SUPPRESSION OF FUSARIUM-OXYSPORUM F-SP RAPHANI PEG-4 IN SOIL FOLLOWING COLONIZATION BY OTHER FUSARIUM SPP

Suppression effects due to the previous colonization of soil by microorganisms related closely (other Fusarium species) or distantly (soil bacterial and other soil fungi) to Fusarium oxysporum f. sp. raphani PEG-4 (PEG-4) on the growth and survival of PEG-4 in soil were investigated. Increases in the numbers of PEG-4 propagules were markedly suppressed by the prior inoculation of sterile soil by other microorganisms. The suppression was greater when Fusarium species rather than soil fungi of other genera or soil bacteria had been inoculated previously. This suggested the occurrene of a ''prior-colonization-possession'' phenomenon. This phenomenon was also observed in non-sterile soil, where the propagule numbers of PEG-4 declined rapidly in soil inoculated previously with other Fusarium species when compared with no prior inoculation. Competition was more severe between PEG-4 and other Fusarium species than between PEG-4 and soil bacteria when PEG-4 and other Fusarium species or soil bacteria were inoculated simultaneously into sterile soil. The results showed that strains of Fusarium sp. might have an important role in the growth and survival of F. oxysporum f. sp. raphani in soil.