The introductory chapter is really well-documented and makes a clear and exhaustive state-of-the-art regarding the studied topic. After having given the conceptual framework of ecology in general and chemical ecology in particular, Mr. Diego Castellano Sanchez explains in detail the definition of allelopathy. He then focuses on applied potential of this recent field of ecology, and demonstrates how it can provide tools for sustainable agriculture.The second chapter is, as far as I know, the first up-to-date review dedicated to methods in allelopathy. Various kind of methods are presented but the most interesting point of this chapter is that Mr. Diego Castellano Sanchez discussed their interest, proposing a positive criticism of the most widely used techniques. He finally pointed out how much important is to standardise a method to screen for biological active compounds which could act as "natural herbicides". To propose such an optimised method for bioassays in allelopathy represents on of the main goals of the experimental work of Mr. Diego Castellano Sanchez.The third chapter describes the objectives of the study. There is no doubt that Mr. Diego Castellano Sanchez performed this work with a permanent mind on applied aspects of allelochemicals in agriculture. This quality is too rare in science not to mention it. For instance, he developed a method allowing searching for biological activity of chemicals, he built a new tool to allow scientists to perform better morphology measurements in lesser time; he built a pluviotron to perform some leaching experiments as in ecosystems...and so on.The following two chapters are respectively dedicated to the results and their discussion and to the detailed presentation of the experimental techniques. As a main result, it is clear that such bioassays should combine at least two methods, a first one to screen for bioactive chemicals and, a second one focusing on the phytotoxicity of the previously selected biologically active compounds. Achieved work is really consistent, innovative and of high quality. Mr. Diego Castellano Sanchez proved that he is creative, combining chemistry with biological sciences. His open mind allowed him to use techniques so far different than osmometry, germination and growth bioassays. He successfully interpreted his data, pointing out the most important ones. His contribution to the science of plant chemical interaction is of great importance because not only he clearly demonstrated that we need tools to improve our search for new natural herbicides but he also proposed some of them. I am sure that the contribution of Mr. Diego Castellano Sanchez for the plant chemical interaction scientists community will be of great interest.Last but not least, quality of the work achieved by Mr. Diego Castellano Sanchez is of international standard as proves the impressive quantity and quality of published manuscripts in first rank international journals.