Ecologic and Taxonomic Studies on Pythium as Pathogenic Soil Fungi : III Population of Pythium ultimum and Other Microorganisms in Rhizosphere

摘要

1. The growth intensity of Pythium ultimum in the rhizosphere of plant with different degree of susceptibility decreases as the resistance of the hosts increases and this is also true to both Pythium sp. and Rhizoctonia solani but not with Fusarium oxysporum f. niveum. 2. The non-susceptible plant has lower microbial population than the resistant and susceptible plants. 3. No antagonistic microorganisms are found in sterilized soil. In non-sterilized soil, the non-susceptible plant has the most number of antagonistic microorganisms while the susceptible has the lowest. 4. Little stimulatory effect of soil extract on conidial germination and mycelial growth was observed. 5. The inhibitory action of root extract on conidial germination increases as the resistance of the hosts increases. Likewise, the non-susceptible plant shows no stimulation on mycelial growth while the resistant and susceptible show stimulation.