2000 Volume 47 Issue 3 Pages 233-238
This study has been done to clarify some characteristics of ultrafine spinel ferrite particles prepared by a chemical coprecipitation method and to investigate their suppressive effect on mycelial growth of turfgrass pathogen, Sclerotinia homoeocarpa. Average particle sizes of these ferrites ranged from 5 to 30nm as determined by X-ray diffraction and TEM observation. Values of saturation magnetization os of these ferrites were 20 to 80emu/g. The optimum growth temperature for the pathogen was 25°C. The suppression rate of MnFe2O4, Fe3O4 and ZnFe2O4 on the mycelial growth was 20 to 50% at 10°C as compared with the control, though the suppression was not clear at 25°C. CoFe2O4 and Ni0.5Zn0.5Fe2O4 showed stronger suppression rate of 40 to 70% at both temperatures. Optical microscopic observation has revealed that additional CoFe2O4 suppresses the 70% of the mycelial growth rate. The origin of the suppression effect of these ultrafine ferrites has been pursued from the viewpoints of electromagnetic field existing on the surface of the ferrite particles and/or extremely small amount of chemical free-ions dissolved from the surface of particles. The suppressive effect becomes higher with the higher σs of many ferrites, except MnFe2O4, Fe3O4 and Ni0.8Zn0.2Fe2O4. Suppressive effects by free-ions of Ni2+, Co2+ increases dramatically at higher concentration than 100μM.
