The rhizosphere microbial community in a hydroponics system with multiple parallel mineralization (MPM) can potentially suppress root-borne diseases. This study focused on revealing the biological nature of the suppression against Fusarium wilt disease, which is caused by the fungus Fusarium oxysporum, and describing the factors that may influence the fungal pathogen in the MPM system. We demonstrated that the rhizosphere microbiota that developed in the MPM system could suppress Fusarium wilt disease under in vitro and greenhouse conditions. The microbiological characteristics of the MPM system were able to control the population dynamics of F. oxysporum, but did not eradicate the fungal pathogen. The roles of the microbiological agents underlying the disease suppression and the magnitude of the disease suppression in the MPM system appear to depend on the microbial density. F. oxysporum that survived in the MPM system formed chlamydospores when exposed to the rhizosphere microbiota. These results suggest that the microbiota suppresses proliferation of F. oxysporum by controlling the pathogen's morphogenesis and by developing an ecosystem that permits coexistence with F. oxysporum.

Soil-less substrates are unable to catalyse nitrification because the addition of a high concentration of organic substances suppresses nitrification. We used a previously developed multiple parallel mineralization method, which enables the use of organic fertilizers in hydroponics, to support nitrification in soil-less substrates. In this method, microorganisms immobilized on porous substrates produced inorganic nitrate from organic substances, as in a natural soil. Phosphate and potassium ions were also released. Microorganisms produced nitrate from organic substances when immobilized on polyurethane resin, rockwool, vermiculite, oyster shell lime, and rice husk charcoal. The optimal amount of organic substance added daily to 100 mL of substrate held 6 mg of organic N. The optimal incubation temperature ranged from 25 to 42 °C. A high relative humidity (51% or higher) was more suitable than drier conditions (20%). The optimal amount of fish fertilizer added to the substrate was 6 mg organic N. The lower the C/N ratio of the organic substance, the better the result. Vegetable plants grew well on inoculated substrates but not on uninoculated substrates. These results show that soil-less substrates can be used to create artificial soils in which plants can be grown with the addition of organic fertilizer, as in a natural soil.

Artificial soil materials are unable to catalyse nitrification because added organic substances suppress nitrifying bacteria. We used a multiple parallel mineralization method, which enables the use of organic fertilizers in hydroponics, to support nitrification in non-soil materials. In this method, microorganisms immobilized on porous carriers produce inorganic nitrate from organic substances, as in natural soil. The carriers also released phosphate and potassium ions. Microorganisms produced nitrate from organic substances when immobilized on polyurethane resin, rockwool, vermiculite, oyster shell lime, and rice husk charcoal. The optimal amount of organic material added daily to 100 mL of carrier held 6 mg of organic N. Vegetable plants grew on inoculated materials but not on uninoculated materials. These results show that non-soil materials can be used to create artificial soils in which plants can be grown with the addition of organic fertilizer, as in natural soil.