5.6.7
CONTROL OF BACTERIAL WILT OF TOMATO USING A PYRIDINIUM-TYPE POLYMER

N KAWABATA1, H KISHIMOTO1, K YAMANAKA21, T IKAWA1 and I FURUSAWA2

1Department of Chemistry and Materials Technology, Kyoto Institute of Technology, Matsugasaki, Kyoto 606, Japan; 2Laboratory of Plant Pathology, Kyoto University, Kitashirakawa, Kyoto 606, Japan

Background and objectives
Control of soilborne plant diseases is a difficult subject in agriculture. Conventional treatment processes involve disinfection using methyl bromide, chloropicrin or other related chemicals. However, alternative methods are eagerly desired, because chloropicrin is strongly toxic, and methyl bromide is prohibited within few years since it destroys the ozone layer like a flon gas. On the other hand, disinfection of microorganisms by chemicals is not desirable for the protection of ecological system. Therefore, this work was aimed at controlling soil borne plant diseases without chemical disinfection based on a new concept using a pyridinium-type polymer that shows strong affinity with microorganisms [1]. We expected predominance of interaction between pathogenic micro-organisms with the polymer over that with roots of plant, and control of soil borne plant diseases by decreased contact of roots with pathogenic micro-organisms. Preliminary results were reported at an annual meeting of the Phytopathological Society of Japan [2].

Materials and methods
Tomato and Pseudomonas solanacearum wereused as a test plant and a pathogenic micro-organism, respectively. Equimolar copolymer of styrene with N-benzyl-4-vinylpyridinium chloride was used as a test pyridinium-type polymer. Sterilized soil was mixed with P. solanacearum and 5 or 10 g/kg of sawdust that was coated by 4.4 wt% of the pyridinium-type polymer. Seedlings of tomato were planted in the mixed soil, and cultivated in a plant incubator. Extent of disease was evaluated based on index of symptoms of disease.

Results and conclusions
When the population of P. solanacearum in soil was in the order of 106 c.f.u./g, addition of 5-10 g/kg of the coated sawdust exerted 84-100% reduction of the index of symptoms of disease. When the population was in the order of 107 c.f.u./g, addition of 10 g/kg of the coated sawdust exerted 75-77% reduction of the index. However, population of P. solanacearum in the test soil was not affected by the addition of the coated sawdust. Therefore, control of bacterial wilt of tomato by addition of the coated sawdust to soil appeared to be attributed to decrease of contact of tomato roots with the pathogenic bacteria exerted by the presence of sawdust coated with the pyridinium-type polymer.

References
1. Kawabata N, 1992. Progress in Polymer Science 17, 1-34.
2. Kawabata N, Kishimoto H, Yamanaka K, Ikawa T, Furusawa I, 1997. Annals of the Phytopathological Society Japan 63, 253.