Abstract
Soil microorganisms, i.e. fungi, actinomycetes and bacteria, were isolated from soils collected in both reclaimed and matured fields. Some of them were randomly selected, and their antagonistic actions were tested against three plant pathogens, Fusarium solani f. sp. radicicola, Rhizoctonia solani and Corticium rolfsii on potato sucrose agar plates. The percentage of antagonistic microorganisms in soils from reclaimed fields increased year by year, but it was still lower than that from matured fields even four years after reclamation. This was attributed partly to few chances to have been invaded by plant pathogens, and partly to species and nature of soil microorganisms in reclaimed fields. Results obtained suggest that careful attention must be paid to the control of soil-borne diseases in reclaimed fields for at least more than four years after reclamation. The results also indicate that crop rotation or growing of grasses may be effective for increasing the population of antagonistic microorganisms in soil.
