Kiyohiko Nakasaki*, Yoshiyuki Kishiro* and Sachiko Hiraoka*

* Department of Materials Science & Chemical Engineering, Faculty of Engineering, Shizuoka University

+ Correspondence should be addressed to Kiyohiko Nakasaki:
(3-5-1 Johoku, Hamamatsu 432 Japan)

Abstract

Inoculation of suppressive bacteria into compost raw material was carried out in order to make a functional compost aimed at repressing lawn disease. A spontaneous streptomycin-resistant mutant of suppressive bacterium, B. subtilis N4-1 was used to investigate the dynamic change of the inoculated strain during composting. It was concluded that it is important to keep the concentration of the bacteria indigenous in the raw material as low as possible in order to enable the growth of N4-1. The compost product made from the raw material containing other bacteria less than 4.3X105CFU/g-ds showed a suppressive effect on the pathogen. The feasibility of repeatedly using the compost product as a seed for the next composting was also examined. The concentration of N4-1, and the ratio of N4-1 to total bacteria (estimated by summing up the N4-1 and the other bacteria) in the compost product decreased rapidly as the number of repetitions was increased. The compost product lost the suppressive effect after the 5th repetition. It was also ascertained that the ratio of N4-1 to total bacteria had a strong effect on existence and degree of suppressiveness. The suppressive test experiment using cell suspension mixtures of pure cultured N4-1 and insuppressible bacterium, Escherichia coli E2 was performed to ascertain this.

Key words: composting, inoculum, plant disease, biological control, Bacillus subtilis