The mechanism of suppression by the legume Desmodium uncinatum of the parasitic weed Striga

在撒哈拉以南的萨凡纳农业中，非洲农民面临着一系列的虫害问题，但却无法获得现代杀虫剂。在通过与驱避植物间作和与吸引成虫蛾的植物诱捕来控制害虫，特别是本地和引进蛾的钻茎幼虫的工作过程中，发现一种间作对非洲独脚金，Striga物种提供了显着的控制。金鱼草科的这些寄生杂草是该地区1亿多人主食作物的主要威胁。控制寄生虫的间作作物是牛饲料豆类，通常称为山蚂蝗，当在农场种植玉米和其他维生谷物（如高粱）之间的一对一间作时，寄生的Striga被控制到可以将远低于1吨/公顷的玉米产量提高到5吨/公顷以上的程度。在实验中，证明了可以通过使水流过山蚂蝗的根，然后进入含有独脚金和玉米种子的土壤中来提供该效果。此外，当山蚂蝗生长在有营养但没有土壤的水中时，水捕获了活性，然后可以转移到土壤中的Striga和玉米种子中，并再次控制寄生虫。分馏的化学品从水的影响，这种控制确定了一个馏分，影响发展，这是简单地通过测量减少胚根生长的寄生虫记录。已经鉴定了这些馏分中的化学品，这些化学品说明了所述的活性。然而，这些化学物质防止Striga侵扰的确切方式尚未确定。因此，该项目的目的是确定受山蚂蝗根分泌物中存在的抑制性化合物影响的独脚金生命周期的阶段，纯化其中一些化合物并使用它们来测试它们负责抑制野外观察到的独脚金的假设。最后，另一种豆科植物的根分泌物，这是常用的分子研究，百脉根，我们知道也产生抑制独脚金胚根生长的根分泌物，将进行检查，以确定它们是否含有抑制独脚金感染的化合物。虽然L.日本豆科植物在农学上不适合实际控制独脚金，但这种模式豆科植物丰富的基因组信息和可用的工具将使未来能够阐明新型黄酮合成中涉及的生物合成途径。这项工作将首次阐明一个有价值的杂草抑制是如何发生的，并将为英国农业中控制杂草的尝试提供基础。

In sub-Saharan savannah agriculture, African farmers have a range of pest problems with which to contend and yet without access to modern pesticides. During the course of work on controlling insect pests, particularly the stem-boring larvae of indigenous and introduced moths, by intercropping with repellent plants and trap cropping with plants that attract the adult moths, an intercrop was found that provided dramatic control of the African witchweed, Striga species. These parasitic weeds in the snapdragon family are a major threat to the staple food crops of over 100 million people in the region. The parasite-controlling intercrops were cattle forage legumes, commonly called desmodium, and when grown on-farm as a one-to-one intercrop between maize and other subsistence cereals such as sorghum, the parasitic Striga was controlled to the extent that a yield of well under 1 tonne/hectare of maize could be raised to over 5 tonnes/hectare. Experimentally, it was demonstrated that the effect could be provided by passing water over the roots of desmodium and then into soil containing the Striga and maize seeds. Furthermore, when desmodium was grown in water with nutrients but without soil, the water captured the activity, which could then be transferred to the Striga and maize seeds in soil, and again conferred control of the parasite. Fractionation of the chemicals from the water effecting this control identified a fraction that affected development, which was recorded simply by measuring the reduction in radicle growth of the parasite. Chemicals from these this fractions accounting for the activities described, have been identified. However, the exact way in which these chemicals work to prevent Striga infestation has not been determined. Thus, the aim of this project is to identify the stage(s) of the Striga lifecycle affected by the inhibitory compounds present in desmodium root exudates, to purify some of these compounds and to use them to test the hypothesis that they are responsible for the suppression of Striga seen in the field. Finally, the root exudates of another legume, that is commonly used in molecular studies, Lotus japonicus, that we know also produces a root exudates that inhibits Striga radicle growth, will be examined to determine whether they contain compounds that suppress Striga infection. Although L. japonicus would not be agronomically suitable for practical control of Striga, the wealth of genomic information and tools available for this model legume would enable the biosynthetic pathways involved in the synthesis of the novel flavones to be elucidated in the future. This work will provide the first elucidation of how a valuable weed suppression occurs and will provide the basis for attempts to control weeds in UK agriculture.