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6.On an Antibiotic Producing Microorganism AB89 Isolated from a Rice Leaf

Naruto Furuya, Masakazu Kawanami, Kazuhiro Iiyama and Nobuaki Matsuyama
(Faculty of Agriculture, Kyushu University)

A microorganism which is antagonistic to various phytopathogenic bacteria and fungi, especially to Ralstonia solanacearum and Phloeospora maculans, was isolated from the surface of a rice leaf and designated as an isolate AB89. From biological and biochemical data, this organism was identified as Bacillus subtilis. Treating of tomato roots with B. subtilis AB89 at the time of transplanting in R. solanacearum-infested soil increased the percentage of seedling survival. Pretreatment of the mulberry leaves with the bacterial suspension or the culture filtrate of isolate AB89 also suppressed the severity of mulberry leaf spot incited by challenge inoculation with P. maculans. Furthermore, in sericulture using the mulberry leaves infected with isolate AB89, no growth damage of silk worms was observed. In vitro, the isolate AB89 produced several kinds of antibacterial substance against R. solanacearum. Moreover, the anti-P. maculans substance was characterized as heat-stable, sugar-relating substance with several rings, and molecular weight of this substance was decided as MW 819 by the result of the fast atom bombardment mass-spectrometry (FAB-MS). These results indicated that B. subtilis AB89 may possibly become an effective agent for biological control of plant diseases caused by bacteria and fungi.

Keywords: Bacillus subtilis, Antibiotic substance, Bacterial wilt of tomato, Mulberry leaf spot, Biological control