<論文>低毒性防かび剤の研究 : (1)ゴムノキの防かび

Abstract

ゴムノキは,従来の有用森林資源の枯渇が進む中で,これらの代替材料となる諸性質を備えているが,生物劣化に対する抵抗性が極めて低く,資源量の割にはあまり利用されていない。本研究では,微生物に侵害されたゴムノキ丸太から変色菌や汚染菌を分離し,分離菌を含む数種の供試菌に対する各種薬剤の防かび効力を検討した.分離された菌には,ゴムノキの代表的な青変菌であるBotryodiplodia theobromae PAT.の他,Pemicillium sp.,Gliocladium sp.などの汚染菌があった。ゴムノキ辺材から採取した試験片(4×4×0.45cm)を各処理薬液中に30秒間浸漬濡後,風乾し,シャーレ内の人工組成培地上に置き,供試菌の胞千態濁波を試験片上および周辺にまき,26土2°C下で4週間培養した。培養開始後1週間毎に肉眼による観察を行い,薬剤による供試菌の生育防止の程度を判定した。この結果,有機ョウ素化合物とベンツイミダゾール系化合物との混合物の防かび性能がもっとも優れており,特に,混合割合を3:1にした時の防かび効果が顕著であった。 この混合物は,現在汎用されている防かび剤に代る低音院防かび剤として実用の可能性があり,今後さらに温度安定性,効力持続性などに関する研究を推進していく価値があろう。

Rubber wood is a potential substitute of currently used commercial timbers as the trees grow last and are felled every 20～30 years for replanting due to the decrease in latex yield. However, a major problem in rubber wood utilization is concerned with its poor resistance against insect and fungal attacks. If the problem is led to resolution, the extensive development could be promising in the near future. Deterioration of rubber wood after felling is initiated by microorganisms such as sap-staining fungi and molds. It is, therefore, essential to prevent their invasion for obtaining stain-free rubber wood materials in wood industries. The present investigation is related to the isolation of fungi and to the evaluation of effectiveness of some chemicals and mixtures in controlling fungal growth in the laboratory. Isolation of sap-staining fungi, molds and basidiomycetes from fungus-infected rubber logs showed the heavy infestation of Botryodiplodia theobromae PAT., a typical blue-staining fungus, and a few species of mold. The isolated B. theobromae and three other fngi were served to the next experiment of which various chemicals and mixtures were tested for their effectiveness in controlling fungal growth on the treated sapwood specimens of rubber wood (Hevea brasiliensis MUELL.-ARG.) placed on the nutrient agar medium in Petri dishes. Wood specimens, measuring 4(T) × 4(L) × 0.45(R) cm, were dipped in treating solutions for 30 seconds and then air-dried. Each of the treated specimens was placed in a Petri dish with spore suspension of a test fungus. Visual evaluation was made every once a week for 4 weeks at 26±2℃. Among the tested chemicals and mixtures, a mixture of 4-chlorophenyl-3-iodopropagylibrmal and 2-(4-thiazolyl) benzimidazole (mixing ratio 3:1) was superior to others in effectiveness. At 2% treating level, the growth of all the test fungi was completely inhibited, whereas tributyltin oxide, trichlorophenol and benomyl [1-(butylcarbamoyl)-2-benzimidazole carbamic acid, methyl ester] failed to prevent fungal growth on the wood specimens at the same level. The results seem to expect that the mixture becomes an alternative low toxicity anti-sapsatin agent instead of world-wide commercial trichlorophenol and pentachlorophenol.