with water and soil. In flood-fallowed lakes, larger Fusarium populations survived longer on the lake floor and in the water than in submerged soil. Under anaerobic conditions, Fusarium did not survive 14 wks. in any field soil used. The maximum length of survival in saturated soil under anaerobic conditions was 6 wk. and at least 7 wk. in soils 50% saturated. In addition to soil moisture content, temp, and substrate influenced survival under anaerobic conditions. Length of survival was greater at 13[degree]C than at 24-34[degree]C, but the differences were smaller than those in submerged soils in room and refrigerator atmospheres. Survival was at least 4-6 wk. longer in potato dextrose agar cultures than in soil. Aeration of submerged soils by flowing water increases Fusarium survival and length cf survival at least 70 days over those in soils submerged under stagnant or non-aerated water. It is suggested that gaseous relationships of a chemical nature rather than a biological nature, and the physiol. state of the fungus, are more important factors in determining survival than is the direct action of microorganisms. The latter may be important indirectly in their utilization or production of O2 and other compounds.