Abstract
The macroconidial germination of Fusarium solani f. sp. phaseoli was inhibited in the field soil of Kitami Agricultural Exp. Sta. in Kun-neppu (K-soil) which was suppressive to common bean root rot. The inhibition was nullified by autoclaving or steaming (60-82C), and partially nullified by γ radiation of the soil. It was re-established when the autoclaved soil was inoculated with a small amount (1/100) of original soil or Tokachi soil which is conducive to the disease. Also, it was partially re-established by the inoculation with the water extract of K-soil, but was failed to re-establish when the extract was autoclaved or filtered through membrane filter. From these results, the suppression of germination in K-soil was suggested to be biological origin. Furthermore, in autoclaved, aerated steamed or γ radiated K-soil, the germination rate of macroconidia was slow in comparison with equally treated conducive Tokachi soil and the morphology of germ tubes was abnormal. This germination delaying effect found in sterilized K-soil possibly operates in untreated K-soil and concerned with the inhibition of germination of macroconidia.
