Soil bacterial community structure was analyzed using model soil systems (microcosms) contaminated with 4 different levels of Cu^<2+>. We used length polymorphism (LPM) of PCR-amplified DNA fragments of 16S ribosomal RNA gene (16S rDNA) to evaluate the diversity of soil bacteria in the model soil systems. PCR (polymerase chain reaction) primers were designed to classify the soil bacteria into three groups as follows: 1) α and δ subclasses of Proteobacteria, 2) β and γ subclasses of Proteobacteria, and 3) Gram-positive bacteria. Bacterial DNA was extracted directly from the soil samples, and LPM patterns for the PCR-amplified DNA fragments were obtained using a high-resolution gel. Considerable changes in the LPM pattern were observed for the β and γ subclasses of Proteobacteria when the Cu^<2+> concentration increased, while minor changes were observed for the other groups. New bands appeared when the Cu^<2+> concentration increased, suggesting that the number of Cu-resistant bacteria species increased, while that of sensitive bacteria decreased with time after the addition of Cu^<2+> to the soil.
Three types of soil, CF-soil (amended with chemical fertilizers for 14 y), CF+FYM-soil (amended with chemical fertilizers and 40 t ha^<-1> y^<-1> of farmyard manure for 14 y) and FYM-soil (amended with 400 t ha^<-1> y^<-1> of farmyard manure for 14 y), were inoculated with Ralstonia solanacearum and tomato plants were grown in order to evaluate the degree of suppressiveness of bacterial wilt of tomato by the soils. More than 70% of the tomato plants showed wilt symptoms in the CF- and CF+FYM-soils after 30 days of cultivation in a climatron, whereas less than 10% of tomato plants wilted in the FYM-soil. The survival of the pathogen was higher in the CF- and CF+FYM-soils than in the FYM-soil. Soil pH appeared to affect the disease incidence in all the soil treatments, whereas it may not have been involved in the major suppression mechanisms in the FYM-soil. The disease incidence was reduced when the CF- and CF+FYM-soils were mixed with the FYM-soil, indicating that the disease suppressive property of the FYM-soil could be transferred. When the FYM-soil was irradiated with γ-rays, the disease suppressiveness was lost, implying that the suppressive nature of the FYM-soil could be attributed to biological factors. The disease incidence decreased when the CF-soil was amended with calcium chloride, suggesting that chemical factors might also be involved in the suppression mechanisms. Results of this study suggested that the suppression of bacterial wilt caused by R. solanacearum in the FYM-soil was due to the combined effects of biotic and abiotic factors associated with repeated application of a larger amount of farmyard manure.
O. brassicaeの分布を明らかにするため,国内の1道,1府,12県から73地点の耕地土壌(一部は植物根)を収集し,捕捉植物(ササゲ,マクワウリ,レタス,タバコ,野生エンバクまたはキャベツ)に接種して,O. byassicaeの寄生の有無を調査した。その結果,58地点の試料(供試試料の79%)において,いずれかの植物でO. byassicaeの寄生が観察された。本菌が検出された58地点のうち,ササゲでは55地点,マクワウリでは50地点の土壌で本菌が検出された。一方,レタスでは17地点の検出にとどまり,その他野生エンバク,キャベツ,タバコでの検出は極めて少なかった。なお,ササゲやマクワウリを用いて分離された菌の植物寄生性を調査したところ,レタスあるいはキャベツに対する寄生性の分化が認められた。次に,O. brassicaeのTMMMV媒介能を調査するため,49菌株(うち11菌株は単遊走子嚢分離株)をポットに植え付けたTMMMV感染チューリップにそれぞれ接種し,その周囲に健全チューリップ球根(検定株)を植え付けて,この検定株へのウイルス感染の有無を調査したところ,供試菌株の少なくとも40菌株が本ウイルスを媒介することが明らかになった。