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6.Production of Compost Containing Bacillus subtilis and Its Effectiveness to Suppression of Plant Disease

Makoto Shoda (Research Laboratory of Resources Utilization, Tokyo Institute of Technology)

A newly isolated Bacillus subtilis showed suppressive effect on 20 kinds of plant pathogens in vitro. In order to prove its applicability for practical use, the following three items were investigated.

① In the composting process of sewage sludge as a starting material, the cells of B. subtilis were introduced to the material and the survivability of the bacterium during thermophilic reaction was investigated. The cell number was maintained at constant level during 50℃ operation and the final compost product exhibited a suppression to growth of plant pathogens in vitro.

② The cell suspension of B. subtilis was mixed with compost products derived from two raw materials and placed at 30℃. By periodical samplings, the composts were subjected to suppressive test on 6 kinds of plant pathogens to confirm duration of the bacterial antifungal effect. When the initial cell concentration was maintained at more than 107cells/g, the suppressive effect was observed for more than 30 days.

③ The bacterium was cultivated on the solid residue, Okara, from food industry and the product was introduced into soil in a pot which contained a plant pathogen, Rhizoctonia solani. When the seeds of tomato were inoculated in the soil, the occurrence of damping-off of tomato was compared with a control which contained only a plant pathogen. The diseased rate of the soil with B. subtilis was significantly lower and the existence of the bacterium, iturin A and surfactin, antifungal antibiotics produced by the bacterium, was proved, indicating that the bacterium suppressed the occurrence of the disease in soil by producing the antibiotics.

枯草菌/Bacillus subtilis、堆肥化/composting、植物病原菌/plant pathogens、病害抑制/suppressiveness、抗菌物質/antifungal substances