Chemical Factors Regulating Soil Borne Plant Diseases Produced by Microorganisms Surviving in Soil

土壤传播的作物病害受土壤微生物区系多样性的影响很大。植物病理学家对这一现象进行了长期的研究，提出调节土传病害的因素主要是由微生物产生的抗生素和/或植物毒性物质等化学基础引起的。本研究通过对洋葱假单胞菌和荧光假单胞菌产生的一系列抗菌肽进行分离和结构分析，分析了与土传病害相关的典型化学因素。它们的大部分结构是由D-木糖和几种特殊氨基酸组成的糖肽。作为另一个例子，调查了一种土传真菌产生的植物毒素。大麦斑点病病原菌小斑病菌的乙酸乙酯提取物能诱导大麦叶片坏死，抑制根的伸长。从培养物中分离出两种毒素A和B作为活性成分。A毒素的结构经波谱分析确定为1，7-二甲基-8-羟甲基-4-异丙基-双环[3.2.1]辛烷-6-酮，B的结构正在研究中。在50ppm时，毒素专一地诱导大麦叶片的坏死。

Siol borne crop diseases are highly affected by the variety of soil flora containing numerous kinds of microorganisms. This phenomenon has been investigated for a long tine by plant pathologists and it has been proposed that the factors regulating the soil borne diseases are mainly caused by chemical basis such as antibiotic and/or phytotoxic substances produced by the microorganisms. This research aimed to analyze typical examples of chemical facors related to soil borne diseases.We isolated a series of antibiotic peptides produced by Pseudomonas cepacia and P.fluorescens, structures of which were extensively investigated. Most of their structures were elucidated to be glycopeptides consisting of D-xylose and several kinds of unusual amino acids. As another example, phytotoxins produced by a soil borne fungus were investigated. Ethyl acetate extract of cultures of Bipolaris sorokiniana, the causal agent of barley spot blotch, induced the necrosis of leaves and the inhibition of root elongation on barley. Two toxic compounds from the cultures, toxin A and B, were isolated as the active principles. The structure of toxin A was elucidated to be 1,7-dimethyl-8-hydroxy methyl-4-isopropyl-bicyclo[3.2.1]octane-6-one by spectometric methods, and the structure elucidation of B is in progress. At 50 ppm the toxins host-specifically induced the necrosis for leaves of barley.